Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview and Volume 2: Guidelines (2017)

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Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms Volume 1: Research Overview NCHRP RESEARCH REPORT 864 NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

TRANSPORTATION RESEARCH BOARD 2017 EXECUTIVE COMMITTEE* OFFICERS Chair: Malcolm Dougherty, Director, California Department of Transportation, Sacramento ViCe Chair: Katherine F. Turnbull, Executive Associate Director and Research Scientist, Texas A&M Transportation Institute, College Station exeCutiVe DireCtor: Neil J. Pedersen, Transportation Research Board MEMBERS Victoria A. Arroyo, Executive Director, Georgetown Climate Center; Assistant Dean, Centers and Institutes; and Professor and Director, Environmental Law Program, Georgetown University Law Center, Washington, DC Scott E. Bennett, Director, Arkansas State Highway and Transportation Department, Little Rock Jennifer Cohan, Secretary, Delaware DOT, Dover James M. Crites, Executive Vice President of Operations (retired), Dallas–Fort Worth International Airport, TX Nathaniel P. Ford, Sr., Executive Director–CEO, Jacksonville Transportation Authority, Jacksonville, FL A. 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Semonite (Lieutenant General, U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers, Washington, DC Karl Simon, Director, Transportation and Climate Division, U.S. Environmental Protection Agency Richard A. White, Acting President and CEO, American Public Transportation Association, Washington, DC K. Jane Williams, Executive Director, Federal Transit Administration, U.S. DOT Frederick G. (Bud) Wright, Executive Director, American Association of State Highway and Transportation Officials, Washington, DC Paul F. Zukunft (Admiral, U.S. Coast Guard), Commandant, U.S. Coast Guard, U.S. Department of Homeland Security * Membership as of October 2017.

2017 N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP RESEARCH REPORT 864 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms Volume 1: Research Overview M. Saiid Saiidi Mostafa Tazarv Sebastian Varela Infrastructure InnovatIon, LLc Reno, NV Stuart Bennion M. Lee Marsh Iman Ghorbani BergeraBaM Seattle, WA Thomas P. Murphy ModjeskI and Masters, Inc. Mechanicsburg, PA Subscriber Categories Bridges and Other Structures Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

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C O O P E R A T I V E R E S E A R C H P R O G R A M S AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 12-101 by Infrastructure Innovation, LLC in collaboration with BergerABAM and Modjeski and Masters, Inc. The principal investigator (PI) on this project was M. Saiid Saiidi. M. Lee Marsh of BergerABAM and Thomas P. Murphy of Modjeski and Masters, Inc. were the co-PIs of the project. Senior research associate, Mostafa Tazarv, and research associate, Sebastian Valera, performed the research under the supervision of the PI. Stuart Bennion and Iman Ghorbani developed the design examples under the supervision of M. Lee Marsh (Co-PI). The research team is indebted to Dr. Amir Mirmiran of the University of Texas at Tyler for his feedback on concrete-filled fiber-reinforced polymer tube columns. The authors would like to thank Mr. Scott Arnold of FYFE Co. LLC, Mr. Dominique Corvez and Mr. Paul White of Lafarge North America Inc., Mr. Kevin Friskel of Dynamic Isolation Systems Inc., Mr. Rich LaFond of Saes Smart Materials, and Mr. Edward Little of FiberMatrix Inc. for providing cost estimates for novel materials. Dr. Toutlemonde of Institut Français des Sciences et Technologies des Transports, de l’Aménagement et des Réseaux (IFSTTAR) is thanked for sharing UHPC design recommendations. CRP STAFF FOR NCHRP RESEARCH REPORT 864, VOLUME 1 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Senior Program Officer Eileen P. Delaney, Director of Publications Scott E. Hitchcock, Senior Editor NCHRP PROJECT 12-101 PANEL Field of Design—Area of Bridges Elmer E. Marx, Alaska DOT and Public Facilities, Juneau, AK (Chair) Anne M. Rearick, Indiana DOT, Indianapolis, IN Ronald J. Bromenschenkel, California DOT, Sacramento, CA David W. Fish, Rhode Island DOT, Providence, RI Jugesh Kapur, Burns and McDonnell, Kansas City, MO Jamshid Mohammadi, Illinois Institute of Technology, Chicago, IL Amgad F. Morgan-Girgis, eConstruct USA, LLC, Omaha, NE Sheila Rimal Duwadi, FHWA Liaison Stephen F. Maher, TRB Liaison

This report describes the evaluation of new materials and techniques for design and construction of novel bridge columns meant to improve seismic performance. These techniques include shape memory alloy (SMA), engineered cementitious composite (ECC), fiber-reinforced polymer (FRP), and rocking mechanisms. The report includes two volumes: Volume 1: Research Overview and Volume 2: Guidelines. The guidelines cover a quantita- tive evaluation method to rate novel columns as well as design and construction methods for three specific novel columns: (1) SMA-reinforced ECC columns, (2) SMA-reinforced FRP-confined concrete/columns, and (3) FRP-confined hybrid rocking columns. More than 2,250 analyses in the form of moment-curvature, pushover, cyclic, and dynamic simu- lations were carried out to investigate the behavior of the selected columns and to develop proposed design guidelines according to the AASHTO LRFD Bridge Design Specifications and the AASHTO Guide Specifications for LRFD Seismic Bridge Design. The material in this report will be of immediate interest to bridge owners. The primary objective of the AASHTO LRFD Bridge Design Specifications and the AASHTO Guide Specifications for LRFD Seismic Bridge Design is to prevent bridge collapse in the event of earthquakes. Reinforced concrete bridge columns are designed to dissipate earthquake energy through considerable ductile nonlinear action that is associated with severe spalling of concrete and yielding of reinforcement. Proven detailing procedures have been developed for reinforced concrete bridge columns that provide this type of behavior and are intended to prevent bridge collapse. However, for columns to successfully dissipate energy, they have to behave as nonlinear elements subject to substantial damage and possibly permanent drift to the point that the bridge would have to be decommissioned for repair or replacement. The impact of bridge closure on the traveling public and the economy is significant. Therefore, alternative design approaches using advanced materials and uncon- ventional seismic techniques are needed to improve current practice. Despite the superior performance of columns with the innovative materials reported in the literature, design guidelines and methods of structural analysis are not addressed in the current seismic bridge design specifications. Research was needed to develop proposed AASHTO guidelines to help bridge owners incorporate innovative seismic energy dissipation principles into practice. Research was performed under NCHRP Project 12-101 by Infrastructure Innovation, LLC to develop (1) proposed guidelines for the evaluation of new techniques for the design and construction of bridge columns with energy dissipation mechanisms meant to minimize bridge damage and replacement after a seismic event and (2) design and construction concepts based on new materials and techniques (e.g., post-tensioning, SMA, ECC, rubber pads, and F O R E W O R D By Waseem Dekelbab Staff Officer Transportation Research Board

FRP wrapping) and analytical techniques (e.g., current design practice, direct displacement based design, and substitute structure design method). The guidelines included analysis procedures, evaluation criteria (e.g., constructability, serviceability, inspectability, seismic and non-seismic system performance, and post-event repair), design procedures, construction details, and detailed design examples. A number of deliverables, provided as appendices, are not published but are available on the TRB website (trb.org) by searching for “NCHRP Research Report 864.” These appendices are titled as follows: • Appendix A: Literature Review • Appendix B: Survey of State Departments of Transportation • Appendix C: Synthesis of Literature • Appendix D: Novel Column and Construction Concepts • Appendix E: Demonstration of Evaluation Guidelines • Appendix F: Detailed Design Examples for Three Novel Columns • Appendix G: Benefits and Economic Impact of Novel Columns • Appendix H: Relationship Between Drift Ratio and Displacement Ductility • Appendix I: Modeling Methods and Validation for Novel Columns

1 Summary 3 Chapter 1 Introduction 3 1.1 Problem Statement 3 1.2 Research Objectives 4 1.3 Document Organization 5 Chapter 2 Guidelines for Evaluation of Novel Columns 6 Chapter 3 Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 7 3.1 Proposed Seismic Design and Construction of SMA-Reinforced ECC Columns 7 3.1.1 Introduction 7 3.1.2 Application of SMA-Reinforced ECC Columns 7 3.1.3 Materials 7 3.1.3.1 SMA 8 3.1.3.2 ECC 10 3.1.4 Analysis of SMA-Reinforced ECC Columns 10 3.1.4.1 Selection of Analysis Procedure to Determine Seismic Demand 10 3.1.4.2 Effective Section Properties 11 3.1.4.3 Damping Ratio for Dynamic Analysis 11 3.1.4.4 Displacement Modification for Damping 12 3.1.4.5 Displacement Modification for Short-Period Bridges 13 3.1.4.6 Displacement Ductility versus Drift Ratio 14 3.1.4.7 Column Drift Demand Requirement 15 3.1.4.8 Column Force Demand 15 3.1.4.8.1 Moment Demand 15 3.1.4.8.2 Shear Demand 15 3.1.4.8.3 Column Adjoining Member Force Demand 16 3.1.4.9 Residual Drift 16 3.1.5 Design of SMA-Reinforced ECC Columns 16 3.1.5.1 Analytical Plastic Hinge Length 17 3.1.5.2 Column Drift Capacity 17 3.1.5.2.1 Minimum Drift Capacity 17 3.1.5.3 Shear Capacity 19 3.1.5.4 Axial Capacity 19 3.1.5.5 Minimum Lateral Strength 19 3.1.5.6 Other Loading and Strength Design 19 3.1.5.7 Serviceability Design 20 3.1.5.7.1 Shrinkage and Creep 20 3.1.5.7.2 Axial Deformations C O N T E N T S

20 3.1.6 Details for SMA-Reinforced ECC Columns 20 3.1.6.1 Partially or Fully Cast ECC Columns 20 3.1.6.2 Reinforcement Details 20 3.1.6.2.1 Longitudinal SMA Reinforcement 21 3.1.6.2.2 SMA Bar Size 21 3.1.6.3 Splicing of SMA Reinforcement 22 3.1.6.4 Maximum Axial Load 22 3.1.6.5 Maximum Aspect Ratio 23 3.1.7 Construction of SMA-Reinforced ECC Columns 23 3.1.7.1 Quality Control Tests 23 3.1.7.2 Construction Procedures 23 3.1.7.3 Construction Tolerance 23 3.1.8 References 25 3.2 Proposed Design and Construction of SMA-Reinforced FRP-Confined Concrete Columns 25 3.2.1 Introduction 25 3.2.2 Application of SMA-Reinforced FRP-Confined Concrete Columns 26 3.2.3 Materials 26 3.2.3.1 SMA 27 3.2.3.2 FRP-Confined Concrete 29 3.2.4 Analysis of SMA-Reinforced FRP-Confined Concrete Columns 29 3.2.4.1 Selection of Analysis Procedure to Determine Seismic Demand 29 3.2.4.2 Effective Section Properties 29 3.2.4.3 Damping Ratio for Dynamic Analysis 31 3.2.4.4 Displacement Modification for Damping 31 3.2.4.5 Displacement Modification for Short-Period Bridges 31 3.2.4.6 Displacement Ductility versus Drift Ratio 33 3.2.4.7 Column Drift Demand Requirement 33 3.2.4.8 Column Force Demand 33 3.2.4.8.1 Moment Demand 33 3.2.4.8.2 Shear Demand 34 3.2.4.8.3 Column Adjoining Member Force Demand 34 3.2.4.9 Residual Drift 35 3.2.5 Design of SMA-Reinforced FRP-Confined Concrete Columns 35 3.2.5.1 Analytical Plastic Hinge Length 35 3.2.5.2 Column Drift Capacity 35 3.2.5.2.1 Minimum Drift Capacity 36 3.2.5.3 Shear Capacity 37 3.2.5.4 Axial Capacity 37 3.2.5.5 Minimum Lateral Strength 37 3.2.5.6 Other Loading and Strength Design 38 3.2.5.7 Serviceability Design 38 3.2.5.7.1 Shrinkage and Creep 38 3.2.5.7.2 Axial Deformations 38 3.2.6 Details for SMA-Reinforced FRP-Confined Concrete Columns 38 3.2.6.1 FRP Jacket 39 3.2.6.2 Reinforcement Details 39 3.2.6.2.1 Longitudinal SMA Reinforcement 39 3.2.6.2.2 SMA Bar Size

39 3.2.6.3 Splicing of SMA Reinforcement 40 3.2.6.4 Maximum Axial Load 41 3.2.6.5 Maximum Aspect Ratio 41 3.2.7 Construction of SMA-Reinforced FRP-Confined Columns 41 3.2.7.1 Quality Control Tests 41 3.2.7.2 Construction Procedures 41 3.2.7.3 Construction Tolerance 41 3.2.8 References 43 3.3 Proposed Design and Construction of FRP-Confined Hybrid Rocking Columns 43 3.3.1 Introduction 43 3.3.2 Application of FRP-Confined Hybrid Rocking Columns 44 3.3.3 Materials 44 3.3.3.1 Steel Tendons 44 3.3.3.2 FRP-Confined Concrete 46 3.3.4 Analysis of FRP-Confined Hybrid Rocking Columns 46 3.3.4.1 Selection of Analysis Procedure to Determine Seismic Demand 46 3.3.4.2 Effective Section Properties 46 3.3.4.3 Damping Ratio for Dynamic Analysis 47 3.3.4.4 Displacement Modification for Damping 47 3.3.4.5 Displacement Modification for Short-Period Bridges 47 3.3.4.6 Displacement Ductility Versus Drift Ratio 48 3.3.4.7 Column Drift Demand Requirement 49 3.3.4.8 Column Force Demand 49 3.3.4.8.1 Moment Demand 50 3.3.4.8.2 Shear Demand 50 3.3.4.8.3 Column Adjoining Member Force Demand 50 3.3.4.9 Residual Drift 51 3.3.5 Design of FRP-Confined Hybrid Rocking Columns 51 3.3.5.1 Analytical Plastic Hinge Length 52 3.3.5.2 Column Drift Capacity 52 3.3.5.2.1 Minimum Drift Capacity 52 3.3.5.3 Shear Capacity 54 3.3.5.4 Axial Capacity 54 3.3.5.5 Minimum Lateral Strength 54 3.3.5.6 Other Loading and Strength Design 54 3.3.5.7 Serviceability Design 54 3.3.5.7.1 Shrinkage and Creep 54 3.3.5.7.2 Axial Deformations 55 3.3.6 Details for FRP-Confined Hybrid Rocking Columns 55 3.3.6.1 FRP Jacket 55 3.3.6.2 Reinforcement Details 55 3.3.6.2.1 Longitudinal Reinforcing Steel Bars 56 3.3.6.2.2 Longitudinal Steel Tendons 56 3.3.6.2.3 Longitudinal Steel Tendon Initial Stresses 57 3.3.6.3 Maximum Axial Load 57 3.3.6.4 Maximum Aspect Ratio 58 3.3.7 Construction of FRP-Confined Hybrid Rocking Columns 58 3.3.7.1 Quality Control Tests 58 3.3.7.2 Construction Procedures

58 3.3.7.3 Construction Tolerance 58 3.3.7.4 Ducts 59 3.3.8 References 60 Chapter 4 Summary and Conclusions 60 4.1 Summary 61 4.2 Conclusions 61 4.2.1 Proposed AASHTO Guidelines for Evaluation of Novel Columns 61 4.2.2 Seismic Design and Construction of Novel Columns 62 4.2.3 Key Conclusions from Appendix Documents 62 4.2.3.1 Literature Review 62 4.2.3.2 State DOT Survey 62 4.2.3.3 Literature Synthesis and Knowledge Gaps 62 4.2.3.4 Novel Column and Construction Concepts 62 4.2.3.5 Demonstration of Evaluation Guidelines 63 4.2.3.6 Design Examples of Select Novel Columns 63 4.2.3.7 Qualitative Benefits and Economic Impact 63 4.2.3.8 Drift Ratio Displacement Ductility Relationship 63 4.2.3.9 Modeling and Validation for Novel Columns 64 Appendices A–I Note: Photographs, figures, and tables in this report may have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org) retains the color versions.

1 S U M M A R Y Standard reinforced concrete bridge columns are generally designed to dissipate earth- quake energy through yielding of longitudinal reinforcing steel and spalling of concrete that collectively cause large plastic deformations in columns. Even though bridge collapse is expected to be prevented using current design specifications, excessive plastic hinge damage and large post-earthquake permanent lateral deformations may cause decommissioning of bridges for repair or replacement. The impact bridge closure has on access to the affected area shortly after an earthquake, on the traveling public, and on the economy of the region is significant. A new paradigm is emerging among bridge owners, requiring that bridges remain functional with minimal interruption of the traffic flow after earthquakes. To materialize this paradigm, bridge column construction practice would need to explore unconventional materials and techniques that possess characteristics that make bridge columns resilient. Despite the superior performance of columns with advanced materials reported in the literature, design guidelines and methods of structural analysis are not addressed in the cur- rent seismic bridge design specifications. NCHRP project 12-101 was initiated to achieve two main objectives of developing (1) proposed AASHTO guidelines for the evaluation of new techniques for the design and construction of bridge columns with energy dissipation mechanisms to minimize bridge damage and replacement after a seismic event and (2) design and construction concepts based on new materials and techniques [e.g., post-tensioning, shape memory alloy (SMA), engineered cementitious composite (ECC), rubber pads, and fiber-reinforced polymer (FRP) wrapping] and analytical techniques. Several tasks were undertaken in this project to achieve the aforementioned objectives. A state-of-the-art literature review was carried out to highlight the benefits of novel materials and new technologies; to establish mechanical properties of novel materials; and to identify design, construction, and performance knowledge gaps. A survey of state departments of transpor- tation on past and future application of advanced materials in bridges was also conducted. Thirty-nine new concepts, each with an improved energy dissipation system, were developed for bridge columns incorporating SMA, ECC, FRP, ultra-high performance concrete (UHPC), rubber, or rocking mechanisms. Of the 39 concept columns, only eight have been proof tested at the time of this writing, but the remaining columns are believed also to be feasible. Other novel column concepts are likely to emerge in the future, each aiming to improve the seismic performance compared to conventional reinforced concrete columns. To assess any existing or emerging novel columns, evaluation guidelines were developed using 14 param- eters to determine suitability and performance of the columns. The parameters included in the evaluation guidelines were (1) plastic hinge damage, (2) displacement capacity, (3) residual displacement, (4) availability of proof test data, (5) availability of analysis tool, (6) availability of design guidelines, (7) past field applications, (8) initial cost, (9) advanced material limitations, Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview

2 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview (10) ease of construction, (11) inspectability, (12) maintenance, (13) post-earthquake repair need, and (14) system performance. These parameters were quantified and scored with dif- ferent weights. The overall evaluation result was converted to a five-star rating method to help bridge owners and designers compare different alternatives and to make the final selection. The current AASHTO Guide Specifications for LRFD Seismic Bridge Design uses displace- ment ductility as the measure of deformability. However, this parameter may not be suitable for novel columns since the yield mechanism in novel and conventional columns can be dif- ferent. To address this difference, drift ratio was used as the design parameter in the present report to evaluate deformability. A comprehensive parametric study was carried out to relate the displacement ductility to the drift ratio for practical ranges of reinforced concrete bridge column geometry and axial loading. Three of the 39 novel columns were selected by the project panel for further investigation: (1) SMA-reinforced ECC columns, (2) SMA-reinforced FRP-confined concrete columns, and (3) FRP-confined hybrid rocking columns. Comprehensive analysis, design, and construction guidelines were developed for these three novel columns. Step-by-step comprehensive design examples were developed for each of the three columns to better show the use of the proposed guidelines. The framework used to develop these guidelines can be used by researchers to develop guidelines for other existing or emerging novel columns. The present document includes four main chapters and nine appendices (not printed herein but available for download on TRB.org) summarizing the findings of the individual tasks. The chapters address the main objectives of the project, and the appendices provide background, summary of survey findings, modeling methods, and supporting information that were utilized in the development of the proposed guidelines. Each chapter or appendix may be used as a standalone document. Overall, this report aims to draw the bridge engineering community’s attention to the potential benefits of the use of advanced materials in bridge columns by providing introduc- tory information, design guidelines and examples, and assessment of new bridge column technologies.

3 1.1 Problem Statement Standard reinforced concrete bridge columns are generally designed to dissipate earthquake energy through yielding of longitudinal reinforcing steel and spalling of concrete that collec- tively cause large plastic deformations in columns. Even though bridge collapse is expected to be prevented using current design specifications, excessive plastic hinge damage and large post- earthquake permanent lateral deformations may cause decommissioning of bridges for repair or replacement. The impact bridge closure has on access to the affected area shortly after an earthquake, to traveling public, and to the economy of the region is significant. A new para- digm is emerging among bridge owners, requiring that bridges remain functional with minimal interruption of the traffic flow after earthquakes. To materialize this paradigm, bridge column construction practice would need to explore unconventional materials and details that possess characteristics that make bridge columns resilient. 1.2 Research Objectives Despite the superior performance of columns with advanced materials reported in the lit- erature, design guidelines and methods of structural analysis are not addressed in the current seismic bridge design specifications. NCHRP project 12-101 was initiated to achieve two main objectives, developing (1) proposed AASHTO guidelines for the evaluation of new techniques for the design and construction of bridge columns with energy dissipation mechanisms meant to minimize bridge damage and replacement after a seismic event, and (2) design and construc- tion concepts based on new materials and techniques [e.g., post-tensioning, shape memory alloy (SMA), engineered cementitious composite (ECC), rubber pads, and fiber-reinforced polymer (FRP) wrapping] and analytical techniques. Four phases and 13 tasks were completed in this project to achieve the aforementioned objec- tives. The four phases of the project were (I) planning, (II) analytical approach, (III) guideline development, and (IV) final products. Interim Report 1 included the activities of Phase I of the project and consisted of five tasks: (1) review literature; (2) synthesize literature and identify gaps; (3) identify concepts, pros and cons, and cost; (4) develop analytical approach for Phase II; and (5) prepare Interim Report 1 (IR-1). Interim Report 2 described the work of Phase II of the project, consisting of three tasks: (6) execute the approved work plan for the analytical approach; (7) prepare a detailed outline with annotated description for the proposed guidelines in AASHTO format (the proposed guidelines should include, as a minimum, analysis procedures, evaluation criteria, design procedures, construction details, and detailed design examples for the identified concepts); and (8) prepare Interim Report 2 that documents Tasks 6 through 7 and provides an updated work plan for the remainder of the project. Interim Report 3 documented the work C H A P T E R 1 Introduction

4 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview conducted under Phase III of the project that consisted of three tasks: (9) develop guidelines with detailed examples for each concept, (10) qualitatively identify the benefits and potential economic impact of the proposed guidelines, and (11) prepare Interim Report 3. The proposed guidelines and the design examples were updated based on the project panel comments under Task 12 of Phase IV. A final report documenting the summary of all previous tasks was prepared under Task 13 of the NCHRP 12-101 project. 1.3 Document Organization This report is organized into four main chapters and nine appendices. Chapter 1 summarizes the project objectives. Chapter 2 includes guidelines to quantitatively assess any new or existing novel columns with improved seismic performance. The quantita- tive evaluation results are further interpreted using a star-based rating system. Comprehensive design and construction guidelines for three novel columns are presented in Chapter 3. Sum- mary and conclusions are presented in Chapter 4. Appendices A through C address the potential of advanced materials and familiarize the bridge engineering community with these materials. Thirty-nine novel column concepts are presented in Appendix D, including those with test data from large-scale model testing under seismic loading. Appendices E and F provide step-by-step examples to show the application of the proposed guidelines. Qualitative benefits and economic impacts of novel columns are presented in Appendix G. Appendices H and I provide a summary of more than 2,000 nonlinear analyses carried out in this project to establish design equations for three selected novel columns. Chapters 2 and 3 and the appendices form the basis of potential AASHTO guidelines with a possible title of “AASHTO Guidelines on the Design of Resilient Novel Columns.”

5 A conventional reinforced concrete (RC) bridge column is generally designed to dissipate earthquake energy through yielding of longitudinal reinforcing steel combined with cracking and spalling of concrete that leads to large plastic deformations in columns. The performance objective for conventional RC bridges in current bridge seismic design codes is collapse pre- vention, while allowing for substantial damage in column plastic hinges. Even though this per- formance objective is met, plastic hinge damage and large post-earthquake permanent lateral displacements may render the bridge unusable, leading to the need for major repair or replace- ment. The impact of a bridge closure shortly after an earthquake on the traveling public and the economy of a region could be substantial. A new paradigm is emerging among bridge owners requiring that bridges remain functional with minimal interruption to traffic after earthquakes. Recent research has revealed that this paradigm can be realized by using unconventional materials and techniques that possess characteristics that make bridge columns resilient. Novel column designs hold the potential for greatly reducing the amount of damage sustained during a seismic event when compared with conventional reinforced concrete columns. Subsequent to strong earthquakes, a novel column is expected to exhibit minimal or no damage, and low or no residual lateral displacement. The advantages of this behavior include eliminating the need for total replacement as well as significant reductions to the economic impact of a seismic event due to reduced repair costs as well as decreasing the return-to-service time for bridge structures. Whereas the combination of steel reinforcement and conventional concrete provides only one alternative for bridge columns with respect to materials, combining non-ferrous metallic and alter- native cementitious materials, FRPs, rubber, etc., would lead to a large number of alternatives for novel column design. Although some of these combinations have been investigated in recent years, many more could emerge. Evaluation criteria and guidelines are essential to aid in determining the suitability of these novel columns. As part of the NCHRP 12-101 project, guidelines were developed to provide a framework for the evaluation and implementation of novel bridge column design within the existing AASHTO design specification methodology. The guidelines are published as NCHRP Research Report 864, Volume 2, and hence are not duplicated in this section. C H A P T E R 2 Guidelines for Evaluation of Novel Columns

6The project panel selected three novel columns for further studies: (1) SMA-reinforced ECC columns; (2) SMA-reinforced FRP-confined concrete; and (3) FRP-confined concrete hybrid rocking columns. More than 2,250 analyses in the form of moment-curvature, pushover, cyclic, and dynamic simulations were carried out to investigate the behavior of the selected columns and to develop design guidelines. The proposed guidelines for the design and construction of the three selected columns are presented in this chapter. C H A P T E R 3 Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 7 3.1 Proposed Seismic Design and Construction of SMA-Reinforced ECC Columns 3.1.1 Introduction The main objectives of this study were to develop (1) proposed AASHTO guidelines for the evaluation of new techniques for the design and construction of bridge columns with energy dis- sipation mechanisms meant to minimize bridge damage and replacement after a seismic event and (2) design and construction concepts based on new materials, techniques, and analytical methods. The first objective was addressed in Chapter 2, Guidelines for Evaluation of Novel Col- umns. Three novel column concepts were selected by the panel for further study to address the second objective of the project. The focus of this section is on the development of design and construction guidelines for novel column Type 31 (Appendix D), columns with SMA-reinforced ECC plastic hinges. Step-by-step design examples are presented in Appendix F. Economic impact analysis of novel columns is presented in Appendix G. The AASHTO Guide Specifications for LRFD Seismic Bridge Design (AASHTO SGS) (2011) serves as the baseline for the development of the present guideline. All limitations, consider- ations, applicability, and analysis and design methods shall be according to AASHTO SGC except those presented herein. 3.1.2 Application of SMA-Reinforced ECC Columns Reinforcing superelastic shape memory alloy (SE SMA) bars is a viable alternative to reinforc- ing steel bars. SE SMA residual strains are relatively small during cyclic actions ensuring that SMA-reinforced members will regain their original positions after yielding. Engineered cementi- tious composite (ECC) is a fiber-reinforced concrete that is expected to exhibit minimal dam- age under cyclic loadings. The low damage in ECC helps keep the bridge in service after strong earthquakes. The combination of SE SMA and ECC (SE SMA-reinforced ECC) in bridge column plastic hinges results in minimal concrete and reinforcement damage after severe earthquakes and reduces or eliminates the need for post-earthquake repair. SMA-reinforced ECC bridge columns are proposed for sites in which the 1-second period acceleration coefficient, SD1, is greater than 0.3, which is equivalent to the seismic design category (SDC) C or D according to AASHTO SGS (2014). Conventional bridges located in these sites are expected to exhibit severe inelastic deformations. While there is no adverse effect in using SMA-reinforced ECC columns in bridges in SDC A and B and bridge owners may exploit the enhanced durability of ECC and SMA, no benefit is gained from the seismic perspective because of the relatively small seismic demand. 3.1.3 Materials 3.1.3.1 SMA In absence of sufficient information about SMA with other alloys, only nickel-titanium (NiTi) superelastic reinforcing SMA bars are proposed for use as bridge column longitudinal bars at time of this writing. Nonlinear material model and mechanical properties for NiTi SE reinforcing SMA bars should conform to Fig. 3.1.3.1-1 and Table 3.1.3.1-1. A symmetric stress- strain material model based on the expected tensile properties is permitted for the design of SMA-reinforced columns. Currently, only plain undeformed SMA bars are available ranging from No. 4 (Ø13 mm) to No. 18 (Ø57 mm). It is suggested that the austenite finish temperature (Af) (the temperature below which the bar is no longer superelastic) of NiTi SE SMA be equal to or less than the smaller of 14°F

8 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview (–10°C) and the “average low temperature” (a metrological measure) of the site of the structure less 9°F (5°C). The density and Poisson’s ratio of SMA may be considered as 405 lb/ft3 (6,500 kg/m3) and 0.33, respectively (McCormick, 2006). Coefficient of thermal expansion of SE SMA can be taken as 6.1 × 10–6/°F (11 × 10–6/°C) (Otsuka and Wayman, 1998). Electrical resistivity of SE SMA is 32.3 µW-in. (820 µW-mm) (Faulkner et al., 2000). Research has shown that welding of NiTi SMA should not be permitted since SMA may become brittle by reacting to oxygen, nitrogen, and hydro- gen at high temperature (Schlossmacher et al., 1997). A recent study showed that steel will corrode faster if coupled NiTi SMA steel bars are submerged in chloride solution (Alarab et al., 2016). There- fore, in absence of extensive test data, the use of NiTi SMA bars coupled with steel bars in marine environments (e.g., underwater columns) shall be avoided. 3.1.3.2 ECC The stress-strain relationship for unconfined ECC is allowed to be the same as that utilized in practice for the unconfined conventional concrete with no tensile strength (Fig. 3.1.3.2-1a). The secant modulus of elasticity (EECC) shown in the figure should be used in the calculation of uncracked properties of ECC sections. The confined compressive strength of ECC, f ′ce, shall be calculated based on Motaref ’s model as shown in Fig. 3.1.3.2-1b. Strain (%) St re ss k1 k2fy b .fy Nonlinear Model k2 k1 euer k3=a.k1 Source: Tazarv and Saiidi, 2014b Figure 3.1.3.1-1. Superelastic SMA bar stress-strain model. Parameter Minimum(a) Expected(b) Austenite modulus, 4500 ksi (31025 MPa) 5500 ksi (37900 MPa) Post-yield stiffness, -- 250 ksi (1725 MPa) Strain hardening stiffness, -- 1650 ksi (11370 MPa) Austenite yield strength, 45 ksi (310 MPa) 55 ksi (380 MPa) Lower plateau stress factor, 0.45 0.65 Recoverable superelastic strain, 6% 6% Secondary post-yield stiffness ratio, 3.0-- Ultimate strain, 10% 10% Note: (a)To be used in material production and for non-seismic design (e.g., service limit state). (b) To be used in seismic design of SMA-reinforced concrete members. Source: Tazarv and Saiidi, 2014b. Table 3.1.3.1-1. Minimum and expected tensile NiTi superelastic SMA bar mechanical properties.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 9 ( )′ = ′ − + + ′ ′ − ′ ′f f f f f fce ECC l ECC l ECC1.25 2 1 10.5 2 (3.1.3.2-1) where f ′ECC is the compressive strength of the unconfined ECC and f ′l is ( )′= ′2 (3.1.3.2-2)f A f sDl sp yh where Asp is the area of the transverse reinforcement, fyh is the yield strength of the transverse reinforcement, s, is the spacing of the transverse reinforcement, and D′ is the core concrete diameter measured from center to center of the transverse reinforcement. f ′ce shall be taken equal to f ′ECC when f ′l/f ′ECC is less than 0.035. ′ = ′0.4 (3.1.3.2-3)f fue ce [ ]( )ε = + ′ ′ −0.0025 1 2.7 1 (3.1.3.2-4)f fce ce ECC ε = + ρ ε ′0.004 1.4 (3.1.3.2-5)f fue s yh su ce where rs is the volumetric ratio of the transverse reinforcement relative to the core and esu is the transverse reinforcement strain at the peak stress (may use values presented in AASHTO SGS Table 8.4.2-1). A complete stress-strain relationship for confined ECC may conform to Eq. 3.1.3.2-6: = ′ − +1 (3.1.3.2-6)f f Xn n X ECC ce n where = ε ε (3.1.3.2-7)X ce = ′ +0.2 2 (3.1.3.2-8)n f ce ef is the strain in the descending branch where stress drops to f ′ue. ef may be calculated as: [ ]( )ε = ε − ′9.5 0.8 1000 (3.1.3.2-9)Ln ff ce ce f ′ce in Eq. 3.1.3.2-8 and 3.1.3.2-9 shall be in ksi. Source: (b) Motaref et al., 2011. Strain St re ss 0.0020.005 f 'ECC Compression Tension EECC EECC=1400( f 'ECC)1/3(ksi) EECC=5100( f 'ECC)1/3(MPa) Strain St re ss f 'ce f 'ue Compression Tension (a) Unconfined ECC (b) Confined ECC eue ef ece Figure 3.1.3.2-1. ECC stress-strain model.

10 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview (a) Circular Sections (b) Rectangular Sections 0.1 0.15 0.2 0.25 0.3 0.35 E la st ic S tif fn es s R at io (I eff / I g) E la st ic S tif fn es s R at io (I eff / I g) Axial Load Index, P / ( f 'ECC Ag) Axial Load Index, P / ( f 'ECC Ag) Circular SMA-ECC Sections 0.1 0.15 0.2 0.25 0.3 0.35 Rectangular SMA-ECC Sections ASMA/Ag =0.04 ASMA/Ag =0.03 ASMA/Ag =0.02 ASMA/Ag =0.01 ASMA/Ag =0.04 ASMA/Ag =0.03 ASMA/Ag =0.02 ASMA/Ag =0.01 0 0.05 0.1 0.15 0.2 0.25 0.3 0 0.05 0.1 0.15 0.2 0.25 0.3 Figure 3.1.4.2-1. Effective moment of inertia for SMA-reinforced ECC columns [Ieff is the effective moment of inertia, Ig is the moment of intertia of gross section, P is the axial load, Ag is the gross area of member cross-section (in.2), ASMA is the column longitudinal SMA reinforcement area (in.2)]. 3.1.4 Analysis of SMA-Reinforced ECC Columns 3.1.4.1 Selection of Analysis Procedure to Determine Seismic Demand Analysis methods to obtain the seismic demands are according to AASHTO SGS (2011, Article 4.2). 3.1.4.2 Effective Section Properties The effective moment of inertia (Ieff) should be used for the modeling of SMA-reinforced ECC columns. Ieff may be estimated by Fig. 3.1.4.2-1, or the slope of M – Ø curve between the origin and the first SMA bar yield point as: = (3.1.4.2-1)E I MECC eff y yØ where My is yield moment and Øy is yield curvature. All material mechanical properties are the expected values. Appendix I presents the derivation and validation of the graphs.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 11 3.1.4.3 Damping Ratio for Dynamic Analysis For elastic and nonlinear dynamic analyses of SMA-reinforced ECC columns, the damping ratio should be taken as 3.2%, rather than the 5% used for RC. The lower damping ratio recom- mended for SMA-reinforced ECC accounts for the lower hysteretic damping in columns with flag-shaped behavior that could result in higher displacement demands. Fig. 3.1.4.3-1a shows hysteretic damping ratio versus displacement ductility for bridge col- umns with flag-shaped hysteresis. The study by Billah and Alam (2015) was specifically for SMA- reinforced bridge columns. It can be seen that hysteretic damping of columns with flag-shaped behavior is lower than that of conventional RC columns, as expected. Furthermore, the ratio of the flag-shaped column damping to the RC column damping is approximately constant for ductilities greater than 2 (Fig. 3.1.4.3-1b). Table 3.1.4.3-1 presents a summary of damping ratios. The average ratio of flag-shaped hysteretic damping to that of RC columns was 63%. Based on these findings, the damping ratio of SMA-reinforced columns is proposed to be 3.2%, which is 64% of the typical 5% damping. 3.1.4.4 Displacement Modification for Damping The displacement demand for SMA-reinforced ECC columns (RD) calculated using equivalent static or spectral analysis method shall be increased by 20% to account for the lower damping ratio of SMA-reinforced ECC columns as: = ξ   =   = 0.05 0.05 0.032 1.20 (3.1.4.4-1) 0.4 0.4 RD (a) Hysteretic Damping (b) Flag-Shaped Damping (wFlag) over RC Damping (wRC) 0 5 10 15 20 Ductility RC Columns Dwairi et al. (2007) Priestley et al. (2007) Billah and Alam (2015) 0 0.2 0.4 0.6 0.8 1 Ductility Dwairi et al. (2007) Priestley et al. (2007) Billah and Alam (2015)Re co m m en de d 1 2 3 4 5 6 7 1 2 3 4 5 6 7 H ys te re tic D am pi ng (% ) y F la g- Sh ap ed / y R C Figure 3.1.4.3-1. Damping for columns with flag-shaped hysteresis. Dwairi et al. (2007) 0.72 3.60 1.14 Priestley et al. (2007) 0.56 2.80 1.26 Billah and Alam (2015) 0.62 3.12 1.21 Average of Three Refs 0.63 3.17 1.20 Recommended for SMA- Reinforced Columns 0.64 3.20 1.20 Note: = flag-shaped damping, = RC damping, = displacement ductility, RD = displacement demand for SMA-reinforced ECC columns. References (Ave. for ) Flag-Shaped Damping RD Table 3.1.4.3-1. Damping for SMA-reinforced columns.

12 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview An extensive nonlinear parametric study of more than 90 SMA-reinforced ECC columns was conducted in this study. Details of the study are shown in Appendix I. Two aspect ratios, 4 and 6, were selected for 5-ft (1.52-m) diameter columns. Four longitudinal reinforcement ratios (1%, 2%, 3%, and 4%) with one transverse steel ratio (1.07%) were assumed for col- umns. To be able to cover a wide range of structural period, the axial load index (ALI) varied from 0.0% to 20% at 2% increments. The ALI was subsequently converted to mass. The design spectrum was the AASHTO spectrum for downtown, Los Angeles, which falls in the seismic design category (SDC) D, and the ground motion (EQ1) was a synthetic motion generated based on the full design spectral acceleration matching. The results were nearly the same for another synthetic motion, EQ3, that was fully matched with the design acceleration spectrum. Fig. 3.1.4.4-1a shows that the spectral displacements calculated based on 5% damping ratio are approximately the same as the displacement demands calculated based on nonlinear dynamic analyses with a 3.2% damping ratio. The suggested 20% increase in spectral displacement (Fig. 3.1.4.4-1b) ensures that spectral displacements are always larger than the demands obtained from nonlinear dynamic analysis. 3.1.4.5 Displacement Modification for Short-Period Bridges No modification is needed for short-period SMA-reinforced ECC columns since the 20% increase in the spectral displacements due to lower damping ratio guarantees higher spectral displacement for practical bridge columns including short-period columns. (a) Original Spectral Displacements 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 3 D isp la ce m en t ( in .) Period (sec) SDC-D (5%) Sd for EQ1 (5%) Disp. Demand (3.2%) Short Period Limit Sd versus Nonlinear Displacement Demands Results for 93 Columns under EQ1 (b) Amplified Spectral Displacements 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 3 D isp la ce m en t ( in .) Period (sec) Amplified SDC-D (5%) Disp. Demand (3.2%) Short Period Limit Sd versus Nonlinear Displacement Demands Results for 185 Analyses (EQ1, EQ3) Figure 3.1.4.4-1. Spectral displacement (Sd) vs. nonlinear dynamic displacement demands for SMA-reinforced ECC columns.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 13 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 D ri ft R at io (% ) Displacement Ductility Aspect Ratio= 4 Aspect Ratio= 6 Aspect Ratio= 8 Practical Range Proposed relationships are the upper bound Figure 3.1.4.6-1. Drift-ductility relationships for RC columns. Parameters Column Aspect Ratio 4 Column Aspect Ratio 6 Column Aspect Ratio 8 Note: “ ” is the drift ratio (%) and “ ” is the displacement ductility. Proposed Equation Table 3.1.4.6-1. Proposed relationships between drift and ductility. 3.1.4.6 Displacement Ductility versus Drift Ratio Displacement ductility demand, µD, for conventional columns is calculated as µ = + ∆ ∆ 1 (3.1.4.6-1)D pd yi where Δpd is the plastic displacement demand and Δyi is the idealized yield displacement cor- responding to the idealized yield curvature. This measure for SMA-reinforced columns usually results in a misleading value since the yield strain of SMA bars is 5 times higher than that of steel bars resulting in a higher idealized (effective) yield displacement and thus a lower calculated ductility even though the displacement capacity of a SMA-reinforced column may substantially exceed that of a comparable conventional column. Drift ratio, the ratio of column lateral displace- ment to the column height, was proposed as an alternative measure to estimate the deformation capacity and demand of novel columns, including SMA-reinforced ECC columns. Because current bridge seismic codes utilize displacement ductility rather than the drift capac- ity in design, it was important to determine the relationship between ductility and drift ratio so that displacement ductilities for conventional columns in current codes can be translated to drift ratios that may be utilized in novel column design. An extensive parametric study on conven- tional RC columns was conducted to establish a relationship between the displacement ductility and drift ratio for these columns (Appendix H). Fig. 3.1.4.6-1 shows the condensed result of the parametric study. Equations were developed to relate drift ratio and ductility and are listed in Table 3.1.4.6-1. Detailed results of the parametric study are presented in Appendix H. Linear

14 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview interpolation is allowed for intermediate aspect ratios. Alternatively, the following equation can be used for intermediate aspect ratios: ( ) ( )δ = µ −0.26 0.18 (3.1.4.6-2)0.81 0.57A Ar r where µ is displacement ductility and Ar is the column aspect ratio (Fig. 3.1.4.6-2). For single- column bents, the aspect ratio is defined as the ratio of the column height to the column side dimension parallel to the loading direction. For multi-column bents, the aspect ratio is the ratio of a portion of the column length (length of column from point of maximum moment to the point of contraflexure) to the column side dimension parallel to the loading direction. The full column length is used if one end of the column is pinned. 3.1.4.7 Column Drift Demand Requirement The recommended limits on drift ratio demand, dD, for novel columns are listed in Table 3.1.4.7-1. The values are based on the displacement ductility demand limits for conventional columns Member ConventionalColumns Novel Columns Single-column bents Aspect Ratio 4: Aspect Ratio 6: Aspect Ratio 8: Multiple-column bents Aspect Ratio 4: Aspect Ratio 6: Aspect Ratio 8: Note: “ ” is the drift ratio demand (%) and “ ” is the displacement ductility demand. Use linear interpolation for intermediate aspect ratios. Table 3.1.4.7-1. Bridge column drift ratio demand requirements. (c) Multi-Column Bent with One-End-Pinned Joints LD Pinned Joint (a) Single-Column Bent L D D L (b) Multi-Column Bent with Fixed Ends Figure 3.1.4.6-2. Aspect ratio definition [D is the diameter of the column (or the largest side dimension) and L is the column height from point of maximum moment to the point of contraflexure].

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 15 multiplied by the deformability factor, W, which should be taken as 1.2 for SMA-reinforced ECC columns. Linear interpolation can be used for intermediate aspect ratios. Extrapolation for a col- umn with a lower aspect ratio than 4 is valid if the column behavior is dominated by flexure. Available test data on the SMA-reinforced ECC columns (Saiidi et al. 2009; Nakashoji and Saiidi 2014; Tazarv and Saiidi 2015a) confirm that these columns even with a low aspect ratio of 4.5 can withstand more than 10% drift ratio demand. The mode of failure for these columns was SMA bar fracture at higher drifts. 3.1.4.8 Column Force Demand Columns will ideally be designed to resist all internal forces developed during an earthquake or those associated with a collapse mechanism. 3.1.4.8.1 Moment Demand. The column design moment is the smaller of that obtained from (a) the demand at the design level earthquake and (b) the idealized plastic capacity of the column cross-section. The column design moment obtained from (a) and (b) shall not be less than the column failure moment (Mu) when the column failure moment is greater than 1.2 times the idealized plastic moment (Mu ≥ 1.2Mp). The general approach for conventional columns is that the plastic moment calculated using the idealized method is approximately the same as the actual plastic moment capacity, thus the maxi- mum possible moment demand is the plastic moment. This condition may not always be true for novel columns. The SMA-reinforced member moment-curvature (or force-displacement) relationship is usually tri-linear (Fig. 3.1.4.8.1-1). When the moment (or force) demand calculated from linear analysis falls on the third branch, the plastic moment (or force) calculated using the idealized method may be significantly lower than the demand. In this case, the column failure moment should be used as specified. 3.1.4.8.2 Shear Demand. The column shear demand is the smaller of that obtained from (a) the demand at design level earthquake and (b) the shear associated with 1.2 times the plastic moment calculated using the idealized method. The column shear obtained from (a) and (b) shall not be less than the shear associated with 1.44 times the idealized plastic moment when the calcu- lated failure moment exceeds 1.2Mp (Mu ≥ 1.2Mp). All possible plastic hinge locations should be considered in the determination of shear forces using (b). 3.1.4.8.3 Column Adjoining Member Force Demand. Column adjoining members (e.g., footings, cap beams, and connections) are designed to resist the overstrength plastic hinging Idealized M om en t Actual ØYi Øy Øu Curvature Mp Mu My ØYi Øy Øu Mp Mu My Idealized M om en t Actual Curvature (a) Conventional RC Sections (b) SMA-Reinforced Sections Figure 3.1.4.8.1-1. Typical moment-curvature relationships (Mu is failure moment, Mp is plastic moment, My is yield moment, �Y is yield curvature, �Yi is idealized yield curvature, �u is ultimate curvature).

16 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview moment, see Sections 3.1.4.8.1 and 3.1.4.8.2, and the associated forces (e.g., shear and overturn- ing axial forces) in an essentially elastic manner. This design approach is known as capacity design and is outlined in the AASHTO SGS. 3.1.4.9 Residual Drift The residual drift of SMA-reinforced ECC columns is insignificant for all practical cases due to the superelastic effect of reinforcing SMA bars. Therefore, the residual drift for these columns can be categorized as “low” (dr ≤ 1.0%). Fig. 3.1.4.9-1 shows the residual drift-peak drift relationship for all practical SMA-reinforced ECC columns (based on the limitations specified in this guideline such as minimum and maxi- mum longitudinal reinforcement ratios, maximum aspect ratio). The analytical results are shown up to the failure point (drift capacity) of each column. It can be seen that the residual drift ratios for all SMA-reinforced ECC columns are less than 1.0%. The left cluster of the data (solid black lines), mid-cluster of the data (solid gray lines), and the bottom-right cluster of the data are respectively for columns with aspect ratios of 4, 6, and 8. The residual-peak drift relationships measured in a conventional RC bridge column test (dashed gray line) as well as an SMA-reinforced ECC column test (dashed black line) are also shown in the figure. 3.1.5 Design of SMA-Reinforced ECC Columns SMA-reinforced ECC columns ideally will be designed conforming to requirements presented in this section. 3.1.5.1 Analytical Plastic Hinge Length The analytical plastic hinge length of SMA-reinforced ECC columns may be estimated using = + ≥0.08 0.15 0.3 (3.1.5.1-1)L L f d f dp ye bl ye bl where fye (ksi) is the expected austenite yield strength of the longitudinal column-reinforcing SMA bars and dbl (in.) is the nominal diameter of longitudinal-column reinforcing SMA bars. Nakashoji and Saiidi (2014) showed utilizing all available test data that the plastic hinge length of SMA-reinforced ECC columns can be conservatively estimated using the equation presented in AASHTO SGS (2011). 0 0.2 0.4 0.6 0.8 1 1.2 1.4 R es id ua l D ri ft R a tio (% ) Peak Drift Ratio (%) Results for 56 columns (Practical Range) 1% Limit (Low Residual) SMA/ECC Column Test (Tazarv and Saiidi, 2014b) Conv. Column Test (Haber et al., 2013) 0 1 2 3 4 5 6 7 8 9 10 Figure 3.1.4.9-1. Residual drifts for all practical SMA-reinforced ECC columns.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 17 3.1.5.2 Column Drift Capacity Column drift capacity (Δc) is defined as a displacement at fracture of the column longitudinal bar or compressive failure of the column core concrete. Either moment-curvature or pushover analyses may be used for the estimation of a SMA-reinforced ECC column displacement capac- ity. However, a pushover analysis is preferred since it includes the entire bridge model, frame actions, and geometric nonlinearities. When moment-curvature analysis is used, the displace- ment capacity is 3 2 (3.1.5.2-1) 2Ø Ø ØL L L Lc Yi u Yi p p( )∆ = + − −  where ØYi is the idealized yield curvature calculated using the idealized method (Appendix H, Fig. H-1), Øu is the ultimate curvature associated with either SMA bar fracture or core ECC fail- ure, L is the column height from point of maximum moment to the point of contraflexure, and Lp is the analytical plastic hinge length. Column drift capacity (dc) is defined as the ratio of the column displacement capacity to the column height as δ = ∆ (3.1.5.2-2) L c c 3.1.5.2.1 Minimum Drift Capacity. The recommended minimum drift ratio capacity for SMA-reinforced ECC columns is listed in Table 3.1.5.2.1-1. The drift ratios correspond to the minimum displacement ductility capacity for conventional columns. Columns shall be designed to provide at least this level of drift ratio. Linear interpolation can be used for intermediate aspect ratios. 3.1.5.3 Shear Capacity The shear capacity of SMA-reinforced ECC columns within the plastic hinge calculated based on the nominal material strength properties should satisfy: (3.1.5.3-1)ØV Vs n u≥ in which: = + (3.1.5.3-2)V V Vn c s Where the strength reduction factor, Øs, is 0.9, Vn is the nominal shear capacity of member, Vs is the reinforcing steel contribution to shear capacity, and Vc is the ECC contribution to shear capacity: ( )= min , (3.1.5.3-3)1 2V V Vc c c Member ConventionalColumns Novel Columns Single- or multi-column bents Aspect Ratio 4: Aspect Ratio 6: Aspect Ratio 8: Note: “ ” is the drift ratio capacity (%) and “ ” is the displacement ductility capacity. Use linear interpolation for intermediate aspect ratios. Table 3.1.5.2.1-1. Minimum bridge column drift ratio capacity requirements.

18 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview where Vc1 is based on AASHTO SGS (2011) and Vc2 is according to the JSCE Concrete Library 127 (2008) as = 0.8 (3.1.5.3-4)1V v Ac c g vc is zero if the column is under tensile axial loads. Otherwise: ( )= ′α +  ′ ≤ ′ ′α ′0.032 1 2 min 0.11 , 0.047 (3.1.5.3-5)v P A f f fc u g ECC ECC ECC For a circular column with spiral or hoop reinforcing: ′α = + − µ 0.15 3.67 (3.1.5.3-6) fs D = ρ ≤ 0.35 (3.1.5.3-7)f fs s yh ρ = ′ 4 (3.1.5.3-8) A sD s sp where Ag is the gross area of the member cross-section (in. 2), Pu is the ultimate compressive force acting on the section (kips), Asp is the area of the spiral or hoop reinforcing bar (in. 2), s is the pitch of the spiral or spacing of hoops or ties (in.), D′ is the core diameter of the column measured from center of spiral or hoop (in.), fyh is the nominal yield stress of transverse reinforcing (ksi), f ′ECC is the nominal ECC compressive strength (ksi), µD is the displacement ductility demand calculated from drift demand, and a′ is the ECC shear stress adjustment factor. = + (3.1.5.3-9)2V V Vc cd fd where Vcd and Vfd are, respectively, the contribution of ECC and fiber to shear capacity. The ECC contribution to shear strength is as follows: = β β β γ. . . . . (3.1.5.3-10)V f b dcd d p n vcd w b where [ ] ( ) ( ) = ′ ≤ β = ≤ β = ≤ β = + ≤ ≥ β = + ≥ < 0.039 0.07 ksi 2.5 1 1.5 is in in. 100 1.5 (3.1.5.3-11) 1 2 0 1 2 0 0 3 4 3 f f d d p M M P M M P vcd ECC d p w n o u u n o u u where Pu is the design axial compressive force, Mu is the design bending moment, Mo is the bend- ing moment necessary to cancel stress due to axial force at extreme tension fiber corresponding to design bending moment Md, bw (in.) is the width of member (in the case of circular section with diameter of D, bw = 0.55D), d (in.) is the distance from the extreme compression fiber to the centroid of extreme longitudinal tension reinforcement, pw = ASMA/(bw.d) (in the case of circular section, pw = ASMA/Ag), ASMA is the column longitudinal SMA reinforcement area (in.2), and gb is a safety factor and may be taken as 1.3.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 19 The contribution of fibers to shear strength is as follows: ( )= γ β . . tan (3.1.5.3-12)V f b z fd vd w b u where fvd is the design tensile strength of ECC (may be taken as 0.29 ksi) and must be taken as zero when it is smaller than 0.2 ksi, z is the distance from location of compressive stress resultant to the centroid of tensile steel and may generally be taken as 0.87d, bu is the angle of the diagonal crack surface to the member axis and may be taken as 45°. For members that are reinforced with circular hoops, spirals, or interlocking hoops or spirals, the nominal shear reinforcement strength, Vs is: = pi ′ 2 (3.1.5.3-13)V nA f D s s sp yh where n is the number of individual interlocking spirals or hoops within the spacing s. Refer to AASHTO SGS for the calculation of Vs for other types of cross-sections. 3.1.5.4 Axial Capacity The axial capacity of an SMA-reinforced ECC column shall be calculated as ( )( )= ′ − +0.75 (3.1.5.4-1)1P z f A A A fn ECC g SMA SMA yØ where f ′ECC is the nominal ECC compressive strength (ksi), Ag is the gross area of member cross-section (in.2), ASMA is the column longitudinal SMA reinforcement area (in. 2), fy is the nominal austenite yield strength of SMA bars, and the upper limit strength modifier for ECC is = − ′ ≤ ′ ≤1 0.02 0.85 for 11.6 ksi (3.1.5.4-2)1z f fECC ECC The axial load capacity for steel reinforced ECC sections was based on the JSCE Concrete Library 127 (2008) and was modified in this section to include SMA bars. 3.1.5.5 Minimum Lateral Strength Each bent shall have a minimum lateral flexural capacity to resist a lateral force of 0.1Pdl, where Pdl is the tributary dead load applied at the center of gravity of the superstructure. 3.1.5.6 Other Loading and Strength Design The estimation, analysis, and design of SMA-reinforced ECC columns for non-seismic loads are based on the AASHTO LRFD Bridge Design Specifications (2014) in which ECC can be treated as the conventional concrete but with ECC properties (e.g., modulus of elasticity) and reinforcing SMA bars can be treated as conventional steel bars but with SMA properties (the austenite yield strength, the modulus of elasticity). Only for preliminary design under the load combination of “Extreme Event I,” the AASHTO response modification factors (AASHTO LRFD, Table 3.10.7.1-1) may be used to reasonably size the columns and the adjoining mem- bers. Nevertheless, SMA-reinforced ECC columns should be analyzed and designed according to the present guideline for seismic loads. 3.1.5.7 Serviceability Design An SMA-reinforced ECC column will ideally be designed to withstand service loads during the life of the bridge. Actions to be considered for these columns at the service limit state should

20 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview be short- and long-term deformations. Serviceability for conventional RC and ECC is addressed through the minimum shrinkage and temperature reinforcement requirement. The relatively high transverse reinforcement to satisfy seismic design requirements in novel columns exceeds the minimum shrinkage and temperature reinforcement requirement AASHTO LRFD. 3.1.5.7.1 Shrinkage and Creep. In the absence of test data, the ECC shrinkage strain may be assumed to be 0.00046 after 1 year of drying. Other shrinkage parameters can be based on current AASHTO LRFD requirement for concrete. Creep coefficient of ECC may be assumed to be 1.5. These recommendations are according to the JSCE Concrete Library 127 (2008). Sample test data are shown in Fig. 3.1.5.7-1. 3.1.5.7.2 Axial Deformations. Instantaneous axial deformation due to loads and long- term shortening due to shrinkage and creep should be determined for ECC columns only when these columns are post-tensioned. Design of post-tensioned ECC columns is beyond the scope of this report. The estimation of deformations in SMA-reinforced ECC elements at a limit state of service- ability should be based on two assumptions: (1) strain is proportional to the distance from the neutral axis of the cross-section and (2) ECC and SMA are linear elastic materials with moduli of elasticity specified in section 3.1.3. Analysis can be performed assuming perfect bond between reinforcing SMA bars and ECC. 3.1.6 Details for SMA-Reinforced ECC Columns SMA-reinforced ECC columns shall be detailed conforming to requirements presented in this section. 3.1.6.1 Partially or Fully Cast ECC Columns The incorporation of ECC only over partial length of columns should be permitted. The length of the ECC portion of columns in the plastic hinge region shall be at least 1.5 times the largest column cross-sectional dimension. 3.1.6.2 Reinforcement Details 3.1.6.2.1 Longitudinal SMA Reinforcement. The area of longitudinal reinforcing SMA bars (ASMA) in the SMA-reinforced ECC columns should satisfy: ≤ ≤0.01 0.04 (3.1.6.2-1)A A Ag SMA g Source: JSCE Concrete Library 127, 2008. (a) ECC Shrinkage (b) ECC Creep Coefficient Cr ee p co e ffi ci en t ECC CEP-FIP Ordinary concrete with the same level of compressive strength Age of loading (day)Age (day) Test method: JIS A 1129 Sh rin ka ge s tra in (x 10 -6) Drying shrinkage strain of ordinary concrete Figure 3.1.5.7-1. ECC shrinkage and creep properties.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 21 where Ag is the gross area of member cross-section (in. 2). Since the austenite yield strength of SMA bars is usually lower than the steel bar yielding, higher longitudinal reinforcement than con- ventional columns is expected, but the reinforcement area should be within the specified range. 3.1.6.2.2 SMA Bar Size. The available size of reinforcing SMA bars is presented in Table 3.1.6.2.2-1. 3.1.6.3 Splicing of SMA Reinforcement The incorporation of SMA bars over only a partial length of columns ideally will be permitted and suggested to save cost. The length of SMA bars shall not be less than the analytical plastic hinge length and 75% of the largest column cross-sectional dimension (0.75D). SMA bars are plain (with smooth surfaces), behaving similarly to debonded bars under cyclic loading. When SMA bars are used over the entire length of members, mechanical anchorage shall be used to anchor the bars in the adjoining members. When SMA bars are utilized only in the plastic hinge region, reinforcing SMA bars should be connected to reinforcing steel bars using mechanical bar splices approved by the bridge owner. Threaded (only those with parallel threads but not those with tapered threads) and headed bar couplers have exhibited satisfactory performance in large-scale tests. Splicing should be permitted in the plastic hinge region of the columns pending owner approval. A recent study by Tazarv and Saiidi (2015b) showed that the mechanical bar splices in the column plastic hinges reduce the displacement ductility capacity as ( )µ µ = − β   β 1 0.18 (3.1.6.3-1) 0.1H L sp CIP sp sp where µsp is the displacement ductility capacity of a mechanically spliced column, µCIP is the conventional non-spliced cast-in-place column displacement ductility capacity, b is the cou- pler rigid length factor obtained from the splice tensile tests or the coupler manufacturer (a range from 0 to 1), Hsp is the distance between the coupler end to the column adjoining member interface (Fig. 3.1.6.3-1), and Lsp is the splice length. Hsp should be taken 0.1 in. (2.5 mm) when couplers are installed at the column to adjoining member interface. Fig. 3.1.6.3-1 is intended to clarify the parameters in Eq. 3.1.6.3-1. SMA bars require two splices as shown in Fig. 3.1.7.2-1. In this case, the coupler properties in Eq. 3.1.6.3-1 should be based on the coupler that is near the column end. Since there is a linear relationship between the displacement ductility and the drift ratio, the ratio of the spliced to cast-in-place (CIP) column ductilities presented in the equation is approximately the same as the ratio of the spliced to CIP column drift ratios. More information can be found in the NCHRP Project 12-105 final report. Bar Size No. (mm) Nominal Diameter in. (mm) Cross-Sectional Area in.2 (mm2) #4 (Ø13) 0.500 (12.7) 0.20 (129) #5 (Ø16) 0.625 (15.9) 0.31 (199) #6 (Ø19) 0.750 (19.1) 0.44 (284) #7 (Ø22) 0.875 (22.2) 0.60 (387) #8 (Ø25) 1.000 (25.4) 0.79 (510) #9 (Ø29) 1.128 (28.7) 1.00 (645) #10 (Ø32) 1.270 (32.3) 1.27 (819) #11 (Ø36) 1.410 (35.8) 1.56 (1006) #14 (Ø43) 1.693 (43.0) 2.25 (1452) #18 (Ø57) 2.257 (57.3) 4.00 (2581) Table 3.1.6.2.2-1. Plain SMA bar dimensions.

22 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview 3.1.6.4 Maximum Axial Load The axial load acting on an SMA-reinforced ECC column, including gravity and seismic demands (Pu) where a pushover analysis is not performed, should satisfy: ≤ ′0.15 (3.1.6.4-1)P f Au ECC g where Ag is the gross area of member cross-section (in. 2) and f ′ECC is the nominal ECC com- pressive strength (ksi). A higher axial load value may be used provided that pushover analysis including the P – Δ effect is performed to compute the maximum drift capacity of the column. 3.1.6.5 Maximum Aspect Ratio The aspect ratio of SMA-reinforced ECC bents should not exceed 8. Columns with larger aspect ratios may fail at low drift ratios due to the P – Δ effect. Source: Tazarv and Saiidi, 2015b. Hsp Lsp Footing Co up le rs Cap Beam M ec ha ni ca lly S pl ic ed C ol um n Figure 3.1.6.3-1. Mechanical bar splices. Source: Tazarv and Saiidi, 2014a. Not all reinforcement are shown for clarity Reinforcing Steel Bar Cast-in-Place Column Footing Reinforcing Steel Bar Reinforcing SMA Bar Precast Column Reinforcing SMA Bar Reinforcing Steel BarGroutFilled Ducts Footing Reinforcing Steel Bar (a) Cast-in-Place Detailing (b) Precast Detailing Figure 3.1.7.2-1. Construction of SMA-reinforced ECC columns.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 23 3.1.7 Construction of SMA-Reinforced ECC Columns 3.1.7.1 Quality Control Tests ASTM F2516-07 (2007) should be utilized for tensile testing of NiTi SE SMA to compute the mechanical properties according to the procedure presented in Tazarv and Saiidi (2014b). Only reinforcing SMA bars satisfying the “minimum” material properties (sec. 3.1.3) shall be allowed for the design and construction of SMA-reinforced bridge columns. ECC testing method for the computation of compressive and tensile strengths, strain capacities, workability, and durability should be according to the JSCE Concrete Library 127 (2008). 3.1.7.2 Construction Procedures CIP and precast construction ideally will be permitted for SMA-reinforced ECC columns. Fig. 3.1.7.2-1 shows one example for each construction method. The design of precast column connections should be according to bridge-owner approved guidelines. 3.1.7.3 Construction Tolerance Tolerance limits normally used for conventional RC construction are applicable to SMA/ECC columns. Quality control for precast columns should be according to PCI MNL-116-99 (1999). Construction tolerance for precast column connections should be according to bridge-owner approved guidelines. 3.1.8 References AASHTO. (2011). AASHTO Guide Specifications for LRFD Seismic Bridge Design. Washington, D.C.: American Association of State Highway and Transportation Officials. AASHTO. (2014). AASHTO LRFD Bridge Design Specifications. Washington, D.C.: American Association of State Highway and Transportation Officials. Alarab, L. A., Ross, B. E., and Poursaee, A. (2016). Corrosion Assessment of Coupled Steel Reinforcement with Ni-Ti–Based Shape Memory Alloy in Simulated-Concrete Pore Solution. ASCE Journal of Materials in Civil Engineering, Vol. 28, No. 8, 6 pp. https://doi.org/10.1061/(ASCE)MT.1943-5533.0001565. ASTM. (2007). Standard Test Method for Tension Testing of Nickel-Titanium Superelastic Materials, F2516-07, West Conshohocken, PA. Billah, A. H. M. M., and Alam, M. S. (2015). Damping-Ductility Relationship for Performance Based Seismic Design of Shape Memory Alloy Reinforced Concrete Bridge Pier. Proceeding of Structures Congress 2015, ASCE, 474–484. https://doi.org/10.1061/9780784479117.042. Dwairi, H. M., Kowalsky, M. J., and Nau, J. M. (2007). Equivalent Damping in Support of Direct Displacement- Based Design. Journal of Earthquake Engineering, 11(4), 512–530. https://doi.org/10.1080/13632460601033884. Faulkner, M. G., Amalraj, J. J., and Bhattacharyya, A. (2000). Experimental Determination of Thermal and Electrical Properties of Ni-Ti Shape Memory Wires. Smart Materials and Structures, 9(5), 632–639. https://doi.org/10.1088/0964-1726/9/5/307. Haber, Z. B., Saiidi, M. S., and Sanders, D. H. (2013). Precast Column-Footing Connections for Accelerated Bridge Construction in Seismic Zones, Center for Civil Engineering Earthquake Research, Department of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-13-08, 612 pp. JSCE Concrete Library 127. (2008). Recommendations for Design and Construction of High Performance Fiber Reinforced Cement Composites with Multiple Fine Cracks (HPFRCC). Japan Society of Civil Engineers. McCormick, J. P. (2006). Cyclic Behavior of Shape Memory Alloys Materials Characterization and Optimization, PhD Dissertation, Georgia Institute of Technology, 351 pp. Motaref, S., Saiidi, M. S., and Sanders, D. (2011). Seismic Response of Precast Bridge Columns with Energy Dis- sipating Joints, Center for Civil Engineering Earthquake Research, Department of Civil and Environmental Engineering, University of Nevada, Reno, Report No. CCEER-11-01. Nakashoji, B., and Saiidi, M. S. (2014). Seismic Performance of Square Nickel-Titanium Reinforced ECC Columns with Headed Couplers, Center For Civil Engineering Earthquake Research, Department Of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-14-05, 252 pp. Otsuka, K., and Wayman, C. M. (1998). Mechanism of Shape Memory Effect and Superplasticity (pp. 27–48). Cambridge, U.K.: Cambridge University Press.

24 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview PCI MNL-116-99. (1999). Manual for Quality Control for Plants and Production of Structural Precast Concrete Products, Precast/Prestressed Concrete Institute, Chicago, IL, 328 pp. Priestley, M. J. N., Calvi, G. M., and Kowalski, M. J. (2007). Displacement-Based Seismic Design of Structures. Pavia: IUSS press. Saiidi, M. S., O’Brien, M., and Sadrossadat-Zadeh, M. (2009). Cyclic Response of Concrete Bridge Columns Using Superelastic Nitinol and Bendable Concrete. ACI Structural Journal, 106(1), 69–77. Schlossmacher, P., Haas, T., and Schüssler, A. (1997). Laser-Welding of a Ni-Rich TiNi Shape Memory Alloy: Mechanical Behavior. Journal De Physique IV France, 07(C5, No. C5), 251–256. https://doi.org/10.1051/ jp4:1997539. Tazarv, M., and Saiidi, M. S. (2014a). Next Generation of Bridge Columns for Accelerated Bridge Construction in High Seismic Zones, Center For Civil Engineering Earthquake Research, Department of Civil and Environ- mental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-14-06, 400 pp. Tazarv, M., and Saiidi, M. S. (2014b). Reinforcing NiTi Superelastic SMA for Concrete Structures. In Journal of Structural Engineering. ASCE; https://doi.org/10.1061/(ASCE)ST.1943-541X.0001176. Tazarv, M., and Saiidi, M. S. (2015a). Low-Damage Precast Columns for Accelerated Bridge Construction in High Seismic Zones. In Journal of Bridge Engineering. ASCE; https://doi.org/10.1061/(ASCE)BE.1943-5592.0000806. Tazarv, M., and Saiidi, M. S. (2015b). Design and Construction of Bridge Columns Incorporating Mechanical Bar Splices in Plastic Hinge Zones, Center For Civil Engineering Earthquake Research, Department of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-15-07, 149 pp.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 25 FRP Jacket Reinforcing SMA Bars Concrete Co up le r Footing G ap Figure 3.2.1-1. SMA-reinforced FRP-confined plastic hinge detail at column base. 3.2 Proposed Design and Construction of SMA-Reinforced FRP-Confined Concrete Columns 3.2.1 Introduction The main objectives of the present study was to develop (1) proposed AASHTO guidelines for the evaluation of new techniques for the design and construction of bridge columns with energy dissipation mechanisms meant to minimize bridge damage and replacement after a seis- mic event and (2) design and construction concepts based on new materials and techniques and analytical techniques. The first objective was addressed in Chapter 2: Guidelines for Evaluation of Novel Columns. Three novel column concepts were selected by the panel for further study to address the second objective of the project. This section describes the development of design and construction guidelines for novel columns (Type 8 in Appendix D) incorporating SMA reinforcement and FRP-confined concrete in the plastic hinge region (Fig. 3.2.1-1). SMA longitudinal bars are con- nected to steel bars via mechanical bar splices, and the column is encased with a hard FRP tube or wrapped with FRP fabrics with fibers confining concrete and providing shear strength for the column. Step-by-step design examples are presented in Appendix F. Economic impact analysis of novel columns is discussed in Appendix G. The AASHTO Guide Specifications for LRFD Seismic Bridge Design (AASHTO SGS) (2011) serves as the baseline for the development of the present guideline. All limitations, consider- ations, applicability, and analysis and design methods shall be according to AASHTO SGS except those presented herein. 3.2.2 Application of SMA-Reinforced FRP-Confined Concrete Columns Reinforcing superelastic shape memory alloy (SE SMA) bars are viable alternative to reinforc- ing steel bars. SE SMA residual strains are relatively small during cyclic loading ensuring that SMA-reinforced members will regain their original positions after yielding. The concrete damage is minimal when it is jacketed by fiber-reinforced polymer (FRP) sheets. The low damage in FRP-confined concrete helps keep the bridge in service after strong earthquakes. The combina- tion of SE SMA and FRP jacket (SMA-reinforced FRP-confined concrete) in bridge column plastic hinges results in minimal concrete and reinforcement damage after severe earthquakes and reduces or totally eliminates the need for post-earthquake repair.

26 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview SMA-reinforced FRP-confined concrete bridge columns are suggested for sites in which the 1-sec period acceleration coefficient, SD1, is greater than 0.3, which is equivalent to the seismic design category (SDC) C or D according to AASHTO SGS (2011). Conventional bridges located in these sites are expected to undergo large inelastic deformations under strong earthquakes. While there is no adverse effect in using SMA-reinforced FRP-confined columns in bridges under SDC A and B, bridge owners may take advantage of the enhanced durability of SMA and the ease of construction with FRP tubes that serve as permanent formwork, even though there is no benefit from the seismic performance perspective because of the relatively small seismic demand in SDC A and B. 3.2.3 Materials 3.2.3.1 SMA In the absence of sufficient information about other SMA with other alloys, only nickel-titanium (NiTi) superelastic reinforcing-SMA bars are suggested for use as bridge column longitudinal bars at time of this writing. The available NiTi bars are composed of approximately equal amount of nickel and titanium. NiTi with other compositions meeting the requirements specified in these guidelines shall be permitted. Nonlinear material model and mechanical properties for SE NiTi reinforcing SMA bars should conform to Fig. 3.2.3.1-1 and Table 3.2.3.1-1. A symmetric Source: Tazarv and Saiidi, 2014b. Strain (%) St re ss k1 k2 fy ß.fy k3=a.k1 Nonlinear Model k2 k1 euer Figure 3.2.3.1-1. Superelastic SMA bar stress-strain model. Parameter Minimum(a) Expected(b) Austenite modulus, k1 4500 ksi (31025 MPa) 5500 ksi (37900 MPa) Post-yield stiffness, k2 -- 250 ksi (1725 MPa) Strain hardening stiffness, k3 -- 1650 ksi (11370 MPa) Austenite yield strength, fy 45 ksi (310 MPa) 55 ksi (380 MPa) Lower plateau stress factor, β 0.45 0.65 Recoverable superelastic strain, εr 6% 6% Secondary post-yield stiffness ratio, α -- 0.3 Ultimate strain, εu 10% 10% Note: (a)to be used in material production and for non-seismic design (e.g., service limit state). (b)to be used in seismic design of SMA-RC members. Source: Tazarv and Saiidi, 2014b. Table 3.2.3.1-1. Minimum and expected tensile NiTi superelastic SMA bar mechanical properties.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 27 stress-strain material model based on the expected tensile properties is permitted for the design of SMA-reinforced columns. Currently, only plain undeformed SMA bars are available ranging from No. 4 (Ø13 mm) to No. 18 (Ø57 mm). It is proposed that the austenite finish temperature (Af) (the temperature below which the bar is no longer superelastic) of NiTi SE SMA be equal to or less than the smaller of 14°F (–10°C) and the “average low temperature” (a metrological measure) of the site of the structure less 9°F (5°C). The density and Poisson’s ratio of SMA may be considered as 405 lb/ft3 (6500 kg/m3) and 0.33, respectively (McCormick, 2006). The coefficient of thermal expansion of SE SMA can be taken as 6.1 × 10–6/°F (11 × 10–6/°C) (Otsuka and Wayman, 1998). Electrical resistivity of SE SMA is 32.3 µW-in. (820 µW-mm) (Faulkner et al., 2000). Research has shown that welding of NiTi SMA should not be permitted since SMA may become brittle by reacting to oxygen, nitrogen, and hydrogen at high temperature (Schlossmacher et al., 1997). A recent study showed that steel will corrode faster if coupled NiTi SMA steel bars are submerged in chloride solution (Alarab et al., 2016). Therefore, in absence of extensive test data, the use of NiTi SMA bars coupled with steel bars in a marine environment (e.g., underwater columns) shall be avoided. 3.2.3.2 FRP-Confined Concrete When a concrete member is encased by an FRP jacket intended to provide confinement, the entire section should be considered to be confined. The confined properties of FRP jack- eted concrete shall be calculated based on the ACI model (ACI 440.2R-08, 2008) as shown in Fig. 3.2.3.2-1. The maximum compressive strength of a FRP-confined concrete section (f ′cc) is ′ = ′ + 3.135 (3.2.3.2-1)f f k fcc c a l where f ′c is the unconfined cylinder compressive strength of concrete, ka is the section efficiency factor, and fl is the confining pressure = ε2 (3.2.3.2-2)f E n t Dl f f f fe where Ef is the modulus of elasticity of FRP, nf is the number of FRP layers, tf is the thickness of each FRP layer, D is the section diameter (or the equivalent diameter for a non-circular section), and ε = ε = =0.58 0.58 0.58 (3.2.3.2-3) f E C f E fe fu fu f E fu f  Source: ACI 440.2R-08, 2008. 1E2 Tension confined Strain unconfined St re ss Compression ecu e 't eco f 'cc f 'c Figure 3.2.3.2-1. FRP-confined concrete stress-strain model.

28 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview where f *fu is the guaranteed FRP design tensile strength reported by the manufacturer and CE is the environmental reduction factor according to Table 3.2.3.2-1. The ratio of fl/f ′c shall not be less than 0.08. The maximum compressive strain (ecu) can be calculated as ε = ε + ′ ε ε       ≤1.5 12 0.01 (3.2.3.2-4) 0.45 k f f cu co b l c fe co where unconfined strain, eco, can be taken as 0.002. ka and kb are the section efficiency factors (1.0 for circular sections). For a rectangular section with a width of b and a depth of h, ( ) ( ) =   =   = − − + −   − ρ − ρ and 1 2 2 3 1 (3.2.3.2-5) 2 0.5 2 2 k A A b h k A A h b A A b h h r h b b r A a e c b e c e c c c g g g where rc is the radius of the corner of the effective confining area, rg is the longitudinal SMA reinforcement ratio, and Ag is the cross-section area. The complete stress-strain relationship of an FRP-confined concrete is calculated as ( ) = ε − − ′ ε ≤ ε ≤ ′ε ′+ ε ′ε < ε ≤ ε    f E E E f f E c c c c c c c t c c t c cu 4 0 (3.2.3.2-6) 2 2 2 2 where ec is the FRP-confined concrete strain, Ec is the modulus of elasticity of concrete, which for normal weight concrete is ( )= ′1820 ksi (3.2.3.2-7)E fc c and = ′ − ′ ε ′ε = ′ − 2 (3.2.3.2-8) 2 2 E f f f E E cc c cu t c c Exposure Fiber Type CE Exterior exposure (bridges, piers, and unenclosed parking garages) Carbon Glass Aramid 0.85 0.65 0.75 Aggressive environment (chemical plants and wastewater treatment plants) Carbon Glass Aramid 0.85 0.50 0.70 Source: ACI 440.2R-08 (2008). Table 3.2.3.2-1. Environmental reduction factor (CE) for FRP.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 29 The confinement provided by an FRP jacket alone may not be sufficient to achieve large displace- ment capacities. Thus, supplementary transverse steel reinforcement may be needed in addition to the FRP jacket. Note that the confinement effect by an FRP jacket may be added to the confinement effect by the transverse steel reinforcement in a way that the confined concrete stress at each strain is the summation of the stresses calculated with each method as shown in Fig. 3.2.3.2-2. The strain capacity to be used in analysis is the greater of that from the two methods. 3.2.4 Analysis of SMA-Reinforced FRP-Confined Concrete Columns 3.2.4.1 Selection of Analysis Procedure to Determine Seismic Demand Analysis methods to obtain the seismic demands are according to AASHTO SGS (2011, Article 4.2). 3.2.4.2 Effective Section Properties The effective moment of inertia (Ieff) should be used for modeling of the SMA-reinforced FRP-confined concrete columns. Ieff may be estimated using Fig. 3.2.4.2-1, or the slope of M – Ø curve between the origin and the first SMA bar yield point as: (3.2.4.2-1)ØE I Mc eff y y= All material mechanical properties are the expected values. 3.2.4.3 Damping Ratio for Dynamic Analysis For elastic and nonlinear dynamic analyses of SMA-reinforced FRP-confined columns, the damping ratio should be taken as 3.2%, rather than the 5% used for RC. The lower damping ratio accounts for the lower hysteretic damping in columns with flag-shaped behavior that could result in higher displacement demands. Fig. 3.2.4.3-1a shows hysteretic damping ratio versus displacement ductility for bridge columns with flag-shaped hysteresis. The study by Billah and Alam (2015) was specifically for SMA-reinforced bridge columns. It can be seen that hysteretic damping of columns with flag- shaped behavior is lower than that of conventional RC columns, as expected. Furthermore, the ratio of the flag-shaped column damping to the RC column damping is approximately constant for ductilities greater than 2 (Fig. 3.2.4.3-1b). Table 3.2.4.3-1 presents a summary of damping St re ss Combined Strain confined #2 Compression confined #1 Tension Figure 3.2.3.2-2. Confinement by two confining mechanisms.

30 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview (a) Circular Sections 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 0.25 0.3 Circular SMA-Reinforced FRP-Confined Concrete Sections El as tic St iff ne ss R at io (I e ff / I g ) Axial Load Index, P / ( f 'c Ag) ASMA/Ag =0.04 ASMA/Ag =0.03 ASMA/Ag =0.02 ASMA/Ag =0.01 (b) Rectangular Sections Rectangular SMA-Reinforced FRP-Confined Concrete Sections 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 0.25 0.3 El as tic St iff ne ss R at io (I e ff / I g ) Axial Load Index, P / ( f 'c Ag) ASMA/Ag =0.04 ASMA/Ag =0.03 ASMA/Ag =0.02 ASMA/Ag =0.01 Figure 3.2.4.2-1. Effective moment of inertia for SMA-reinforced FRP-confined columns. (a) Hysteretic Damping (b) Flag-Shaped Damping (wFlag) over RC Damping (wRC) 0 5 10 15 20 Ductility RC Columns Dwairi et al. (2007) Priestley et al. (2007) Billah and Alam (2015) 0 0.2 0.4 0.6 0.8 1 Ductility Dwairi et al. (2007) Priestley et al. (2007) Billah and Alam (2015)Re co m m en de d 1 2 3 4 5 6 7 1 2 3 4 5 6 7 H ys te re tic D am pi ng ( % ) y F la g- Sh ap ed / y R C Figure 3.2.4.3-1. Damping for columns with flag-shaped hysteresis. References (Ave. for l ê 2) Flag-Shaped Damping RD Dwairi et al. (2007) 0.72 3.60 1.14 Priestley et al. (2007) 0.56 2.80 1.26 Billah and Alam (2015) 0.62 3.12 1.21 Average of Three Refs 0.63 3.17 1.20 Recommended for SMA- Reinforced Columns 0.64 3.20 1.20 Note: = flag-shaped damping, = RC damping, µ = displacement ductility, RD = displacement demand for SMA-reinforced ECC columns. Table 3.2.4.3-1. Damping for SMA-reinforced columns.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 31 ratios. The average ratio of flag-shaped hysteretic damping to that of RC columns was 63%. Based on these findings, the damping ratio of SMA-reinforced columns is proposed to be 3.2%, which is 64% of the 5% damping ordinarily used for RC columns. 3.2.4.4 Displacement Modification for Damping The displacement demand for SMA-reinforced FRP-confined columns calculated using equivalent static or spectral analysis method shall be increased by 20% to account for the lower damping ratio of SMA-reinforced sections as: = ξ   =   = 0.05 0.05 0.032 1.20 (3.2.4.4-1) 0.4 0.4 RD Note that the damping ratio and the modification factor for damping are based on the find- ings of the parametric study presented in the SMA-reinforced ECC design guideline. The hys- teretic behavior of an RC member is dominated by the longitudinal reinforcement behavior, thus the damping of the SMA-reinforced ECC columns can be adopted for SMA-reinforced FRP-confined concrete columns. 3.2.4.5 Displacement Modification for Short-Period Bridges No additional modification is needed for short-period SMA-reinforced FRP-confined col- umns since the 20% increase in the spectral displacements due to lower damping ratio guaran- tees higher spectral displacement for practical bridge columns including short-period columns. 3.2.4.6 Displacement Ductility versus Drift Ratio Displacement ductility demand, µD, for conventional columns is calculated as µ = + ∆ ∆ 1 (3.2.4.6-1)D pd yi where Δpd is the plastic displacement demand and Δyi is the idealized yield displacement correspond- ing to the idealized yield curvature. The calculated ductility for SMA-reinforced columns from this equation may be misleading because the yield strain of SMA bars is 5 times higher than that of steel bars, resulting in a higher idealized yield displacement and thus a lower calculated displacement ductility even though the displacement capacity of a SMA-reinforced column may substantially exceed that of a comparable conventional column. Drift ratio, the ratio of column lateral top dis- placement to the column height, is proposed as an alternative measure to estimate the deformation capacity and demand of novel columns including SMA-reinforced FRP-confined concrete columns. Because current bridge seismic codes utilize displacement ductility rather than drift capacity in design, it is important to determine the relationship between ductility and drift ratio so that dis- placement ductilities for conventional columns in current codes can be translated to drift ratios that may be utilized in novel column design. An extensive parametric study on conventional RC columns was conducted to establish a relationship between the displacement ductility and drift ratio for these columns (Appendix H). Fig. 3.2.4.6-1 shows the condensed result of the parametric study. Equations were developed to relate drift ratio and ductility and are listed in Table 3.2.4.6-1. Detailed results of the parametric study are presented in Appendix. H. A linear interpolation is allowed for intermediate aspect ratios. Alternatively, the following equation can be used for intermediate aspect ratios: ( ) ( )δ = µ −0.26 0.18 (3.2.4.6-2)0.81 0.57A Ar r where Ar is the column aspect ratio (Fig. 3.2.4.6-2). For single-column bents, the aspect ratio is defined as the ratio of the column height to the column side dimension parallel to the loading

32 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 D ri ft R at io (% ) Displacement Ductility Aspect Ratio= 4 Aspect Ratio= 6 Aspect Ratio= 8 Practical Range Proposed relaonships are the upper bound Figure 3.2.4.6-1. Drift-ductility relationships for RC columns. Parameters Proposed Equation Column Aspect Ratio 4 Column Aspect Ratio 6 Column Aspect Ratio 8 Note: “ ” is the drift ratio (%) and “ ” is the displacement ductility. Table 3.2.4.6-1. Proposed relationships between drift and ductility. (c) Multi-Column Bent with One-End-Pinned Joints LD Pinned Joint L D D L (a) Single-Column Bent (b) Multi-Column Bent with Fixed Ends Figure 3.2.4.6-2. Aspect ratio definition [D is the diameter of the column (or the largest side dimension) and L is the column height from point of maximum moment to the point of contraflexure].

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 33 direction. For multi-column bents, the aspect ratio is the ratio of a portion of the column length (length of column from point of maximum moment to the point of contraflexure) to the col- umn side dimension parallel to the loading direction. The full column length is used if one end of the column is pinned. 3.2.4.7 Column Drift Demand Requirement The recommended limits on drift ratio demand, dD, for novel columns are listed in Table 3.2.4.7-1. The values are based on the displacement ductility demand limits for con- ventional columns multiplied by the deformability factor, W, which should be taken as 1.2 for SMA-reinforced FRP-confined columns. A linear interpolation can be used for intermediate aspect ratios. Extrapolation for a column with a lower aspect ratio than 4 is valid if the column behavior is dominated by flexure. The available test data on the SMA-reinforced columns (Saiidi et al., 2009; Nakashoji and Saiidi, 2014; Tazarv and Saiidi, 2015a) confirms that these columns even with a low aspect ratio of 4.5 can withstand more than 10% drift ratio. The mode of failure for these columns was SMA bar fracture at higher drifts. 3.2.4.8 Column Force Demand Columns ideally will be designed to resist all internal forces developed during an earthquake or those associated with a collapse mechanism. 3.2.4.8.1 Moment Demand. The column design moment is the smaller of that obtained from (a) the demand at the design level earthquake and (b) the idealized plastic capacity of the column cross-section. The column design moment obtained from (a) and (b) shall not be less than the column failure moment (Mu) when the column failure moment is greater than 1.2 times the idealized plastic moment (Mu ≥ 1.2Mp). The general approach for conventional columns is that the plastic moment calculated using the idealized method is approximately the same as the actual plastic moment capacity, thus the maxi- mum possible moment demand is the plastic moment. This condition may not always be true for novel columns. The SMA-reinforced member moment-curvature (or force-displacement) rela- tionship is usually tri-linear (Fig. 3.2.4.8.1-1). When the moment (or force) demand calculated from linear analysis falls on the third branch, the plastic moment (or force) calculated using the idealized method might be significantly lower than the demand. In this case, the column failure moment should be used as specified. 3.2.4.8.2 Shear Demand. The column shear demand is the smaller of that obtained from (a) the demand at design level earthquake and (b) the shear associated with 1.2 times the plastic moment calculated using the idealized method. The column shear obtained from (a) and (b) Member ConventionalColumns Novel Columns Single-column bents Aspect Ratio 4: Aspect Ratio 6: Aspect Ratio 8: Multiple-column bents Aspect Ratio 4: Aspect Ratio 6: Aspect Ratio 8: Note: “ ” is the drift ratio demand (%) and “ ” is the displacement ductility demand Use linear interpolation for intermediate aspect ratios. Table 3.2.4.7-1. Bridge column drift ratio demand requirements.

34 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview shall not be less than the shear associated with 1.44 times the idealized plastic moment when the calculated failure moment exceeds 1.2Mp (Mu ≥ 1.2Mp). All possible plastic hinge locations should be considered in the determination of shear forces using (b). 3.2.4.8.3 Column Adjoining Member Force Demand. Column adjoining members (e.g., footings, cap beams, and connections) are designed to resist the overstrength plastic hinging moment, see sections 3.2.4.8.1 and 3.2.4.8.2, and the associated forces (e.g., shear and overturn- ing axial forces) in an essentially elastic manner. This design approach is known as capacity design and is outlined in the AASHTO SGS. 3.2.4.9 Residual Drift The residual drift of SMA-reinforced FRP-confined concrete columns is insignificant for all practical cases due to the superelastic effect of reinforcing SMA bars. Therefore, the residual drift for these columns can be categorized as “low” (dr ≤ 1.0%). Fig. 3.2.4.9-1 shows the residual drift-peak drift relationship for all practical SMA-reinforced FRP-confined concrete columns (based on the limitations specified in this guideline such as Idealized M om en t Actual ØYi Øy Øu Curvature Mp Mu My ØYi Øy Øu Mp Mu My Idealized M om en t Actual Curvature (a) Conventional RC Sections (b) SMA-Reinforced Sections Figure 3.2.4.8.1-1. Typical moment-curvature relationships (Mu is failure moment, Mp is plastic moment, My is yield moment, �Y is yield curvature, �Yi is idealized yield curvature, �u is ultimate curvature). 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 R es id ua l D ri ft R a tio (% ) Peak Drift Ratio (%) Results for 63 columns (Practical Range) 1% Limit (Low Residual) SMA-Steel Confined Concrete Column Test (Saiidi et al., 2009) Conv. Column Test (Haber et al., 2013) 0 1 2 3 4 5 6 7 8 9 10 Figure 3.2.4.9-1. Residual drifts for all practical SMA-reinforced FRP-confined concrete columns.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 35 minimum and maximum longitudinal reinforcement ratios, maximum aspect ratio). The ana- lytical results are shown up to the failure point (drift capacity) of each column. The confining effect of the transverse steel was ignored. Appendix I presents complete information regarding material properties, modeling methods, and the variables. It can be seen that the residual drift ratios for all columns are less than 1.0%. The left cluster of the data (solid black lines), mid-cluster of the data (solid gray lines), and the bottom-right cluster of the data are respectively for columns with aspect ratios of 4, 6, and 8. The residual-peak drift relationships measured in a conventional RC bridge column test (dashed gray line) as well as an SMA steel-confined concrete column test (dashed black line) are also shown in the figure. 3.2.5 Design of SMA-Reinforced FRP-Confined Concrete Columns SMA-reinforced FRP-confined concrete columns ideally will be designed conforming to requirements presented in this section. 3.2.5.1 Analytical Plastic Hinge Length The analytical plastic hinge length of SMA-reinforced columns may be estimated using = + ≥0.08 0.15 0.3 (3.2.5.1-1)L L f d f dp ye bl ye bl where fye (ksi) is the expected austenite yield strength of the longitudinal column reinforcing SMA bars and dbl (in.) is the nominal diameter of longitudinal column reinforcing SMA bars. Nakashoji and Saiidi (2014) showed utilizing all available test data that the plastic hinge length of SMA-reinforced columns can be conservatively estimated using the equation presented in AASHTO SGS (2011). Nonetheless, transverse steel is needed to increase the FRP-confined column displacement capacities in high seismic zones because of the low strain capacity of FRP-confined concrete. Therefore, the ultimate displacement capacity is governed by steel confinement. 3.2.5.2 Column Drift Capacity Column displacement capacity (Δc) is defined as a displacement at fracture of the column longitudinal bar or compressive failure of the confined concrete. Either moment-curvature or pushover analyses may be used for the estimation of a SMA-reinforced FRP-confined con- crete column displacement capacity. However, a pushover analysis is preferred since it includes the entire bridge model, frame actions, and geometric nonlinearities. When moment-curvature analysis is used, the displacement capacity is ( )∆ = + − − 3 2 (3.2.5.2-1) 2L L L L c Yi u Yi p pØ Ø Ø where ØYi is the idealized yield curvature calculated using the idealized method (Appendix H, Fig. H-1), Øu is the ultimate curvature associated with either SMA bar fracture or confined con- crete failure, L is the column height from point of maximum moment to the point of contra- flexure, and Lp is the calculated plastic hinge length. Column drift capacity (dc) is defined as the ratio of the column displacement capacity to the column height as δ = ∆ (3.2.5.2-2) L c c 3.2.5.2.1 Minimum Drift Capacity. The proposed minimum drift ratio capacity for SMA-reinforced FRP-confined concrete columns is listed in Table 3.2.5.2.1-1. The drift ratios

36 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview correspond to the minimum displacement ductility capacity for conventional columns. Col- umns shall be designed to provide at least this level of drift ratio. A linear interpolation can be used for intermediate aspect ratios. 3.2.5.3 Shear Capacity The shear capacity of SMA-reinforced FRP-confined columns, within the plastic hinge, calcu- lated based on the nominal material strength properties shall satisfy: (3.2.5.3-1)ØV Vs n u≥ in which: = + + 0.95 (3.2.5.3-2)V V V Vn c s f where the strength reduction factor, Øs, is 0.9, Vn is the nominal shear capacity of member, Vs is the reinforcing steel contribution to shear capacity, Vc is the concrete contribution to shear capacity, and Vf is the FRP contribution to the shear. Vc and Vs are computed according to AASHTO SGS and are repeated here for circular columns: = 0.8 (3.2.5.3-3)V v Ac c g vc is zero if the column is under tensile axial loads. Otherwise: ( )= ′α +  ′≤ ′ ′α ′0.032 1 2 min 0.11 , 0.047 (3.2.5.3-4)v P A f f fc u g c c c For circular column with spiral or hoop reinforcing: ′α = + − µ 0.15 3.67 (3.2.5.3-5) fs D = ρ ≤ 0.35 (3.2.5.3-6)f fs s yh ρ = ′ 4 (3.2.5.3-7) A sD s sp where Ag is the gross area of member cross-section (in. 2), Pu is the ultimate compressive force acting on section (kips), Asp is the area of spiral or hoop reinforcing bar (in. 2), s is the pitch of spiral or spacing of hoops or ties (in.), D′ is the core diameter of column measured from center of spiral or hoop (in.), fyh is the nominal yield stress of transverse reinforcing (ksi), f ′c is the nomi- nal concrete compressive strength (ksi), µD is the displacement ductility demand calculated from drift demand, and a′ is the concrete shear stress adjustment factor. Member ConventionalColumns Novel Columns Single- or multi-column bents Aspect Ratio 4: Aspect Ratio 6: Aspect Ratio 8: Note: “ ” is the drift ratio capacity (%) and “ ” is the displacement ductility capacity. Use linear interpolation for intermediate aspect ratios. Table 3.2.5.2.1-1. Minimum bridge column drift ratio capacity requirements.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 37 For members that are reinforced with circular hoops, spirals, or interlocking hoops or spirals, the nominal shear reinforcement strength, Vs, is: = pi ′ 2 (3.2.5.3-8)V nA f D s s sp yh where n is the number of individual interlocking spirals or hoops within the spacing s. Refer to AASHTO SGS for the calculation of Vs for other types of cross-sections. The contribution of FRP to shear strength is calculated according to ACI 440.2R-08 (2008) as follows: ( )= α + α2 (3.2.5.3-9)V n t f sin cos Df f f fe where nf is the number of FRP layers, tf is the thickness of each FRP layer, a is the angle between the direction of the FRP principal fibers and the longitudinal axis of the member, D is the diameter of the column (or the largest side dimension), and = ε (3.2.5.3-10)f Efe fe f where Ef is the modulus of elasticity of the FRP, and ε = ≤0.004 0.75 (3.2.5.3-11)f Efe fu f where ffu is the FRP design tensile strength including the environmental reduction factor. The sum of shear strengths provided by the steel and FRP shall be limited to + ≤ ′V V f As f c e0.25 (3.2.5.3-12) where Ae is the effective area of the cross-section for shear resistance (0.8Ag). 3.2.5.4 Axial Capacity The axial capacity of an SMA-reinforced FRP-confined concrete column shall be calculated according to ACI 440.2R-08 (2008), modified for SMA bars as 0.85 (3.2.5.4-1)Ø ØP f A A A fn cc g SMA SMA y( )( )= ′ − + where f ′cc is the maximum compressive strength of an FRP-confined concrete section (ksi), Ag is the gross area of member cross-section (in.2), ASMA is the column longitudinal SMA reinforce- ment area (in.2), fy is the nominal austenite yield strength of SMA bars, and Ø is 0.75 and 0.7 for members with spirals and ties, respectively. 3.2.5.5 Minimum Lateral Strength Each bent shall have a minimum lateral flexural capacity to resist a lateral force of 0.1Pdl, where Pdl is the tributary dead load applied at the center of gravity of the superstructure. 3.2.5.6 Other Loading and Strength Design The estimation, analysis, and design of SMA-reinforced FRP-confined concrete columns for non-seismic loads are based on the AASHTO LRFD Bridge Design Specifications (2014) in which reinforcing SMA bars can be treated as conventional steel bars but with SMA proper- ties (austenite yield strength, modulus of elasticity). The AASHTO response modification

38 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview factors (AASHTO LRFD, Table 3.10.7.1-1) may be used to reasonably size the columns and their adjoining members, only for preliminary design under the load combination of “Extreme Event I.” Nevertheless, SMA-reinforced FRP-confined columns should be analyzed and designed according to the present guideline for seismic loads. 3.2.5.7 Serviceability Design An SMA-reinforced FRP-confined concrete column ideally will be designed to withstand ser- vice loads during the life of the bridge. Actions to be considered for these columns at the service limit state should be short- and long-term deformations. Serviceability for conventional RC and ECC is addressed through the minimum shrinkage and temperature reinforcement require- ment. The relatively high transverse reinforcement to satisfy seismic design requirements in novel columns exceeds the minimum shrinkage and temperature reinforcement requirement in AASHTO LRFD. 3.2.5.7.1 Shrinkage and Creep. The AASHTO LRFD Bridge Design Specifications (2014) shall be used to compute shrinkage and creep of concrete. Service load stresses of an FRP jacket shall not exceed the creep-rupture stress limit, which is 0.2ffu for glass FRP (GFRP), 0.3ffu for Aramid FRP (AFRP), and 0.55ffu for carbon FRP (CFRP). ffu is the FRP design ten- sile strength including the environmental reduction factor. Note that the stress that has to be checked for the creep-rupture is the section maximum tensile stress due to the interaction of axial loads and bending moments in the axial direction of the member under service load combinations. 3.2.5.7.2 Axial Deformations. Instantaneous axial deformation due to loads, and long- term shortening due to shrinkage and creep, should be determined for concrete columns only when these columns are post-tensioned. Design of post-tensioned FRP-confined concrete col- umns is beyond the scope of this report. The estimation of deformations in SMA-reinforced FRP-confined concrete columns at a limit state of serviceability is based on two assumptions: (1) strain is proportional to the distance from the neutral axis of the cross-section and (2) concrete and SMA are linear elastic materials with moduli of elasticity specified in 3.2.3. The contribution of the FRP jacket to axial stiffness may be neglected. Analysis can be performed assuming perfect bond between reinforcing SMA bars and FRP-confined concrete. 3.2.6 Details for SMA-Reinforced FRP-Confined Concrete Columns SMA-reinforced FRP-confined concrete columns shall be detailed conforming to requirements presented in this section. 3.2.6.1 FRP Jacket FRP jacketing is through either wrapping the FRP sheets around the column or the uti- lization of prefabricated FRP tubes, which are available with different diameters and wall thicknesses. Furthermore, FRP tubes serve as permanent formwork, which can accelerate the construction. Normally there is a 2-in. (50-mm) gap between the end of the jacket and the col- umn adjoining member face. The jacket might extend to the entire length of column, except the 2-in. (50-mm) gap at the column ends, if it serves the dual purpose of plastic hinge damage control and stay-in-place form. In this case, only the column section outside the gap shall be used for the analysis. If FRP is utilized only in the plastic hinge region, the FRP jacket height shall be the greater of (a) the analytical plastic hinge length and (b) 1.5 times the column largest side dimension.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 39 3.2.6.2 Reinforcement Details 3.2.6.2.1 Longitudinal SMA Reinforcement. The area of longitudinal reinforcing SMA bars (ASMA) in SMA-reinforced FRP-confined concrete columns should satisfy: ≤ ≤0.01 0.04 (3.2.6.2-1)A A Ag SMA g where Ag is the gross area of the member cross-section (in. 2). Since the austenite yield strength of SMA bars is usually lower than the steel bar yielding, higher longitudinal reinforcement than con- ventional columns is expected, but the reinforcement area should be within in the specified range. 3.2.6.2.2 SMA Bar Size. The available size of reinforcing SMA bars is presented in Table 3.2.6.2.2-1. 3.2.6.3 Splicing of SMA Reinforcement The incorporation of SMA bars over only partial length of columns ideally will be permitted and suggested to save cost. The length of SMA bars shall not be less than the analytical plastic hinge length and 75% of the largest column cross-sectional dimension (0.75D). SMA bars are plain (with a smooth surface) behaving similarly to debonded bars under cyclic actions. When SMA bars are used over the entire length of members, mechanical anchorage shall be used to anchor the bars in the adjoining members. When SMA bars are utilized only in the plastic hinge region, reinforcing SMA bars should be connected to reinforcing steel bars using mechanical bar splices approved by the bridge owner. Threaded (only those with parallel threads and not those with tapered threads) and headed bar couplers have exhibited satisfactory performance in large-scale tests. Splicing should be permitted in the plastic hinge region of the columns. A recent study by Tazarv and Saiidi (2015b) showed that the mechanical bar splices in the column plastic hinges reduce the displacement ductility capacity as ( )µ µ = − β   β 1 0.18 (3.2.6.3-1) 0.1H L sp CIP sp sp where µsp is the displacement ductility capacity of a mechanically spliced column, µCIP is the conventional non-spliced CIP column displacement ductility capacity, b is the coupler rigid length factor obtained from the splice tensile tests or the coupler manufacturer (a range from 0 to 1), Hsp is the distance between the coupler end to the column adjoining member interface (Fig. 3.2.6.3-1), and Lsp is the splice length. Hsp should be taken as 0.1 in. (2.5 mm) when couplers are installed at the column to adjoining member interface. Fig. 3.2.6.3-1 is intended to clarify the parameters in Equation 3.2.6.3-1. SMA bars require two splices as shown in Fig. 3.2.7.2-1. Bar Size No. (mm) Nominal Diameter in. (mm) Cross-Sectional Area in.2 (mm2) #4 (Ø13) 0.500 (12.7) 0.20 (129) #5 (Ø16) 0.625 (15.9) 0.31 (199) #6 (Ø19) 0.750 (19.1) 0.44 (284) #7 (Ø22) 0.875 (22.2) 0.60 (387) #8 (Ø25) 1.000 (25.4) 0.79 (510) #9 (Ø29) 1.128 (28.7) 1.00 (645) #10 (Ø32) 1.270 (32.3) 1.27 (819) #11 (Ø36) 1.410 (35.8) 1.56 (1006) #14 (Ø43) 1.693 (43.0) 2.25 (1452) #18 (Ø57) 2.257 (57.3) 4.00 (2581) Table 3.2.6.2.2-1. Plain SMA bar dimensions.

40 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview In this case, the coupler properties in Eq. 3.2.6.3-1 should be based on the coupler that is near the column end. Since there is a linear relationship between the displacement ductility and the drift ratio, the ratio of the spliced to CIP column ductilities presented in the equation is approximately the same as the ratio of the spliced to CIP column drift ratios. More information can be found in the NCHRP Project 12-105 final report. 3.2.6.4 Maximum Axial Load The axial load acting on SMA-reinforced FRP-confined concrete columns, including gravity and seismic demands (Pu) where a pushover analysis is not performed should satisfy: ≤ ′0.15 (3.2.6.4-1)P f Au c g where Ag is the gross area of member cross-section (in. 2) and f ′c is the nominal concrete compressive strength (ksi). A higher axial load value may be used provided that pushover Source: Tazarv and Saiidi, 2015b. Hsp Lsp Footing Co up le rs Cap Beam M ec ha ni ca lly S pl ic ed C ol um n Figure 3.2.6.3-1. Mechanical bar splices. (a) Cast-in-Place Detailing (b) Precast Detailing Ca st- in -P la ce Co lu m n Not all reinforcement are shown for clarity Reinforcing Steel Bar Reinforcing SMA Bar2-in. Gap Reinforcing Steel Bar FRP Jacket Footing Pocket Connection Footing Pr ec as t C ol um n Reinforcing Steel BarFRP Jacket Reinforcing SMA Bar2-in. Gap Figure 3.2.7.2-1. Construction of SMA-reinforced FRP-confined concrete columns.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 41 analysis including the P – Δ effect is performed to compute the maximum drift capacity of the column. 3.2.6.5 Maximum Aspect Ratio The aspect ratio of SMA-reinforced FRP-confined concrete bents should not exceed 8. Columns with larger aspect ratios may fail at low drift ratios due to the P – Δ effect. 3.2.7 Construction of SMA-Reinforced FRP-Confined Columns 3.2.7.1 Quality Control Tests ASTM F2516-07 (2007) should be utilized for tensile testing of NiTi SE SMA to compute the mechanical properties according to the procedure presented in Tazarv and Saiidi (2014). Only reinforcing SMA bars satisfying the “minimum” material properties (Section 3.2.3) shall be allowed for the design and construction of SMA-reinforced bridge columns. FRP testing method for the computation of mechanical properties, fire and life safety, service temperature, and many other parameters should be according to Appendix H of the ACI 440.2R-08 (2008). 3.2.7.2 Construction Procedures IP and precast construction is permitted for SMA-reinforced FRP-confined concrete col- umns. Fig. 3.2.7.2-1 shows one example for each construction method. The design of precast column connections should be according to bridge-owner approved guidelines. When an FRP tube is used in a precast detailing (e.g., pocket connection), the FRP shall not be extended into the adjoining member. The primary role of FRP in this report is to reduce damage in the plastic hinge regions. Natural roughness of the prefabricated FRP tubes should be preserved to ensure the bond between the tube and concrete. 3.2.7.3 Construction Tolerance Tolerance limits normally used for conventional RC construction are applicable to SMA- reinforced FRP-confined concrete columns. Quality control for precast columns should be according to PCI MNL-116-99 (1999). Construction tolerance for precast column connections should be according to bridge-owner approved guidelines. 3.2.8 References AASHTO. (2011). AASHTO Guide Specifications for LRFD Seismic Bridge Design. Washington, D.C.: American Association of State Highway and Transportation Officials. AASHTO. (2014). AASHTO LRFD Bridge Design Specifications. Washington, D.C.: American Association of State Highway and Transportation Officials. Alarab, L. A., Ross, B. E., and Poursaee, A. (2016). Corrosion Assessment of Coupled Steel Reinforcement with Ni-Ti–Based Shape Memory Alloy in Simulated-Concrete Pore Solution, ASCE Journal of Materials in Civil Engineering, Vol. 28, No. 8, 6 pp. ACI 440.2R-08. (2008). Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures, Reported by American Concrete Institute Committee 440, 80 pp. ASTM. (2007). Standard test method for tension testing of nickel-titanium superelastic materials, F2516-07, West Conshohocken, PA. Billah, A. H. M. M, and Alam, M. S. (2015) Damping-Ductility Relationship for Performance Based Seismic Design of Shape Memory Alloy Reinforced Concrete Bridge Pier. Proceeding of Structures Congress 2015, ASCE, 474–484. https://doi.org/10.1061/9780784479117.042. Dwairi, H. M., Kowalsky, M. J., and Nau, J. M. (2007). Equivalent Damping in Support of Direct Displacement- Based Design. Journal of Earthquake Engineering, 11(4), 512–530. https://doi.org/10.1080/13632460601033884.

42 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview Haber, Z. B., Saiidi, M. S., and Sanders, D. H. (2013). Precast Column-Footing Connections for Accelerated Bridge Construction in Seismic Zones, Center for Civil Engineering Earthquake Research, Department of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-13-08, 612 pp. Faulkner, M. G., Amalraj, J. J., and Bhattacharyya, A. (2000). Experimental Determination of Thermal and Electrical Properties of Ni-Ti Shape Memory Wires. Smart Materials and Structures, 9(5), 632–639. https:// doi.org/10.1088/0964-1726/9/5/307. McCormick, J. P. (2006). Cyclic Behavior of Shape Memory Alloys Materials Characterization and Optimization, PhD Dissertation, Georgia Institute of Technology, 351 pp. Nakashoji, B., and Saiidi, M. S. (2014). Seismic Performance of Square Nickel-Titanium Reinforced ECC Columns with Headed Couplers, Center For Civil Engineering Earthquake Research, Department Of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-14-05, 252 pp. Otsuka, K., and Wayman, C. M. (1998). Mechanism of Shape Memory Effect and Superplasticity, 27–48. Cambridge, U.K.: Cambridge University Press. PCI MNL-116-99. (1999). Manual for Quality Control for Plants and Production of Structural Precast Concrete Products, Precast/Prestressed Concrete Institute, Chicago, IL, 328 pp. Priestley, M. J. N., Calvi, G. M., and Kowalski, M. J. (2007). Displacement-based Seismic Design of Structures. Pavia: IUSS press. Saiidi, M. S., O’Brien, M., and Sadrossadat-Zadeh, M. (2009). Cyclic Response of Concrete Bridge Columns Using Superelastic Nitinol and Bendable Concrete. ACI Structural Journal, 106(1), 69–77. Schlossmacher, P., Haas, T., and Schüssler, A. (1997). Laser-Welding of a Ni-Rich TiNi Shape Memory Alloy: Mechanical Behavior. Journal De Physique IV France, 07(C5, No. C5), 251–256. https://doi.org/10.1051/ jp4:1997539. Tazarv, M., and Saiidi, M. S. (2014). Reinforcing NiTi Superelastic SMA for Concrete Structures. In Journal of Structural Engineering. ASCE; https://doi.org/10.1061/(ASCE)ST.1943-541X.0001176. Tazarv, M., and Saiidi, M. S. (2015a). Low-Damage Precast Columns for Accelerated Bridge Construction in High Seismic Zones. In Journal of Bridge Engineering. ASCE; https://doi.org/10.1061/(ASCE)BE. 1943-5592.0000806. Tazarv, M., and Saiidi, M. S. (2015b). Design and Construction of Bridge Columns Incorporating Mechanical Bar Splices in Plastic Hinge Zones, Center For Civil Engineering Earthquake Research, Department of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-15-07, 149 pp.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 43 3.3 Proposed Design and Construction of FRP-Confined Hybrid Rocking Columns 3.3.1 Introduction The main objectives of this study were to develop (1) proposed AASHTO guidelines for the evaluation of new techniques for the design and construction of bridge columns with energy dissipation mechanisms meant to minimize bridge damage and replacement after a seismic event and (2) design and construction concepts based on new materials and techniques as well as analytical techniques. The first objective was addressed in Chapter 2, Guidelines for Evaluation of Novel Col- umns. Three novel column concepts were selected by the panel for further study to address the second objective of the project. The focus of this section is on the development of design and construction guidelines for novel column Type 3 (Appendix D), steel-reinforced FRP-confined columns with unbonded steel tendons (Fig. 3.3.1-1). Since these columns are longitudinally reinforced with both steel bars and steel tendons, they are referred to as “hybrid rocking” col- umns in this study. Hard FRP tubes or FRP sheets wrapped around the column are meant to confine the concrete and to reduce the damage close to the rocking interface. “Simple rocking” columns, which are longitudinally reinforced with only tendons, were excluded from this guide- line since experimental studies by Thonstad et al. (2016) showed that simple rocking column drift demands can be 3 times larger than those measured for hybrid rocking columns exceeding the AASHTO displacement ductility demand requirement by approximately a factor of 3. Step- by-step design examples are presented in Appendix F. The economic impact of novel columns is discussed in Appendix G. The AASHTO Guide Specifications for LRFD Seismic Bridge Design (AASHTO SGS) (2011) serves as the baseline for the development of the present guidelines. All limitations, consider- ations, applicability, and analysis and design methods shall be according to AASHTO SGS except those presented herein. The proposed guidelines for FRP-confined hybrid rocking columns are general and may be used for the design of other hybrid rocking columns incorporating reinforc- ing steel bars and unbonded steel tendons. 3.3.2 Application of FRP-Confined Hybrid Rocking Columns Columns can be pre-stressed or post-tensioned using tendons to reduce column lateral residual displacements after severe earthquakes. Tendon restoring forces help bring the struc- ture back to its original position. Rocking columns usually suffer from significant damage FRP Jacket Reinforcing Steel Bars St ee l T en do n G ap Footing Concrete Figure 3.3.1-1. FRP-confined hybrid rocking columns.

44 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview in the vicinity of the rocking interface. The concrete damage can be minimized when it is jacketed by FRP sheets. The low damage in FRP-confined concrete helps keep the bridge in service after strong earthquakes. The combination of the rocking mechanism and the FRP jacket (FRP-confined hybrid rocking columns) in bridge columns results in minimal concrete damage and small residual displacements after severe earthquakes, and reduces or eliminates the need for post-earthquake repair. FRP-confined hybrid rocking bridge columns are recommended for sites in which the 1-sec period acceleration coefficient, SD1, is greater than 0.3, which is equivalent to SDC C or D accord- ing to AASHTO SGS. Conventional bridges located in these sites are expected to undergo large inelastic deformations under strong earthquakes. While there is no adverse effect in using FRP-confined hybrid rocking columns in bridges under SDC A and B, bridge owners may take advantage of the ease of construction with FRP tubes that serve as permanent formwork, even though there is no benefit from the seismic performance perspective because of the relatively small seismic demand in SDC A and B. 3.3.3 Materials 3.3.3.1 Steel Tendons Steel tendon mechanical properties and material model shall be according to AASHTO SGS (AASHTO, 2011, Article 8.4.3). Yielding of tendons shall not be allowed for hybrid rocking col- umns at the design level earthquake to minimize residual displacements (section 3.3.6.2). There- fore, the use of Grade 270 strands is preferred over Grade 250 strands. The initial linear elastic stress-strain relationship for Grade 270 steel strands with a yield strength of 245 ksi according to AASHTO is = ε ε ≤fps ps ps28500 0.0086 (3.3.3.1-1) where fps is the tendon stress (ksi) and eps is the tendon strain. 3.3.3.2 FRP-Confined Concrete When a concrete member is encased by an FRP jacket intended to provide confinement, the entire section should be considered to be confined. The confined properties of FRP-jacketed concrete shall be calculated based on the ACI model (ACI 440.2R-08, 2008) as shown in Fig. 3.3.3.2-1. Source: ACI 440.2R-08, 2008. 1E2 Tension confined Strain unconfined St re ss Compression ecu e 't eco f 'cc f 'c Figure 3.3.3.2-1. FRP-confined concrete stress-strain model.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 45 The maximum compressive strength of a FRP-confined concrete section ( f ′cc) is ′ = ′ + 3.135 (3.3.3.2-1)f f k fcc c a l where f ′c is the unconfined cylinder compressive strength of concrete, ka is the section efficiency factor, and fl is the confining pressure = ε2 (3.3.3.2-2)f E n t Dl f f f fe where Ef is the modulus of elasticity of FRP, nf is the number of FRP layers, tf is the thickness of each FRP layer, D is the section diameter (or the equivalent diameter for a non-circular section), and ε = ε = =0.58 0.58 0.58 (3.3.3.2-3) f E C f E fe fu fu f E fu f  where f *fu is the guaranteed FRP design tensile strength reported by the manufacturer and CE is the environmental reduction factor according to Table 3.3.3.2-1. The ratio of fl/f ′c shall not be less than 0.08. The maximum compressive strain (ecu) can be calculated as ε = ε + ′ ε ε       ≤1.5 12 0.01 (3.3.3.2-4) 0.45 k f f cu co b l c fe co where eco can be taken as 0.002. ka and kb are the section efficiency factors (1.0 for circular sections). For a rectangular section with a width of b and a depth of h, ( ) ( ) =   =   = − − + −   − ρ − ρ and 1 2 2 3 1 (3.3.3.2-5) 2 0.5 2 2 k A A b h k A A h b A A b h h r h b b r A a e c b e c e c c c g g g where rc is the radius of the corner of the effective confining area, rg is the longitudinal reinforcing steel bar ratio, and Ag is the cross-section area. The complete stress-strain relationship of an FRP-confined concrete section is calculated as ( ) = ε − − ′ ε ≤ ε ≤ ′ε ′ + ε ′ε < ε ≤ ε    f E E E f f E c c c c c c c t c c t c cu 4 0 (3.3.3.2-6) 2 2 2 2 Exposure Fiber Type CE Exterior exposure (bridges, piers, and unenclosed parking garages) Carbon Glass Aramid 0.85 0.65 0.75 Aggressive environment (chemical plants and wastewater treatment plant) Carbon Glass Aramid 0.85 0.50 0.70 Source: ACI 440.2R-08 (2008). Table 3.3.3.2-1. Environmental reduction factor (CE) for FRP.

46 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview where Ec is the modulus of elasticity of concrete, which for normal weight concrete is ( )= ′1820 ksi (3.3.3.2-7)E fc c and = ′ − ′ ε ′ε = ′ − 2 (3.3.3.2-8) 2 2 E f f f E E cc c cu t c c The confinement provided by FRP jacket alone may not be sufficient to achieve large displace- ment capacities. Thus, supplementary transverse steel reinforcement may be needed in addition to the FRP jacket. Note that the confinement effect by an FRP jacket may be added to the confinement effect by the transverse steel reinforcement in a way that the confined concrete stress at each strain is the summation of the stresses calculated with each method as shown in Fig. 3.3.3.2-2. 3.3.4 Analysis of FRP-Confined Hybrid Rocking Columns 3.3.4.1 Selection of Analysis Procedure to Determine Seismic Demand Analysis methods to obtain the seismic demands are according to AASHTO SGS (2011, Article 4.2). 3.3.4.2 Effective Section Properties The effective moment of inertia (Ieff) should be used for modeling of hybrid rocking columns including the FRP-confined hybrid rocking columns. Ieff shall be estimated using the slope of the M – Ø curve between the origin and the idealized yield point as: (3.3.4.2-1)ØE I Mc eff y y= where My and Øy are the yield moment and curvature, respectively. 3.3.4.3 Damping Ratio for Dynamic Analysis For elastic and inelastic dynamic analysis of hybrid rocking columns, including the FRP- confined hybrid rocking columns, the damping ratio should be taken as 5% unless otherwise St re ss Combined Strain confined #2 Compression confined #1 Tension Figure 3.3.3.2-2. Confinement by two confining mechanisms.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 47 stated (Section 3.3.6.2). These columns dissipate a significant amount of energy through yielding of reinforcing steel bars. 3.3.4.4 Displacement Modification for Damping The displacement modification for hybrid rocking columns, including the FRP-confined hybrid rocking columns, accounting for different damping ratios is according to AASHTO SGS (AASHTO, 2011, Article 4.3.2). 3.3.4.5 Displacement Modification for Short-Period Bridges The displacement modification for hybrid rocking columns, including the FRP-confined hybrid rocking columns, accounting for the short-period effect is according to AASHTO SGS (AASHTO, 2011, Article 4.3.3). The displacement ductility demand required in the short-period displacement modification factor can be estimated using the drift-ductility relationship pre- sented in the next section. 3.3.4.6 Displacement Ductility Versus Drift Ratio Displacement ductility demand, µD, for conventional columns is calculated as µ = + ∆ ∆ 1 (3.3.4.6-1)D pd yi where Δpd is the plastic displacement demand and Δyi is the idealized yield displacement corre- sponding to the idealized yield curvature. Generally, the calculated ductility for novel columns from this equation may be misleading. Drift ratio, the ratio of column lateral top displacement to the column height, is proposed as an alternative measure to estimate the deformation capacity and demand of novel columns. Both the ductility-based design (according to the AASHTO SGS) and the drift-based design (according to the present guideline) shall be permitted for the design of hybrid rocking columns, including the FRP-confined hybrid rocking columns. Because current bridge seismic codes utilize displacement ductility rather than drift capacity in design, it is important to determine the relationship between ductility and drift ratio so that displacement ductilities for conventional columns in current codes can be translated to drift ratios that may be utilized in novel column design. An extensive parametric study on conven- tional RC columns was conducted to establish a relationship between the displacement ductility and drift ratio for these columns (Appendix H). Fig. 3.3.4.6-1 shows the condensed result of the parametric study. Equations were developed to relate drift ratio and ductility and are listed in 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 D ri ft R at io (% ) Displacement Ductility Aspect Ratio= 4 Aspect Ratio= 6 Aspect Ratio= 8 Practical Range Proposed relationships are the upper bound Figure 3.3.4.6-1. Drift-ductility relationships for RC columns.

48 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview Table 3.3.4.6-1. Detailed results of the parametric study are presented in Appendix H. Linear interpolation is allowed for intermediate aspect ratios. Alternatively, the following equation can be used for intermediate aspect ratios: ( ) ( )δ = µ −0.26 0.18 (3.3.4.6-2)0.81 0.57A Ar r where Ar is the column aspect ratio (Fig. 3.3.4.6-2). For single-column bents, the aspect ratio is defined as the ratio of the column height to the column side dimension parallel to the load- ing direction. For multi-column bents, the aspect ratio is the ratio of a portion of the column length (length of column from point of maximum moment to the point of contraflexure) to the column side dimension parallel to the loading direction. The full column length is used if one end of the column is pinned. 3.3.4.7 Column Drift Demand Requirement The proposed limits on drift ratio demand, dD, for novel columns are listed in Table 3.3.4.7-1. The values are based on the displacement ductility demand limits for conventional columns Parameters Proposed Equation Column Aspect Ratio 4 Column Aspect Ratio 6 Column Aspect Ratio 8 Note: “ ” is the drift ratio (%) and “ ” is the displacement ductility. Table 3.3.4.6-1. Proposed relationships between drift and ductility. (a) Single-Column Bent (b) Multi-Column Bent with Fixed Ends L D D L (c) Multi-Column Bent with One-End-Pinned Joints LD Pinned Joint Figure 3.3.4.6-2. Aspect ratio definition [D is the diameter of the column (or the largest side dimension) and L is the column height from point of maximum moment to the point of contraflexure].

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 49 multiplied by the deformability factor, W, which should be taken as 1.0 for hybrid rocking col- umns, including the FRP-confined hybrid rocking columns. Linear interpolation may be used for intermediate aspect ratios. Extrapolation for a column with a lower aspect ratio than 4 is valid if the column behavior is dominated by flexure. 3.3.4.8 Column Force Demand Columns ideally will be designed to resist all internal forces developed during an earthquake or those associated with a collapse mechanism. 3.3.4.8.1 Moment Demand. The column design moment is the smaller of that obtained from (a) the demand at the design level earthquake and (b) the idealized plastic capacity of the column cross-section. The column design moment obtained from (a) and (b) shall not be less than the column failure moment (Mu) when the column failure moment is greater than 1.2 times the idealized plastic moment (Mu ≥ 1.2Mp). The general approach for conventional RC columns is that the plastic moment calculated using the idealized method is approximately the same as the actual plastic moment capacity, thus the maximum possible moment demand is the plastic moment. This condition may not always be true for novel columns (Fig. 3.3.4.8.1-1). Hybrid rocking columns with minimal reinforcing steel bars may gain strength after the bar yielding due to rocking. In this case, the column failure moment should be used as specified. Member ConventionalColumns Novel Columns Single-column bents Aspect Ratio 4: Aspect Ratio 6: Aspect Ratio 8: Multiple-column bents Aspect Ratio 4: Aspect Ratio 6: Aspect Ratio 8: Note: “ ” is the drift ratio demand (%) and “ ” is the displacement ductility demand. Use linear interpolation for intermediate aspect ratios. Table 3.3.4.7-1. Bridge column drift ratio demand requirements. (a) Conventional RC Sections (b) Hybrid Rocking Columns w/ Low Steel Bars Mp Mu My Idealized Øy M om en t Actual ØYi Curvature Øu ØYi Øy Øu Mp Mu My M om en t Actual Curvature Idealized Figure 3.3.4.8.1-1. Typical moment-curvature relationships (Mu is failure moment, Mp is plastic moment, My is yield moment, �Y is yield curvature, �Yi is idealized yield curvature, �u is ultimate curvature).

50 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview The moment-curvature analysis of a hybrid rocking column section is the same as that for a conventional column with an additional axial load representing the post-tensioning force after all losses. 3.3.4.8.2 Shear Demand. The column shear demand is the smaller of that obtained from (a) the demand at design level earthquake and (b) the shear associated with 1.2 times the plas- tic moment calculated using the idealized method. The column shear obtained from (a) and (b) shall not be less than the shear associated with 1.44 times the idealized plastic moment when the calculated failure moment exceeds 1.2Mp (Mu ≥ 1.2Mp). All possible plastic hinge locations should be considered in the determination of shear forces using (b). 3.3.4.8.3 Column Adjoining Member Force Demand. Column adjoining members (e.g., footings, cap beams, and connections) are designed to resist the overstrength plastic hinging moment, see Sections 3.3.4.8.1 and 3.3.4.8.2, and the associated forces (e.g., shear and overturn- ing axial forces) in an essentially elastic manner. This design approach is known as the capacity design and is outlined in the AASHTO SGS. 3.3.4.9 Residual Drift An extensive parametric study was carried out to establish a relationship between the residual and peak drift ratios (Appendix I). It was found that the tendon initial stress ratio ( fpi/fpy) and the column longitudinal reinforcing steel bar ratio are the most important parameters to control the residual drifts, and the effect of other column parameters such as the aspect ratio and the axial load is minimal. In the absence of nonlinear dynamic analyses, the residual drift ratio (dr, the ratio of column lateral residual displacement to the column height in %) for hybrid rocking columns, including the FRP-confined hybrid rocking columns, with a reinforcing steel bar ratio (As/Ag) of 1.0% or greater, can be conservatively calculated (Appendix I) as: δ = δ + δ + (3.3.4.9-1)2a b cr where d is the peak drift ratio (%), As is total area of longitudinal reinforcing steel bars, Ag is the gross area of the member cross-section, and the polynomial constraints are ( ) ( ) ( ) = + = − + = − 0.026 0.047 0.55 0.32 (3.3.4.9-2) 0.36 0.27 a f f b f f c f f pi py pi py pi py where fpi is the tendon initial stress after all losses and fpy is the yield strength of the tendon. Fig. 3.3.4.9-1a shows the residual drift–peak drift relationship for a wide range of initial tendon stresses. The analysis leading to this figure is presented in Appendix I. It can be seen that the residual drift ratio of the hybrid rocking columns exceeds the 1% drift limit when the peak drift ratio demand exceeds 4% in all practical cases. The residual drift ratio (dr in %) for hybrid rocking columns with a reinforcing steel bar ratio (As/Ag) between 0.5% and 1.0% is 80% of that calculated using Eq. 3.3.4.9-1. The residual drift ratio for hybrid rocking columns with a reinforcing steel bar ratio (As/Ag) of 0.5% or smaller is negligible (dr ≤ 1.0%). Table 3.3.4.9-1 presents a summary of the residual drift ratio estimation for hybrid rocking columns. Fig. 3.3.4.9-1b and c show the measured and calculated (using Equation 3.3.4.9-1) residual-peak drift ratio relationships for 2 half-scale hybrid rocking columns tested by Larkin et al. (2012). Good correlation between the measured and calculated results was observed for both columns.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 51 (a) Proposed Equation for As/Ag > 0.01 (b) Proposed Equation vs. Measured Data (As/Ag = 0.013 and fpi/fpy = 0.23) (c) Proposed Equation vs. Measured Data (As/Ag = 0.007 and fpi/fpy = 0.18) 0 1 2 3 4 5 6 7 R es id ua l D ri ft R a tio (% ) Peak Drift Ratio (%) fpi/fpy = 0.0 fpi/fpy = 0.15 fpi/fpy = 0.30 fpi/fpy = 0.45 1% Limit (Low Residual) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 R es id ua l D ri ft R a tio (% ) Peak Drift Ratio (%) PTHL-Larkin et al. (2012) Calculated for PTHL 1% Limit (Low Residual) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 R es id u a l D ri ft R a tio (% ) Peak Drift Ratio (%) PTLL-Larkin et al. (2012) Calculated for PTLL 1% Limit (Low Residual) 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 Figure 3.3.4.9-1. Residual drifts for hybrid rocking columns. Longitudinal Reinforcing Steel Bar Ratio (As /Ag) Residual Drift Ratio (%) Damping Ratio (%) (See Sec. 3.3.6.2) / 3.2 / 3.2 / 5 Note: “ ” is the peak drift ratio (%) and “ ” is the residual drift ratio (%). Table 3.3.4.9-1. Residual drift ratio for hybrid rocking columns. 3.3.5 Design of FRP-Confined Hybrid Rocking Columns FRP-confined hybrid rocking columns ideally will be designed conforming to the require- ments presented in this section. 3.3.5.1 Analytical Plastic Hinge Length The analytical plastic hinge length of hybrid rocking columns shall be according to AASHTO SGS (AASHTO, 2011): = + ≥0.08 0.15 0.3 (3.3.5.1-1)L L f d f dp ye bl ye bl where fye (ksi) is the expected yield strength of the longitudinal column reinforcing steel bars and dbl (in.) is the nominal diameter of longitudinal column reinforcing steel bars.

52 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview The AASHTO analytical plastic hinge length for RC columns is suggested for the design of hybrid rocking columns because the plastic hinge length is controlled by longitudinal reinforcing steel that is common to both RC and hybrid rocking columns. 3.3.5.2 Column Drift Capacity Column displacement capacity (Δc) is defined as a displacement at fracture of the column longitudinal bar or compressive failure of the confined concrete. Minimum requirements of the present guideline ensure that steel tendons remain linear-elastic at the fracture of steel bars or the failure of confined concrete (section 3.3.6.2). Either moment-curvature or pushover analysis may be used for the estimation of a hybrid rocking column displacement capacity. However, a push- over analysis is preferred since it includes the entire bridge model, frame actions, and geometric nonlinearities. When moment-curvature analysis is used, the displacement capacity is ( )∆ = + − − 3 2 (3.3.5.2-1) 2L L L L c Yi u Yi p pØ Ø Ø where ØYi is the idealized yield curvature calculated using the idealized method (Appendix H, Fig. H-1), Øu is the ultimate curvature associated with either steel bar fracture or confined concrete failure, L is the column height from point of maximum moment to the point of contra- flexure, and Lp is the calculated plastic hinge length. Column drift capacity (dc) is defined as the ratio of the column displacement capacity to the column height as δ = ∆ (3.3.5.2-2) L c c 3.3.5.2.1 Minimum Drift Capacity. The suggested minimum drift ratio capacity for hybrid rocking columns is listed in Table 3.3.5.2.1-1. The drift ratios correspond to the minimum dis- placement ductility capacity for conventional columns. Columns shall be designed to provide at least this level of drift ratio. Linear interpolation may be used for intermediate aspect ratios. 3.3.5.3 Shear Capacity The shear capacity of FRP-confined hybrid rocking columns, within the plastic hinge, calcu- lated based on the nominal material strength properties shall satisfy: ≥ (3.3.5.3-1)V Vs n uØ in which: = + + 0.95 (3.3.5.3-2)V V V Vn c s f Member ConventionalColumns Novel Columns Single- or multi-column bents Aspect Ratio 4: Aspect Ratio 6: Aspect Ratio 8: Note: “ ” is the drift ratio capacity (%) and “ ” is the displacement ductility capacity. Use linear interpolation for intermediate aspect ratios. Table 3.3.5.2.1-1. Minimum bridge column drift ratio capacity requirements.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 53 Where the strength reduction factor, Øs, is 0.9, Vn is the nominal shear capacity of member, Vs is the reinforcing steel contribution to shear capacity, Vc is the concrete contribution to shear capacity, and Vf is the FRP contribution to the shear. Vc and Vs are computed according to AASHTO SGS and are repeated here for circular columns: = 0.8 (3.3.5.3-3)V v Ac c g vc is zero if the column is under tensile axial loads. Otherwise: ( )= ′α +  ′≤ ′ ′α ′0.032 1 2 min 0.11 , 0.047 (3.3.5.3-4)v P A f f fc u g c c c For circular columns with spiral or hoop reinforcing: ′α = + − µ 0.15 3.67 (3.3.5.3-5) fs D = ρ ≤ 0.35 (3.3.5.3-6)f fs s yh ρ = ′ 4 (3.3.5.3-7) A sD s sp where Ag is the gross area of member cross-section (in. 2), Pu is the ultimate compressive force acting on section (kips), Asp is the area of the spiral or hoop reinforcing bar (in. 2), s is the pitch of spiral or spacing of hoops or ties (in.), D′ is the core diameter of column measured from cen- ter of spiral or hoop (in.), fyh is the nominal yield stress of transverse reinforcing (ksi), f ′c is the nominal concrete compressive strength (ksi), µD is the displacement ductility demand calculated from drift demand, and a’ is the concrete shear stress adjustment factor. For members that are reinforced with circular hoops, spirals, or interlocking hoops or spirals, the nominal shear reinforcement strength, Vs, is: = pi ′ 2 (3.3.5.3-8)V nA f D s s sp yh where n is the number of individual interlocking spirals or hoops within the spacing s. Refer to AASHTO SGS for the calculation of Vs for other types of cross-sections. The contribution of FRP to shear strength is calculated according to ACI 440.2R-08 (2008) as follows: ( )= α + α2 (3.3.5.3-9)V n t f sin cos Df f f fe where nf is the number of FRP layers, tf is the thickness of each FRP layer, a is the angle between the direction of the FRP principal fibers and the longitudinal axis of the member, D is the diameter of the column (or the largest side dimension of the column section), and = ε (3.3.5.3-10)f Efe fe f where Ef is the modulus of elasticity of the FRP, and 0.004 0.75 (3.3.5.3-11)f Efe fu fε = ≤ where ffu is the FRP design tensile strength including the environmental reduction factor.

54 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview The sum of shear strengths provided by the steel and FRP shall be limited to + ≤ ′0.25 (3.3.5.3-12)V V f As f c e where Ae is the effective area of the cross-section for shear resistance (0.8Ag). 3.3.5.4 Axial Capacity The axial capacity of an FRP-confined hybrid rocking column shall be calculated according to ACI 440.2R-08 (2008) as ( )( )= ′ − +0.85 (3.3.5.4-1)P f A A A fn cc g s s yØ Ø where f ′cc is the maximum compressive strength of an FRP-confined concrete section (ksi), Ag is the gross area of member cross-section (in.2), As is the column longitudinal reinforcing steel bar area (in.2), fy is the nominal yield strength of the column longitudinal reinforcing steel bars, and Ø is 0.75 and 0.7 for members with spirals and ties, respectively. 3.3.5.5 Minimum Lateral Strength Each bent shall have a minimum lateral flexural capacity to resist a lateral force of 0.1Pdl, where Pdl is the tributary dead load applied at the center of gravity of the superstructure. 3.3.5.6 Other Loading and Strength Design The load estimation, analysis, and design of FRP-confined hybrid rocking columns for non-seismic loads are based on the AASHTO LRFD Bridge Design Specifications (2014). Only for preliminary design under the load combination of “Extreme Event I,” the AASHTO response modification factors (AASHTO LRFD, Table 3.10.7.1-1) may be used to size the columns and their adjoining members. Nevertheless, FRP-confined hybrid rocking columns ideally will be analyzed and designed according to the guidelines presented in this document. 3.3.5.7 Serviceability Design An FRP-confined hybrid rocking column ideally will be designed to withstand service loads during the life of the bridge. The service limit state for these columns should include short- and long-term deformations. Serviceability for conventional RC and ECC is addressed through the minimum shrinkage and temperature reinforcement requirement. The relatively high transverse reinforcement to satisfy seismic design requirements in novel columns exceeds the minimum shrinkage and temperature reinforcement requirement in AASHTO LRFD. 3.3.5.7.1 Shrinkage and Creep. The AASHTO LRFD Bridge Design Specifications (2014) shall be used to compute shrinkage and creep of concrete. Service load stresses of an FRP jacket shall not exceed the creep-rupture stress limit, which is 0.2ffu for glass FRP (GFRP), 0.3ffu for Aramid FRP (AFRP), and 0.55ffu for carbon FRP (CFRP). ffu is the FRP design tensile strength including the environmental reduction factor. Note that the stress that has to be checked for the creep-rupture is the section maximum tensile stress under combined axial loads and bending moments due to service loads. 3.3.5.7.2 Axial Deformations. Instantaneous axial deformation due to loads and long- term shortening due to shrinkage and creep should be determined according to the AASHTO LRFD Bridge Design Specifications (2014).

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 55 The estimation of deformations in FRP-confined hybrid rocking columns at a limit state of serviceability is based on two assumptions: (1) strain is proportional to the distance from the neutral axis of the cross-section and (2) concrete and steel bars are linear elastic materials with moduli of elasticity specified in the AASHTO LRFD Bridge Design Specifications (2014). The contribution of the FRP jacket to axial stiffness may be neglected. 3.3.6 Details for FRP-Confined Hybrid Rocking Columns FRP-confined hybrid rocking columns shall be detailed conforming to requirements pre- sented in this section. 3.3.6.1 FRP Jacket FRP jacketing is through either wrapping the FRP sheets around the column or the utilization of prefabricated FRP tubes, which are available with different diameters and wall thicknesses. FRP tubes are advantageous in many cases because they could serve as permanent formwork, thus expediting the construction. Normally there is a 2-in. (50-mm) gap between the end of the jacket and the column adjoining member face. The jacket might extend over the entire length of column, except the 2-in. (50-mm) gap at the column ends, if it serves the dual purpose of plastic hinge damage control and stay-in-place form. If FRP is utilized only in the plastic hinge region, the FRP jacket height shall be the greater of (a) the analytical plastic hinge length and (b) 1.5 times the column largest side dimension. 3.3.6.2 Reinforcement Details 3.3.6.2.1 Longitudinal Reinforcing Steel Bars. The total area of longitudinal reinforcing steel bars (As) in hybrid rocking columns should satisfy ≤ ≤0.0025 0.025 (3.3.6.2.1-1)A A Ag s g where Ag is the gross area of member cross-section (in. 2). Hybrid rocking columns with As < 0.0025Ag tend to exhibit inadequate energy dissipation and those with As > 0.025Ag tend to exhibit signifi- cant residual displacements comparable to those in conventional columns. When As < 0.01Ag, the damping ratio for dynamic analyses shall be taken as 3.2% since a flag-shaped hysteretic behavior is expected. Consequently, the displacement demand for hybrid rocking columns with As < 0.01Ag calculated using equivalent static or spectral analysis method shall be increased by 20% to account for the lower damping ratio. The modification factor for short-period structures when As < 0.01Ag may be taken as 1.0. Fig. 3.3.6.2.1-1a shows hysteretic damping ratio versus displacement ductility for bridge columns with flag-shaped hysteresis curves. It can be seen than hysteretic damping of col- umns with flag-shaped behavior is lower than that of conventional RC columns, as expected. (b) Flag-Shaped Damping over RC Damping 0 5 10 15 20 Ductility RC Columns Dwairi et al. (2007) Priestley et al. (2007) 0 0.2 0.4 0.6 0.8 1 Ductility Dwairi et al. (2007) Priestley et al. (2007) RecommendedRe co m m e n de d (a) Hysteretic Damping 1 2 3 4 5 6 7 1 2 3 4 5 6 7 H ys te re tic D am pi ng (% ) y F la g- Sh ap ed / y R C Figure 3.3.6.2.1-1. Damping for columns with flag-shaped hysteresis.

56 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview Furthermore, the ratio of the flag-shaped column damping to the RC column damping is approximately constant for ductilities greater than 2 (Fig. 3.3.6.2.1-1b). Table 3.3.6.2.1-1 presents a summary of damping ratios. The average ratio of flag-shaped hysteretic damp- ing to that of RC columns was 64%. Based on these findings, the damping ratio of hybrid rocking columns with As < 0.01Ag is proposed to be 3.2%, which is 64% of the typical 5% damping. 3.3.6.2.2 Longitudinal Steel Tendons. The total area of longitudinal steel tendons (Ap) in hybrid rocking columns should satisfy: ≥ 0.004 (3.3.6.2.2-1)A Ap g where Ag is the gross area of member cross-section (in. 2). This requirement ensures that steel tendon yielding is avoided. Parametric studies of more than 650 hybrid rocking columns (Appendix C) showed that steel tendon stress at the ultimate displacement of the column may exceed the tendon yield strength if the column aspect ratio is high, the axial load level is low, and the longitudinal steel ratio is small. For example, Fig. 3.3.6.2.2-1 shows tendon stresses at the ultimate displacement of a hybrid rocking column with extreme properties (axial load = 0.02f ′c Ag, aspect ratio = 8, As = 0.0025Ag, and fpi = 0.3fpy) that increases the tendon stress at the column failure. The only variable in this figure is the area of the column longitudinal steel tendons. It can be seen that when the tendon area exceeds 0.004Ag, the tendon does not yield and the column fails either due to the steel bar fracture or the confined concrete failure. 3.3.6.2.3 Longitudinal Steel Tendon Initial Stresses. The initial stress of longitudinal steel tendons in hybrid rocking columns after all losses ( fpi) shall satisfy: ≤ 0.3 (3.3.6.2.3-1)f fpi py Dwairi et al. (2007) 0.72 3.60 1.14 Priestley et al. (2007) 0.56 2.80 1.26 Average of Two Refs 0.64 3.20 1.20 Recommended 0.64 3.20 1.20 References (Ave. for ) Flag-Shaped Damping RD Table 3.3.6.2.1-1. Damping for hybrid rocking columns with As < 0.01Ag. 0.6 0.7 0.8 0.9 1 1.1 0 0.002 0.004 0.006 0.008 0.01 Te n do n S te el St re ss R a tio (f p s / f p y) Tendon Steel Ratio (Ap / Ag) Hybrid Rocking Columns P / f'c Ag = 0.02 As / Ag = 0.0025 AR = 8 fpi / fpy = 0.30 M in im um Re co m m en de d Tendon Yielding Figure 3.3.6.2.2-1. Hybrid rocking column tendon stress at column failure.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 57 where fpy is the yield strength of steel tendons. The calculation of steel tendon stress losses shall be according to the AASHTO LRFD Bridge Design Specifications (2014, Article 5.9.5). Parametric studies (Appendix C) showed that when steel tendon initial stress (after all losses) is large, tendon yields before reinforcing steel bar fractures or the confined concrete fails result- ing in small displacement capacities. For example, Fig. 3.3.6.2.3-1 shows tendon stresses at the ultimate displacement of a hybrid rocking column with extreme properties (axial load = 0.02f ′c Ag, aspect ratio = 8, As = 0.0025Ag, and Ap = 0.004Ag). The only variable in this figure is the initial steel tendon stress. It can be seen that when the tendon initial stress is more than 0.35fpy, the tendon yields before the reinforcing steel bar fractures or the confined concrete fails. Eq. 3.3.6.2.3-1 is more stringent that the analytical results due to uncertainty in the estimation of tendon stress losses. 3.3.6.3 Maximum Axial Load The axial load acting on a hybrid rocking column with As ≥ 0.01Ag including gravity and seis- mic demands (Pu), but excluding the prestress force, when a pushover analysis is not performed should satisfy: ≤ ′0.15 (3.3.6.3-1)P f Au c g where Ag is the gross area of member cross-section (in. 2) and f ′c is the nominal concrete compressive strength (ksi). The axial load may exceed this limit provided that pushover analysis, including the P – Δ effect, is performed to compute the maximum drift capacity of the column. For a hybrid rocking column with As < 0.01Ag, ≤ ′0.1 (3.3.6.3-2)P f Au c g The P – Δ effect is more significant for hybrid rocking columns compared to conventional columns specifically when the longitudinal steel ratio is relatively small. 3.3.6.4 Maximum Aspect Ratio The aspect ratio of hybrid rocking columns, including the FRP-confined hybrid rocking col- umns, should not exceed 8. Columns with larger aspect ratios may fail at low drift ratios due to the P – Δ effect. As / Ag = 0.01 0.6 0.7 0.8 0.9 1 1.1 0 0.1 0.2 0.3 0.4 0.5 Hybrid Rocking Columns Tendon Yielding M ax im um Re co m m en de d St ee l T en do n S tr es s R a tio (f p s / f p y) Initial Steel Tendon Stress Ratio (fpi / fpy) P / f'c Ag = 0.02 Ap / Ag = 0.004 AR = 8 Figure 3.3.6.2.3-1. Hybrid rocking column initial tendon stresses.

58 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview 3.3.7 Construction of FRP-Confined Hybrid Rocking Columns 3.3.7.1 Quality Control Tests FRP testing method for the computation of mechanical properties, fire and life safety, ser- vice temperature, and many other parameters should be according to Appendix H of the ACI 440.2R-08 (2008). 3.3.7.2 Construction Procedures CIP and precast construction is permitted for FRP-confined hybrid rocking columns. Fig. 3.3.7.2-1 shows one example for each construction method. The design of precast col- umn connections should be according to bridge-owner approved guidelines. When FRP tube is used in precast construction (e.g., pocket connections for precast columns), FRP shall not be extended into the adjoining member. Recall that the role of FRP-confined rocking col- umns is to reduce damage in the plastic hinge regions. Natural roughness of the prefabricated FRP tubes should be preserved to ensure bond between the tube and concrete. 3.3.7.3 Construction Tolerance Tolerance limits normally used for conventional RC construction are applicable to FRP- confined hybrid rocking columns. Quality control for precast columns should be according to PCI MNL-116-99 (1999). Construction tolerance for precast column connections should be according to bridge-owner approved guidelines. 3.3.7.4 Ducts Minimum requirements for ducts are according to the AASHTO LRFD Bridge Design Specifi- cations (2014). Ducts shall not be grouted. Several tendons are needed for large-diameter columns. In this case, the number and the size of tendons per duct should be maximized and the number of ducts per column section should be minimized. There is currently a 37-strand anchorage available in the U.S. for 0.6-in. (15-mm) diameter steel strands. If multiple ducts cannot be avoided, the minimum number of ducts should be taken as 3 to be radially distributed in the section close to the column center. The minimum spacing of ducts in any direction of a section shall not be smaller than 1.5 times the largest aggre- gate size of the column concrete mix. Reinforcing Steel Bar FRP Jacket Te nd on a nd D uc t 2-in. Gap Cast-in-Place Column Footing FRP Jacket Te nd on a nd D uc t 2-in. Gap Pr ec as t C ol um n Reinforcing Steel Bar Pocket Connection Footing All reinforcement not shown (a) Cast-in-Place Detailing (b) Precast Detailing Figure 3.3.7.2-1. Construction of FRP-confined hybrid rocking columns.

Guidelines for Seismic Design and Construction of Bridge Columns with Improved Energy Dissipating Mechanisms 59 3.3.8 References AASHTO. (2011). AASHTO Guide Specifications for LRFD Seismic Bridge Design. Washington, D.C.: American Association of State Highway and Transportation Officials. AASHTO. (2014). AASHTO LRFD Bridge Design Specifications. Washington, D.C.: American Association of State Highway and Transportation Officials. ACI 440.2R-08. (2008). Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures, Reported by American Concrete Institute Committee 440, 80 pp. Dwairi, H. M., Kowalsky, M. J., and Nau, J. M. S. (2007). Equivalent Damping in Support of Direct Displacement- Based Design. Journal of Earthquake Engineering, 11(4), 512–530. https://doi.org/10.1080/13632460601033884. Larkin, A. S., Sanders, D., and Saiidi, M. S. (2012). Unbonded Prestressed Columns for Earthquake Resistance, Center for Civil Engineering Earthquake Research, Department of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-12-02, 256 pp. https://doi.org/10.1061/9780784412367.048. PCI MNL-116-99. (1999). Manual for Quality Control for Plants and Production of Structural Precast Concrete Products, Precast/Prestressed Concrete Institute, Chicago, IL, 328 pp. Priestley, M. J. N., Calvi, G. M., and Kowalski, M. J. (2007). Displacement-based Seismic Design of Structures. Pavia: IUSS press. Thonstad, T., Mantawy, I., Stanton, J., Eberhard, M., and Sanders, D. (2016). Shaking Table Performance of a New Bridge System with Pretensioned Rocking Columns, Journal of Bridge Engineering, ASCE, 14 pp. https://doi.org/10.1061/(ASCE)BE.1943-5592.0000867, 04015079.

60 4.1 Summary Standard RC bridge columns are generally designed to dissipate earthquake energy through yielding of longitudinal reinforcing steel and spalling of concrete that collectively cause large plastic deformations in columns. Even though bridge collapse is expected to be prevented using current design specifications, excessive plastic hinge damage and large post-earthquake perma- nent lateral deformations may cause the decommissioning of bridges for repair or replacement. The impact of bridge closure on access to the affected area shortly after an earthquake, traveling public, and economy of the region is significant. A new paradigm is emerging among bridge owners, requiring that bridges remain functional with minimal interruption of the traffic flow after earthquakes. To materialize this paradigm, bridge column construction practice would need to explore unconventional materials and techniques that possess characteristics that make bridge columns resilient. The objectives of the study were to develop (1) proposed AASHTO guidelines for the evalu- ation of new techniques for the design and construction of bridge columns with energy dis- sipation mechanisms meant to minimize bridge damage and replacement after a seismic event and (2) design and construction concepts based on new materials and techniques [e.g., post- tensioning, shape memory alloy (SMA), engineered cementitious composite (ECC), rubber pads, and fiber-reinforced polymer (FRP) wrapping] and analytical techniques. The objectives were accomplished through four phases encompassing 13 tasks. A literature review on the state- of-the-art was carried out to highlight the benefits of novel materials and new technologies, to establish mechanical properties of novel materials, and to identify design, construction, and performance knowledge gaps. A survey of state departments of transportation on past and future application of advanced materials in bridges was also conducted. Thirty-nine new bridge col- umn concepts, each with an improved energy dissipation system, were developed incorporating SMA, ECC, FRP, ultra-high performance concrete (UHPC), rubber, or rocking systems. Of the 39 concepts, only eight have been proof tested at the time of this writing but the remaining columns are believed also to be feasible. Other novel column concepts are likely to emerge in the future, each aiming to improve seismic performance compared to conventional RC columns. To assess any existing or emerging novel column, evaluation guidelines were developed using 14 parameters to determine suitability and performance of the columns. The parameters included in the evaluation guidelines were (1) plas- tic hinge damage, (2) displacement capacity, (3) residual displacement, (4) availability of proof test data, (5) availability of analysis tools, (6) availability of design guidelines, (7) past field appli- cations, (8) initial cost, (9) advanced material limitations, (10) ease of construction, (11) inspect- ability, (12) maintenance, (13) post-earthquake repair need, and (14) system performance. These parameters were quantified and scored with different weights. The overall evaluation result was C H A P T E R 4 Summary and Conclusions

Summary and Conclusions 61 converted to a five-star rating method to help bridge owners and designers compare different alternatives and make the final selection. The current AASHTO Guide Specifications for LRFD Seismic Bridge Design uses displacement ductility as a measure of column deformability. However, this parameter may not be suitable for novel columns since the yield mechanism in the novel and conventional columns can be dif- ferent. To address this difference, drift ratio was used in this study to evaluate deformability. A comprehensive parametric study was carried out to relate the displacement ductility to the drift ratio for practical ranges of RC bridge column geometry and axial loading. Three of the 39 novel columns were selected by the project panel for further investigation: (1) SMA-reinforced ECC columns, (2) SMA-reinforced FRP-confined concrete columns, and (3) FRP-confined hybrid rocking columns. Comprehensive analysis, design, and construction guidelines were developed for these three novel columns. Step-by-step comprehensive design examples were developed for each of the three columns to better show the use of the proposed guidelines. The framework used to develop these guidelines can be used by researchers to develop guidelines for other existing or emerging novel columns. 4.2 Conclusions The study presented in this report consisted of many tasks all aimed at accomplishing the two primary objectives of the project, which were development of (1) AASHTO guidelines for the evaluation of novel bridge columns and (2) design, construction, and analytical techniques for bridge columns utilizing advanced materials. The request for proposals (RFP) called for addi- tional tasks to address other aspects of novel columns. The deliverables addressing the primary objectives were presented in the main body of this document. Documents describing the work on other tasks stated in the RFP and the supporting studies related to the primary objectives are presented in the appendices. 4.2.1 Proposed AASHTO Guidelines for Evaluation of Novel Columns With the new paradigm of requiring infrastructure to be resilient to serve the public effec- tively, novel bridge columns utilizing unconventional construction material are likely to emerge. The proposed AASHTO guidelines identified 14 parameters to consider in assessing any novel column. These parameters encompass structural seismic performance, damage tolerance, seis- mic design tools, construction, cost, maintenance, and post-earthquake repair among others. Qualitative metrics to assess these parameters were provided. A flow chart integrating all the parameters was developed and was found to be an effective tool to help determine the suitability of a given novel column. It was found that the analysis procedure in the AASHTO Guide Speci- fications for LRFD Seismic Bridge Design (AASHTO SGS) could generally be used for novel col- umns with adjustments to address the particular characteristics of various novel columns. The work leading to the guidelines also concluded that drift ratio rather than displacement ductility is an appropriate measure of deformability of novel columns. 4.2.2 Seismic Design and Construction of Novel Columns The common features of resilient bridge columns are the ability to recover lateral displace- ments (recentering) and resistance to damage in plastic hinges. The three novel columns that were selected for detailed studies address these features using different techniques. It was found that recentering might be successfully implemented in design methods by either the use of superelastic SMA longitudinal bars in the plastic hinge or prestressing. Controlling damage to

62 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 1: Research Overview the cementitious material in the plastic hinge could be achieved by the use of damage tolerant materials or through external FRP jackets. The study showed that many of the provisions of the AASHTO SGS are applicable to analysis and design of novel columns, but the design has to also incorporate recent research results that address the characteristics of the particular advanced materials used in the columns. Furthermore, it was found that peculiarities of advanced materials could affect the method by which design forces are determined. 4.2.3 Key Conclusions from Appendix Documents The most important observations and conclusions from the documents presented in the appendices are as follows: 4.2.3.1 Literature Review The literature review was focused on materials that provide recentering and that control plastic hinge damage. Past work on superelastic SMA was reviewed to address recentering. The results indicated that nickel-titanium SMA bars are the only feasible SMAs at the time of this writing. The existing specifications for SMAs are conservative by necessity due to a lack of extensive test data. To address plastic hinge damage reduction, the literature on cementitious low-damage materials (ECC UHPC), rubber, and FRPs was reviewed. It was concluded that, although design provisions for cementitious materials are still emerging, there are sufficient guidelines to pro- ceed with preliminary design recommendations for these materials. It was also found that exist- ing guidelines for rubber and FRPs are sufficiently developed and are ready for adoption. 4.2.3.2 State DOT Survey The purpose of the survey was to determine familiarity, past deployment, and possible future application of advanced materials in bridges. Thirty-four states participated in the survey. Not surprising was the finding that many states are familiar with FRPs and have used FRPs due to its relatively long history of application in bridge engineering. Other novel materials such as SMA and ECC were known only to a limited number of participants. The survey results were encouraging and demonstrated the receptiveness of the bridge engineering community to new concepts. 4.2.3.3 Literature Synthesis and Knowledge Gaps Based on the literature review, key attributes of novel materials were compiled and major knowledge gaps were identified. The attributes included various consideration such as past application, commercial availability, durability, constructability, knowledge gaps, cost, etc. It was concluded that climatic consideration may limit the suitability of certain advanced materi- als, and a lack of specifications could pose a barrier to preventing widespread application of these materials. 4.2.3.4 Novel Column and Construction Concepts The literature review of novel materials and the seismic performance of novel columns led to the conclusion that 39 combinations of materials may be made to form details of plausible novel columns. This assessment was made based on the material, large drift capacity, minimizing damage, and recentering. Of the 39 novel column types, only eight have been proof tested. 4.2.3.5 Demonstration of Evaluation Guidelines The proposed AASHTO evaluation guidelines that were developed to address the first objec- tive of the project were applied to the 39 novel column types identified in Appendix D. The

Summary and Conclusions 63 star rating discussed under the guidelines was applied to both seismic performance and other considerations and were combined into a single star rating. It was concluded that non-seismic considerations could offset a higher star rating given to seismic performance for some of the columns, leading to a relatively low overall number of stars for these columns. 4.2.3.6 Design Examples of Select Novel Columns Four design examples, one on a reference conventional RC bridge and three each incorporat- ing one of the three novel columns selected by the project panel, were prepared to demonstrate the application of the design guidelines developed to address the second objective of NCHRP Project 12-101. It was concluded that, to satisfy the design guidelines, column cross-sectional dimensions and reinforcement may have to vary depending on the type of the novel column. The examples also pointed out the need for refinement of some of the provisions in the guide- lines, which were subsequently revised and presented in the main body of this document. 4.2.3.7 Qualitative Benefits and Economic Impact Although the RFP called for a qualitative estimate of the benefits and cost impact, a somewhat detailed quantitative evaluation was made for two versions of a five-span bridge, one with a con- ventional RC column and the other with a column incorporating SMA/ECC in plastic hinges. It was concluded that the combined initial and repair cost of the bridge with novel columns could exceed that of a conventional bridge by 5% to 10%. However, the novel bridge might cost less than the conventional bridge when the user cost, right of way, traffic control, and impact on other aspects of prolonged repair of conventional RC bridges are considered. For example, the saving by using SMA/ECC instead of RC could exceed 10% of the total cost when the user cost is considered in addition to the initial and repair cost. 4.2.3.8 Drift Ratio Displacement Ductility Relationship Because novel columns could be more flexible than RC columns, their yield displacement is relatively large, which could lead to an erroneous conclusion that the displacement ductility capacity of novel columns is lower than that of RC columns despite the higher overall displace- ment capacity of novel columns. It was concluded that the deformability of novel columns is best represented by the drift ratio instead of displacement ductility. The study summarized in Appendix H led to the development of formulas relating the drift ratio to displacement ductility to help designers to convert one to the other. 4.2.3.9 Modeling and Validation for Novel Columns Background analytical work leading to some of the provisions in the three novel column design guidelines (Objective 2 of NCHRP Project 12-101) is summarized in Appendix I. The modeling methods were verified against the available test data. The analytical results demon- strated the strong recentering capability of the three novel columns regardless of the recentering mechanism.

64 Appendices A through I are not printed herein but are available for download from the TRB website (trb.org) by searching for “NCHRP Research Report 864.” The appendices include the following: Appendix A: Literature Review Appendix B: Survey of State Departments of Transportation Appendix C: Synthesis of Literature Appendix D: Novel Column and Construction Concepts Appendix E: Demonstration of Evaluation Guidelines Appendix F: Detailed Design Examples for Three Novel Columns Appendix G: Benefits and Economic Impact of Novel Columns Appendix H: Relationship Between Drift Ratio and Displacement Ductility Appendix I: Modeling Methods and Validation for Novel Columns A p p e n d i c e s A – i

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation