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 2: Guidelines 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. Stewart Fotheringham, Professor, School of Geographical Sciences and Urban Planning, Arizona State University, Tempe John S. Halikowski, Director, Arizona DOT, Phoenix Susan Hanson, Distinguished University Professor Emerita, Graduate School of Geography, Clark University, Worcester, MA Steve Heminger, Executive Director, Metropolitan Transportation Commission, Oakland, CA Chris T. Hendrickson, Hamerschlag Professor of Engineering, Carnegie Mellon University, Pittsburgh, PA Jeffrey D. Holt, Managing Director, Power, Energy, and Infrastructure Group, BMO Capital Markets Corporation, New York S. Jack Hu, Vice President for Research and J. Reid and Polly Anderson Professor of Manufacturing, University of Michigan, Ann Arbor Roger B. 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Wise, Vice President of Network Strategy, Burlington Northern Santa Fe Railway, Fort Worth, TX Charles A. Zelle, Commissioner, Minnesota DOT, Saint Paul EX OFFICIO MEMBERS Michael Berube, Deputy Assistant Secretary for Transportation, U.S. Department of Energy Mary R. Brooks, Professor Emerita, Dalhousie University, Halifax, Nova Scotia, Canada, and Chair, TRB Marine Board Mark H. Buzby (Rear Admiral, U.S. Navy), Executive Director, Maritime Administration, U.S. DOT Steven Cliff, Deputy Executive Officer, California Air Resources Board, Sacramento Howard R. Elliott, Administrator, Pipeline and Hazardous Materials Safety Administration, U.S. DOT Audrey Farley, Executive Director, Office of the Assistant Secretary for Research and Technology, U.S. DOT LeRoy Gishi, Chief, Division of Transportation, Bureau of Indian Affairs, U.S. Department of the Interior, Washington, DC John T. 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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 2: Guidelines 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

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research is the most effective way to solve many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation results in increasingly complex problems of wide inter- est to highway authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRB’s recognized objectivity and understanding of modern research practices. 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Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administra- tion and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement, rather than to substitute for or duplicate, other highway research programs. Published research reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet by going to http://www.national-academies.org and then searching for TRB Printed in the United States of America NCHRP RESEARCH REPORT 864, VOLUME 2 Project 12-101 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-44668-6 Library of Congress Control Number 2017959576 © 2017 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. 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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 2 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

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 Summary 3 Section 1 General 4 Section 2 Purpose 5 Section 3 Philosophy 6 Section 4 Definitions 8 Section 5 Characteristics of Novel Columns 8 5.1 Plastic Hinge Damage 9 5.2 Displacement Capacity 11 5.3 Residual Displacements 13 Section 6 Non-seismic and Seismic Design Considerations 13 6.1 Non-seismic Design Consideration 13 6.2 Seismic Design Considerations 15 Section 7 Construction and Maintenance Considerations 16 Section 8 Evaluation and Selection Criteria 20 Section 9 Analysis and Design Procedure Development 20 9.1 Analysis Procedure Requirements 21 9.2 Design Procedure Requirements 23 Section 10 Conclusions 24 References C O N T E N T S

1 Standard reinforced concrete bridge columns are generally designed to dissipate earth- quake energy through the yielding of longitudinal reinforcing steel and spalling of concrete that collectively causes 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 the 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, the 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 current seismic bridge design specifications. NCHRP Project 12-101 was initiated to achieve two main objectives of developing (1) proposed AASHTO guidelines for the evalu- ation 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, 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 transportation 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. Three of the 39 novel columns were selected by the project panel for fur- ther 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, detailed design examples for these columns, and overall results of the project were published in NCHRP Research Report 864, Volume 1, and hence are not duplicated in the present report. 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 S U M M A R Y Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 2: Guidelines

2 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 2: Guidelines any existing or emerging novel columns, evaluation guidelines were developed in this docu- ment using 14 parameters to determine suitability and performance of the columns. The parameters included in the evaluation guidelines were (1) plastic hinge damage, (2) displace- ment 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, (10) ease of construction, (11) inspectability, (12) main- tenance, (13) post-earthquake repair need, and (14) system performance. These parameters were quantified and scored with different weights. The overall evaluation results were con- verted to a five-star rating method to help bridge owners and designers compare different alternatives and to make the final selection. The present report presents the proposed evalu- ation guidelines for resilient bridge columns with improved seismic performance.

3 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 prevention, while allowing for substantial damage in column plastic hinges. Even though this performance 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 replacement. 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 RC 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 replace- ment 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. S E C T I O N 1 General

4A variety of resilient novel columns are emerging. Uniform assessment tools are needed to assist bridge owners and designers in selecting the columns that meet various constraints. The purpose of these guidelines is to provide a framework for the evaluation and implementation of novel bridge column designs within the existing AASHTO design specification methodology. They are not intended to provide detailed design specifications, but rather general guidance to aid in the evaluation and potential adoption of novel bridge columns. The guidelines take 14 parameters into account: 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, 10. Ease of construction, 11. Inspectability, 12. Maintenance, 13. Post-earthquake repair need, and 14. System performance. These parameters are quantified and scored with different weights. Finally, the overall evalu- ation result is presented using a five-star rating system for novel columns to help bridge owners and designers compare different alternatives and make the final selection. Before a novel column is implemented in the field, the guidelines ideally will be used in combination with analysis, design, and detailing specifications for that column. Examples of such specification for detailed analysis, design, and construction are presented in this document for three novel columns (1) shape memory alloy (SMA)-reinforced engineered cementitious (ECC) columns, (2) SMA-reinforced fiber-reinforced polymer (FRP)-confined concrete columns, and (3) FRP-confined hybrid rocking columns. Novel column design guidelines are presented in the following chapter and detailed design examples are presented in Appendix F of this present project [available for download from the TRB website (trb.org) by searching for “NCHRP Research Report 864”]. S E C T I O N 2 Purpose

5 Treatment of specific novel column concepts are avoided in these guidelines, as they are intended to apply to a broad range of concepts, both existing and those yet to be developed. This has led to certain modifications of existing seismic design provisions, such as the use of drift ratios in place of ductility. Displacement-based methodology is generally a better design approach for novel columns because these columns may exhibit completely different behavior and capacities compared to conventional columns. Constitutive materials of a ductile member can be accounted for directly using the displacement-based method while force-based design relies on the overall load- carrying capacities of the member. Furthermore, the amount of available test data for existing novel columns is not yet sufficient to reliably establish the response modification (R) factor that is needed in the force-based method. Emerging novel column concepts need to undergo extensive laboratory testing before establishing R-factors. Therefore, the use of “force-based design” methods such as those presented in the AASHTO LRFD Bridge Design Specifications (AASHTO LRFD) (AASHTO, 2014) shall not be used for resilient novel columns at this time. The evaluation methodologies contained in these guidelines were developed to assess quanti- tatively the suitability and feasibility of existing or emerging novel columns for seismic application. Many key parameters are included in the evaluation. The weight that is assigned to each parameter is intended to provide flexibility to designers and owners to emphasize the parameters of their choice. For example, one owner might consider eliminating damage of paramount importance with cost being a secondary consideration, whereas another owner might be tolerant of some level of damage as long as the cost of the novel column is within budget. In these cases, designers can adjust the seismic performance and cost weights to accommodate different needs. S E C T I O N 3 Philosophy

6Definitions of the terms that may not be commonly understood as they pertain to novel column design, construction, behavior, and evaluation are presented herein. Advanced Material: An existing or emerging material that is not commonly used in bridge construction but is used in the design of a novel column. Aspect Ratio (Ar): The ratio of the length of a column (L) to its diameter (D). Design Guideline: A discretionary set of analysis, design, and construction requirements. Displacement Capacity (ΔC): The displacement at which one of the limiting criteria is met, such as a maximum material strain. Displacement Demand (ΔD): The maximum displacement expected to occur at a given seismic hazard level, as determined by analysis. Displacement Ductility (µ): A measure of the displacement of an element in relation to the effective (or idealized) yield displacement. Drift Ratio (δ): The ratio of the displacement of a column divided by the column height, or length. Engineered Cementitious Composite (ECC): A cementitious material designed to exhibit large tensile strain capacity, usually through the use of polyvinyl alcohol fibers. Evaluation Guideline: A methodology that may be used to aid in the evaluation of potential novel column designs for field deployment. Fiber-Reinforced Polymer (FRP): A material consisting of a type of fiber embedded in a polymer matrix, generally characterized by its lightweight, high tensile strength and linear behavior. Hybrid Rocking Column: A rocking column that includes a type of energy dissipating mechanism (e.g., reinforcing bars). Jacket: A structural element on the exterior of a column intended primarily to confine the column concrete, often made of steel or FRP. Mechanical Bar Splice: A mechanical device used to couple two reinforcing bars together in tension and compression. Resilient Novel Column (or Novel Column): A column that has large displacement capacity and exhibits one or both of (1) no or minimal damage and (2) low residual lateral displacements. Rocking Column: A pre- or post-tensioned column intended to exhibit large localized rotations at one or both ends during a seismic event. S E C T I O N 4 Definitions

Definitions 7 Rubber: A natural or fabricated material that can undergo large deformations without failure. Shape Memory Alloy (SMA): An advanced metallic material that exhibits large inelastic deformations without significant permanent deformations upon heating or unloading. Superelastic Shape Memory Alloy (SE SMA): An advanced metallic material that exhibits large inelastic deformations without significant permanent deformations upon unloading. Ultra-High Performance Concrete (UHPC): A cementitious material characterized by substantially higher compressive and tensile strengths and ductility compared to conventional concrete. The reader is referred to Appendices A through D for the state-of-the-art review of advanced materials and new technologies viable for incorporation in novel columns. The appendices are available for download from the TRB website (trb.org) by searching for “NCHRP Research Report 864.”

8A general definition of novel columns was presented in the previous section. For seismic applications, any novel column should minimize plastic hinge damage and residual lateral displacements, while having sufficient lateral displacement capacity. 5.1 Plastic Hinge Damage A conventional RC bridge column designed according to current bridge codes can exhibit sig- nificant inelastic deformations without losing its lateral strength under severe earthquakes. This is achieved by mandating a ductile failure through significant yielding of longitudinal reinforce- ment and confining the column core concrete using sufficient transverse reinforcement. Earthquake damage to column plastic hinges can be generally categorized into four levels: “no damage,” “low,” “moderate,” and “severe” (Fig. 5.1-1). For a conventional standard RC column under high seismic loading conditions, the expected damage is severe when strains in steel bars substantially exceed the yield strain, and for sustained strong ground motions, steel bars may buckle or fracture accompanied with spalling of unconfined concrete or even com- pression failure of the core concrete (the bottom layer in the pyramid in Fig. 5.1-1). Severe damage of bridge columns may result in closure of affected bridges to emergency vehicles and the public, which will impose extra social and economic costs in addition to the repair or replace- ment cost of these bridges. The economic losses could be unacceptably high if the closed bridges are the only routes to access the affected zone Advanced materials that can be used in novel column designs include among others: SMA, ECC, UHPC, FRP, and rubber. Feasible combinations of these and conventional materials can lead to the development of practical novel columns. The damage level could be reduced to “moderate” in a novel column by replacing either steel bars or concrete with these or other emerging advanced materials. For example, if SMA bars are used in lieu of reinforcing steel bars, permanent residual strains will be significantly reduced due to the superelastic behavior of SMA bars. Similarly, if FRP rather than steel longitudinal bars are used, no reinforcement yielding is expected because of the linear elastic behavior of FRP bars. Either modification may improve the column damage level from “severe” to “moderate.” Another means to reduce the damage level to “moderate” is by replacing the conventional concrete in the plastic hinge with high-performance materials such as ECC or UHPC. Damage can be further mitigated by simultaneous incorporation of advanced materials. For example, the combination of reinforcing SMA or FRP bars with ECC or UHPC can limit the damage to the cover material only, which is considered to be a “low” level of damage. When steel reinforcement is used and concrete in the plastic hinge is confined by FRP or replaced with rubber, the damage is limited to only yielding of steel reinforcement, which may also be S E C T I O N 5 Characteristics of Novel Columns

Characteristics of Novel Columns 9 considered to be “low.” When the plastic hinge of a novel column is composed entirely of high- performance, low-damage materials (e.g., FRP jackets or rubber with SMA or FRP bars), seismic damage can be essentially eliminated, which is categorized as the “no-damage” level (the top layer in the pyramid in Fig. 5.1-1). 5.2 Displacement Capacity Conventional bridges are designed to exhibit substantial nonlinear deformations in plastic hinge zones, and this leads to large lateral displacements. Displacement ductility is considered to be a common measure of deformability of the bridge. The AASHTO Guide Specifications for LRFD Seismic Bridge Design (AASHTO SGS) (2011) require that the displacement ductility demand (µD) under the design seismic load should not exceed 5 for single-column bents and 6 for multi- column bents. The calculated minimum column displacement ductility capacity (µc) specified by Caltrans Seismic Design Criteria (SDC) (2013) is 3. To categorize displacement capacity of a novel column, 3 levels of displacement ductility were considered based on the current codes and practice as shown in Fig. 5.2-1: “low,” “normal,” and “high.” Displacement ductility capacity of 3 or less is categorized as “low,” 3 to 5 is considered to be “normal” (expected of a conventional RC column meeting current seismic codes), and more than 5 is considered to be “high.” Displacement ductility is not necessarily a suitable measure to evaluate deformation capacity of novel columns since the effective “yield” displacement in many novel columns may be much higher than conventional columns, or there may be no true yielding behavior in a novel column (e.g., columns reinforced with FRP bars). For the same displacement capacity (the numerator), the larger yield displacement (the denominator) leads to a smaller calculated displacement ductility. In the case where no yielding occurs, displacement ductility becomes a meaningless quantity. A more universal measure of the deformation capacity of novel columns is the drift ratio capacity, which is the ratio of the column lateral displacement at failure to the column height. Because current bridge seismic codes, such as the AASHTO SGS, utilize displacement ductility rather than the drift capacity in design, it is important to determine the relationship between ductility and drift ratio so that displacement ductilities in current codes can be translated to drift No Damage: Several combinations of advanced materials: No plastic hinge damage, no permanent bar yielding. Low Damage: Several combinations of advanced materials: Only cover failure or only steel bar yielding. Moderate Damage: Example: When SMA/FRP bars are used: Cover failure, concrete core failure. Moderate Damage: Example: When ECC or UHPC is used: Cover failure, large steel bar inelastic strains. Severe Damage: Conventional columns: Cover failure, concrete core failure, large steel bar inelastic strains, bar buckling or fracture. Figure 5.1-1. Column plastic hinge damage under seismic loading.

10 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 2: Guidelines 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. Details of the study and the results are included in Appendix H. A total of 696 conventional RC columns were designed based on the AASHTO SGS (2011) using pushover analyses (including the P-D effect). It was found that the column aspect ratio is the major factor that affects the relationship between the drift ratio and the displacement ductility. The results showed that a linear relation- ship exists between drift and ductility for each aspect ratio. Fig. 5.2-2 shows a summary of the parametric study. Equations were developed to relate drift ratio and ductility. The equations are listed in Table 5.2-1 (also see Section 9.2: Design Procedure Requirements). Linear interpolation is allowed for other aspect ratios. The proposed equations were developed so that the equivalent drift ratio of conventional columns may be used in novel column design. As a result, these equations were developed to represent the upper bound of the data from the parametric studies. The threshold was set so that the drift capacity from the equations exceeds the average data by at least 15% with a probability of 95%. In other words, a novel column has to exhibit larger drift capacity than a conventional column to be considered equally ductile. This was done to inclusively cover a wide range of RC columns with different parameters. High Displacement Capacity: Example: When high performance materials such as SMA bars, debonded steel bars, ECC, FRP jackets, or rubber pads are used: µc ≥ 5. Normal Displacement Capacity: Typical conventional columns: 3 ≤ µc < 5. Low Displacement Capacity: When linear-elastic materials are used as reinforcement: µc < 3. Figure 5.2-1. Calculated column displacement capacity under seismic loading. 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 5.2-2. Drift-ductility relationships for conventional RC columns.

Characteristics of Novel Columns 11 5.3 Residual Displacements Excessive lateral residual displacements after a severe earthquake can result in delays in reopening the bridge to traffic or even the need to replace the bridge. Currently, there is no limit on the residual displacement in the U.S. bridge design codes, but FEMA P-58 (2012) proposed four damage states associated with the residual drift to be used as a tool for seismic assessment of buildings. One percent residual drift was considered as damage state of 3 (DS3) in which a major structural realignment is needed to restore the building. A simple method was also proposed to estimate the residual drift based on the peak story drift. Japan’s Design Specifications for Highway Bridges (Japan Road Association, 2002) limits the bridge column residual drift ratio to 1% to keep the bridge in service after earthquakes. Three levels were considered in the present guideline for residual drifts (Fig. 5.3-1): “low,” “moderate,” and “high.” A 1% residual drift ratio (shown as dr) or less for a bridge column at the design level earthquake is categorized as “low.” This limit is expected from novel columns utilizing superelastic reinforcing SMA bars or rocking connections since residual strain in SMA bars under cyclic loading is minimal and prestressing tendons bring the column back to its original position. The maximum residual drift that could be potentially recovered subsequent to an earthquake is expected to be 1.5%. This limit depends highly on the specific bridge and is based on engineering judgment rather than scientific studies. However, a study by Ardakani and Saiidi (2013) determined that the majority of bridge columns meeting current standards are safe even with a residual drift ratio of 1.5%. Therefore, a “moderate” level of residual drift is assumed to be Parameters Proposed Equaon Column Aspect Ratio 4 Column Aspect Ratio 6 Column Aspect Ratio 8 Note: “δ” is the drift ratio (%), “µ” is the displacement ductility, and δ = 0.8µ – 0.40 δ = 1.1µ – 0.45 δ = 1.4µ – 0.60 “Ar = L/D ” is the column aspect ratio. Use linear interpolation for other aspect ratios. Table 5.2-1. Proposed relationships between drift and ductility for RC columns. Low Residual Displacement: Example: When SMA bars, FRP bars, or post-tensioning tendons are used: Lower or negligible residual displacement compared to conventional columns is expected δr ≤ 1.0% Moderate Residual Displacement: Example: When FRP jacket or hybrid rocking are used: Residual displacement may not be significant and may be mitigated 1.0% < δr ≤ 1.5%. High Residual Displacement: Conventional columns: Residual displacement is significant due to extensive yielding of steel bars δr > 1.5%. Figure 5.3-1. Column residual displacement under seismic loading.

12 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 2: Guidelines between 1.0% to 1.5%. A residual drift exceeding 1.5% may lead to bridge closure and replace- ment after a severe earthquake and must be treated as “high.” Conventional columns are usually susceptible to high residual drifts even for design level earthquakes when they are near an active fault. Near-fault earthquakes are known to lead to high residual displacements due to the high velocity pulse (Choi et al., 2010). Nonlinear response history analysis is the most appropriate method for the estimation of residual displacements. However, simple methods may be used to estimate the residual displace- ment (or drift) for conventional columns such as the equations developed by Ardakani and Saiidi (2013) as follows: δ = βδ (5.3-1)r y where dr is the residual drift ratio, dy is the yield drift ratio, and ( )β = µ + µ µ > µ ≤   0.04 0.14 1.0 0 1.0 (5.3-2) 2 D D D D where µD is the displacement ductility demand. Simple equations for estimating residual dis- placements for the three select novel columns are presented in the guidelines for each column. Equations for other column concepts have yet to be developed.

13 Many parameters need to be considered for each novel column before field deployment. These parameters can be categorized as (1) seismic performance, (2) design considerations, and (3) construction and other considerations. Parameters pertaining to the seismic performance were presented in the previous section. The design considerations including non-seismic and seismic issues are discussed herein followed by description of construction considerations. 6.1 Non-seismic Design Considerations The estimation, analysis, and design of novel columns for non-seismic loads should be based on the AASHTO LRFD Bridge Design Specifications (AASHTO LRFD) (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 reasonably size the columns and their adjoining members. All of the applicable strength and service limit states need to be investigated. For the purposes of non-seismic design, high performance materials such as SMA reinforcing bars can be treated as conventional materials, and the design methodologies for them contained in the specifications applied. When existing ASTM standards or AASHTO specifications do not sufficiently address testing of a particular novel material, new testing methods are required to ensure that the novel material satisfies the design assumptions. For those novel column concepts that introduce significant flexibility when compared to conventional design, extra attention should be paid to displacements under service loading. Bridges incorporating these columns may exhibit displacements under wind and braking loads well in excess of past designs, and the engineer will need to confirm that this will not negatively impact the serviceability or service life of the bridge. 6.2 Seismic Design Considerations The design of novel columns for seismic events follows the procedures described in the AASHTO SGS. An analysis is performed to determine the displacement demand: The displace- ment capacity of a bridge with novel columns needs to be determined based on the structural arrangement of the column and the materials used. Maximum and minimum limits on how much displacement ductility, or in the case of novel columns, drift ratio, is required and provided in the column design. There are two general seismic design methodologies: force-based and displacement-based. Forces are the target in the force-based design method (e.g., AASHTO LRFD). In this method, ultimate axial, shear, and flexural capacities are calculated and are compared with corresponding factored force demands under different load combinations using response modification factors. S E C T I O N 6 Non-seismic and Seismic Design Considerations

14 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 2: Guidelines Linear-elastic analysis is usually conducted to calculate the demand in the force-based design method. In the displacement-based design, the displacement is the target (e.g., AASHTO SGS). In this method, the displacement demands are calculated from a suitable analysis, and capacity can be calculated using nonlinear moment-curvature or pushover analysis. The ultimate force capacities can also be accurately estimated in this method as a secondary check. The displacement-based method is a better approach for novel columns since they may exhibit completely different behavior and capacities compared to conventional columns. For example, SMA-reinforced columns may exhibit displacement capacities as high as twice the capacity of the corresponding steel-reinforced columns. Furthermore, the amount of available test data for novel columns is not yet sufficient to reliably establish the response modification factor that is needed in the force-based method. Therefore, the use of “force-based design” methods such as those presented in the AASHTO LRFD Bridge Design Specifications (AASHTO, 2014) shall be avoided for novel columns.

15 In addition to the seismic performance and design considerations, many other parameters may affect an owner’s decision in selecting a novel column for field deployment. These param- eters include: (1) initial cost, (2) material limitations, (3) ease of construction, (4) inspectability, (5) maintenance, (6) post-earthquake repair, and (7) system performance. Because novel columns may incorporate materials not commonly used in bridge construction, estimating costs will require additional effort to obtain accurate unit cost values. As the volume of a specific material used in construction increases, the costs will decrease, and this needs to be kept in mind when making programmatic decisions. In addition to cost, each material has its own limitations, which must be taken into consider- ation for different bridge sites. One example is that FRP jacket should not be used in salt water since the resin in FRP, as well as glue between the FRP and concrete, may dissolve. Each novel column must be sufficiently easy to construct with a minimum of components that might require extra construction steps (e.g., mechanical bar couplers, post-tensioning, and rubber pads). Based on the material limitations, some novel columns may require regular inspection to ensure func- tionality of the columns during earthquakes. For example, FRP jackets require UV protection as well as a fire resistant coating. These coatings need to be regularly inspected. For post-tensioned columns, the prestressing system needs to be detailed to limit corrosion potential. Viewing ports to allow for inspection may be incorporated in post-tensioned columns. Rocking connections built with unbonded post-tensioning steel tendons must be detailed to be waterproof. After identifying any issues in the routine inspection, the affected components must be maintained to ensure adequate performance. For instance, coatings used for exposed steel and FRP must be renewed based on the manufacturer’s suggested schedule. Advanced materials usually exhibit better durability and life span compared to conventional materials. The need for post-earthquake repair can be directly related to the plastic hinge damage. Furthermore, the seismic performance levels suggested in the present guideline for novel columns are to ensure minimal plastic hinge damage and thus minimal need for post-earthquake repairs. Nevertheless, based on the selected performance level, the repair costs will vary across the various types of novel columns. Finally, the seismic performance of novel columns may affect design and construction of other bridge components (system performance). For example, if rubber pads and reinforcing SMA bars are used in column plastic hinges, the overall bridge lateral dis- placement demand may be increased because of the relatively small stiffness of these columns. Therefore, larger movement is anticipated that may require greater support length than that of conventional bridges. S E C T I O N 7 Construction and Maintenance Considerations

16 Figure 8-1 illustrates a flowchart for comprehensive evaluation of existing or emerging novel columns. A quantitative evaluation technique developed to compare different alternatives to facilitate the decision-making process in choosing among novel column concepts is presented in Table 8-1. Three categories are individually evaluated and rated: (1) seismic performance, (2) design considerations, and (3) construction and other considerations. The seismic perfor- mance evaluation includes (1) plastic hinge damage, (2) displacement capacity, and (3) residual displacement. The design consideration evaluation includes (1) proof testing, (2) analysis tools, (3) design guideline, and (4) prior field applications. The construction consideration is evaluated based on (1) initial cost, (2) material limitation, (3) constructability, (4) inspectability, (5) main- tenance, (6) post-earthquake repair need, and (7) system performance. It is expected that a novel column will ultimately be selected by the bridge owner based on the seismic performance. Novel column concepts are expected to emerge using novel materials and/or innovative connections or could be selected from the novel column inventory identified in the present project (Appendix D). In either case, the selected column is expected to address the owner’s needs with respect to the seismic performance, but its suitability will be evaluated through the guidelines in this document, which include design and construction considerations in addition to the seismic performance. The proposed quantitative evaluation method is intended to guide the designer or developer. It is suggested that the evaluation results be condensed into a simple, star-based rating system to be easily understood by the owner who might have limited knowledge of design requirements for novel columns. The star-based rating system has been widely used in marketing, traveling, health care, and entertainment businesses to demonstrate quickly the relative merit of different alternatives. This rating method was also utilized by the Structural Engineers Association of Northern California (SEAONC) to communicate infor- mation about seismic risk of buildings to the general public (SEAONC Existing Buildings Committee, 2011). A score between 0.0 to 1.0 at increments of 0.25 can be assigned to each parameter with unity (maximum possible score) indicating full readiness, desired performance, and substantial improvement compared to conventional columns. Table 8-1 includes general conditions that lead to quantification of each parameter. The damage level can be accurately estimated after the column has been designed based on the seismic demands. If none of the plastic hinge materials exceeds its strength under the design earthquake, the damage is categorized as “no-damage” and a score of 1.0 can be assigned to the column. A score of 0.75, 0.25 and 0.0 can be given to a column with low-damage, moderate, and severe-damage level, respectively. The displacement capacity and the residual displacement of a novel column under the design earthquake can be accurately evaluated after the design is completed according to the limitations shown in the table. S E C T I O N 8 Evaluation and Selection Criteria

Evaluation and Selection Criteria 17 A score of 1.0 is given to the “Proof Test” parameter if the concept has been experimentally evaluated with sufficient test data. “Analysis Tools” are given a score of 1.0 if existing modeling methods can estimate the overall behavior with reasonable accuracy. If there is neither proof test nor published analytical studies of the concept, no design guidelines are expected to be available for the concept. In this case, the highest penalty can be assigned to “Guideline Readiness” parameter. If there are past field applications of the concept or any are anticipated in the subsequent three years, the “Field Application” parameter can be a score of unity. A score of 1.0 can be given to “Initial Cost” when the initial cost is comparable to the conven- tional RC column cost. This can be accurately calculated after the design, and the ratio of RC column cost to novel column cost will be the score, but not to exceed unity. Material limitations may completely prevent application of a novel column in a certain climate or site conditions. For example, rubber shows brittle behavior in cold weather, thus it should not be used in a novel column located in cold region. The long-term performance of novel materials is another important consideration in evaluation of novel columns. Sufficient data should be available to demonstrate that the material can withstand the field environmental effects that are normally expected without any adverse effect on serviceability and performance of the bridge. Construc- tability is evaluated considering the ease of construction and the need for skilled labor. Some of the advanced materials or novel connections require more extensive field quality control Seismic Performance Displacement Capacity Plastic Hinge Damage Residual Displacement Try a Novel Column Design Considerations Owner Approval No Select the Novel Column Yes Plastic Hinge Damage: • Severe • Moderate • Low • None Displacement Capacity: • Low Disp. Capacity • Normal Disp. Capacity • High Disp. Capacity Residual Displacement: • High Residual Displacement • Moderate Residual Displacement • Low Residual Displacement Design Considerations: • Proof Tests • Analysis Tool Availability • Design Guideline Availability • Past Field Application Construction and other Considerations: • Initial Cost • Material Limitations • Ease of Construction • Inspectability • Maintenance • Post-Earthquake Repair Need • System Performance “Owner” is the bridge owner who can be a federal or state/county/city agency, a private company, or an individual Evaluate/Rate Evaluate/Rate: • Quantitative Evaluation by Designer/Developer • Star-Based Rating for Owner Goal: Minimize Bridge Column Damage and Enhance Serviceability after Earthquakes Construction and other Considerations Figure 8-1. Evaluation of novel columns.

18 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 2: Guidelines Parameter Quantification (deduction(a) form unity unless stated otherwise) Weight Seismic Performance Plastic Hinge Damage Based on demands of column materials and engineering judgment comment on the score as: 1.0 for no-damage (Figure 5.1-1). 0.75 for low damage (Figure 5.1-1). 0.25 for moderate damage (Figure 5.1-1). 0.0 for severe damage (Figure 5.1-1). 1.0 Displacement Capacity 1.0 for high displacement capacity: µc 5. 0.5 for normal displacement capacity: c3 ≤ µ 5. 0.0 for low displacement capacity: µc 3. 1.0 Residual Displacement 1.0 for low residual displacement: δr 1.0%. 0.5 for moderate residual displacement: 1.0% r 1.5%. 0.0 for high residual displacement: δr 1.5%. 1.0 Design Considerations Proof Test 1.0 when laboratory test data is available.0.0 when there is no test data. 1.0 Analysis Tools 1.0 when material models and all analysis tools are available for accurate estimation of demands and capacities. Penalize by a factor of 0.25 when more information is needed for accurate estimation of demands and capacities (e.g., UHPC steel-confined properties are unknown). 0.75 Guidelines Readiness 1.0 when sufficient number of test data leading to development of design guideline, or a design guideline is available. Penalize for other conditions as: 0.25 when the concept was tested, but there are no guidelines. 0.50 when there is no concept test and there are no guidelines. 0.25 Field Application 1.0 when novel system has been used in actual bridges, 0.0 when there is no field application. 0.25 Construction and other Considerations Initial Cost Estimate the cost, then the ratio of the RC column cost to the novel column cost will be the score, but not to exceed 1. 0.25 Material Limitation A novel column cannot be used in an environment where its constituents have significant limitations in that environment (e.g., rubber in cold weather). Pass/ Fail(b) Constructability 1.0 when construction of a novel column is similar to conventional column construction. Penalize by a factor of 0.25 when construction of a novel column is tedious, requires skilled labor, and needs special tools (e.g., post-tensioning or coupler installation). 1.0 Inspectability 1.0 when inspection of a novel column is similar to conventional column inspection. Penalize by a factor of 0.25 when a novel column constituents require special inspection program or tighter schedule (e.g., corrosion of steel tendons). 0.75 Maintenance 1.0 when maintenance of a novel column is similar to conventional column maintenance. Penalize by a factor of 0.25 when novel column constituents require special maintenance program (e.g., providing UV protection for exposed FRP). 0.75 System Performance 1.0 when overall performance of a novel bridge is similar to the conventional bridge performance. Penalize by a factor of 0.25 when novel column constituents impose extra design considerations on other bridge elements (e.g., increase in seat width when rubber pad is used). 1.0 Note: (a) Deductions are additive for each parameter. Post-earthquake repair is needed when column is built with materials susceptible to damage. This parameter is implicit in the plastic hinge damage. µc is the displacement ductility capacity and δr is the residual drift ratio. (b) The evaluation process shall be stopped and the column shall be prohibited for field application if the bridge column incorporates a material that does not meet the minimum requirements due to the bridge site environment. δ Table 8-1. General quantification of novel column evaluation parameters.

Evaluation and Selection Criteria 19 measures than conventional columns to ensure their functionality during earthquakes. A novel column may incorporate a material or mechanism that affects inspectability by limiting access to the column components. Alternative inspection procedures would be needed in such cases. Maintenance need is evaluated based on the need of constituent materials for inspection and repair. Concepts with less maintenance requirement earn the highest score. Post-earthquake repair is implicit in the plastic hinge damage and is eliminated in the evaluation process to avoid double counting. System performance may be important when stiffness of the novel column is lower than conventional column stiffness, resulting in larger displacement demands. The rightmost column in the table is the weight of the parameters for overall evaluation. These weights are suggested values and could be changed according to the owner’s preference. For example, the cost of a novel column may be as important as the seismic performance for an owner, thus the cost weight may be increased to 1.0. Appendix E demonstrates the use of the proposed quantitative guidelines for 39 novel columns as well as conventional RC columns.

20 Analysis and design of novel columns is based on the provisions of the AASHTO SGS. Force-based design procedures such as those presented in AASHTO LRFD should not be used for the design of novel columns since these methods are not intended for advanced materials: the seismic force modification factors (R-factors) and the overstrength factors are currently unknown for columns with advanced materials. The same forms of analysis that are used for conventional columns also apply to novel columns. Adjustments are required to account for the different behaviors of novel columns, and the calculation of capacities will vary depending on the specific novel column design utilized. 9.1 Analysis Procedure Requirements Analysis procedures provided in AASHTO SGS (Section 4) can be used for bridges incorpo- rating novel columns. Equivalent static, response spectrum, and time history analyses can be used. The stiffness of the column used in the analysis should account for the expected behavior of the column. An effective moment of inertia, which accounts for cracking in the concrete, should be used in the analysis. This does not account for the yielding and/or inelastic behavior, but rather the reduction in stiffness of the concrete prior to the yield point in the reinforcing. The stiffness of novel columns may be lower than that of conventional columns. In this case, the effect of P-D is significant. Therefore, more stringent limitations should be used to avoid column geometric failure (excessive strength degradation at low displacements). Because of differences in the behavior of novel columns, it may be necessary to adjust the level of damping assumed in the analysis. Bridges with conventional columns are typically assumed to have a damping level of 5%, to which the response spectra used in seismic analysis are calibrated. For columns that dissipate less energy through yielding and plastic material behavior, such as those including SMA reinforcing bars or other self-centering mechanisms, a reduction in the assumed damping level is needed. This can be accomplished by either adjusting the design-level response spectrum prior to analysis or by modifying the resulting displacements after the analysis is conducted. The following equation may be used in the latter approach: = ξ     0.05 (9.1-1) 0.4 RD where RD is the displacement modification factor and x is the target damping level in decimal format. The remaining aspects of the analysis proceed as for conventional bridges. S E C T I O N 9 Analysis and Design Procedure Development

Analysis and Design Procedure Development 21 9.2 Design Procedure Requirements The application of capacity design principles for novel columns is the same as that for con- ventional columns. Once the displacement demands have been determined through an analysis, the column displacement capacity must be checked, as well as minimum and maximum drift limits. Shear demands are determined and checked against shear capacity. Axial demands and capacities are then also checked. Residual drift is checked, although this is more of a “deemed to satisfy” check unless a nonlinear time-history analysis has been conducted, as simplified estimates of residual drifts suitable for use with equivalent static or response spectra analysis are not available for most novel columns. The displacement capacity of a novel column equipped bridge can be determined by the moment-curvature method or using pushover analysis. In either method, the ultimate curvature will depend on the specifics of the novel column design and the limiting strains in the reinforcing, prestressing, concrete, and other constitutive materials. Determination of the plastic hinge length in a novel column may be significantly different than in a conventional column and will depend on the specifics of the column design. In place of a minimum displacement ductility, novel columns should satisfy a minimum drift ratio to ensure adequate capacity even if the calculated demands are small. The conversion of displacement ductility to drift ratio is provided by the equation: ( ) ( )δ = µ −0.26 0.18 (9.2-1)0.81 0.57A Ar r where Ar is the aspect ratio of the column defined as the ratio of the column length, L, to the column diameter, D, as shown in Fig. 9.2-1, µ is the displacement ductility, and δ is the drift (a) Single-Column Bents (b) Multi-Column Bents with Fixed Ends (c) Multi-Column Bents with One-End-Pinned Joints L D D L LD Pinned Joint Figure 9.2-1. 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].

22 Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms, Volume 2: Guidelines ratio in percent. This equation relates displacement ductility to drift ratio in conventional RC columns. It is intended to help compare the drift ratio of a novel column to that of an equivalent RC column and estimate the displacement ductility of the RC column used in current code design equations. The estimation of novel column design forces is the same as that for conventional columns. However, for shear design of novel columns, the design shear is based on the smaller of an amplified plastic moment (e.g., lmo Mp where lmo is the overstrength factor for novel columns in a rage of 1.2 to 1.44 and Mp is the plastic moment) calculated for the plastic hinge and the moment demand at the design level earthquake. This is because novel columns may have moment-curvature (or force-displacement) relationships that significantly deviate from the idealized elasto-plastic curves (Fig. 9.2-2), thus the conventional column overstrength factor may not be sufficient. (a) Conventional RC Sections (b) A Novel Column Section uM u y p Idealized Ø M om en t y Actual Ø Curvature Ø M M Yi Mu u y p Idealized Ø M om en t y Actual Ø Curvature Ø M M Yi Figure 9.2-2. 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).

23 With the new paradigm of requiring infrastructure to be resilient to serve the public effectively, new 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 flowchart 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 SGS could generally be used for novel columns 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. The guidelines would potentially form the basis for AASHTO guidelines on the design of resilient novel columns. S E C T I O N 1 0 Conclusions

24 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 Specification. Washington, D.C.: American Association of State Highway and Transportation Officials. Ardakani, S. M. S., and Saiidi, M. S. (2013). Design of Reinforced Concrete Bridge Columns for Near-Fault Earthquakes. Center for Civil Engineering Earthquake Research, Department of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-13-13, 393 pp. Caltrans. (2013). Seismic Design Criteria (SDC), version 1.7. Sacramento, CA: California Department of Transportation. Choi, H., Saiidi, M. S., Somerville, P., and El-Azazy, S. (2010). An Experimental Study of RC Bridge Columns Subjected to Near-Fault Ground Motions. American Concrete Institute, ACI Structural Journal 107 (1): 3–12. FEMA P-58. (2012). Seismic Performance Assessment of Buildings. Federal Emergency Management Agency, vol. 1. Washington, D.C.: FHWA. Japan Road Association. (2002). Tokyo, Japan: Design Specifications for Highway Bridges. SEAONC Existing Buildings Committee. (2011). SEAONC Rating System for the Expected Earthquake Perfor- mance of Buildings. Proceedings of Annual Convention of the Structural Engineers Association of California (SEAOC 2011), 11 pp. References

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