Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders (2022)

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2022 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 994 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders Bahram M. Shahrooz Richard A. Miller University of Cincinnati Cincinnati, OH Kent A. Harries University of Pittsburgh Pittsburgh, PA Reid W. Castrodale Castrodale Engineering Consultants, PC Concord, NC 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, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transporta- tion results in increasingly complex problems of wide interest to high- way 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). 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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 following companies are acknowledged and thanked for their generosity: Contractors Materials Company/CRR, Cincinnati, Ohio, provided the reinforcing bars for two T-beams and the necessary supplies required to fabricate the test specimens. Flood Testing Laboratories, Inc., Chicago, Illinois, tested high- strength concrete samples. Janell Concrete and Masonry Equipment, Inc., Cincinnati, Ohio, supplied all the formwork. MMFX Steel Corporation of America provided all the Gr. 100 reinforcing bars used in the project. Terracon Consultants, Inc., Cincinnati, Ohio, tested normal- strength concrete samples. Tincher’s Welding, Harveysburg, Ohio, fabricated many of the test fixtures, including those for pre stressing bed at the University of Cincinnati Large Scale Test Facility. Coreslab Structures (Omaha, Nebraska), Inc. fabricated all the test specimens except for two T-beams. Their cooperation and assistance with installation of internal instruments is greatly appreciated. Hilltop Basic Concrete, Cincinnati, Ohio, supplied the concrete for two T-beams cast at the University of Cincinnati Large Scale Test Facility. The following current and former graduate students are acknowl- edged for their participation in the reported project: University of Cincinnati: Carlos Andres Tamayo was responsible for design, fabrication, testing, and data reduction. Payne Ball conducted design parametric studies. Venkata Sathiraju conducted stability analyses and debugged stability Excel spreadsheet. Dr. Matthew Bolduc, Sandip Chitri, Clark Karlie Dallas, Ambar Alverez-Garcia, Mallory Gooding, Abdullah Haroon, Sushil Kunwar, Dr. Muthana Muhaisin, and Jalyn Stewart partici- pated in fabrication and testing of various components and full-scale girders. University of Pittsburgh: Dr. Abdullah Alabdulkarim conducted the experimental pro- gram and stability and finite element analyses. Dr. Tianqiao Liu developed the finite element models. Dr. Shawn Platt and Charles (Scooter) Hager participated in various aspects of the experimental program. CRP STAFF FOR NCHRP RESEARCH REPORT 994 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Associate Program Manager, National Cooperative Highway Research Program Deborah Irvin, Program Coordinator Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications NCHRP PROJECT 12-109 PANEL Field of Design—Area of Bridges Bijan Khaleghi, Washington State Department of Transportation, Tumwater, WA (Chair) Geetha Chandar, Texas Department of Transportation, Austin, TX Brian Hanks, North Carolina Department of Transportation, Raleigh, NC Catherine Hovell, HNTB Corporation, Bellevue, WA Jim Ma, California Department of Transportation (CALTRANS), Sacramento, CA Henry G. Russell, Henry G Russell, Inc., Glenview, IL Michael B. Twiss, Albany, NY Benjamin A. Graybeal, FHWA Liaison Stephen F. Maher, TRB Liaison

NCHRP Research Report 994 presents the design methodology for precast pretensioned girders using 0.7-in. diameter strands based on comprehensive analytical and testing pro- grams. In particular, the design methodology addressed (1) bond and material characteriza- tion; (2) transfer and development length; (3) strand spacing; (4) longitudinal reinforcement requirements and details at ends of girders; (5) anchorage of 0.7-in. diameter strands into diaphragms; (6) flexure and shear capacity and ductility of girders using 0.7-in. diameter strands; and (7) stability of long-span girders during all phases of construction. In addition, the report includes guidelines for detailing, fabricating, handling, shipping, and erecting of precast pretensioned girders using 0.7-in. diameter strands. The material in this report will be of immediate interest to bridge engineers and precast pretensioned girder fabricators. Long-span bridges are often used in environmentally sensitive terrains, water crossings, and in locations with traffic and geometric restrictions. Bridges with long-span precast pre- tensioned girders are advantageous due to their ease and speed of construction, lower cost, and long-term durability. The use of 0.7-in. diameter strands would help bridge designers extend the spans of the existing girder shapes. However, the current AASHTO bridge design and construction specifications do not address the use of 0.7-in. diameter strands for precast pretensioned girders. Bridge owners, fabricators, and contractors need specifications and guidelines to implement the use of 0.7-in. diameter strands in practice. Under NCHRP Project 12-109, “Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders,” the University of Cincinnati was asked to develop (1) guidelines for fabrication of precast pretensioned girders using 0.7-in. diameter strands; (2) guidelines for handling, shipping, and erection of long-span girders; and (3) proposed language for consideration by AASHTO to incorporate the research results in the next update of the AASHTO bridge design and construction specifications. In addition to the conduct of research that documents the entire research effort pub- lished as NCHRP Research Report 994, a number of deliverables, provided as appendices, are available as NCHRP Web-Only Document 315 on the National Academies Press website (www.nap.edu) by searching for NCHRP Research Report 994: Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders. F O R E W O R D By Waseem Dekelbab Staff Officer Transportation Research Board

1 Chapter 1 Background 1 1.1 Introduction 2 1.2 Motivations for Using 0.7-In. Strands 3 1.3 Objectives of Research Program 3 1.4 Review of State of the Art and Practice 3 1.4.1 Past Experimental Studies 7 1.4.2 Past Analytical Studies 9 1.4.3 Demonstration Projects Using 0.7-In. Strands 9 1.4.4 Synthesis of Previous Studies 10 1.4.5 Synthesis of Past Analytical Studies 10 1.5 U.S. and International Codes 10 1.5.1 Minimum Distance between Strands 11 1.5.2 Strand Spacing in U.S. Practice and the Transition from 0.5-In. to 0.6-In. Strands 12 1.5.3 Transfer and Development Length 16 1.5.4 Synthesis of Current Design Codes and Design 17 1.6 Overview of Bond Characteristics 18 1.7 Hoyer Effect 19 1.7.1 Concrete Stresses Due to Strand Anchorage 20 1.7.2 Dilation of Prestressing Strand 21 1.8 Long-Span Girder Stability 22 1.8.1 PCI Method of Stability Analysis 23 1.8.2 Hanging Girders 24 1.8.3 Seated Girders 25 1.8.4 Additional Lateral Forces during Transportation 25 1.8.5 Interpreting and Revising Stability Analyses 27 Chapter 2 Analytical Research Approaches and Findings 27 2.1 Introduction 27 2.2 Case Studies 27 2.2.1 Design Parameters 28 2.2.2 Assumed Design Loads 28 2.2.3 Results and Discussions 35 2.3 Design Verification/Validation Study: Finite Element Modeling of Full-Length Girders 40 2.3.1 Effects at Girder Ends 41 2.4 Analytical Modeling of End Regions 41 2.4.1 Strut-and-Tie Modeling of Transverse Tie Reinforcement Requirement 43 2.4.2 Flange Transverse Reinforcement Requirements for Case Studies 48 2.4.3 Lateral Splitting Behavior C O N T E N T S

48 2.5 Mechanistic Modeling of Effects of Prestress Transfer 50 2.5.1 Application of Hoyer Effect in Prestress Transfer Peeling Model 50 2.5.2 Peeling Due to Eccentric Prestress Force 51 2.5.3 Peeling Stress Calculations 55 2.5.4 FEM of Strand Release Sequence 58 2.6 Strand Spacing 59 2.7 FEM of Strand Transfer Lengths 59 2.7.1 ABAQUS Finite Element Models 68 2.8 Long-Span Girder Stability 68 2.8.1 Stability Case Study—223-Ft-Long WF100G 74 2.8.2 Evaluation of Cases Reported in Section 2.2 78 2.9 Summary of Analytical Studies 80 Chapter 3 Experimental Research Approach and Findings— Component Tests 80 3.1 Introduction 80 3.2 Bond Characterization of Prestressing Strand 80 3.2.1 Characterization of Strand Geometry and Material Properties 80 3.2.2 Characterization of Strand “Deformations” 82 3.2.3 Hoyer Effect Testing 84 3.3 Beam-End Tests 87 3.3.1 Straight Strand Beam-End Test Results 91 3.3.2 90-Degree Hooked Strand Embedment Beam-End Tests 94 3.3.3 Potential Utility of 90-Degree Strand Anchorage 98 3.4 Bond Evaluation per ASTM A1081 101 3.5 Summary of Component Test Results and Observations 103 Chapter 4 Experimental Research Approach and Findings 103 4.1 Introduction 103 4.2 Girder Details 108 4.2.1 Material Properties 109 4.3 Transfer Length 111 4.4 Loading 112 4.4.1 Support Conditions 114 4.5 Instrumentation 114 4.6 Test Results and Discussions 116 4.6.1 Group 1: Girders G1 and G2 118 4.6.2 Group 2: Girders G3, G4, G5, and G7 122 4.6.3 Group 3: Girders G6 and G8 128 4.6.4 Effect of Extent of Bottom Flange Confinement Reinforcement 130 4.6.5 Group 4: Girders G9 and G10 131 4.6.6 Group 5: Girders G11 and G12 132 4.7 Assessment of Development Length and Capacity Calculation Based on AASHTO 135 4.8 Impact of Extension of Bottom Flange Confinement Reinforcement on Capacity 137 4.9 Example Highlighting Additional Extension of Bottom Flange Confinement 137 4.10 State of Practice on Bottom Flange Confinement 137 4.11 Summary of Full-Scale Girder Test Results and Observations

141 Chapter 5 Conclusions and Proposals 141 5.1 Conclusions 142 5.2 Proposed Detailing Guidelines for Prestressed Girders Having 0.7-In. Strands 142 5.3 Fabrication, Handling, Shipping, and Erection Guidelines 143 5.4 Suggestions for Future Research 143 5.5 Proposed Revisions to AASHTO LRFD Bridge Design Specifications 146 References 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.nap.edu) retains the color versions.