Application of LRFD Bridge Design Specifications to High-Strength Structural Concrete: Shear Provisions (2007)

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TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2007 www.TRB.org 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 REPORT 579 Subject Areas Bridges, Other Structures, and Hydraulics and Hydrology Application of LRFD Bridge Design Specifications to High- Strength Structural Concrete: Shear Provisions Neil M. Hawkins Daniel A. Kuchma UNIVERSITY OF ILLINOIS Urbana, IL 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 provides the most effective approach to the solution of 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 develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. 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CRP STAFF FOR NCHRP REPORT 579 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs David B. Beal, Senior Program Officer Eileen P. Delaney, Director of Publications Beth Hatch, Editor NCHRP PROJECT 12-56 PANEL Field of Design—Area of Bridges Julius F. J. Volgyi, Jr., Virginia DOT (Chair) David Hohmann, Texas DOT Ralph J. DeStefano, Pennsylvania DOT Fouad H. Fouad, University of Alabama–Birmingham Jen-Chi Hsieh, Washington State DOT Jay Puckett, BridgeTech, Inc., Laramie, WY Madhwesh Raghavendrachar, California DOT Bala Sivakumar, Lichtenstein Consulting Engineers, Inc., Paramus, NJ Joey Hartmann, FHWA Liaison Stephen F. Maher, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 12-56 by the Department of Civil and Environmental Engineering (CEE) at the University of Illinois at Urbana-Champaign (UIUC), with subcontracting and consulting services provided by Wiss, Janney, Elstner Associates and Henry Russell. The Principal Investigators (PIs) on this project were Neil M. Hawkins (PI) and Daniel A. Kuchma (Co-PI) from the University of Illinois at Urbana-Champaign. The other Co-PIs and authors of this report are Gary Klein, Neal Anderson, and Henry Russell. The work was done under the general supervision of Neil M. Hawkins and Daniel A. Kuchma, with the additional leadership by four PhD students, Kang Su Kim, Tom Nagle, Shaoyun Sun, and Heui Hwang Lee. Other student assistants on this project were Nathan Carroll, Joe Wilkey, Justin Barton, Monica Lim, Ayodele Ogunsola, Katrina Willenborg, Chris Wu, Charlie McLean, Sang Ho Kim, Jun Ji, Zhenhua Huang, Joe Podge, Tina Kidwell, Markus Haiden, and Ken Marley. The PIs also wish to express their sincere appre- ciation to Prestress Engineering Corporation for fabrication of the test girders, to the CEE machine shop for assistance in preparation of the test set-up and girder handling, to the CEE department for support of undergraduate research assistants, to the Precast/Prestressed Concrete Institute for substantial financial support, to the National Science Foundation for support on a synergistic project, and to the NCHRP proj- ect panel and manager, David Beal, for their project oversight and valuable insight and feedback. 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

This report contains the findings of research performed to extend the applicability of shear design provisions for reinforced and prestressed concrete structures in the AASHTO LRFD Bridge Design Specifications to concrete compressive strengths greater than 10 ksi. The report details the research performed and includes recommended revisions to the specifi- cations. The material in this report will be of immediate interest to bridge designers. The AASHTO LRFD Bridge Design Specifications state: “Concrete strengths above 10.0 ksi shall be used only when physical tests are made to establish the relationships between the concrete strength and other properties.” When the LRFD specifications were written, the data were insufficient to demonstrate that the provisions were applicable to concrete com- pressive strengths above 10 ksi (high-strength concrete). Nevertheless, recent research has started to address design issues with high-strength concrete, and the FHWA Showcase Proj- ects are encouraging the use of high-strength concrete in bridge structures. There is a need to expand the LRFD specifications to allow greater use of high-strength concrete. The objective of this research was to develop recommended revisions to the AASHTO LRFD Bridge Design Specifications to extend the applicability of shear design provisions for reinforced and prestressed concrete structures to concrete compressive strengths greater than 10 ksi. The research effort also included an article-by-article review of Section 5 of the specifications to identify all provisions that directly or indirectly have the potential for pre- venting the extension of the specifications to high-strength concrete. Companion NCHRP projects 12-60 and 12-64 address transfer and development length, and flexure and com- pression, respectively; these projects are scheduled for completion in 2007. This research was performed by the University of Illinois at Urbana-Champaign. The report fully documents the research leading to the recommended specifications. The rec- ommendations are under consideration for possible adoption by the AASHTO Highway Subcommittee on Bridges and Structures in 2007. F O R E W O R D By David B. Beal Staff Officer Transportation Research Board

C O N T E N T S 1 Summary 5 Chapter 1 Introduction and Research Approach 5 1.1 AASHTO LRFD Shear Design Specifications 16 1.2 Project Objectives 17 1.3 Description of Project Tasks and Research Approach 20 Chapter 2 Findings 20 2.1 Collection, Analysis, and Use of Existing HSC Information 21 2.2 Development and Analysis of Shear Database 29 2.3 Description of Experimental Research Program 52 2.4 Measured and Code-Calculated Strengths Plus Modes of Failure 68 2.5 Cracking 85 2.6 Reinforcement and Other Strains 109 2.7 Components of Shear Resistance 122 2.8 Shear Friction Tests 136 2.9 Deformation Patterns in End Regions 148 2.10 Prediction of Behavior of Girders Using Finite Element Analyses 168 Chapter 3 Interpretation, Appraisal, and Applications 168 3.1 Overview 168 3.2 Extension of LRFD Sectional Design Model to HSC (S5.8.3) 170 3.3 Extension of Other Shear Design Methods to HSC 171 3.4 Minimum Shear Reinforcement Requirements (S5.8.2.5) 172 3.5 Maximum Shear Design Stress Limit 173 3.6 Serviceability 173 3.7 Design of End Regions 174 3.8 Interface Shear Transfer 175 3.9 Summary of Proposed Changes to LRFD Specifications 176 3.10 Proposed Changes in LRFD Specifications Format 177 3.11 Implications for Bridge Design Practice 185 Chapter 4 Conclusions 185 4.1 Introduction 185 4.2 Conclusions 190 4.3 Background Statement to Suggested Research 190 4.4 Suggested Research and Changes to the Code Development Practice 192 References 194 Appendices 195 Notation