Application of the LRFD Bridge Design Specifications to High-Strength Structural Concrete: Flexure and Compression 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 595 Subject Areas Bridges, Other Structures, and Hydraulics and Hydrology Application of the LRFD Bridge Design Specifications to High-Strength Structural Concrete: Flexure and Compression Provisions Sami Rizkalla NORTH CAROLINA STATE UNIVERSITY Raleigh, NC Amir Mirmiran FLORIDA INTERNATIONAL UNIVERSITY Miami, FL Paul Zia NORTH CAROLINA STATE UNIVERSITY Raleigh, NC Henry Russell HENRY G. RUSSELL, INC. Chicago, IL A N D Robert Mast BERGER/ABAM ENGINEERS, INC. Seattle, WA Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

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CRP STAFF FOR NCHRP REPORT 595 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 Hilary Freer, Senior Editor NCHRP PROJECT 12-64 PANEL Field of Design—Area of Bridges Harry A. Capers, Jr., Arora and Associates, P.C., Lawrenceville, NJ (Chair) John M. Holt, Texas DOT, Austin, TX Elmer Marx, Alaska DOT, Juneau, AK Richard Miller, University of Cincinnati, Cincinnati, OH Michael R. Pope, California DOT, Sacramento, CA Jerry L. Potter, Livingston, TX Samia Shaaban, Shaaban Engineering, Newark, NJ Joey Hartmann, FHWA Liaison Stephen F. Maher, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research documented herein has been performed under NCHRP Project 12-64 by the Department of Civil, Construction, and Environmental Engineering at North Carolina State University; Department of Civil and Environmental Engineering at Florida International University; Henry G. Russell, Inc.; and Berger/ABAM Engineers, Inc. North Carolina State University is the prime contractor for this study. The work undertaken at Florida International University, Henry G. Russell, Inc., and Berger/ABAM Engi- neers, Inc., are through separate subcontracts with North Carolina State University. Sami Rizkalla, Distinguished Professor of Civil and Construction Engineering at the North Carolina State University, is the principal investigator. Co-Principal Investigators of this project are Amir Mirmiran, Professor and Chair of the Department of Civil and Environmental Engineering at Florida International University, and Paul Zia, Distinguished University Professor Emeritus at North Carolina State Univer- sity. Consultants for the project are Henry G. Russell, Vice President of Henry G. Russell, Inc., and Robert Mast, Senior Principal, Berger/ABAM Engineers, Inc. Graduate students who participated in this project are Halit Cenan Mertol, Zhenhua Wu, Wonchang Choi, SungJoong Kim, and Andrew Logan. 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 documents research performed to develop recommended revisions to the AASHTO LRFD Bridge Design Specifications to extend the applicability of the flexural and compression design provisions for reinforced and prestressed concrete members to con- crete strengths greater than 10 ksi. The report details the research performed and includes recommended revisions to the Specifications. The material in this report will be of immedi- ate 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 flexural and compression design provisions for reinforced and prestressed concrete members to concrete strengths greater than 10 ksi. Companion NCHRP Projects 12-56 (published as NCHRP Report 579) and 12-60 (publication pending) address shear and transfer and development length, respectively. This research was performed by North Carolina State University, Florida International University, Henry G. Russell, Inc., and Berger/ABAM Engineers. The report fully docu- ments the research leading to the recommended revisions to Section 5 of the AASHTO LRFD Bridge Design Specifications. 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 Chapter 1 Introduction 1 1.1 Problem Statement 1 1.2 Research Objective 1 1.3 Research Approach 1 1.4 Report Organization 3 Chapter 2 Research Findings 3 2.1 Introduction 3 2.2 Material Properties 3 2.2.1 Compressive Strength 3 2.2.2 Modulus of Elasticity 4 2.2.3 Modulus of Rupture 5 2.2.4 Poisson’s Ratio 5 2.2.5 Creep 7 2.2.6 Shrinkage 7 2.3 Flexural Members 7 2.3.1 Distribution of Compressive Stresses in Compression Zone of Flexural Members 10 2.3.2 Flexural Behavior of HSC Beams 12 2.3.3 Deflection 12 2.3.4 Cracking 13 2.3.5 Crack Width 13 2.3.6 Ultimate Concrete Strain 14 2.4 Compression Members 14 2.4.1 Axial Resistance 16 2.4.2 Longitudinal Reinforcement Limits 19 2.4.3 Transverse Reinforcement 19 2.4.4 Resistance to Combined Axial and Flexural Loading 20 2.5 Prestressed Concrete 20 2.5.1 Prestress Losses 21 2.5.2 Flexural Resistance 21 2.5.3 Transfer Length 23 Chapter 3 Proposed Revisions to AASHTO LRFD Bridge Design Specifications 25 Chapter 4 Conclusions and Future Research 25 4.1 Conclusions 26 4.2 Future Research 27 References