Transfer, Development, and Splice Length for Strand/Reinforcement in High-Strength Concrete (2008)

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TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2008 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 603 Subject Areas Bridges, Other Structures, Hydraulics and Hydrology Transfer, Development, and Splice Length for Strand/Reinforcement in High-Strength Concrete Julio A. Ramirez PURDUE UNIVERSITY West Lafayette, IN Bruce W. Russell OKLAHOMA STATE UNIVERSITY Stillwater, OK 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 603 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 Ellen M. Chafee, Assistant Editor NCHRP PROJECT 12-60 PANEL Field of Design—Area of Bridges R. Scott Christie, Pennsylvania DOT (Chair) Theresa Ahlborn, Michigan Technological University Thomas Beitelman, Sound Structures Engineering, Inc., Tallahassee, FL Vijay Chandra, PB Americas, Inc., Herndon, VA Allan W. Frank, Kentucky Transportation Cabinet Gregg A. Freeby, Texas DOT Bijan Khaleghi, Washington State DOT David H. Sanders, University of Nevada—Reno Joey Hartmann, FHWA Liaison Eric P. Munley, FHWA Liaison Stephen F. Maher, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 12-60 by Purdue Research Foun- dation through the School of Civil Engineering at Purdue University with subcontracting services being provided by the School of Civil and Environmental Engineering of Oklahoma State University (OSU). The Principal Investigator on this project was Julio A. Ramirez of Purdue University. The other author of this report was Bruce W. Russell of Oklahoma State University. The work was done under the general supervision of Julio A. Ramirez. The work at OSU was under the supervision of Bruce W. Russell. 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 transfer, devel- opment, and splice length provisions for prestressed and non-prestressed concrete mem- bers to concrete strengths greater than 10 ksi. The report details the research performed and includes recommended revisions to the AASHTO LRFD Bridge Design Specifications. The material in this report will be of immediate interest to bridge designers. The AASHTO LRFD Bridge Design Specifications contain barriers to the use of high- strength concrete. These barriers restrict the application of existing and new technology to bridges. The AASHTO LRFD Bridge Design Specifications state that design concrete compressive strengths above 10 ksi shall be used only when allowed by specific articles or when physical tests are made to establish the relationships between the concrete strength and other properties. When the AASHTO LRFD Bridge Design Specifications were written, there was a lack of data to demonstrate that the provisions were applicable to concrete compressive strengths above 10 ksi. Recent research has started to address design issues with higher strength concretes. FHWA Showcase Projects encourage the use of high- performance concretes—including high-strength concrete—in bridge structures. As the industry moves toward the use of high-strength concrete, the need to revise the AASHTO LRFD Bridge Design Specifications is more urgent. There is, therefore, a need to expand the AASHTO LRFD Bridge Design Specifications to allow greater use of high-strength concrete. Two recent NCHRP reports complement the work accomplished in NCHRP Project 12-60 in removing barriers to the use of high-strength concrete. NCHRP Report 579: Application of LRFD Bridge Design Specifications to High-Strength Structural Concrete: Shear Provisions iden- tifies all barriers in the AASHTO LRFD Bridge Design Specifications to the use of high-strength concrete and provides research findings to remove the barriers related to shear. NCHRP Report 595: Application of the LRFD Bridge Design Specifications to High-Strength Structural Concrete: Flexure and Compression Provisions addresses flexural and compression issues. Recommenda- tions from these reports have already been adopted into the AASHTO LRFD Bridge Design Specifications. The objective of NCHRP Project 12-60 was to develop recommended revisions to the AASHTO LRFD Bridge Design Specifications for normal-weight concrete having compres- sive strengths up to 15 ksi, relating to transfer and development length of prestressing strand with diameters up to 0.62 in. and development and splice length in tension and compres- sion of individual bars, bundled bars, and welded wire reinforcement and development length of standard hooks. This research was performed by Purdue University and Oklahoma State University. The report fully documents the research leading to the recommended revi- sions to Section 5 of the AASHTO LRFD Bridge Design Specifications. AASHTO is expected to consider these recommendations for adoption in 2008. 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 4 Chapter 1 Introduction and Research Approach 4 1.1 Problem Statement and Research Objective 4 1.2 Research Approach 6 Chapter 2 Literature Review 6 2.1 Introduction 7 2.2 Literature Review 18 2.3 Identification of Issues and Needs 21 2.4 Issues Related to Testing Protocols 25 2.5 Summary 26 Chapter 3 Experimental Program and Results 26 3.1 Introduction to the Experimental Program 26 3.2 The Standard Test Method for the Bond of Prestressing Strands 31 3.3 The NASP Bond Test in Concrete 38 3.4 Measured Transfer Lengths versus Varying Concrete Strengths and Varying NASP Bond Test Values 54 3.5 Development Length Tests 72 3.6 Discussion of Design Recommendations 77 3.7 The Effect of Concrete Strength on Bond Performance— Summary, Conclusions, and Recommendations 78 3.8 Experimental Program—Mild Steel Anchorage of Uncoated Bars in Tension 89 3.9 Anchorage of Epoxy-Coated Bars in Tension 99 3.10 Anchorage of Bars Terminated with Standard Hooks in Tension 110 Chapter 4 Design Recommendations 110 4.1 Introduction 110 4.2 Design Recommendations 111 4.3 Details of the Design Recommendations 119 References 122 Appendices