Application of LRFD Bridge Design Specifications to High-Strength Structural Concrete

206 Pages·2003·15.73 MB·English

NCHRP
NATIONAL
COOPERATIVE
HIGHWAY
RESEARCH
PROGRAM
REPORT 579
Application of LRFD Bridge
Design Specifications to High-
Strength Structural Concrete:
Shear Provisions
TRANSPORTATION RESEARCH BOARD 2007 EXECUTIVE COMMITTEE*
OFFICERS
CHAIR:Linda S. Watson,CEO, LYNX–Central Florida Regional Transportation Authority, Orlando
VICECHAIR:Debra L. Miller,Secretary, Kansas DOT, Topeka
EXECUTIVEDIRECTOR:Robert E. Skinner, Jr.,Transportation Research Board
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Anne P. Canby,President, Surface Transportation Policy Partnership, Washington, DC
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Susan Hanson,Landry University Professor of Geography, Graduate School of Geography, Clark University, Worcester, MA
Adib K. Kanafani,Cahill Professor of Civil Engineering, University of California, Berkeley
Harold E. Linnenkohl,Commissioner, Georgia DOT, Atlanta
Michael D. Meyer,Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta
Michael R. Morris,Director of Transportation, North Central Texas Council of Governments, Arlington
John R. Njord,Executive Director, Utah DOT, Salt Lake City
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Sandra Rosenbloom,Professor of Planning, University of Arizona, Tucson
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Rosa Clausell Rountree,Executive Director, Georgia State Road and Tollway Authority, Atlanta
Henry G. (Gerry) Schwartz, Jr., Senior Professor,Washington University, St. Louis, MO
C. Michael Walton,Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin
Steve Williams,Chairman and CEO, Maverick Transportation, Inc., Little Rock, AR
EX OFFICIO MEMBERS
Thad Allen(Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, Washington, DC
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Marion C. Blakey,Federal Aviation Administrator, U.S.DOT
Joseph H. Boardman,Federal Railroad Administrator, U.S.DOT
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Edward R. Hamberger,President and CEO, Association of American Railroads, Washington, DC
John H. Hill, Federal Motor Carrier Safety Administrator, U.S.DOT
John C. Horsley,Executive Director, American Association of State Highway and Transportation Officials, Washington, DC
J. Edward Johnson,Director, Applied Science Directorate, National Aeronautics and Space Administration, John C. Stennis Space Center, MS
William W. Millar,President, American Public Transportation Association, Washington, DC
Nicole R. Nason,National Highway Traffic Safety Administrator, U.S.DOT
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*Membership as of March 2007.
NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM
NCHRP
REPORT 579
Application of LRFD Bridge
Design Specifications to High-
Strength Structural Concrete:
Shear Provisions
Neil M. Hawkins
Daniel A. Kuchma
UNIVERSITYOFILLINOIS
Urbana, IL
Subject Areas
Bridges, Other Structures, and Hydraulics and Hydrology
Research sponsored by the American Association of State Highway and Transportation Officials
in cooperation with the Federal Highway Administration
TRANSPORTATION RESEARCH BOARD
WASHINGTON, D.C.
2007
www.TRB.org
NATIONAL COOPERATIVE HIGHWAY NCHRP REPORT 579
RESEARCH PROGRAM
Systematic, well-designed research provides the most effective Project 12-56
approach to the solution of many problems facing highway ISSN 0077-5614
administrators and engineers. Often, highway problems are of local ISBN 978-0-309-09886-1
Library of Congress Control Number 2007928891
interest and can best be studied by highway departments individually
or in cooperation with their state universities and others. However, the © 2007 Transportation Research Board
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
COPYRIGHT PERMISSION
cooperative research.
Authors herein are responsible for the authenticity of their materials and for obtaining
In recognition of these needs, the highway administrators of the
written permissions from publishers or persons who own the copyright to any previously
American Association of State Highway and Transportation Officials published or copyrighted material used herein.
initiated in 1962 an objective national highway research program
Cooperative Research Programs (CRP) grants permission to reproduce material in this
employing modern scientific techniques. This program is supported on publication for classroom and not-for-profit purposes. Permission is given with the
a continuing basis by funds from participating member states of the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA,
FMCSA, FTA, or Transit Development Corporation endorsement of a particular product,
Association and it receives the full cooperation and support of the
method, or practice. It is expected that those reproducing the material in this document for
Federal Highway Administration, United States Department of educational and not-for-profit uses will give appropriate acknowledgment of the source of
Transportation. any reprinted or reproduced material. For other uses of the material, request permission
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requested by the Association to administer the research program
because of the Board’s recognized objectivity and understanding of
NOTICE
modern research practices. The Board is uniquely suited for this
purpose as it maintains an extensive committee structure from which The project that is the subject of this report was a part of the National Cooperative Highway
Research Program conducted by the Transportation Research Board with the approval of
authorities on any highway transportation subject may be drawn; it
the Governing Board of the National Research Council. Such approval reflects the
possesses avenues of communications and cooperation with federal, Governing Board’s judgment that the program concerned is of national importance and
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relationship to the National Research Council is an insurance of
objectivity; it maintains a full-time research correlation staff of The members of the technical committee selected to monitor this project and to review this
report were chosen for recognized scholarly competence and with due consideration for the
specialists in highway transportation matters to bring the findings of
balance of disciplines appropriate to the project. The opinions and conclusions expressed
research directly to those who are in a position to use them. or implied are those of the research agency that performed the research, and, while they have
The program is developed on the basis of research needs identified been accepted as appropriate by the technical committee, they are not necessarily those of
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by chief administrators of the highway and transportation departments
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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
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.
F O R E W O R D
By David B. Beal
Staff Officer
Transportation Research Board
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 Specificationsto 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 Specificationsstate: “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 Specificationsto 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.
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
1
S U M M A R Y
The use ofhigh-strength concrete (HSC) offers considerable economic advantages in the
design,construction,and maintenance of bridge structures.The use of HSC,rather than
normal-strength concrete,enables a section ofa given size to support larger loads or span
longer distances. In addition, the improved durability usually associated with HSC
increases the lifespan of structures and increases the ability to meet larger future loading
demands.
Concretes with compressive strengths up to 24 ksi were commercially available as of2004.
However,designers and bridge owners have not taken full advantage ofHSC.One reason has
been a lack ofexperience in the use ofHSC in bridge structures.This problem was addressed
in a series ofshowcase projects that were completed throughout the United States to demon-
strate the advantages and methods for the effective use ofHSC.A technical barrier to the use
of concrete strengths in excess of 10 ksi is the AASHTO LRFD Bridge Design Specifications
(1),which generally limit the cylinder compressive strength (f´) that can be used in design
c
expressions to 10 ksi.The principal reason for this limitation is that many existing provisions
are based on experimental test data and very little ofthis data is from tests on specimens cast
with HSC.To overcome this problem,the American Association ofState Highway and Trans-
portation Officials (AASHTO) sponsored a series of National Cooperative Highway
Research Program (NCHRP) projects aimed at extending provisions to permit the use of
concrete strengths much higher than 10 ksi.Within these projects,the experiments neces-
sary for extension ofthe provisions have been conducted,and revised provisions have been
developed to enable the use ofHSC.
The primary goal of NCHRP Project 12-56 was the extension of the shear provisions in
the AASHTO LRFD Bridge Design Specificationsto concrete strengths greater than 10 ksi.
This action principally involved the extension of the Sectional Design Model,which is the
specified procedure for determining the required amounts ofshear reinforcement,to higher
concrete strengths.The Sectional Design Model shear procedure was introduced to the U.S.
bridge community with the LRFD specifications.The model was derived from the Modified
Compression Field Theory (MCFT) (2),which is a comprehensive behavioral model for pre-
dicting the shear response of diagonally cracked concrete.Compared with the traditional
shear design model ofthe AASHTO Standard Specifications for Highway Bridges(17th Edi-
tion,2002),the Sectional Design Model provided newer strain-based relationships for eval-
uating the contribution of concrete and vertical transverse reinforcement to the shear
capacity,as well as newer limits for minimum shear reinforcement and maximum shear
design strength.
This summary contains a brief discussion of key issues relevant to the extension of the
Sectional Design Model to HSC,an overview of the research program,a summary of the
results, and a summary of the proposed changes to the AASHTO LRFD Bridge Design
2
Specificationsresulting from this project.Potential difficulties for the extension of the Sec-
tional Design Model to HSC can be divided into five primary areas:
1. Contribution ofconcrete (V).In the LRFD Sectional Design Model,the concrete con-
c
tribution to shear resistance is determined from the tensile stress that can be carried per-
pendicular to the field ofdiagonal compression.Between cracks,this tension is carried by
tensile stresses in the concrete,while at crack locations the tension is assumed to be car-
ried by a combination oflocal increases in reinforcement stresses and shear on the faces
ofthe cracks.The resistance to shear slip on the crack face is evaluated in the LRFD pro-
visions as a function ofcrack width,concrete compressive strength,and maximum aggre-
gate size,where crack width is taken as the average principal tensile strain in the concrete
multiplied by the crack spacing.The crack spacing is assumed to be 12 inches for mem-
bers with shear reinforcement.A potential concern for the extension of this concept to
HSC was that cracks in HSC were likely to be smoother and more widely spaced than in
regular-strength concrete,which could lead to a decreased shear slip capacity and,thus,
a smaller concrete contribution to shear resistance.
2. Contribution ofshear reinforcement (V).Codes ofpractice throughout the world use
s
a parallel chord truss model for evaluating the contribution of shear reinforcement to
shear resistance.By this approach,the contribution ofthe shear reinforcement to resist-
ance is equal to the yield capacity ofan individual stirrup (Af) times the number ofstir-
vy
rups crossing the diagonal compression field (d cotθ/s) where d is the flexural lever arm
v v
or shear depth,sis the spacing ofthe stirrups,and θis the angle ofdiagonal compression.
In the LRFD Sectional Design Model,θcan be taken to be as low as 18.1 degrees,and in
this case stirrups are calculated to provide approximately three times the shear strength,
V,than they would be calculated to provide in accordance with the AASHTO Standard
s
Specificationsfor Highway Bridges (3),in which θis assumed to be 45 degrees.With the
extension to HSC,the accuracy ofthe LRFD-based values for θare more critical because,
with the higher shear design forces permitted by the LRFD Sectional Design Model,larger
contributions from the shear reinforcement are required.
3. Minimum shear reinforcement. The LRFD specifications increase the minimum
required amount of shear reinforcement over that required by the AASHTO standard
specifications.However,no evaluation has been made as to whether the same level of
reinforcement is appropriate for very high-strength concretes in which the energy
released at diagonal cracking is much larger and cracks are smoother and more widely
spaced than in normal-strength concretes.
4. Maximum shear strength limit.In the AASHTO standard specifications,the maximum
design shear force is controlled by a limit on the contribution ofthe shear reinforcement,
V,of 8 f´b d where f´is in psi units.By contrast,in the LRFD specifications,the max-
s c v v c
imum shear design stress is 0.25f´plus the vertical component of the prestressing steel.
c
The ratio ofthese two limits (LRFD limit to standard specification limit) increases as the
concrete strength increases,from 1.42,to 2.25,to 3.18 for reinforced concrete members
cast with 4,10,and 20 ksi concrete,respectively.Thus,it was very important to investi-
gate ifthe LRFD shear stress limit was appropriate for the design ofHSC structures.
5. Validity of assumptions made in derivation of LRFD model. It can be argued that
because the LRFD specifications are derived from a comprehensive behavioral model they
are more likely to be applicable for structures that use new or high-strength materials.It
can also be argued that because there has been considerably less field experience in the
use of the LRFD specifications and because the assumptions made in the derivation of
the Sectional Design Model (4) may not be appropriate for high-strength concrete,there
is a marked need to evaluate this methodology for members cast with HSC.