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Title:Shear Behavior and Capacity of Large-Scale Prestressed High-Strength Concrete Bulb-Tee Girders
Author(s):Sun, Shaoyun; Kuchma, Daniel
Subject(s):shear behavior
Shear behavior
Shear capacity
shear cracking
high-strength concrete
pretressed bulb-tee girders
experimental data visualization
crack displacement field theory
Abstract:The current shear design provisions of the AASHTO LRFD Bridge Design Specifications limit the concrete compressive strength to 10 ksi due to a lack of experimental evidence for their extension to high strength concrete. To overcome this limitation, the National Academy of Sciences funded National Cooperative Highway Research Program (NCHRP) Project 12-56 “Application of the LRFD Bridge Design Specifications to High-Strength Structural Concrete: Shear Provisions”. This report presents an analysis of project 12-56 experimental test data from which an in-depth understanding of the shear response of prestressed girder was obtained and new models were developed. The experimental work comprised a total of 20 tests on ten 52-foot long and 6-foot deep bulb-tee girders. All girders were designed to satisfy the requirements of the LRFD Bridge Design Specifications and then subjected to a uniformly distributed load until failure occurred in shear. The primary test variables were concrete compressive strength (ranging from 10 to 18 ksi), the maximum shear design stress (0.7 to 2.5 ksi), strand anchorage details (straight, unbonded, and draped), and end reinforcement detailing (bar size, spacing, and level of confinement). A large number of both traditional and advanced instrumentation systems were used to measure response. A new data visualization tool was developed to provide a detailed analysis of the dense experimental test data. It was concluded that the AASHTO LRFD Sectional Design Method, as well as the AASHTO Standard Specifications and the Canadian Standard Association A23.3-04 Design Method, could be extended to up to 18 ksi concrete. It is also recommended that the maximum shear design stress be reduced from 0.25 fc’ to 0.18fc’. Both the angle and the strength of diagonal cracking could be accurately predicted using Mohr’s circle of stress. The web shear behavior could be characterized as a tri-linear relationship separated by web cracking, stirrup yielding, and failure and the inelastic tangent stiffness before stirrup yielding could be modeled as a polynomial function of shear reinforcement ratio. Based on the development of 350 crackbased free-body diagrams, the components of the concrete contribution to resistance (two flanges and web) over the loading history was characterized as a function of the geometric and material properties of the girders. A general expression, which adopted the calculated crack angle for the computation of shear reinforcement contribution and provided clear physical explanation for every part of concrete contribution, was suggested for the future shear design practice. From the measured test results, an analytical model, Crack Displacement Field Theory (CDFT), was developed for predicting the shear response of prestressed/reinforced concrete members. Compared to other existing models, it could capture the discrete displacement due to crack opening and crack slip along crack surface and can take account the variation of stresses in reinforcement due to bond. Based on this model, expressions were derived for shear stiffness and shear resistance at stirrup yielding, and the derived equations produced good agreement with test results.
Issue Date:2007-11
Publisher:Newmark Structural Engineering Laboratory. University of Illinois at Urbana-Champaign.
Series/Report:Newmark Structural Engineering Laboratory Report Series 002
Genre:Technical Report
Publication Status:published or submitted for publication
Rights Information:Copyright held by the authors. All rights reserved.
Date Available in IDEALS:2008-03-02

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