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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 11 Abstracts search results
December 1, 1991
Jenn-Chuan Chern and Young-Gee Wu
In modern computerized structural analysis, realistic material laws should be used. This research will present a constitutive law and a numerical procedure based on the finite element method for the analysis of a prestressed concrete structure including the time-dependent effects due to the load history, creep, shrinkage, aging of concrete, and relaxation of prestress. A 32.1 meter (105 ft) long U-shaped railway bridge, composed of two precast post-tensioned concrete girders and an in situ cast prestressed young concrete slab, was instrumented to observe its long-term structural behavior and used for the comparisons with numerical analysis. To evaluate and predict the structural behavior of this concrete structure, the related experiments were designed and performed both in the field and laboratory. Some material properties needed for the analysis were obtained through the extensive program carried out in the laboratory with controlled environments. This paper will describe the details of structure, test program, and experimental results.
Editors: C.C. Fu and M.D. Daye
With today's powerful computers and sophisticated testing methods, new formulation for predicting the structural response of concrete structures to creep and shrinkage of concrete are emerging. Actual structural behavior can now be predicted by mathematical modeling of material behavior. This special publication provides the means for better understanding the important creep and shrinkage characteristics of concrete. Ten papers cover a variety of topics including the theoretical and experimental parts of the long-term behavior of a railway bridge, results for creep in reinforced and prestressed concrete columns, long-term behavior of prestressed concrete beams, evaluation of creep and shrinkage deflection of reinforced concrete members, the rational and approximate methods for time-dependent deflection of prestressed concrete members, predicting and testing for creep and shrinkage, computing stress and strain, and time-dependent analysis for partially prestressed composite members.
N. C. Mickleborough and R. I. Gilbert
The first stage of an experimental investigation into the instantaneous and time-dependent behavior of reinforced concrete columns under sustained load is reported. The experimental work described in the paper involves the testing of 15 large-scale columns in compression and uniaxial bending to obtain comprehensive creep deformation data for the prediction of long-term lateral deflection and instability. Information on the range of slenderness ratios and load levels which cause creep instability for rectangular symmetrically reinforced concrete columns is of particular interest. The experimental data is also for use in the development and calibration of a theoretical model for the prediction of creep deflection and buckling under sustained load. The experimental setup used in this investigation and described in the paper is designed for the simultaneous testing of five slender columns, each up to 6 m in length. The loading frame is such that each column may have different length, different cross-sectional dimensions and reinforcement details, and be subjected to different combinations of axial force and bending moment. In the three series of tests presented here, column length, axial force, and initial eccentricity are the major variables. The loading on each column is monitored independently and maintained automatically at a constant preset value throughout each test. A direct comparison of creep effects on column behavior is therefore possible as different loading parameters are varied.
R. I. Gilbert and N. C. Mickleborough
A nonlinear procedure is described for the time-dependent analysis of reinforced and prestressed concrete columns under sustained eccentric compression. Both material and geometric nonlinearities are take into account in an iterative computer-based solution procedure. Individual cross sections are analyzed using the age-adjusted effective modulus method to include the effects of creep and shrinkage. By dividing the time scale into several increments, the gradual development of time-dependent cracking can be traced as the lateral deflection of the column and the internal secondary moments increase with time due to creep. Analytical predictions are shown to agree with laboratory measurements and numerical results from a parametric study of the behavior of slender columns are presented. The analytical model is also used to make a critical examination of the design provisions in ACI 318-83. Results indicate that the moment-magnifier method contained in the code for the design of slender columns becomes very conservative for very long columns.
B. Vijaya Rangan
The paper presents a summary of treatment of deflection control in the Australian Standard, AS3600-1988. The top-tier method recommended by the standard requires consideration of creep and shrinkage effects on deflections. Simple expressions for calculating creep and shrinkage deflections are given and illustrated by examples.
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