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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
Document:
SP129-03
Date:
December 1, 1991
Author(s):
N. C. Mickleborough and R. I. Gilbert
Publication:
Symposium Papers
Volume:
129
Abstract:
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.
DOI:
10.14359/1254
SP129-04
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.
10.14359/1255
SP129-05
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.
10.14359/1256
SP129-10
Yun-Soo Joo and Maher K. Tadros
The objective of the paper is to develop a computer-based procedure for analysis of members made up of precast prestressed concrete sections with cast-in-place topping. The procedure accounts for cracking under the weight of the cast-in-place topping and superimposed loads. Creep and shrinkage of concrete and relaxation of prestressed steel are taken into account in combination with the effects of cracking. An attempt is made to limit the input data to information commonly available to designers. Linear creep law is used, and time-dependent effects, such as prestress losses and deflection growth, are automatically generated.
10.14359/1257
SP129-06
Alex Aswad
The long-term camber prediction under sustained loads is an important part of the design of pretensioned flexural members. Critical members are noncomposite roofs and bridge members which have medium or large span-depth ratios or elements made of lightweight concrete. Currently the most common approximate design method is one that relies on empirical multipliers applied to initial cambers and deflections. When compared to a rational approach, substantial differences in prediction of long-term camber or deflection are noticed. The approximate method appears to overestimate the permanent sag or underestimate the camber. It also does not consider certain creep, shrinkage, and relaxation properties. It is concluded that such methods may be unreliable for critical members and that the rational method is preferred. For preliminary design of longer spans, revised multipliers are suggested for use with the approximate method.
10.14359/1285
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