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International Concrete Abstracts Portal

Showing 1-5 of 11 Abstracts search results

Document: 

SP129-04

Date: 

December 1, 1991

Author(s):

B. Vijaya Rangan

Publication:

Symposium Papers

Volume:

129

Abstract:

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.

DOI:

10.14359/1255


Document: 

SP129-07

Date: 

December 1, 1991

Author(s):

J. C. Chern, Y. G. Wu, Y. W. Chan, and T. Y. Chou

Publication:

Symposium Papers

Volume:

129

Abstract:

Continuing the study of long-term behavior of a U-type composite prestressed concrete bridge, this paper presents a constitutive law for structural analysis and a nonlinear diffusion theory for the understanding of internal humidity distribution in a structure. The constitutive law was formulated based on a new rheological concrete element, which is a series coupling of a generalized Kalvin chain unit, a cracking unit, and a unit representing thermal strain or shrinkage. The previously obtained exponential algorithm for cracking, treated as strain softening, is combined with the exponential algorithm for generalized Kelvin chain element. The nonlinear diffusion theory, which considers both the pore humidity and aging effects on the diffusivity, was found to give very good fit to the distribution of internal humidity of concrete. The material parameters needed for the constitutive law and diffusion theory were identified. The numerical results using finite element method show the history of the prestress transfer between a young bridge deck and more matured girders. The calculated strains based on the presented method were found to be in good agreement with field measured data.

DOI:

10.14359/1322


Document: 

SP129

Date: 

December 1, 1991

Author(s):

Editors: C.C. Fu and M.D. Daye

Publication:

Symposium Papers

Volume:

129

Abstract:

SP-129 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.

DOI:

10.14359/14161


Document: 

SP129-05

Date: 

December 1, 1991

Author(s):

R. I. Gilbert and N. C. Mickleborough

Publication:

Symposium Papers

Volume:

129

Abstract:

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.

DOI:

10.14359/1256


Document: 

SP129-06

Date: 

December 1, 1991

Author(s):

Alex Aswad

Publication:

Symposium Papers

Volume:

129

Abstract:

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.

DOI:

10.14359/1285


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