Improved Estimation of Long-Term Relaxation Function from Compliance Function of Aging Concrete
Publication: Journal of Engineering Mechanics
Volume 139, Issue 2
Abstract
Based on asymptotic considerations, this paper develops an improved approximate formula for estimating the relaxation function from the given compliance function of concrete, which is considered as aging, linearly viscoelastic material. Compared with the formula developed in 1979 by Bažant and Kim, the new formula prevents any violation of the thermodynamic requirement of nonnegativeness of the relaxation function. It is significantly more accurate for long-time relaxation of concrete loaded at a young age, and, for this reason, it is particularly useful for compliance functions that correctly describe multidecade creep, which is the case for model B3 compliance function (a 1995 international RILEM recommendation) and not, for example, for the compliance functions of the American, European, Japanese, and Canadian standard recommendations, for which the benefit is smaller. The main application of the new formula is to evaluate the aging coefficient of the age-adjusted effective modulus method (AAEM) from the compliance function specified by the standard recommendation. The AAEM, developed in 1972 at Northwestern University and embodied in most standard design recommendations including those of the American Concrete Institute (ACI) and the Fédération internationale du béton (fib), provides an approximate estimate of the creep effects in structures according to the principle of superposition, which itself is a simplification neglecting nonlinear and diffusion effects.
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Acknowledgments
Financial support from the U.S. Department of Transportation through Grant 6002078 from the Infrastructure Technology Institute of Northwestern University is gratefully acknowledged. Additional support was received from the U.S. National Science Foundation under grant CMMI-1129449 to Northwestern University and the Czech Science Foundation under grant No. 105/10/2400 to Czech Technical Univ.
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Information & Authors
Information
Published In
Journal of Engineering Mechanics
Volume 139 • Issue 2 • February 2013
Pages: 146 - 152
Copyright
© 2013 American Society of Civil Engineers.
History
Received: Apr 1, 2011
Accepted: Sep 27, 2011
Published online: Jan 15, 2013
Published in print: Feb 1, 2013
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