A NONLINEAR VISCOELASTIC MODEL FOR CONCRETE’S
CREEP AND CREEP FAILURE
Dinesh Panneerselvam (dinesh@nestor.cwru.edu)
and
Dr. Vassilis P. Panoskaltsis (vpp@nestor.cwru.edu)
Department of Civil Engineering
Case Western Reserve University
10900, Euclid Avenue
Cleveland OH 44106
Abstract
Concrete is a complex and very widely used engineering material with different time and length scales. The constitutive behavior of this material has always been a prime area of research for many years. In this work a new nonlinear viscoelastic model for the behavior of concrete is presented. The model has the ability to describe concrete’s creep and also creep failure and therefore its failure envelope, as it was obtained by the pioneering experiments of Rusch (1)
The proposed model is an important modification and extension of the "The Modified Kuhn Model of Linear Viscoelasticity", developed by J. Lubliner and Panoskaltsis (2). The modified Kuhn Model has both a rheological description, as a series of Kelvin type model as well as an internal variable description and has the unique property that no matter how many Kuhn (Kelvin) elements are used the number of parameters remain the same.
In the present work a non-linear creep function is introduced and equivalently a non-linear evolution equation for its internal variables. The creep function is then appropriately modified to obtain the failure curve of concrete also. An efficient algorithm is introduced for the numerical implementation of the model.The development here is benefited from some of the ideas of the work by I.Carol and J. Murcia(3) and Bazant Z.P. and Chern J.C (4). An extensive fitting in a nonlinear least squares algorithm is presented. The important concepts of instantaneous and equilibrium curves are also carefully examined and discussed.
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