Date of Award

Spring 1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering - (Ph.D.)

Department

Civil and Environmental Engineering

First Advisor

C.T. Thomas Hsu

Second Advisor

George Weng

Third Advisor

M. Ala Saadeghvaziri

Fourth Advisor

Dorairaja Raghu

Fifth Advisor

William R. Spillers

Abstract

Plasticity theory has been used to model the concrete constitutive relationship for about two decades. With the modifications and refinement based on experimental data, achievement has been made in these plasticity models for concrete. Almost all the existing models are developed in stress space. With a lot of experimental data and more understanding about stress states of concrete, the stress-space model shows many advantages. Because of this and also due to conventional engineering practice, the stress-space plasticity approach has been in the dominant position. However, the conventional stress-space plasticity method has one inherent drawback in which it cannot deal with the softening part of materials. To model effectively the descending part of the strain softening materials such as concrete on the basis of plasticity theory, strain space concept must be adopted. Some researcher used it as a supplemental means to the stress-space model for the post-peak stage. Inspired by this basic idea, attempt was made in this study, to set up a strain surface of concrete at critical stress, then an initial yield surface and subsequent yield surfaces were constructed in strain space according to the existing experimental results. A non-proportional hardening rule and a non-associated flow rule were adopted. Finally, a strain-space plasticity theory was presented in modeling the nonlinear multiaxial strain-hardening-softening behavior of concrete.

It has been found that the model predictions of the ascending branch of stress-strain behavior are in good agreement with the experimental results involving a wide range of stress states and different types of concrete. The most important inelastic behavior of concrete, such as brittle failure in tension; ductile behavior in compression; hydrostatic sensitivities; and volumetric dilation under compressive loadings are included in these comparisons. It has also been found that the model can predict well the descending branch of strain-softening behavior of concrete.

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