Date of Award

Fall 2006

Project Type


Program or Major

Civil Engineering

Degree Name

Master of Science

First Advisor

Thomas Attard


In the 1989 Loma Prieta earthquake in the San Francisco-Bay area and also the 1994 Northridge earthquake in Southern California, several buildings experienced significant damage because of inadequate member design. The existing codes of practice used for the structural design approximate the effects of nonlinear material behavior. This work formulates a nonlinear anisotropic material model for systems subjected to biaxial loading conditions such that the true nature of material degradation can be identified. This would aide structural designers in being able to predict accurate cyclic deformations under large earthquake events. The proposed model investigates anisotropic material behavior under bi-axial loading in principal stress space from a snapshot perspective using various material axes of anisotropy. Since the principal axes of stress are assumed to coincide with material axis of anisotropy, the shear stresses are zero on that given plane for the analysis. However, their effect is modeled so that, at each strain increment, a different set of principal axes is considered. Two experimentally verified uniaxial stress functions are coupled in this manner and used to describe the material anisotropy. The model is developed using a distortional energy approach and von Mises type of yielding surface, which is consistent with the snapshot assumption used for each set of material axes.