2015 SIMULIA Community Conference 1 www.3ds.com/simulia Elastoplastic Simulations with a Tangential Plasticity Constitutive Model for a Thin Wall Bridge Pier Subjected to Various Non-proportional Cyclic Loading Conditions Hideto Momii 1 , Seiichiro Tsutsumi 2 , Riccardo Fincato 2 1) ESTECH Corporation 2) Joining and Welding Research Institute, Osaka University Abstract: Various elastoplastic constitutive models have been proposed to predict the structural stiffness; most of them use an associated flow rule, which defines a plastic flow direction normal to the yield surface. These models, based on this assumption, have contributed to the predictions of elastoplastic deformations of solid structures in several applications, however, in some cases, they tend to overestimate the structural stiffness. In order to overcome this defect, we have adopted an unconventional elastoplastic model capable of taking into account the generation of the inelastic strain rate not only along the direction normal to the yield surface but also along the tangential one. In this paper the aforementioned model has been studied by applying a series of non-proportional loading paths to a thin wall pier and comparing the results obtained with the ones derived by neglecting the tangential contribution. Keywords: Non-proportional Cyclic Loading, Elasto-plastic FE Analysis, Tangential Plasticity, Low Cycle Fatigue Life, Constitutive Equation. 1. Introduction Thin wall steel bridge are widely used in highway bridges, buildings, and offshore structures. In Japan, on 17th January 1995, the Hyogoken-Nanbu earthquake hit huge region around Kobe and Osaka and its magnitude, 7.3 degree, was higher than that assumed level. Many bridge piers of the highway were severely damaged due to these cyclic excitations. Seismic solicitations are naturally quite complex, the amplitude changes during earthquake as well as its direction, which usually is not uni-directional but rather bi-directional and non-proportional in lateral direction. Therefore, in order to correctly design the structural stiffness for those conditions, several cyclic non- proportional loadings have been investigated in this work, trying to understand the reliability of the model to catch a realistic behavior for the bridge pier. Moreover, bridges structural parts, buildings and offshore piers may not experience seismic actions only one time, therefore, in addition to the previous considerations, the design method must be able to take account also the cumulative damages due to loading history.