Instabilities in thin-walled steel columns under three dimensional nonproportional cyclic loading.

摘要

This dissertation is concerned with the elasto-plastic large deformation analysis of thin-walled circular cross-sectioned steel columns under multidirectional quasi-static cyclic lateral loading histories.;In the first part of this work, a new time-independent cyclic plasticity is outlined, capable of describing the non-linear behavior of structural steels with yield plateau under complex cyclic load paths. After the mathematical formulation is presented, the performance of the model is validated both at the macroscopic and at the component level using experimental data available in the literature. It is shown the material model developed can be used in finite element applications aimed to determine the nonlinear response of structural components made of structural steels with yield plateau.;In the second part of the study, a detailed finite element study is conducted to evaluate the performance of thin-walled circular steel columns under combined constant axial and nonproportional cyclic lateral loading histories. Investigated performance parameters are hysteretic response, ultimate lateral strength, lateral deformation capacity, energy absorption capacity and local failure modes. The presented results indicate that the response characteristics of thin walled circular columns under nonproportional lateral loading is fundamentally different from proportional loading, due to elasto-plastic coupling.