Finite Element Analysis for Hysteretic Behavior of Thin-Walled CFT Columns with Large Cross Sections

Abstract

Thin-walled CFT columns with large cross sections are often used for elevated highway bridge piers in Japan because of their excellent earthquake resistance. This excellent earthquake resistance is primarily due to the restraint of the cyclic local buckling of the thin-walled steel tube caused by the complicated interface action between thin-walled steel tube with diaphragms and in-filled concrete. To predict the performance of thin-walled CFT columns by FEM in a direct manner, it is necessary to model the above interface action as well as the nonlinear behavior of steel tube and confined in-filled concrete properly. Herein, first, an accurate nonlinear FE model is presented to analyze the bi-directional hysteretic behavior of CFT columns. In this model, steel tube and in-filled concrete are represented by geometrically and materially nonlinear shell elements and solids elements, respectively. For the interface between steel and concrete, contact and friction behaviors are considered. Then, a bi-directional cyclic loading experiment is conducted on thin-walled CFT columns to investigate their ultimate behavior. Based on the failure pattern of the in-filled concrete observed in the experiment, a new concept of crush belt is introduced in the modeling of in-filled concrete. The validity of the proposed model is confirmed by the bi-directional cyclic loading experiment.