Effective stress-strain relationships of steel plates in composite members with tie bars

Abstract

Tie bars are commonly used in concrete-filled steel plate composite shear walls to connect the two steel faceplates. The present study focuses on the effective stress-strain relationships of the faceplates as they are indispensable in analyzing the seismic performance of composite members using fiber models. Elastic buckling analyses were first conducted using the finite element (FE) method. As the horizontal-to-vertical spacing ratio of the tie bars increases, the buckling mode changes from a single bulge in the region bounded by the tie bars and longitudinal edges to separated bulges between two adjacent columns of tie bars. Based on the calculated results, a simplified equation was developed for the elastic buckling stresses. Nonlinear FE analyses were then conducted on 207 models to obtain the effective stress-strain relationships of the faceplates with different yield strength and tie bar constraint conditions. The effective stress-strain relationships are primarily affected by the ratio of the steel yield strength to the elastic buckling stress. Still, they are significantly influenced by the initial geometric imperfections. Based on the FE analysis results, an effective stress-strain model was developed for the steel faceplates. Fiber model analyses of composite members with tie bars were also performed using the developed effective stress-strain model. The developed fiber models can reasonably simulate the behavior of the composite members.