Crack-based model for seismic behaviour of concrete columns under combined compression-bending and torsion

Abstract

A crack-based model for the seismic behaviour of circular concrete columns under combined compression-bending and torsion is proposed and verified experimentally. The coupling effects of compression-bending and torsion can be decoupled depending on the crack angle that is formed by the crack face relative to the horizontal plane. The mechanical performance of the crack face determines the seismic behaviour of the concrete columns. The effect of torsion on the compression-bending capacity of concrete columns includes a reduction in the mechanical properties of the concrete and longitudinal rebars. The compression-bending behaviour of the concrete columns can be calculated based on the moment–curvature analysis of the cross-section. The torsional capacity primarily comes from two parts: one is the torsional couple generated by the stirrups and concrete, and the other is the torsional capacity provided by the non-cracked concrete. Torsional sections I and II are formed separately for these two parts. The torsional behaviour of concrete columns can also be calculated based on the moment–curvature analysis of the torsional sections. The effect of compression-bending on the torsional capacity of concrete columns includes a reduction in the concrete torsional strength and size of torsional section I. The crack-based model can accurately analyse the seismic behaviour of concrete columns under combined compression-bending and torsion and can be easily used in finite element analysis with fibre beam-column elements.