Evaluation and prediction of cyclic response of Q690D steel

Abstract

High-strength structural steel of nominal yield strength greater than 690 MPa is difficult to produce in the hot-rolled condition without heat treatment. Quenching and tempering are thus commonly used to trade ductility for high strength. However, in seismic regions, good ductility of steel structural members is required to endure expected inelastic deformation under severe earthquake actions. This paper describes an experimental investigation on the mechanical properties and hysteretic behaviour of Q690D steel through 29 tensile coupon tests and 14 cyclic loading coupon tests subjected to four different cyclic patterns. The 16 mm and 40 mm quenched and tempered Q690D steel plates used in this study are equivalent to S690Q steel according to EN 10025-6. The test results of Q690D steel were compared with the ductility requirements of current seismic design codes. Under cyclic loading, Q690D steel showed cyclic softening. Based on analysis of the test results, a combined isotropic and kinematic hardening hysteretic model was developed to predict the cyclic behaviour of Q690D steel, with consideration of the Bauschinger effect and cyclic softening behaviour.