Cyclic loading tests and numerical modeling of concrete-filled 700 MPa high-strength steel tubes incorporating deep plasticity

Abstract

Concrete-filled high-strength steel tubes (CFHST) could improve structural efficiency with lighter weight and higher capacity. However, the relative lower ductility and higher yield-to-tensile strength ratio of high-strength steel arouse worries about seismic performance of CFHST. In order to reveal the influence of high-strength steel on the elastoplastic hysteretic behavior of CFHST, 8 cantilever columns with Q550 and Q690 steel were subjected to constant axial load and cyclic top displacement. The actual yield strength of the steel was over 700MPa and the maximum axial load ratio was over 0.5. Based on the experimental observations, a finite element model was developed in ABAQUS that could consider deep plasticity behavior of CFHST members more precisely by introducing full-range elastoplastic constitutive model of high-strength steel and damaging–crushing behavior of infill concrete. The model was validated by the 8 tests of this study and other 34 cyclic-loaded CFST specimen from different researchers. 288 cyclic-loaded CFHST models were simulated by the effective numerical model in the parametric study on the elastoplastic deformation capacity of CFHST columns. The experimental and numerical investigations show that the CFHST could still have considerable deformation capacity if the local deformation of the steel tubes develop moderately. For heavy loaded CFST columns, high-strength thin-walled steel tubes have satisfying elastoplastic deformation capacity and ductility that are not worse than CFST with thick conventional steel tubes. The application of high-strength steel could delay the steel yield and control the damage of the concrete, leading to larger pre-peak deformation capacity. Finally, the empirical formulas were proposed to roughly yet efficiently estimate the ultimate drift θu of cyclic-loaded CFSTs with fy=345∼ 690 MPa, fc’=24∼72 MPa, ξ=1.0∼6.0 and n=0.20∼0.80, which is fairly practical in plastic inter-story-drift check and seismic design of CFHST structures.