Equivalent constitutive model of steel with cumulative degradation and damage

To accurately predict the response of steel frames subjected to strong earthquakes, a uniaxial equivalent constitutive model of structural steel under cyclic loading is proposed for fiber beam element model, considering cumulative degradation and damage of strength and stiffness. The model consists of three types of skeleton curves, hysteresis criteria and degraded criteria, and each criterion is described by mathematical expressions with related dimensional parameters. By using the user subroutine interfaces UMAT provided by finite element software ABAQUS, the equivalent model was implemented as fiber beam element model. The proposed model was proved correct and available with comparison of typical experimental results including static cyclic loading tests of members and non-linear time history tests of structures. In the last, the model was applied in a four-storey frame for dynamic time history analysis with comparison of traditional bilinear model. The research shows that: the proposed model is independent of tests and three-dimensional models well simulate the degraded characteristics of strength and stiffness and accurately predict the failure modes. The model balances both computational accuracy and efficiency, which provides a powerful tool for nonlinear analysis of steel frames subjected to strong seismic excitation.

► An equivalent constitutive model considering degradation and damage was proposed.
► The model was integrated into ABAQUS as a UMAT by formulating with FORTRAN.
► The numerical results of proposed model were in accordance with typical tests.
► The proposed model was applied in nonlinear time history analysis of steel frame.