Finite Element Modelling Of Static Behavior Of Concrete-filled Steel Tubular Members Besed On Improved Plastic-damage Model

Due to the interaction between steel tube and core concrete,concrete-filled steel tube structure has incomparable mechanical properties compared with single steel tube and concrete.Because the core concrete is passively restrained by steel tube,its stress situation is complex.At present,although there are many numerical simulation studies on CFST,these simulations have their own shortcomings.Based on the theoretical framework of ABAQUS plastic damage model,this paper improves the plastic damage model of core concrete.The main work is as follows:1、 The yield criterion,flow criterion,hardening / softening criterion and damage parameters related to constraints are proposed.The yield criterion under triaxial constraint is used to replace the yield criterion under uniaxial compression;the expansion angle in the flow rule is not a single fixed value;the hardening / softening criterion closely related to the constraint stress is imported through ABAQUS user-defined subroutine.The improved concrete plastic damage model can significantly improve the simulation accuracy of the static performance of CFST,and the core concrete strength range of the model is more extensive.2、 In order to study the interaction between steel tube and concrete and the static mechanical properties of concrete filled steel tube more accurately,this paper uses ABAQUS finite element software to simulate 41 pure bending,66 axial compression and 26 eccentric compression concrete filled steel tube members.Considering the contact between the outer steel tube and the core concrete and the nonlinearity of the material,the improved plastic damage material model of concrete is selected Compared with the experimental results,the model proposed in this paper can better simulate the stress of CFST in the plastic stage,which is closer to the actual stress of CFST.Among them,for the pure bending simulation of CFST,the accuracy improvement is the most significant.3、 By comparing the simulation results of two models,the failure mode of CFST under pure bending,axial compression and eccentric compression,the stress change rule and interaction relationship between the outer steel tube and the core concrete are analyzed.The static working mechanism of CFST is further revealed.In this model,the size and shape of the yield surface of core concrete are given more accurately under triaxial compression than under uniaxial compression.In the plastic stage,the hardening / weakening criterion of Han model is fitted by repeated numerical calculation.For the pure bending members,the restraint effect of the outer steel tube on the concrete is weakened,while for the axial compression members,the restraint effect of the outer steel tube on the concrete is strengthened.The hardening / softening criterion of this model considers the constraint stress,which can accurately describe the real stress state of concrete at each constraint level.Finally,it is feasible and accurate to use the improved plastic damage model to simulate the static mechanical properties of CFST.