Simulation On The Progressive Collapse Process Of Concrete Structure Considering Strain Rate Effect

The performance of reinforcing steel and concrete is rate-dependent,so the strain rate will inevitably affect the collapse of the structure.However,there are few researches at home and abroad on the progressive collapse and seismic response of concrete structures considering the effect of the seismic strain rate,and the influence of strain rate on the failure mechanism of the structural collapse is not yet clear and needs further study.At present,the fiber element model is popularly used in the study on structural nonlinear behavior under the dynamic loading,so some,based on fiber beam model,developed fiber beam element material constitutive model considering the effect of the seismic strain rate,but majority of them are just applied into solving the problems of impact load,such as explosion,and researching on seismic strain-rate effect is rare.On the other hand,the strain-rate influence to structure is often considered in manner of the material static strength multiplied by the growth factor.Because of the time-varying characteristics of seismic strain rate and the complexity of strain-rate behavior of reinforcement and concrete,it is unprecise to simply consider the influence of the strength growth caused by strain-rate effect on seismic response and collapse process of structure.In addition,the existing researches on dynamic nonlinear behavior of structures with seismic strain rates is mainly based on comparison of numerical simulations,which lacks test evidences.Based on the above,it is considerably scientific and practical value to develop a beam element subroutine that can considers time-varying characteristics of seismic strain rate on the basis of test result,then study further on the seismic performance the failure mechanism of progressive collapse of concrete structure with strain rate.In this paper,a subroutine of reinforced concrete dynamic fiber beam element for ABAQUS explicit module is coded,considering time-varying characteristics of seismic strain rate.With the material subroutine coded,the strain rate effect on seismic response and progressive collapse process of concrete structure is studied,And the main research contents are as follows:(1)Based on several kinds of classic uniaxial material constitutive models of concrete and reinforced material,rate-dependent material constitutive relation and material maximum strain failure criterion,the subroutine is coded in FORTRAN and can consider the confined effect of concrete,the stiffness degradation of steel,material rate-dependence and material failure behavior,then numerical simulations of the tests on the performance of reinforced concrete materials,the dynamic loading tests of concrete members and the shaking table test are conducted with the material subroutine.the results show that reinforced concrete dynamic fiber beam element subroutine can be effectively applied to the nonlinear dynamic analysis of concrete structure.(2)on the basis of shaking table test,with dynamic and static material constitutive models adopted,the process of test is simulated and the influence of strain rate on seismic response of concrete structure is studied,results show that maximum top displacement and maximum story drift of structure,considering material strain-rate effect,will decrease in a certain extent and are closer to test results.in a word,considering influence of strain rate,the seismic response of concrete structure is more consistent with the actual results,and is also reasonable and accurate.(3)the dynamic elasto-plastic time-history analysis of steel beam-concrete reinforced column composite frame structure is conducted,the strain-rate effect on the seismic response and progressive collapse process of the structure are studied.The results show that strain rate brings about maximum story drift decrease and maximum base shear increase.In addition,after considering the strain rate effect,the anti-collapse capability of the reinforced concrete structure improve,but the progressive collapse mode is unchanged.Therefore,the consideration should be given to the effect of material strain rate in the structural analysis.