Strain Rate Effect Study Of CFST Column Under Blast Load

The enormous destructive forces caused by the explosions encountered in civil engineering may cause serious damage to the structure and may even result in the overall collapse of the structure.Therefore,it is very necessary to properly consider the role of blast load in the structural design.However,the CFST columns subjected to blast loading belong to the state of high strain rate,so the strain rate effect of materials needs to be considered.Therefore,this paper will study the CFST column as a research object.Mainly from the basic concepts of explosion,the dynamic mechanical properties of concrete and steel,the finite element simulation of CFST columns,and strain and strain rate effects,the anti-explosion performance of CFST columns was systematically studied.The main research and achievements are as follows:First,through applying FEM software of ANSYS/LS-DYNA,FEM of CFST column subjected to blast load has been established.Strain-time history curves of CFST column for circular section and square section in blast experiment has been applied to verify via establishing FEM.FEM adopted through fluid-solid coupling method has been proved,including the selection of material model for air and explosive.The model parameter for steel,concrete and blast pit is reasonable.Second,applying established FEM,via changing hoop coefficient,scaled distance,axial force ratio and section form,strain conditions of CFST specimen under different conditions has been analyzed.Results show that increasment of hoop coefficient will promote the increasment of composite elastic modulus of CFST specimen thus will decrease the strain peak and strain response period.Decreasing scaled distance will make the rigidity of CFST component less,which leads to the increasment of peak value and response period.Increasing axial force ratio can reduce the max mid-span strain value of CFST component and increase the second order effect.Compared with the change of strain for equivalent section of circular section and square section,a conclusion can be drawn that circular CFST column has a better blast resistant performance than square CFST column.With the change of hoop coefficient,scaled distance and axial force ratio,regulation of strain alteration of CFST component for exterior steel and inner concrete is the same,the difference of which is the max strain value within 15%.Third,the maximum strain rate is chose in the strain rate time history curve,which is derivatived by the simulated strain time history curve.Besides,through the maximum strain rate,the strain rate formula is fitted from the changing of hoop coefficient,proportional distance and axial compression ratio of the blast load.Through this formula,the dynamic magnification coefficient of CFST can be obtained.Using the dynamic magnification coefficient of CFST,the maximum displacement can be calculated with the simplified equivalent single degree of freedom analysis method.This method can be used to advice the antiknock design.