Study On Influence Of Axial Load On Dynamic Response Of RC Members Under Lateral Impact Load

Since the beginning of the new century,China has witnessed a rapid increase in infrastructure construction.Reinforced concrete(RC)structure is the main structural form so that reinforced concrete(RC)members often act as bearing members of concrete structures.As RC members may be impacted by cars,derailed trains,ships and airplanes during their service life,lacking impact resistance ability or getting damaged will lead to a disastrous impact on the overall structure.The researches on the impact resistance of RC members have been carried out for a long time whereby few are on the non-midspan impact of RC members under impact and axial force.In this dissertation,the impact test of RC members under axial force is carried out to investigate the influence of axial load on the dynamic response of RC members.The main research contents and conclusions are as follows:(1)The drop hammer impact test of the RC column is performed.The results show that the failure mode of FH1 and FH2 is found to be flexure-shear failure,and shear failure is noticed in FH3 with axial load.The larger the impact energy is,the more likely the member exhibits shear failure,and the greater the maximum deflection of the member is.More severe local damage can be observed in the component applied axial load,which indicates that the axial load reduces the impact resistance.(2)LS-DYNA software is utilized to establish the finite element simulation model of the impact process of RC members.This dissertation introduces in detail the settings and parameters employed in the model,compares the advantages and disadvantages of two concrete constitutive models,MAT72R3 model and MAT145 model,and selects MAT72R3 model as the concrete material model in the simulation.The established finite element simulation model can accurately simulate the impact process of the test component.(3)The impact process of FH1 under axial load is simulated.The results of finite element analysis show that the greater the axial load is applied,the greater the peak value of the impact force of the component;when the axial compression ratio is 0.050 ～ 0.13,the larger the axial load is,the larger the impact force platform value of the component is,the smaller the maximum deflection value of the impact point is,and the stronger the impact resistance of the component is;when the axial compression ratio is greater than 0.13,the larger the axial load is,the smaller the impact force platform value of the component is,and the larger the maximum deflection value of the impact point is,which indicates impact resistance of the component becomes weak.(4)The influence of axial load on the failure mechanism of RC members under impact load is analyzed.The component failure can be directly attributed to the failure spalling of local concrete and the through failure zone formed by shear cracks.The stress variation of local concrete and the through time of shear crack are examined using the method of selecting characteristic elements in the model.It is found from the analysis that when the axial compression ratio is 0.05 ～ 0.13,a slight increase is noticed in concrete stress at the impact point,and the concrete collapse occurs slowly together with a slow penetration speed of shear crack and late formation time of shear crack.With the axial compression ratio greater than0.13,the maximum principal stress increases greatly,and the concrete collapses rapidly accompanied by a fast penetration speed of shear crack and early formation time of shear crack.