Study On Impact Behavior Of Assembled Reinforced Concrete Frame Columns

Recently,reinforced concrete structures have been subjected to impact loading,which has a great influence on the prefabricated reinforced concrete frame structure.PC columns,as the main vertical bearing member,play a very important role in the whole structure.Therefore,it is necessary to research the impact performance of PC columns intensively,which provides reference for the disaster resistant design of prefabricated reinforced concrete frame structure.In this paper,the failure mode and dynamic response of PC columns and RC columns are studied by theoretical analysis,drop hammer impact test and finite element simulation.The specific work are summarized as follows:(1)According to the specifications,relevant literatures and the practical engineering,the impact test of PC and RC columns is designed,including the manufacture of RC and PC columns,the design of the test device and the arrangement of measurement device.At the same time,the tensile test is carried out on the reinforcement to obtain its strength index;the compressive test of the concrete block and the grouting block is performed to obtain the measured compressive strength of both.(2)A total of three RC columns and five PC columns are tested using drop hammer testing machine and the crack development process of columns is recorded and analyzed with a high-speed camera.Three main parameters,namely the impact energy,impact velocity and axial pressure ratio,are considered in this research.Based on the experimental results,the impact test phenomenon,the failure mode,the impact force-time history curves,the displacement-time history curves,strain development and energy dissipation are discussed to study the influence of three parameters on the dynamic response and failure effect of PC and RC columns.Furthermore,the difference of dynamic response between PC columns and RC columns is studied.The test results show that the overall performance and impact performance of RC columns are much better than that of PC columns.Larger impact energy and impact speed can significantly improve the peak value of impact force of PC column and shorten the duration of impact force.In addition,the increase of axial compression ratio will shorten the duration of impact force,but has little effect on the peak value of impact force.The impact energy has great influence on the lateral deformation of assembled reinforced concrete columns.The axial compression ratio will lead to asymmetric development of diagonal cracks in PC columns and serious shear failure will occur when the axial compression ratio is 0.3.(3)Based on the impact experiment,the numerical models of three RC columns and five PC columns are established by LS-DYNA and the whole process of PC and RC columnssubjected to falling hammer impact is simulated.The consistency between the experimental results and the numerical simulation results is verified by comparing the damage nephogram of plastic strain,the impact force-time history curves and the displacement-time history curves.Moreover,parametric analysis,of the PC columns,is performed by changing the axial compression ratio of columns under low impact energy.It is found that in the range of 0.2 ~0.5 of axial compression ratio,the axial load will increase the local damage degree and the overall damage degree of PC column,increase the mid span displacement of PC column and reduce the impact resistance of PC column.