Study On Explosion Effect And Blast Resistance Mechanism Of RC Retrofitted Columns

In recent years,accidental explosion and terrorist attacks around the world are happening with increasing frequency.Explosion accidents threaten the safety of buildings in cities and have dramatically influence on the human society.Therefore,the blast-resistance design of buildings has attracted much attention.Reinforced concrete(RC)column is an important bearing member in the reinforced concrete structures.Therefore,it is an crucial aspect which need to be considered in the blast-resistance and disaster reduction of building structures.In order to improve the blast-resistance performance of columns and other key components in existing buildings,the use of the blast-resistance reinforcement is an effective way.In order to investigate the blast-resistance and reinforcement effects of different measures,general RC columns and column specimens retrofitted by steel wire mesh-polymer mortar(SWMPM),steel plate and steel strip,were designed and fabricated.The experimental phenomenon and rules of failure modes and crack development of RC columns were analyzed.The dynamic response characteristics of the strain time history curves and displacement time history curves of RC columns were also investigated.The strength of polymer mortar,the spacing of steel wire mesh and thickness of steel plate reinforcement parameters were also considered,which revealed the blast-resistance reinforcement mechanism of different reinforcement measures.Then,based on the tests of the bearing capacity and residual bearing capacity of the RC columns after the explosion,a damage evaluation method for the reinforced column member was proposed.At the same time,using LS-DYNA finite element explicit dynamic analysis software,the failure mechanism and damage characteristics of reinforced column under blasting load were revealed further.The specific findings were as follows:(1)The steel plate reinforcement method could effectively reduce the collapse damage of the concrete on the back face and the splashing of concrete splinters,and improve the ability of the original columns to against damage and deformation,especially in the displacement response.However,using the reinforcement method,there were separation phenomena between the reinforcement layer and the original RC structure,and the strain response of the internal steel bars was little affected.(2)The reinforcement measure of SWMPM greatly reduced the deformation of the steel bar and the lateral deformation of the middle of the columns,so that the ability of the original RC column to withstand the explosion effect was significantly enhanced.At the same time,the reinforced column could still maintain a high residual bearing capacity under blast loading.Besides,in the test of the static bearing capacity of the undamaged members,the failure characteristics of the reinforced columns had been changed,and the ultimate bearing capacityof the original RC columns were greatly improved.(3)The damage degree of the RC columns has significantly reduced after retrofitted by SWMPM,and the strength of polymer mortar and the spacing of the steel wire meshaffect the damage degree.With the increase of the strength of polymer mortar and the decrease of the spacing of steel wire mesh,the damage degree of the reinforced column gradually decreased,the change amplitude of the strength of polymer mortar was particularly obvious,and the damage degree had changed,from moderate damage to slight damage.(4)After the reinforcement of steel strip,the blast-resistance ability of the RC column has improved because the steel strip played a certain restraining effect on the concrete,but the dynamic response of the displacement and the strain of steel bars was not significant.In addition,in the experimental study of the residual bearing capacity,although the reinforced columns could improve the residual bearing capacity of the specimen and prevent the buckling of the steel bars,the effect was much inferior to the SWMPM.The blast-resistance reinforcement effect was more obvious with the two reinforcement methods used together.(5)Based on the model of the explosion experiment,the numerical model of the unreinforced columns was established by the LS-DYNA finite element explicit dynamics analysis software.The validity and reliability of the numerical model were verified,and the damage phenomenon of the specimens and the rules of the dynamic response of the displacement were analyzed,which confirmed the conclusions drawn from the field explosion tests.