Study On Mechanical Properties Of Hollow Reinforced Concrete Columns Under Lateral Impact Load

Compared with solid reinforced concrete columns,hollow reinforced concrete columns are widely used as load-bearing columns in piers and building structures because of their light weight and good cross-section expansion.In order to further improve the performance of members,hollow reinforced concrete columns lined with steel tubes are formed in the hollow parts of members.With the advantages of high bearing capacity,good ductility and fire resistance,hollow reinforced concrete columns lined with steel tubes are widely used as load-bearing columns in piers and high-rise buildings.They are widely used in long-span bridges and buildings.As a result,they will inevitably be impacted by ships and automobiles,resulting in damage of components and even continuous collapse of buildings.Hollow reinforced concrete columns are mainly round hollow reinforced concrete columns and square hollow reinforced concrete columns.Octagonal hollow columns have the advantages of good stability of circular hollowcolumns and convenient construction of square hollow columns.The lined steel tube can significantly improve the mechanical properties of components and effectively avoid the steel failure caused by fire and corrosion under harsh conditions.Therefore,the mechanical properties of eight-deformed hollow reinforced concrete columns and steel tube-lined hollow reinforced concrete columns under low-speed impact load are studied in this paper.(1)The dynamic responses of 6 hollow reinforced concrete columns with inner eight sides and 4 hollow reinforced concrete columns with inner eight sided steel tubes subjected to lateral low velocity impact loads were tested on a drop hammer test machine independently designed by Taiyuan University of Technology.In the experiment,the failure mode,the time history curve of impact force and mid span displacement time history curve were recorded.The impact resistance of the component is analyzed from the impact height(H),the condition of the boundary and the thickness of the steel tube(T).The experimental results show that the failure modes of hollow reinforced concrete columns with inner eight sides under lateral impact load are mainly divided into two types: local failure(type I)and holistic failure(type II);and the fixed at both ends of the component can improve the role of impact resistance.(2)Using ANSYS/LS-DYNA,the finite element models of hollow reinforced concrete columns with inner eight sides and hollow reinforced concrete columns with inner eight sided steel tubes with inner lining under fixed support at both ends are established.Comparing with the impact force timehistory curve and the mid-span displacement time history curve,it is found that the test results are in good agreement with the finite element simulation results,which verifies the applicability and reliability of the model.(3)Based on the good agreement of finite element model verification,this paper mainly analyses the influence of yield strength of stirrups and longitudinal bars on the impact resistance of hollow reinforced concrete columns with inner eight sides,and the influence of yield strength of stirrups,longitudinal bars and steel tubes on the impact resistance of hollow reinforced concrete columns with inner eight sided steel tubes.The results show that the yield strength of stirrups has an effect on the impact resistance of hollow reinforced concrete columns with inner eight sides;the yield strength of longitudinal bars has no effect on the impact resistance of hollow reinforced concrete columns with inner eight sides;The yielding strength of stirrups and steel tubes has an effect on the impact resistance of hollow reinforced concrete columns with inner eight sided steel tubes,while the yielding strength of longitudinal bars has no effect on the impact resistance of hollow reinforced concrete columns with inner eight sided steel tubes.(4)When the section form of the member is fixed and the yield strength of the steel bar and steel tube contained in the member is fixed,the impact resistance of the member is optimal,and the concrete strength of the member has an optimal strength value.When the strength of concrete does not reach this value,improving the strength of concrete can effectively improve the impactresistance of components;when the strength of concrete exceeds this value,the impact resistance of components will hardly change.When the impact height is fixed,the weight of the drop hammer is fixed,and the constraints at both ends of the component are fixed,the better the impact resistance of the component is,the higher the strength of the material is when the optimal impact resistance is achieved.