| Steel reinforced concrete(SRC)column has been widely used as an important supporting component for vertical load due to its superior seismic performance,durability and high bearing capacity.In practical projects,as a common structural layout to meet the non-uniform force state,the built-in L-shaped SRC column is often used in the side column or corner column of a structure.However,during their normal service life,these vertical members may suffer from various extreme load conditions,such as earthquake,collision or explosion,causing significant differences between the dynamic response and static response.Because these dynamic loads is the main component for bearing load under complex stress state,accidental impact load may lead to structural failure or progressive collapse of buildings.Therefore,it is important to study the dynamic characteristics and residual mechanical properties of these SRC columns under concentrated impact load in order to ensure the structural safety.In this paper,the dynamic response and residual axial mechanical properties of seven built-in L-shaped SRC columns under multi-lateral impact are reported.The main content is as follows:(1)Seven SRC specimens were designed at the prototype scale of 1/2 in this paper.Three lateral impact tests of the mid span of all specimens were carried out with drop hammer impact system.And the data was recorded by dynamic data acquisition system such as the time-history curve of hammer impact force and mid-span impact position of specimens.The failure modes of the specimens after each impact was also observed.The results are as followed: firstly,with no collapse or penetration,this kind of SRC column still has good integrity after several lateral impacts and high anti-impact performance;secondly,the main failure modes of specimens are bending failure and bending shear failure,while the latter is dominant.With the increase of impact times,the peak impact force of the specimen decreases and its middle span displacement constantly increases;thirdly,the increase of stirrup ratio and axial load can enhance the anti-impact performance of the specimen in this study.(2)The first impact finite element analysis model of SRC column with built-in L-shaped steel was established with the nonlinear dynamic finite element software ANSYS/LS-DYNA,and the numerical calculation results were compared with the test results of impact.The analysis results showed that the numerical model can well simulate the loading process of the specimen under the first impact.(3)With the 5000 k N servo pressure tester,the residual axial mechanical properties of the specimens after multiple impacts were studied,and other relationships like their failure modes,residual bearing capacity and the load-axial displacement curve were recorded.Additionally,the influence of impact height,hoop ratio and axial pressure ratio on the test results was discussed.The results indicate that: first,the L-shaped steel SRC column after three impacts has good integrity after axial compression,with no brittle fracture.The failure process of axial compression is shown as the failing of concrete,the yield of section steel and longitudinal reinforcements and the tensile fracture of stirrups,and the specimen has the total "S" deformation;second,the input impact load has the largest effect on the specimen’s bearing capacity as well as its stiffness degradation.The rise of stirrup ratio can enhance the bearing capacity,and the restriction effect could be observed during the initial loading.But the influence of axial compression on residual bearing capacity is not certain,needing further researches. |
