| "Strong column and weak beam" is one of the important concepts in the seismic design of reinforced concrete frame structure.According to the research results of many domestic and foreign scholars,it is shown that when the structural beam end yields before the column end and the plastic hinge occurs,the reinforced concrete frame structure as a whole Will maintain good ductility and energy consumption.However,the actual experience of earthquake damage in the past shows that the failure mechanism of reinforced concrete frame structures designed according to the current codes rarely appears the failure mode of strong columns and weak beams that designers expect.In most structures,the column section has a plastic hinge before the beam section,thus forming a column hinge mechanism and causing the structure to collapse.In order to study this problem,this paper studies the effect of different column end bending moment increase coefficients and floor slabs on the seismic performance and failure modes of reinforced concrete frame structures with respect to strong columns and weak beams.The main research contents of this paper are as follows:(1)According to 2010 seismic design code,a group of reinforced concrete frames with different moment amplification coefficients at column ends are designed.By extracting the middle nodes at the bottom of RC frame,a series of joint models of frame structure are established for quasi-static test.In the experiment,by changing the reinforcement at the end of column,the moment augmentation factor at the end of column can reach 1.4,1.6,1.8 and 2.0 respectively under the condition that the reinforcement at the cross section of beam and slab remains unchanged.A non floor control group is set for the specimen with the augmentation factor of 1.6 to investigate the influence of the moment augmentation factor at the end of column and cast-in-place floor on the failure mode of "strong column and weak beam" and the seismic performance of the joint.The low cycle reciprocating quasi-static loading test was carried out,and the failure mode was analyzed according to the results.(2)In the seismic design code of our country,the key measure to guide the frame structure to realize the energy dissipation mechanism of "strong column and weak beam" under earthquake action is to improve the bending capacity and ductility of column end by changing the moment amplification factor of column end.According to the test results,the influence of different moment augmentation factors on the seismic performance of beam column joints under quasi-static loading is investigated.The results show that the beam column joints designed according to the current seismic design code can achieve the expected design goals of "strong column and weak beam" and "strong joint and weak member" under quasi-static reciprocating loading when considering the strengthening effect of cast-in-place floor slab on beam end stiffness and bearing capacity but not considering the effect of infilled wall.(3)Because of the influence of the floor slab participating in the structure,the seismic measures specified in the seismic requirements may not guarantee the realization of the concept of seismic resistance of strong column and weak beam under the actual earthquake damage condition.According to the test results,the influence of cast-in-place floor slab on the bearing capacity,ductility and failure mode of joints under quasi static loading is studied.The test results show that the failure mode of "strong column and weak beam" appears under the action of reciprocating pseudo static loading whether the effect of cast-in-place floor is considered or not.Both the test bodies were destroyed at the bottom column foot;For the plate specimens,brittle failure occurs at the beam and slab in the joint area.Under the failure mode,the restraint effect of floor slab on the beam end has little effect on the lateral bearing capacity of the whole member,but it can improve the lateral stiffness and nonlinear deformation capacity of the member to a certain extent. |
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