Experimental Study On Progressive Collapse-resisting Performance Of Prestressed Fabricated PC Frame After The Removal Of The Middle Column

In recent years,the problem of preventing progressive collapse of building structures has become one of the hotspots in China's engineering field.At present,scholars at home and abroad mainly focus on cast-in-place concrete structures to prevent and control the progressive collapse of structures,but few people have touched on prefabricated concrete structures.The traditional assembled structure is weak in the joint of beam and column,and it's poor to resist progressive collapse.The prestressed fabricated PC frame is a new structure system which applies the prestressing technology to the assembled structure.It combines the advantages of assembled structure and prestressed concrete structure,and has good seismic performance.In order to study the progressive collapse-resisting performance of prestressed fabricated PC frame when the mid-column fails,a pseudo-static experiment of a two-story two-span prestressed fabricated PC frame is carried out with the support of the National Natural Science Foundation of China.The mechanical characteristics and failure modes of the structure after the removal of the middle column are studied.The load-displacement curve of the structure is obtained,and the progressive collapse-resisting performance and mechanism of the structure are discussed.The finite element software Midas/Gen is used to carry out numerical simulation analysis of the test frame,and the non-linear static Pushdown analysis and non-linear dynamic time history analysis are carried out to further explore and verify the progressive collapse-resisting performance and mechanism of the structure.The main content and results are as follows:(1)A two-story two-span prestressed fabricated PC frame is designed and manufactured.The pseudo-static experiment under vertical loading is carried out to obtain the relationship curves between the horizontal displacement of each story,the strain of steel bars,the corner of beam end,the corner of column base,the vertical load of the frame and the loading displacement of the middle column.The progressive collapse-resisting performance and mechanism of the frame are discussed based on the failure mode of the frame.(2)The results of test show that the plastic hinge first appears at the end of the beam during the loading process,the crack development and failure of the concrete of the frame concentrate on the joint of the beam end and the corbel of the frame column,thebeam end which near the middle column is seriously damaged,the phenomenon of concrete crushing and peeling is obvious,and the cracks on the joint surface of corbel are larger.The frame column is not obviously damaged,and the structure belongs to the structure of "strong column and weak beam".The stress process of the frame is divided into four stages: elastic stage,elastic-plastic stage,plastic hinge stage and catenary mechanism stage.The catenary effect of the frame is obvious,the bearing capacity does not decrease in the plastic hinge stage,the prestressed tendons play a significant role in enhancing the bearing capacity.And the prestressed tendons are still not yielding when the concrete at the end of the beam collapses,the frame has a certain ability to resist progressive collapse.(3)Nonlinear static Pushdown analysis of the test frame is carried out by finite element software,and the results of hinge state and load-displacement curve of the structure after removing the mid-column are obtained.The load-displacement curve and the sequence and development of plastic hinge are analyzed,and compared with the actual situation of the test,the collapse resistance performance and mechanism of the frame are discussed and verified.The results show that the simulation results are in good agreement with the test results.The plastic hinge first appears at the end of the beam and develops more rapidly near the end of the middle column.The structure basically meets the configuration of "strong column and weak beam",and has good ability to resist progressive collapse.(4)Nonlinear dynamic time history analysis of the test frame is carried out by finite element software,and the results of hinge state and related time history curves of the structure after removing the mid-column are obtained.The simulation results are compared with the results of non-linear static analysis and the actual test results,which further verifies the performance and mechanism of the frame resist progressive collapse.The results show that the structure has a certain dynamic performance of resisting progressive collapse,and its collapse failure mechanism is consistent with the laws obtained from the analysis of non-linear static analysis and experimental results.The dynamic amplification coefficient of the structure exceeds the limit value of 2.0 in the GSA code.