Study On Seismic Performance Of New Assembled Beam-column Joints Based On Magnesium Phosphate Cement Concrete

The rapid development and expansion of the city have put forward new challenges and requirements for the traditional construction industry with long construction period and complex process.In order to solve this problem,prefabricated buildings have gradually developed.However,in real projects,prefabricated buildings have problems such as high technical requirements for construction personnel,unguaranteed safety of grouting sleeve connections,and low construction.Aiming at the problems existing in prefabricated buildings,based on the new material magnesium phosphate cement concrete with fast concrete setting speed,high early strength and strong anchorage performance with steel bars,this paper designs and proposes a new type of prefabricated node that simplifies the connection mode of prefabricated columns.Through quasi-static test and finite element analysis,the seismic performance of this type of node is studied,which provides scientific data basis for promoting the further development of prefabricated buildings.This paper mainly carried out the following work :(1)The mechanical properties of magnesium phosphate cement concrete were studied experimentally,and the bonding and anchoring ability of magnesium phosphate cement concrete and grouting sleeve on steel bars,and the bonding ability of magnesium phosphate cement concrete and Portland cement concrete were analyzed,which provided a basis for node design.(2)A cast-in-place silicate cement concrete beam-column joint,a prefabricated post-pouring portland cement concrete joint and four new prefabricated post-pouring magnesium phosphate cement concrete beam-column joints in the core area were designed and fabricated.The anchorage length of the longitudinal reinforcement of the prefabricated column in the core area of the joint was determined by the pull-out test,and the seismic performance indexes such as energy dissipation and ductility of the joints were studied by low-cycle reciprocating load test.The results show that the application of magnesium phosphate cement concrete in the core area of beam-column joints improves the deformation resistance and energy dissipation capacity of the joints.The seismic performance of new assembled beam-column joints based on magnesium phosphate cement concrete is similar to or better than that of cast-in-place and assembled post-cast Portland cement concrete joints.The seismic performance of the joints with the lap length of 175 mm and 210 mm in the core area of the joint is similar.The new joint can effectively reduce the use of steel bars and alleviate the problem of dense steel bars in the core area of the joint to a certain extent.The ultimate bearing capacity of the joint can be effectively improved by enhancing the bonding force of the longitudinal reinforcement of the prefabricated upper and lower columns and increasing the bonding area between the longitudinal reinforcement of the prefabricated column and the magnesium phosphate cement concrete.(3)On the basis of laboratory tests,the numerical models of one cast-in-place joint,one ordinary assembled joint and one new assembled joint were established by using finite element software to study the influence of parameter changes on the seismic performance of joints,and compared with the indoor test data.The results show that the finite element simulation results are similar to the indoor test results,and the variation rules of various seismic performance parameters are almost the same.Because of the high strength of magnesium phosphate cement concrete and the strong anchoring ability of steel bar,the beam end of the new joint is more serious than that of the ordinary joint in the later stage of the test,and the bearing capacity is obviously faster,and the subsequent loading is maintained for a long time.The bearing capacity level is high and the seismic performance is excellent.On the basis of the test,the effective anchorage length of the longitudinal reinforcement of the precast column is shortened to 125 mm,and the reinforcement structure in the core area of the joint is further optimized.