Study On The Influence Of Cast-in-place PC Frame Floor On Seismic Performance Of Structures

Existing studies have shown that plastic hinges often appear at the end of columns of reinforced concrete frame structures under earthquake action.An important reason for this failure mechanism lies in the "overstrength" effect at the end of beams,especially the remarkable strengthening effect of cast-in-place slabs on the bending capacity of beams.Prestressed concrete frame structure(PC frame structure)is not only more difficult to realize the failure mechanism of "strong column and weak beam" because of its long span,large size of main beam and special structural form,but also the influence of cast-in-place floor on its seismic performance is quite different.Therefore,how to consider the "overstrength" effect of cast-in-situ slabs on prestressed concrete beams in practical design and analysis has become an urgent problem to be solved.However,the current research on this issue is seldom seen in the literature.Therefore,this paper systematically studies the impact of castin-situ slabs on the seismic performance of prestressed concrete frame structures,aiming at the design and standard repair of PC frame structures.Provide reference for subscription.The main research contents and conclusions are as follows:1.A series of analysis models of PC framework are established by SAP2000,and the correctness of the modeling method is verified by the existing experiments.The effect of cast-in-situ slab on the overall horizontal stiffness of PC frame structure is analyzed.The results show that the existence of cast-in-situ slab improves the overall stiffness of the structure,and the strengthening effect increases with the increase of slab thickness and beam span and the decrease of beam height.The horizontal stiffness increasing coefficient of PC frame with floor is obtained by calculation,and the thickness,beam height and beam span are obtained by linear regression fitting.The empirical formula of independent variable is used to estimate the increase degree of horizontal stiffness of cast-in-place floor to PC frame structure.2.Through static elastic-plastic analysis,the overall yield and stress distribution of steel bars in PC frame structures with and without floor slabs are obtained.The effects of slab thickness,beam height and beam span on stress distribution and effective flange width of steel bars in negative moment zone at the end of PC frame beams are analyzed.The results show that the existence of cast-in-situ slabs changes the yield mechanism of PC frame structures.The failure mechanism of "strong column and weak beam" of PC frame structure of floor is gradually transformed into mixed yield failure mechanism.The effective flange width of different PC frame beams is calculated,and the empirical formula of the effective flange width in the negative moment zone of PC frame beams is obtained by linear regression.3.Based on the previous conclusions and existing research,the beam-end floor through-joint is applied to PC frame to improve its seismic performance.The PC frame model with different length through-joint is established by OpenSees software,and the correctness of the model is verified by the existing test.Through static elastic-plastic analysis,the effect of setting through joints at beam ends on seismic performance of PC frame is studied.The results show that reasonable setting of through joints can effectively improve the seismic performance of PC frame structure.For middle joints,the length of through joints of PC frame structure should be 1/12 prestressed beam length minus 1/2 column width.For side joints,the length of through joints of PC frame structure should be 1/12 prestressed beam length minus 1/2 column width.It is more appropriate to take the length of 1/10 pre-stressed beam minus 1/2 column width.4.By means of incremental dynamic analysis and vulnerability analysis,the seismic performance of three PC frames is evaluated and compared.The results show that the crossing probability of PC frame with through joints is lower than that of ordinary frame under the same earthquake intensity,and the reserve coefficient of seismic collapse is increased.The reasonable setting of through joints is beneficial to the realization of the yield mechanism of "strong column and weak beam" and the seismic performance of PC frame structure is improved.