| The precast concrete(PC)structure has the advantages of easy control of component quality,high construction efficiency,low environmental impact and labor saving.However,due to the limited overall stiffness of precast concrete structure,it is generally used in low-intensity areas.In this paper,the precast connections and the cast-in-place connections are used to mix and cross along the structure height and the plane reasonably(not in the same node)to form a new structural form of precast reinforced concrete frame structure with hybrid connections.This kind of precast structure can not only take the advantages of the stiffness of cast-in-place connections,but also make full use of the outstanding designability of the precast connections.It can also broaden the maximum applicable height and maximum fortification intensity of the application of the precast connections,and improve the comprehensive economic benefits of the precast concrete structure as far as possible from the perspective of structural design.For the precast connections of the high-rise concrete frame with hybrid connections,the elastic inter-story drift caused by the insufficient stiffness of hybrid connections take a large proportion of the total inter-story drift.In order to realize the advantages of the structure with hybrid connections,it is necessary to estimate the displacement response of the structure with hybrid connections under the earthquake and determine a reasonable mixing mode.In this paper,the PC connection is considered as a semi-rigid connection.By studying the lateral displacement,period and other elastic responses of the structure with semi-rigid connections under frequent earthquakes and the simplified calculation method of the lateral displacement,a practical elastic inter-story drift estimation method of the lateral displacement is obtained.The mixing mode and connection parameters of the structure are determined by multi-objective optimization of the structure.The main contents of this paper are as follows:(1)Through the derivation and case study,the influence of different types of hybrid connections and stiffness parameters on the elastic response of the structure is studied,and the preliminary suggestions on the mix principles of PC structures with hybrid connections are given.For the plane frame model with semi-rigid connections,the expression of the limit value of the stiffness coefficient of the semi-rigid connections of the single-story structure is derived when it reaches the elastic maximum inter-story drift limit.At the same time,the calculation program of the multi-story model is obtained through MATLAB programming,and then the influence of the parameters of the semi-rigid connections on the maximum inter-story drift with is obtained.Meanwhile,the expression of the limit value of the stiffness parameters is obtained through numerical regression by MATLAB programming.Finally,the elastic responses of different arrangements and the stiffness parameters of the semi-rigid connections are compared by using ETABS.The results show that the elastic responses of the structures have a great relationship with the number of semi-rigid connections,but have little relationship with the location of different spans of semi-rigid connections in the plane.When the stiffness parameter of the semi-rigid connections is more than 20,the lateral displacement of the structure with the semi-rigid connections tends to the structure with rigid connections.The results provide an initial estimate for the stiffness of connections and the preliminary mixing principles of precast concrete structures with hybrid connections.(2)A simplified method is proposed to estimate the elastic inter-story drift of PC structure with hybrid connections,which considers the parameters(stiffness parameter and position parameter)and positions(beam end and column end)of semi-rigid connections.The lateral stiffness of the structure with hybrid connections is the key to get the lateral displacement.Considering the parameters(stiffness parameter and position parameter)and positions(beam end and column end)of semi-rigid connections,the Muto's method(D-value method)is modified.A generalized simplified calculation method of the story stiffness and total stiffness matrix is obtained.Based on the simplified method of stiffness,the seismic action is obtained by the response spectrum method,and then a simplified analysis method of lateral displacement under seismic action of the PC structure is obtained.Through the analysis of the cases,it is observe that when only the semi-rigid postion(beam end or colunm end)changes,the story stiffness of the structure with semi-rigid connections on both beam ends and colunm ends is the lowest,the story stiffness of the structure with semi-rigid connections on beam ends only is slightly higher,and the story stiffness of the structure with semi-rigid connections on column ends only is the largest.The influence of the semi-rigid connections located in different parts of the beam ends or the column ends on the elastic inter-story drift under the seismic action of the structure is opposite to the influence of the story stiffness.(3)Based on the simplified calculation method for the elastic inter-story drift,the multi-objective optimization of the stiffness parameter of the semi-rigid connections and sections of beams and columns of the PC structure with hybrid connections is carried out.The performance-based plastic design(PBPD)method is used to get the yield moments of semi-rigid connections and to optimize the structure design.The PC frame structures are optimized under frequent earthquakes with the four specified inter-story drift forms and the lowest cost as the objective,the inter-story drift,axial compression ratio,and stiffness-gravity ratio as the constraint conditions,the sections of beams and columns and stiffness parameter of the semi-rigid connections as the optimization variables.Based on the optimization results under frequent earthquakes,the performance-based plastic design(PBPD)method is used to optimize the structure design.In order to verify the rationality of the optimization results,12-story frame structures and the 20-story frame structures with semi-rigid connections at different locations are analyzed using the proposed optimization process and the results of optimization are compared with the finite element results.Finally,the PBPD method is used to design the optimized 12-story structure(M1),and the finite element analysis is used to verify the rationality of the method. |
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