Seismic Performance Study On Self-centering Prefabricated Concrete Frame With Hub-type Connection

Thousands of important buildings with emergency needs have faced problems like endless maintenance and reinforcement or tedious construction procedures after the earthquake.In view of the demand for functional recovery of such buildings,the concept of self-centering structure was proposed at home and abroad,which aimed to relax part of the constraints so that the whole structure could automatically recover to the pre-earthquake location and continue to bear the load.In this paper,a self-centering prefabricated concrete frame with hub-type connection(HSCF)is designed in an innovative way.The beams,columns and foundations are separately prefabricated,and then be assembled by unbonded prestressed tendons to realize the structure rocking and recentering.The numerical analysis method is used to study the seismic performance of the frame and verify its mechanical performance,through which a new design means for the low-rise multi-span structure with high seismic demand are provided reasonably.The main work carried out is summarized as follows:(1)The design of HSCF was deepened based on the prototype building and the two parts of the beam end and the column base are selected as the object of study.Through abstract mechanical model combined with the small deformation assumption,the axial force,shear force,bending moment and prestress expression of the beam end and column base were derived,while the frame reached a certain horizontal displacement value.(2)An edge joint and an interior joint were choosed from the HSCF.According to different tendons layout and initial prestress,these joints were derived into 6 research objects.The reasonable contact and prestress definition manners of analogous self-centering prefabricated beam-column joints were determined at first to verify the validity of analysis methods,then the finite element analysis software was utilized to complete the three-dimensional modeling of the HSCF.The calculation obtained "flag-shaped" hysteresis curves of these joints,showing the typical self-centering characteristics.The stress analysis also exhibited controllable damage of the components.According to the load-displacement hysteresis curves,the seismic performance including energy dissipation and ductility of the joint was further investigated.(3)Numerical analysis of frames with four different hub-type connecting forms including full prestress,partial prestress,and no prestress were carried out.The force mechanism of hub-type connection was analyzed by examining the whole process of the nonlinear stress subjected to low-cycle repeated loading.From the aspects of stress distribution,hysteresis performance,energy dissipation,ductility and residual deformation,the four frames were compared and the important influence of unbonded prestressed tendons in the frame was analyzed.The main features and performance advantages of the full-prestressed HSCF were obtained.(4)The parameters analysis was carried out on the full-prestressed HSCF.On the basis of standard model,a total of 11 parameters including the bolt preload,initial prestress value,friction coefficient of the contact surface,material strength and reinforcement ratio,frame geometry were changed.Different factors on the hysteretic behavior of the frame were thus be studied,and at the same time the construction design means that was conducive to seismic performance were found.