Seismic Performance And Design Method Of Self-centering Prestressed Concrete Frames With Top And Bottom Friction Dampers

Seismic resilient structure,which are a fundamental part of resilience cities,play an essential role on improving the resiliency of urban and rural infrastructure.The self-centering prestressed concrete(SCPC)frame with enhanced performance characteristics,such as high construction assembly efficiency,small residual deformation and good resilience,has been developed as an important seismic resilient structure.However,this kind of structure may encounter some critical problems,such as large lateral displacement and insufficient shear capacity,when subjected to strong earthquakes.Hence,with the concept of combining the variable friction energy dissipation,post-tensioned(PT)self-centering and hidden corbel(HC)vertical-shear-resistance,a SCPC frame with hidden corbel and variable friction damper(HC-VFD-SCPC)was proposed in this dissertation.The new flag-shaped hysteretic feature including two-stage friction activation and third variable stiffness was achieved.The beam-column connection with self-centering,energy dissipation capacity and sufficient vertical shear capacity are constructed.This dissertation focused on the further improvement and seismic evaluation of the novel SCPC system through theoretical derivation,experimental analysis and numerical simulation.A performance-based seismic design method for the novel SCPC frame was established,and the seismic fragility analysis of the structure considering the failure of FDs and PT tendons was carried out.The detailed research results are listed as follows:(1)A new type of self-centering concrete frame system with variable and controllable post-stiffness was proposed,and a new“flag-shaped”hysteretic feature was achieved.The working mechanism of the SCPC connection with constant friction damper(CFD-SCPC)was analyzed.A HC was used in the CFD-SCPC connection to form a new configuration(recorded as HC-CFD-SCPC)to provide sufficient shear capacity.To acquire excellent seismic performance in terms of controlling higher mode effects and decreasing inter-story drifts,a new type of SCPC connection with HC and VFD(HC-VFD-SCPC)was proposed,in which the energy dissipation and stiffness after the decompression of the beam-column connections can be enhanced.The influence mechanism of the self-centering element,damper element and beam-column element on the load capacity and stiffness change history of the system was clarified,and a new flag-shaped theoretical hysteretic model with two inflection points and three stiffness was proposed.Combined with the construction of HC-VFD-SCPC,the theoretical basis for multi-stage seismic design was given.(2)The constant friction damper was optimized,and the pseudo-static test of the new CFD-SCPC beam-column connections was carried out under multiple working conditions.The combination of NAO friction material and Belleville springs was used to optimize the common CFD,which effectively improves the friction performance of the damper.Theoretical analyses and 14 tests were performed on a full-scale specimen,which were assembled two times,and the friction pads were replaced one time,to investigate the effects of various parameters on the performance of such CFD-SCPC beam-to-column connections.The influence of design parameters such as initial PT forces,friction forces,details of the friction damper and loading history on the hysteretic performance of the system in terms of stiffness,loss of PT forces,self-centering capability,energy dissipation capacity,and load capacity were analyzed.Based on the FEMA P-58,the resilience of the frame system with different parameters was evaluated.Based on the experimental results,theoretical analyses were carried out to study the influence of wear of NAO and loss of PT forces on the?_E,and the optimization effect of the combination of NAO friction material and Belleville springs on the friction performance of the system was verified.(3)A multi-condition pseudo-static test of the new HC-CFD-SCPC beam-column connections was carried out to reveal the self-centering mechanism of the beam-column connections.Varying the dimensions of HC,details of damper,friction material,two full-scale beam-column connection specimens were tested.The influence of the dimensions of corbel on the hysteretic performance of the connection was analyzed,and the influence of the number of friction bolts,the thickness of the external friction devices,and the energy dissipation ratio?_Eon the load capacity and energy dissipation capacity of the connection were studied.The influence of each design parameter on the first stiffness K₁ and the second stiffness K₂ of the connection was clarified.Finally,the effect of the initial damage of the damper(out-of-plane bending of external friction devices)on the energy dissipation of the system was studied,and the relationship between?_E,the maximum displacement of the structure,the energy dissipaters and the residual deformation of the structure was established,which is the key to evaluate the seismic performance of the structure.Combined with theoretical analysis,the design principle of hidden corbel-variable friction damper connection was proposed,which lays the foundation for the research and application of structure.(4)The seismic performance test of HC-VFD-SCPC was carried and the failure mode of self-centering concrete system with friction dampers was clarified.Taking the type of HC and the key parameters of the damper as variables,two HC-VFD-SCPC connection specimens,designed with steel hidden corbel(SHC)and concrete hidden corbel(CHC),respectively,were tested.The control mechanism of the slope sliding part angle?,the ratio of distance of the plane sliding part to distance of the slope sliding part,?,the stiffness of the combination of Belleville springs,K_CBS and the self-centering element on the post-decompression stiffness(K₂ and K₃),energy dissipation capacity,loading capacity was clarified and the control methods for the second activation of VFD was proposed.Based on the ultimate state test of the connection under large deformation(9.0%drift),the failure mode of the bolt-connected SCPC frame was analyzed,and seismic design criteria of“strong column-weak beam”and"repairable after earthquake"were given.(5)The finite element model of the HC-VFD-SCPC connection was established,and the parametric analyses of HC-VFD-SCPC frame were performed.The finite element model of HC-VFD-SCPC connection was established using Open Sees,and the model was verified based on the test results.Based on the performance objectives of the structure under different earthquake intensities,the design method of VFD was proposed.Based on the nonlinear time history analysis results of a 6-story and 8-story HC-VFD-SCPC frame,the influence of the K₂,K₃,and?on maximum inter-story drift,residual inter-story drift,and energy dissipation capacity was evaluated.Finally,the control effect of each parameter on the higher mode effects of the structure was evaluated,which provides reference for the investigation of seismic design method and seismic fragility analyses.(6)The multi-stage seismic performance objectives were determined,and the seismic design method of the HC-VFD-SCPC frame was established.Combining the seismic requirements of different earthquake intensities and the new“flag-shaped”hysteretic characteristics in terms of“two inflection points and three stiffness",the seismic performance objectives of the SCPC frame were proposed.Combining the working mechanism of each stage of the VFD,a seismic design method based on performance objectives was established.Based on the analyses of a design example,three design methods for controlling the weak story in the SCPC frames were given.Combined with FEMA P-58,the seismic performance and resilience of the self-centering frame with constant friction dampers and the self-centering concrete frame with variable friction dampers were compared.(7)The theoretical model of the HC-VFD-SCPC beam-column connections considering the bolt bearing was established,and the seismic fragility assessment based on the failure of VFD and the yield of the PT tendons was carried out.The theoretical model of shear force-deformation from the process of bolt bearing to failure was derived,and the load capacity of the HC-VFD-SCPC connections during the whole process was obtained,and its theoretical hysteretic model was established;A finite element analysis model considering bolt failure was established in the Open Sees finite element analysis platform,and the model was checked based on the ultimate state test.Combining FEMA P-58 and FEMA 356,the nonlinear incremental dynamic analyses and seismic fragility analyses were carried out on a HC-VFD-SCPC frame,and the exceedance probability of the structure in different damage states was studied.The seismic performance of the structure during the whole process from the bolt bearing to the failure of VFD was analyzed,and the resilience of the structure after the earthquake and the redundancy of the collapse capacity were explored,which provides a theoretical basis for the resilient design of the structure.