Study On Seismic Performance And Design Method Of Self-Centering Steel-Concrete Hybrid Frame Structure

To improve the seismic performance of traditional precast concrete structures,an innovative self-centering steel-concrete hybrid frame(SH)frame,which combines the advantages of the bolted connections in construction ability and the post-tensioned connections in resilient performance is proposed in this thesis.The proposed SH frame is assembled by prefabricated prestressed reinforced concrete(RC)columns and prefabricated prestressed steel-concrete hybrid(PPH)beams using steel end plates and high-strength bolts.Among them,the PPH beam is assembled by two short steel arms and a prefabricated RC beam using post-tensioned(PT)unbonded steel strands as self-centering elements and web friction devices(WFDs)as energy dissipation elements.Compared with traditional self-centering RC frames,the proposed SH frame can achieve the prestressing within the PPH beam,avoiding the complex prestressing procedure in multi-span frames.In the proposed frame,the self-centering ability was mainly provided by the elastic deformation of the PT steel strands,and the energy dissipation capacity was mainly provided by the WFDs and the plastic deformation of steel arms and the column feet by stages.If designed rationally,the aforementioned SH frame can achieve many merits such as convenient construction and functional recovery after earthquake excitation,and has a promising future in engineering application.In this thesis,the seismic performance of the SH frame structure system was thoroughly explored from a structural member to the overall structure by pseudo-static tests,theoretical modeling,and numerical analysis,and the main achievements were as follows.(1)Quasi-static tests were conducted on five SH beam-column connection specimens,two SH frame specimens,and one non-prestressed hybrid(NH)frame specimen to investigate the hysteretic behavior.Firstly,a prestressing technique within the single-span beam was developed,and there is no need for direct contact between the oil jack and the anchor in the proposed technique,whose feasibility was verified by the experiments of the SH beam-column connections and the SH frames.Then,the damage evolution mechanism of the connections and the SH frames was summarized and analyzed.The hysteresis curve,skeleton curve,displacement ductility ratio,self-centering ability,energy dissipation capacity,stiffness degradation,variation of stresses of the PT strands in the PPH beams and the stress developments of critical parts of each specimen were studied and analyzed in detail.The influence of the initial prestress in the PPH beams and the friction force in the WFDs on the seismic performance of the connection and the frame were analyzed.(2)A theoretical model for predicting moment-rotation relationship of the SH beam-column connection was carried out based on the two connection interfaces,namely,the bolts-extended endplate connection interface and the opening-and-closing interface in the PPH beam,respectively.Based on the elastic model of the PT strands and the rigid-plastic model of the WFDs,a two-stage theoretical model of the moment-rotation relationship of the opening-and-closing interface was proposed,which considers the prestress loss of the PT strands and the softening behavior of the steel arms.The calculated results were in good agreement with the experimental results.In addition,the calculation formula of shear bearing capacity of the two connection interfaces was also proposed based on the model mentioned above.(3)Based on the software Open Sees,the finite element(FE)models of the SH beam-column connections,the SH frames,and the traditional RC frames were established to investigate the cyclic behavior.Among them,the modeling method of EPPG material considering damage for the zero-length element was proposed to simulate the prestress loss of the PT strands and the softening behavior of the steel arms.Then,the reliability of the FE models of the SH beam-column connections and the SH frames was verified by comparing and analyzing the results between the FE models and experiments in the aspects of the hysteresis curves,skeleton curves,residual deformation curves,cumulative energy dissipation curves and stress curves of the PT strands in the PPH beams.Then,the corresponding parametric studies were also carried out with the main parameters being the arrangement of the PT strands in the PPH beams,the friction force of the WFDs,the length of the steel arms,the strength of the steel arms,the reinforcement ratio of the longitudinal reinforcement in the column,et al..Through the comparison between the test results of the SH frame and the FE results of the RC frame,the advantages of the SH frame structure are further verified in terms of earthquake resistance.(4)A performance-based seismic design method for the SH frame structure was proposed based on the experimental and finite element analysis results.Firstly,a four-level seismic fortification objective of the performance-based design was defined as “ no damage under minor earthquake,maintenance free under moderate earthquake,replaceable under major earthquake,and no collapse under mega earthquake”;Secondly,the seismic design procedure was proposed for achieving the targets mentioned above,including the design of SH beam-column connections,the PT strands in the PPH beams,the WFDs,et al.Then,the recommended values were put forward to control the moment of gap-opening,the self-centering ratio,the energy dissipation coefficient,the relationship between the column moment and the beam moment,and the minimum reinforcement ratio in the column;Finally,some general design regulations and construction measures of the SH frame structure were put forward.