Seismic Performance Investigation Of A Novel Prefabricated Concrete Frame Joint With Composite Disc Springs And SMA Bars

Prefabricated concrete structures have significant significance for the development of construction industrialization due to their advantages such as short construction period,stable quality,construction safety,environmental protection,energy saving,and standardized technology.However,compared to traditional cast-in-place concrete structures,the connection problem of prefabricated concrete structures is the main bottleneck restricting their application in high-intensity seismic zones.Based on this,this paper proposes a new type of connection form for prefabricated concrete frame beam-column joints.By using shape memory alloy(SMA)bars with self-resetting function at the beam end and combining it with a composite disc spring device,the aim is to reduce damage to the frame joints and achieve self-resetting function of the frame structure.Through literature research,experimental studies,and theoretical analysis using a multi-dimensional analysis method,this paper systematically studies the seismic performance of the new joints.The main work and achievements are as follows:(1)Four prefabricated half-scale exterior beam-column joint specimens and one cast-inplace half-scale exterior beam-column joint specimen were designed and fabricated for comparative tests under horizontal low-cycle reciprocating loads.According to the test results,the failure mode of the new joint is plastic hinge failure at the beam end,which meets the design requirement of "strong column,weak beam." Moreover,the connection method using fully grouted sleeves can achieve the effect of "equivalent cast-in-place."(2)The seismic performance indicators of each joint specimen,including failure mode,hysteresis characteristics,stiffness degradation,ductility capacity,energy dissipation capacity,and residual deformation,were analyzed.The analysis results show that the disc spring device can move the plastic hinge of the frame joint away from the core area of the joint,improving the energy dissipation capacity and ductility of the structure.The maximum increase in cumulative energy dissipation is 32.1%,and the maximum increase in ductility is 25.1%.The SMA bars provides good self-resetting performance for the joint,reducing the structural residual deformation by approximately 3%.(3)By considering the tensile stiffening effect of longitudinal reinforcement,the effective stiffness method was extended to study the load-displacement variation law of beam-column joints before failure.The joint was divided into three stages based on the elastic-plastic behavior of the component: the pre-cracking elastic stage,the crack propagation stage,and the plastic stage.The effective stiffness of the test joints was theoretically calculated in each stage,and the horizontal displacement of the column top was calculated based on the effective stiffness.The theoretical calculation results agree well with the experimental results,although overall,the theoretical results are slightly underestimated.(4)Considering the structural characteristics of the built-in disc spring device and SMA bars in the new joint,the section analysis method was used for theoretical analysis to provide a load-bearing capacity calculation formula suitable for this joint,which was then validated.The results show that the theoretical values match the experimental values,indicating sufficient safety reserves.