Seismic Performance Of Precast Recycled Concrete Members With Pressed Sleeve Connections

Precast concrete is the main direction of development of the construction industry.Precast concrete structures are distinctive and have been developing rapidly in recent years,a reliable connection system is the key factor to ensure its seismic performance.Recycled aggregate concrete(RAC)is green,energy-saving and emission-reducing,but it is less used in precast concrete structures.In this paper,RAC was used in precast concrete structural members,and pressed sleeves were used to connect the longitudinal reinforcements in the post-cast area.The seismic performance of the precast RAC structures was investigated through a combination of experimental research,numerical simulation and theoretical analysis,providing an engineering basis for the application of pressed sleeves and RAC in precast structural members.The main tasks and conclusions are as follows:(1)A precast beam-column joint with vertical longitudinal reinforcements connected by pressed sleeves was proposed,with the upper and lower precast columns and the left and right precast beams prefabricated using recycled fine aggregate(RFA)concrete and the core joint using normal aggregate concrete(NAC).Seven precast specimens with RAC and two precast specimens with NAC connected by pressed sleeves,and one cast-in-situ specimen with RAC were subjected to cyclic loading tests,and the results showed that the spliced joint connected by pressed sleeves could transmit forces effectively and that RFA concrete could be utilized in precast beam-column joints,the seismic performance was similar to that of traditional cast-insitu beam-column joints.(2)A precast column with longitudinal reinforcement connected by pressed sleeves in the plastic hinge area at the base of the column was proposed,where both the upper precast column and the post-cast area were cast with RFA concrete.Eight precast specimens with RFA concrete,one precast column specimen with NAC connected by pressed sleeves,and one fully cast-insitu specimen with RFA concrete were subjected to cyclic loading tests.The results showed that the spliced joints connected by pressed sleeves could transmit forces effectively,and RFA concrete could be used in precast columns with seismic performance similar to that of cast-insitu columns.(3)A precast shear wall with pressed sleeves at the bottom and lapped spliced connections for vertical longitudinal reinforcements in the wall and the edge members was proposed,with precast wall panels and post-cast connection areas cast with RFA concrete.Eight precast specimens with RFA concrete,one precast specimen with NAC connected with pressed sleeves,and one cast-in-situ specimen with RFA concrete were subjected to cyclic loading tests.The results showed that the seismic performance of precast shear walls with RAC using pressed sleeve connections was similar to that of cast-in-situ shear walls.(4)The finite element method was established and simulated for the beam-column joints,columns and shear walls of the precast RAC specimens with pressed sleeve connections,and the comparison between the finite element analysis results and the test results showed that the established finite element models could simulate the loading curves accurately,unloading curves,peak loads,residual deformation,bearing capacity,failure modes,which basically reflected the behavior of the specimens in the proposed cyclic test.Then,by varying different parameters of the finite element model,the research scope of the three members proposed in this paper was extended and supplemented to analyze the variation of their seismic performance under different parameters.Based on the finite element results,the mechanism of the pressed sleeve in the post-cast area of the member was analyzed.The results showed that the pressed sleeve affected the concrete stresses in its vicinity,and corresponding structural measures should be taken in practical engineering to avoid the early spalling of the concrete protection layer in the post-cast area.(5)With reference to the current Chinese code,methods for calculating the load carrying capacity of the precast RFA concrete beam-column joints,columns and shear walls connected by pressed sleeves were proposed,which was accurate in predicting the damage mode and load carrying capacity of the members.Based on the simplified skeleton curve model and the regression analysis of the stiffness degradation data,the restoring force model of the precast RFA members connected by pressed sleeves was proposed,which can reflect the hysteretic performance of the specimens.In conjunction with the processing,fabrication,lifting,splicing and operation of the test specimens in this paper,as well as the experimental study,finite element simulation and working mechanism analysis,a number of suggestions were given for the design process of the precast RFA members connected by pressed sleeves.The results of this study,such as the connection form,working mechanism,calculation method and application analysis of the precast RAC members connected by pressed sleeves,could provide reference for the relevant design,and have important academic value and engineering application.