Study On The Mechanical Properties Of Prefabricated Concrete Beam And Slab Composite Joints

With the development of prefabricated building,the prefabricated reinforced truss concrete composite structure develops rapidly to solve the problems of poor integrity of fully prefabricated structures,large consumption of cast-in-place structure formwork and long construction period.At present,the commonly used beam-side composite slab support joints are mainly composed of precast slabs with overhanging reinforcement,post-poured concrete layers and beams.However,the reinforcement of the slab edges causes problems such as low production efficiency in factory,inconvenient transportation and the construction site installation is difficult,which seriously hinders the popularization and application of components.So it is urgent to develop the composite slab without reinforcement at the support to replace the traditional composite slab,solve the problems in the production,construction,installation,and specification the standardized production of the composite slabs and other components in the factory.It provides references for engineering applications and promotes the rapid development of assembly buildings.This paper proposes a new beam-slab composite(reinforced lap)joint structure with no reinforcement on the prefabricated bottom plate,and designs test pieces to carry out mechanical performance tests and finite element simulations.A total of 13 specimens were produced,including 6 bending specimens,4 in-plane shear specimens and 3 specimens under in-plane reversed cyclic loading,and appropriate test equipment,loading devices and loading methods were selected for the test.In the bending test,the crack shape,failure characteristics,load-deflection curve,reinforced concrete strain,bearing capacity and deformation capacity of the specimens were compared and analyzed.The results show that be compared with the cast-in-place joint,this beam-slab composite(reinforced lap)joint structure with no reinforcement on the prefabricated bottom plate can effectively improve the crack development pattern and failure location,reduce the width of the crack,increase the bearing capacity,and have better ductility.At the same time,a short-term stiffness formula is established by considering the coupling effect.By comparing the calculated value with the test value,it is found that the formula can well reflect the bending stiffness of the specimen.In the in-plane shear test,the crack shape,failure characteristics,load-deflection curve,reinforced concrete strain and bearing capacity of the specimen were compared and analyzed.The results show that the beam-slab composite(reinforced lap)joint structure with no reinforcement on the prefabricated bottom plate can increase the shear stiffness of the specimens,reduce the width of cracks and make the distribution of cracks more uniform.The bearing capacity of reinforcement lap joint is not much different from that of direct extension reinforcement and they have a good ability to transfer horizontal loads.Based on concrete structure design code in China and the relevant codes of the American,the calculation formula of shear capacity is obtained,and it is found that the calculation value is in good agreement with the test value,which provides a certain reference for the project.Under in-plane reversed cyclic loading test,the failure characteristics,hysteresis curve,skeleton curve,bearing capacity,stiffness degradation and energy dissipation capacity of the specimens were compared and analyzed.The results showed that the beam-slab composite(reinforced lap)joint structure with no reinforcement on the prefabricated bottom plate is superior to the reinforcement of the slab edges joint in all aspects,and has a good ability of transfer of the seismic load.The numerical model of beam-slab composite(reinforced lap)joints structure with no reinforcement on the prefabricated bottom plate of prefabricated concrete beams and slabs was established with the finite element software ABAQUS,and the load-deflection curves and failure modes obtained were compared with the results obtained from the original tests,so as to verify the rationality and effectiveness of the established model and provide a certain finite element reference for the actual engineering.