Mechanical Performance Of Composite Joints In Primary And Secondary Beam Connections

The steel-concrete composite beam is tensioned in the positive bending moment area,and the concrete is compressed,which can give full play to the performance of the two materials.However,in the negative moment area,cracks are easily generated on the concrete floor under tension,which will affect the structural appearance and normal use.The primary and secondary beam connections are usually designed as hinge joint at present.While in actual engineering no joints can be completely free of negative moments.Negative moments would cause tensile stress on the concrete floor and even cause cracking.There have been cases of cracks in composite floor in actual engineering,which shows that the design of the combined joints in the negative bending moment area is not enough,and the research on the combined joints of the primary and secondary beams needs to be further studied.This paper conducted research on the primary and secondary beam composite joint.Based on the field monitoring of the main and secondary beam joint areas of two projects under construction,the causes of concrete slab cracks in the project were analyzed.And the effects of different main and secondary beam joint forms and different construction processes on the stress of slab reinforcement were studied.A composite joint of primary and secondary beams with end-plates connected was proposed.On this basis,five primary and secondary beam composite joints were designed and subjected to static loading test.The influence of reinforcement ratio of the slab under negative bending moments,the crack development mechanism of the floor and the mechanical properties of the joints are studied.Based on the experiments,the ABAQUS finite element software was used to analyze the end-plate connection composite joints.The influence of the floor reinforcement ratio,the strength of the steel bar,the strength of the steel beam and the position of the bolts on themechanical properties of the joints were studied.The calculation method of elastic flexural bearing capacity and crack control method in the negative bending moment area of the primary and secondary beam end-plate connection combined joints were proposed.The research results of this paper indicated: The stress on the concrete slab is the key factor that slab cracks in the project.Properly increasing the reinforcement ratio of the concrete floor can increase the joint bearing capacity and effectively control the development of cracks.The use of corrugated steel plate made the floor deformation earlier than the reinforcement,which was beneficial to the joints.The working performance of hinged joints,rigid joints and end-plate connection joints was obvious.End-plate connection joints had good working performance and can meet engineering design requirements.The proposed design method can provide a reference for further theoretical research and engineering design of primary and secondary beam end-plate connection joints.