Research On Crack Resistance Of Segmental Precast Bending Members With Epoxy Joints

The segmental precast bridge belongs to a branch of the prefabricated building,which is being used widely in constructions of railway bridges.Prefabricated bridge can help minimize traffic delays and community disruptions by reducing onsite construction time and improving quality,traffic control and safety.The epoxy joints are the main joints forms between segments.In the last years,there were few studies based on the mechanical properties of the prestressed concrete beams with epoxy joints mainly subjected to bending.In the code for design of railway bridges,there was no clear provision for checking the crack resistance of components with epoxy joints.The static load test and the finite element numerical simulation method were used to study the crack resistance of the segmental precast concrete beams with epoxy joints.The main work and conclusions are as follows:(1)The calculation formulas for checking the crack resistance of the prefabricated components with epoxy joints that in the design code of highway and railway bridges at home and abroad were introduced and compared.Combined with recent engineering cases and application studies on railway bridges with epoxy joints,relevant crack resistance formulas were analyzed.(2)Five prestressed concrete prefabricated assembled test beams with epoxy joints were designed,manufactured and statically loaded.The length of three test beams is1.84m,and the length of the other two test beams is 2.08m.The cracking load of the test beams were analyzed and compared with the existing related formulas for crack resistance.The test results show that the existing formulas for checking the crack resistance of the bending members with epoxy joints underestimated the crack resistance of the members.(3)Combined with the test results of bending beams with epoxy joints and the existing related researchs,a proposed formula for checking the crack resistance of the railway bridges with epoxy joints is proposed in this paper.(4)The failure form and crack extension of the bending beams were recorded.The failure were caused by the crushing of the concrete near the epoxy joints in the compression zone near the loading point,resulting in the loss of bearing capacity.The cracking positions of the test beams were located near the epoxy joints,and basically extended upward along the epoxy joints under the load,and there were no cracks in other positions.(5)The load-displacement relation of the test beams,the relation of the strain along the beams height,the stress-strain difference at the epoxy joints and the stress change of the prestressed steel bars were analyzed.Compared with the elastic modulus E_c of concrete,the elastic modulus E_j of the material in the epoxy joints area decreased to a certain extent,E_jwas about(0.62～0.84)E_c,and the average value was about 0.73 E_c.(6)The numerical analysis models of the bending beams with epoxy joints were established.The process of the test beams from cracking to loss of bearing capacity were analyzed and simulated.The calculation results are in good agreement with the test.(7)Three groups of prefabricated bending members with epoxy joints and three groups of integral bending members were designed and manufactured,and four groups of them were pre-reinforced with Carbon Fiber Reinforced Plastic(CFRP).When CFRP was pasted in the area near the epoxy joints,the phenomenon that the epoxy joints were easy to crack could be improved.