Study On A New High Strength U-Shaped Bolt Shear Connector

Steel-concrete composite beams with bolts as shear connectors have advantages of good construction quality,short construction period and disassembly.On the basis of previous research,a new U-shaped bolt shear connector was proposed in this paper.In order to fully understand the mechanical properties of U-shaped bolted shear connectors,it is necessary to study its shear capacity,load-slip curve,stiffness and mechanism.And provide theoretical basis for the design of such shear connectors.This paper mainly includes the following parts:(1)Seventeen push-out specimens with high-strength U-shaped bolt shear connectors were designed.The parameters include the bolt diameter,diameter of reserved aperture of concrete slab,screw spacing,anchorage depth and thickness of concrete slab.The test results show that the larger the length-diameter ratio is the better the anchorage effect of the bolt.Whereas,the failure mode of the pulling out of the concrete can be found.Increasing the bolt diameter can improve the shear bearing capacity,characteristic slip and shear rigidity of the specimens.The diameter of reserved aperture of slab and the thickness of concrete slab have moderate effect on the shear capacity of specimens.Reasonable diameter of reserved aperture of concrete slab can facilitate the assembling of specimens.The smaller the thickness of slab,the easier the cracking of concrete.Too small screw span will affect the stability of screw force transmission,leading to early failure of specimens.(2)The finite element(FE)software ABAQUS was used to simulate the test results of the push-out specimens.The appropriate material model,interaction and boundary conditions were selected.Based on test results,the shear damage parameters of the high-strength U-shaped bolt shear connectors were calibrated.The FE simulation results are in good agreement with test results.Based on this model,the force transfer mechanism and failure mechanism of high strength U-shaped bolt shear connectors were analyzed.The distribution and development of contact stress and internal stress of each component were analyzed.(3)Based on the FE model,the influence of bolt pretension force,concrete strength,grouting strength,diameter of reserved aperture of concrete slab,construction error and other parameters on the shear performance of such high-strength U-shaped bolt shear connectors is analyzed.Based on test results and theoretical analysis,a simplified formula for calculating the shear capacity and characteristic slip of U-shaped bolted shear connectors and a simplified load-slip model were proposed.The simplified calculation results are in good agreement with the test results.