Mechanical Properties Of Single-bolt Lap Shear Connection Of Cold-formed Thick-walled Steel

As a kind of steel structure,cold-formed steel has a satisfactory ratio of strength to weight compared with hot-rolled steel.With the improvement of production technology,more and more cold-formed thick wall steel is applied in architectural design.According to the Chinese,European and American codes,it can be found that the calculation of the bearing capacity of cold-formed thick wall steel bolt connections is based on the research results of hot-rolled section steel.The calculation formula is exactly the same as that of hot-rolled section steel,and its applicability to cold-formed thick wall steel has yet to be verified.Therefore,the main research work of this paper is as follows(Bolt end distance:the distance from the edge of the plate to the center of the bolt hole along the direction of force;Bolt pitch:the distance from the edge of the plate to the center of the bolt hole perpendicular to the direction of force;d0 is the bolt hole diameter):(1)single bolt double shear joint test.The effects of plate thickness,bolt end distance and side distance on shear capacity and deformation capacity were investigated through 54 double-shear connectors.The connecting plate includes three kinds of cold-formed steel plates with different thickness of 2mm,6mm and 10mm.The end distances are 1.0d0,1.2d0,1.5d0,2.0d0 and 2.5d0,respectively.The margins are 1.0d0,1.2d0,1.5d0 and 2.0d0,respectively.(2)single bolt single shear joint test.36 single shear joint tests were carried out.The joint plates included 10mm cold bent plate and 10mm hot rolled plate.The end margin is the same as the double shear test.The effects of different joint materials(cold formed or hot rolled)and plate warping on joint bearing capacity and deformation capacity were investigated.The results show that:(1)there are three failure modes in both double shear joint and single shear joint:hole wall pressure failure,shear failure(fracture failure and tear failure)and net section failure.(2)in the double shear test,when the net section failure occurred,the specification underestimated the shear bearing capacity of steel plates with 2mm and 6mm joints,by 12.8%and 5.0%,respectively.When the steel plate is a 10mm connector and the bolt spacing is 1.0d0,the code underestimates the shear capacity by 9.3%and overestimates the shear capacity by 7.4%when the bolt spacing is 1.2d0.When shear failure occurs,the prediction of the bearing capacity of the European code is conservative,underestimating the thick-walled steel by about 26%.The American specification overestimated the shear capacity of joints in the interval of 1.90d0<e1<2.80d0,and the maximum overestimated value was 11.3%when e1=2.50d0.(3)steel plate warping in single shear joints will reduce the bearing capacity of joints.The shear capacity of cold bending-cold bending joints was reduced by 5.1%on average.For cold-bending-hot-rolled type connectors,the average reduction of about 4.7%.(4)in the single shear test,when the joint plate is cold bending-hot rolling,the damage occurs in the hot rolling steel plate.Compared with the cold bending-cold bending of the joint plate,the shear capacity of the cold bending-hot rolled joint is about 3.9%lower and the deformation capacity is more than 10% higher.