Investigation On Performance And Design Method Of High Strength Steel Welded And Bolted Connections

Compared with ordinary strength steel structures,high strength steel structures could reduce the steel consumption,transportation and installation costs,due to their advantages in economical benefit,sustainable development,energy conservation and emission reduction.However,the the performance of high strength steel,welding materials,members and connections,would be changed.The design method and design theory need to be updated.This research forms part of the fundamental work to underpin the development of the specification for design of high strength steel structures.By means of a large amount of experimental and numerical investigations,the performance of high strength steel welded and bolted connections was studied in this dissertation.The design suggestions and calculation formulae were proposed.The main research works covered in this dissertation include:(1)The test data of 5 grades of structural steels(i.e.390 MPa,460MPa,550 MPa,690MPa and 890MPa)and 4 types of welding materials were obtained by monotonic tension tests and have been used to establish the exponential-hardening constitutive model.Meanwhile 3 grades of structural steels(i.e.390 MPa,550MPa and 690MPa)and 4 types of welding materials were numerically calibrated for the void growth model(VGM)and the stress modified critical strain mode(SMCS),due to circumferentially notched tension specimens.(2)A total of 14 transverse fillet weld specimens,9 longitudingal fillet weld specimens,27 bearing-type high strength bolted connections and 19 slip-critical high strength bolted connections were tested under static tension to investigate the influence of grade of material strength and geometric sizes on the strength and deformation.(3)The finite element numerical models of high strength steel welded and bolted joints were generated and carefully validated,based on the test results in this dissertation and other literatures.(4)Two micromechanics-models VGM and SMCS had been used to accurately predict the ductile fracture of high strength steel transverse fillet weld specimens.Using numerical methods the length reduction coefficient of high strength steel longitudingal fillet weld specimens were calculated.The current design method for welded connections is still applicable for high strength steels.(5)Based on the criterion of bolt hole deformation,the numerical analysis was conducted on the bearing capacity of 460 MPa,550MPa,690 MPa,800MPa,890 MPa and 960 MPa high strength steels.The influence of the steel strength,edge distance,end distance,plate thickness,bolt diameter and bolt hole clearance on the bolt hole bearing strength was studied.A new formula of bearing strength was suggested according to the failure modes of steel plates in bolted connections for high strength steel.