Study On Seismic Behavior Of Q460 High Strength Steel Welded Cruciform Beam-column Connections

In this paper,from the two aspects of improving the stress distribution in the connection area and the plastic hinge displacement,the seismic performance of the cruciform high strength steel beam-to-column welded connections with different local connection structures(different welding hole forms and locally widened beam flange)was studied through the pseudo-static loading tests and finite element simulations of the connection specimens.On this basis,eight improved connection specimens were designed to explore the seismic performance of the improved connections.The specific work is as follows:Firstly,the material properties of Q460 D steel and ER55-G welding material used in connection specimens were tested to obtain the mechanical properties such as elastic modulus and yield strength,and the key data points of material plasticity were obtained by processing the test results,which was prepared for the finite element analyses in the following part.Secondly,four cruciform Q460 high-strength steel beam-to-column welded connection specimens were designed.Different forms of welding holes were adopted for three connection specimens,and the structural form of side plate partial reinforcement beam flange was adopted for the other connection specimen.Quasi-static tests were conducted for the four high strength steel beam-to-column connection specimens,and the plastic deformation,hysteretic performance,energy dissipation coefficient and shear deformation of the connection specimens were analyzed.The results show that the seismic performance of the connection is basically not affected by the shape of the welding hole,and locally widening the beam flange can improve the initial stiffness,yield displacement and load of the connection,but the bearing capacity and ductility of the connection were not effectively increased due to the fracture of the connection area in the test.The improved welding hole and FEMA welding hole improve the ductility of the connection,but FEMA welding hole makes the bearing capacity of the connection lower.Then,the material data were substituted into the ABAQUS finite element analyses of the connection tests,and the finite element analysis results are in good agreement with the test results.By predicting the fracture of the connection and analyzing the stress path,it isconcluded that local side plate strengthening and JGJ improved welding hole have no obvious effect on the stress of the middle unit of the flange at the welding hole,and FEMA welding hole can effectively reduce the stress concentration around the welding hole.With the increase of beam end displacement,the stresses of the initial section and arc section of welding hole were increased obviously.The difference of stress values of webs of different structural connections is mainly shown in a certain range above the welding hole in the tensile section(below when the upper flange is under tension).At last,eight improved high strength steel connections were designed,including two singly strengthened connections,two singly weakened connections and four weakened connections,to study the influence of different local structural improvement forms on the seismic performance of high strength steel connections.The stress values in the direction of flange length far from the connection area,in the middle of the web near the connection area,were increased for the strengthened connections,while the stress around the welding holes was reduced to some extent,which not only increased the bearing capacity of the connections,but also prevented the fracture at the connection weld.The design of reasonable weakened connection can realize the goal of shifting the plastic hinge out while ensuring a small reduction in the bearing capacity of the connection,and the recommended design parameters are given.