FRACTURE BEHAVIOR OF BEAM-COLUMN CONNECTIONS USING HIGH STRENGTH STEEL BASED ON FRACTURE MECHANICS

To investigate the fracture behavior of beam-column connections using high strength structural steel Q460C with nominal yield strength of 460MPa, which is widely applied in China in recent years, fracture toughness of weld metal and heat affected zone (HAZ) of Q460C high strength steel was calculated based on fracture mechanics in this study. A three-dimensional finite element fracture model was proposed to provide quantitative estimates of fracture toughness demands in terms of the elastic stress intensity factor (K_I) and inelastic J-Integral (J_I) around crack tips. The elastic analyses indicated that K_I was distributed along the width of beam flange as a ‘W’ shape, with the maximum value appearing at the center of beam flange, and was linearly related to the nominal bending stress, while the initial crack at weld interface required more toughness demands than the crack at HAZ. The elasto-plastic analyses indicated that J_I approached the maximum value at the edge of beam flange and initial crack at weld interface required less toughness demands than that of the crack at HAZ. Based on the results, fracture of the connection was more likely to occur at weld interface area, and the critical resistance was approximately the plastic load of beam section, with a critical rotation of less than 0.02rad. It is recommended that welding techniques or local configurations be improved to guarantee adequate rotation capacity.