The Effect Of Brittle Fracture Performance Of Energy Release Rate On Stud Welded Steel Connections

With the rapid development of national economy, steel structure is widely used in many fields, such as large industrial equipment, factories and bridges, especially on buildings, because of its good mechanical properties, economic performance and service performance. However, in the Northridge Earthquake and Hyogoken-Nanbu Earthquake, it can be seen that many destructions of steel structure buildings resulted from the failure destruction of welding beam-column nodes, which the crack in the steel node connections resulted in the brittle fracture of steel structure due to the effects of welding process in most cases. The domestic code for design of steel structures for the control of brittle fracture of steel structure was far from perfect at present, whether the components'brittle fracture will take place or not, which can not carry out quantitative accurate judgment and analysis.Aimed at beam-column stud welded connection joints of disabled steel structure in the Northridge Earthquake, this paper used the fracture mechanics as theoretical foundation, and applied the crack modelâ… , and used the theory of J integral equal to the energy release rate theory as the research premise under the linear elastic situation, and used large finite element software ABAQUS6.9.1, and selected low carbon steel Q235B, and adopted different section forms and size beam-column stud welded connection nodes, and utilized collapsed elements technique to simulate the singular stress field around the crack tip, and modeled six groups of nodes, and analyzed energy release rate of around the crack tip to effect brittle fracture property of steel structure nodes, and then provided some auxiliary foundations for the judgment and analysis of brittle fracture of steel structure in the future. The results indicate that the maximum energy release rate around the crack tip occurs at beam lower flange. The energy release rate around the crack tip decreases with increasing the beam-column section under the same load. When column section is unvarying, the energy release rate around the crack tip decreases with the increase of beam section and reduces as the increase of Young's modulus and largen as radius of gyration increases, in other words, the bigger beam section moment of inertia is, the stronger the node bearing capacity is. The fracture property of the steel node of square column and H-beam is better than that of the H-steel node, and the square steel node's the maximum energy release rate around the crack tip is smaller than the H-steel node's. Crack unstable failure in two connection nodes takes place in different positions, that is to say, crack unstable failure of the H-steel column node takes place in the center of column weld interface while that of the square steel column node occurs at the edge of column weld interface 150mm.In addition, the crack located in beam lower flange ripped prior to one located in beam upper flange. Before the energy release rate around the crack tip achieves the maximum energy release rate, flexural buckling will successively come about at the crack of beam upper flange and column stiffener corresponding it, which will reduce critical energy release rate around the crack tip located in beam lower flange. The load action position has no effect on the energy release rate around the crack tip. As long as load achieves fracture toughness, crack unstable propagation occurs. Besides, material Young's modulus has effect on the energy release rate around the crack tip.