Study On Earthquake Resistance Of Rigid Beam-to-Column Connection Of Steel Structure

Steel structure, which was supposed to have excellent earthquake resistant property, suffered a lot of brittle fracture during the American Northridge earthquake and Japanese Kobe earthquake. The brittle fractures mostly originated at the welded beam-to-column connections. For steel structure is widely used in many fields, investigation on the earthquake resistance of welded steel structure will greatly benefit the social and economic performance. The article aims to investigate the anti-earthquake property of rigid beam-to-column connections of steel structure. The earthquake resistance of rigid beam-to-column connections was analyzed and compared by establishing three-dimensional finite element models in great detail of web-bolted and flange-welded connection and welded connection. The results show that, compared with welded connection, both ends of the fillet weld of shear plate of web-bolted and flange-welded connection have obviously lower stress concentration factor. The elastic stiffness and bearing capacity of web-bolted and flange-welded connection are higher that those of welded connection. The web-bolted and flange-welded connection is recommended for its better combination property. The effect of geometrical configuration of weld access hole and strength of panel zone on the anti-earthquake property of rigid beam-to-column connection was investigated by three-dimensional elastic-plasticity finite element analysis. The fracture potential of the root of the access hole is greatly reduced through improving the configuration of access hole. For the improvement of earthquake resistant property is not obvious and the bearing capacity is pretty low, the connection with enlarged access hole is not recommended. The anti-earthquake property of connection with access hole configuration recommended by American Federal Emergency Management Agency is remarkably improved. However, it is impractical to set the angle at the intersection of access hole and beam flange as an important parameter controlling the configuration. It is recommended that the distance from the root of access hole to column flange replace that angle as a parameter. The optimum length of the distance is determined by the size of the groove weld of beam flange. Increasing the panel zone strength can remarkably reduce the fracture potential of the toe of fillet weld of beam web. The two reinforcement plates with a thickness of 6mm established at both sides of the panel zone would surely work. Three-dimensional finite element method was employed to investigate the effect of the strength mismatching of the groove weld of beam flange on the fracture toughness requirements in terms of stress intensity factor K and crack tip opening displacement (CTOD). As for rigid beam-to-column connections, the inelastic rotation angle of the beam flange is roughly linearly proportional to the requirements of fracture toughness. The overmatching butt groove weld of beam flange is recommended because the fracture toughness demands are much smaller and the possibility of brittle fracture of connections is lower. The effects of dynamic loading and prestrain which are the main characteristics of earthquake loading on the mechanical properties and fracture behavior of welded joints of structural steel (Q235B and 16Mn steel) were investigated by tests. The yield and tensile strength of the welded joints of the two kinds of materials increase under dynamic loading and prestrain condition that have little effect on the plasticity of structural steel. At room temperature, the fracture toughness of welds and parent metal of 16Mn and welds of Q235B increases under dynamic loading at the level of 50mm/s and 100mm/s compared with that under static loading. However, the fracture toughness of parent metal of Q235B obviously decreases under above-mentioned dynamic loading. The fracture toughness of welds and parent metal of the two kinds of materials decrease without exception under prestrain. It can be concluded that prestrain has greater unfavorable effect on the fracture toughness of welded joints of structural steel than dynamic loading. During designing beam-column connections and choosing materials, the effect of prestrain on the fracture toughness of materials should be given careful consideration.