Research Of Seismic Demage And Anti-seismic Ductility Strategy Of Beam-column Connections For Multistoried And Tall Steel Structures

As more and more multistoried and tall steel structures appeared in China recent years, seismic performance of beam-column connections for steel structures is becoming more and more predominant, if not handled properly, steel structures which are regarded as having good seismic performance may suffer greet demage, the seismic damage in Northridge and Hyogoken-Nanbu earthquakes of beam-column connections proved the importance of ductility design for connections deeply.Plenty of beam-column connections occurred brittle failure in American Northridge earthquake in 1994 and Japan Hyogoken-Nanbu earthquake in 1995, the causes of this phenomenon can be summarized as follows:issues related to the earthquake ground motion; issues related to design; issues related to welding; issues related to steel and other issues. The measures to prevent brittle failure of beam-column connections should take selection of materals, design, construction and inspection into account.The improvements of connections after the earthquakes are mainly on:(â… ) Reduce the stress concentration. The methods that can be used are:improve the cope hole; deal with the backing strip used for beam flange; strict the requirements for welding; reduce welding defects; remove the cracked parts; partial substitution of components. (â…¡) Remove the plastic hinge away from the column face. The methods that can be used are:local reinforcement measures and local reducing measures. Haunched connections and coverplate connections are included in local reinforcement measures, reduced beam section connections and slotted web connections are included in local reducing measures. Results of experiments and finite-element analysis manifest that these connections have good anti-seismic ductility.In addition, the factors influencing anti-seismic ductility of steel connections also consist of column webs transverse stiffener, panel zone yielding, strong column weak beam requirements, weak axis column bending, lateral torsional and local buckling, deep columns, box columns, effect of composite slabs, thermal effects, dynamic effects. This article discuss how these factors influecne anti-seismic ductility of connections based on the experiments done by the joint establishment of FEMA-SAC, give the requirements in order to get good anti-seismic ductility of connections influencing by these factors too.The yield mechanisms and failure modes dominate the anti-seismic ductility of all connections.Yield mechanisms provide a location and source of yield deformation where large plastic rotations can occur before fracture or deterioration of connection resistance can develop. Failure modes result in fracture and loss of resistance. The yield mechanisms and failure modes of the common connections are given in this article.By comparing Chinese codes with the results of exotic researchs, the design parameters which influence anti-earthquake ductility of connections not considered in Chinese codes are given, this thesis also outlooks the development direction of Chinese codes about anti-seismic ductility of steel structure connections.