Study On Extended End Plate Connection Reinforced By Backing-plates

Beam-column connections of the multiple-story and high-rise steel frame structure use high-strength bolts end-plate connection, it is a connection of more general use of the steel structure. At end-plate beam-column connections, because of the relative thickness of column flange is thinner than end-plate and reduced the stiffness of column flange at the bolt holes, resulting in lower column flange bending capacity and punching shear bending failure around bolt holes. In order to prevent the occurrence of this phenomenon, China's design approach is replacing the scope of end-plate of column flange with the thick plate. This design approach resulted in large amount of steel and complex construction. Eurocode3 recommend to increase the backing plates at the tensile region of column flange to increase the bending capacity of column flange at bolt holes, this method can be avoided the manner of replacing the scope of end-plate of column flange with the thick plate. The construction of method is simpler and more convenient. EC3 provides the range of height and width of the backing plate, but did not provide its thickness. In addition, EC3 design approach makes the installation of transverse stiffener of column to be problem. In this paper, through the study on backing plates' thickness values of high-strength bolts end-plate connections and capacity, stiffener of end-plate connections by different ways to strengthen the column connection domain, in order to find a more economic and affordable mode of end-plate connections.At first, this paper deduced the capacity and initial stiffness formula of the T-stubs strengthened by backing-plates using the simplified method - component method. It can be seen from the formula that backing-plates can increase the tension capacity and bending rigidity of T-stubs which can increase the bending capacity of the end-plate and column flange. Then, the thickness values of backing-plates of high-strength bolts extended end-plate connections under the static load were analyzed in the finite element analysis software ANSYS. The influence to the capacity of connection, deformation of column flange in tension, as well as the impact of stress distribution were researched with different thickness values of backing-plates of column flange. Analysis of results showed that the connection with the column flange strengthened by backing-plates can increase the bending capacity of the column flange and prevent punching shear bending failure around bolt holes. This paper gives the recommended thickness value of backing-plates. Finally, common connection series models, column flange strengthened by backing-plates series models, column flange thickening series models and model of setting Morris stiffeners under static load were analyzed in the finite element software ANSYS. The influence to the initial stiffness, the initial shear stiffness, shear deformation and shear angle of column with different strengthened ways of column connection domain were analyzed and compared. It is can be drawn that the connection with horizontal, diagonal stiffeners and the column flange strengthened by backing-plates have a better performance. It can replace our traditional approach to strengthen the column flange. Connection performance by setting Morris Stiffener is a little lower than the connection with horizontal, diagonal stiffeners and the column flange strengthened by backing-plates. It can be used to medium-sized projects which bears smaller load and requirements of shorter construction period.