Research On Some Issues Of Extended End-Plate Beam-to-Column Bolted Connections

Extended end-plate bolted connections are widely used in steel frames. In order to simplify connections' detailing, end-plate stiffeners and column web stiffeners aren't used in western countries. But these stiffeners are used in most structures in China. There has been much research on extended end-plate connections without stiffeners in western countries. But the research on stiffened extended end-plate connections is very limited and this research is just beginning in China.Triple nonlinear finite element method is used to study the behaviors of extended end-plate bolted connections. The effects of end-plate stiffeners, web stiffeners in panel zone on the initial stiffness of the connection, failure modes and the load-carrying capacity, prying force distribution on the faying face are studied. Tests have been carried out to study T-stub connections with different shape and thickness of end-plate stiffeners. At last, design suggestions of extended end-plate H-section beam-to-box column connections are proposed.End-plate stiffener provides another load path for the bolts on the extended portion of the end plate. But there are no specifications for the design of end-plate stiffeners. In practice, the stiffeners are always equilateral-triangular with thickness of beam web in steel portal frames. This thesis proposed a method of end-plate stiffener which concerns with its shape and thickness. The proposed method is based on the requirement of transmitting forces and equal distribution of forces among bolts within and outside of the beam flange. The finite element method is used to analyze the effects of stiffeners designed by the proposed method and stiffeners used in current practice on the joint behavior. Tests have been carried out to study stiffened T-stub connections which are similar to tension zone of extended end-plate connections. The study shows that the stiffener designed by the proposed method can meet the requirements of providing effective support to the end plate in CECS 102:2002. The stiffness and capacity of end plate connections with 45W stiffeners are very lower.The bolt may fail prematurely due to prying forces. There are no reliable theories to describe the prying force distribution and simplified equations to calculate the prying force. The finite element method in thisthesis is used to study the changes of bolt force, contact pressure on the connecting face, prying force in the tension zone. The bolt force distribution between inner and outer bolts and area of prying force distribution are presented. The formulas to compute bolt prying force are proposed, which are applicable to T-stub connections and extend end-plate connections without stiffeners and with stiffeners.The rotational stiffness has a great influence on steel frame stiffness and deformation. The decrease of the frame lateral stiffness, due to connection rotational deformability, leads to the increase of the period of vibration and the frame sensitivity to second-order effects. This thesis divides the end plate into several parts equivalent to different Timoshenko's beams to determine their contribution to rotational stiffness of the connection. The stiffness of all parts and bolts is given, and then the component method is used to calculate rotational initial stiffness of extended end plate connections. Comparisons with results of ANSYS and related tests show that the proposed equations have excellent precision. And the calculating process is simple and easily applicable in practice.In order to diminish the local deformation of column flange around tensile bolts, column flange baking plate is proposed. And the design method of backing plate in panel zone with web stiffeners is presented. Comparisons with the connection, whose thickness of column flange is equal to that of end plate, show that the backing plate designed in the proposed method has the same stiffness as the thickened column flange, but the proposed method in this thesis is more economic and material-saving.To increase panel zone shear stiffness in extended end plate connections and overcomes the difficulties of bolt arrangement associated with diagonal stiffeners, the "Morris" stiffener is proposed. And the design method of "Morris" stiffeners is presented. The effectiveness of "Morris" stiffeners is studied too.To increase the load carrying capacity of beam-to-column connection and reduce joint deformation for extended end plate H-section beam-to- box column connections, a U-steel is needed on the outside of the tube in the joint The design method of the U-steel is proposed, and the design suggestions of bolt array and column stiffeners are suggested. Based on the finite element analysis, a new joint detail is proposed, in which the column head is flushed with the beam upper flange, the U-steel is welded to the column web, and the extended portion of U-steel has a stiffener.