Mechanical Behavior Of Corner Gusset Connections Of Steel Buckling-restrained Braced Frame Considering Seismic Frame Action

Buckling-restrained braces(BRBs) are one kind of bracing members, which will not buckle under compression and also have outstanding energy dissipation capacity. BRBs are generally connected to the steel frame by gusset plates, which are further connected to the beam(referred to as the middle gusset plate when BRBs are arranged in Chevron or V-type configurations) or both beam and column(referred to as the corner gusset plate). These traditional connections have the advantages of easy assembly and fast construction. Generally, the BRB gusset plate is designed considering the axial force of BRB only. However, related researches showed that the opening and closing of beam and column joints due to frame action may lead to premature fracture of the corner gusset plate and under severe earthquake. This failure mode would be detrimental to the BRBs and the structural system.To give full play to the energy dissipation and deformation capacity of the buckling- restrained brace in steel frame structure under the strong earthquake, research of the new gusset plate structures which can reduce seismic frame action and the effect of different kinds of gusset plate structures on seismic frame action and the steel frame' mechanical properties were implemented in this paper, with the combination methods of the finite element method and the theory analysis. The main aspects are as follows:Firstly, by comparing the existing design methods of the gusset plate considering seismic frame action and selecting the appropriate methods for engineering design, the design steps of the gusset plate considering seismic frame action were given. Through the analyses of numerical examples to explore ways to reduce the effect of seismic frame action. The results show that changing the thickness of the gusset plate or adding stiffeners on free edges of it cannot effectively reduce the impact of seismic frame action. The shear stress between the gusset plate and the frame edge is the main contribution of s eismic frame action. The effect of stiffeners and the thickness of the gusset plate on the shear stress is tiny.Secondly, the interaction between gusset plate and steel frame under the effect of seismic frame action alone(no brace) was researched. Considering the plate size and co nnections between gusset plates and frames, 7 steel frame beam-column- gusset plate sub-structures were analyzed by finite element. The results show that the gusset plate will significantly increase the lateral stiffness of the frame(82%, the highest increase range). As to the influence of the lateral stiffness of the frame, the welded gusset plate is greater than the gusset plate without friction(the ideal model of a new kind of gusset plate: the surface between the gusset plate and frame has no friction horizontally and hard contact vertically which can't be separated, so as to reduce the shear stress of the gusset plate). As to the influence of the lateral stiffness of the frame, the large gusset plate is greater than the smaller one. Welded gusset plates will make the beam plastic hinge move to the end of gusset plate, while the beam plastic hinge of gusset plates without friction lies near the joint panel zone. The gusset plate without friction realizes the goal of reducing the shear stress on the connecting edge, but the distribution of its normal stress is different from that of welded gusset plates.Thirdly, the interaction between the gusset plate and steel frame under the effect of seismic frame action and the axial force of buckling-restrained brace was researched. With the size of gusset plates, connection modes, free edge stiffeners as design parameters, 8 steel frame beam-column- gusset plate-BRBs sub-structures were analyzed by finite element. The results show that the stiffeners ha ve no significant effect on the mechanical behavior of welded gusset plates, but they will significantly decrease the Mises stress of the connecting edges' endpoints of gusset plates without friction. After Setting free edge stiffeners, the largest Mises stress of gusset plates without friction is at the intersection of two connecting edges.Last, put forward an actual structure of gusset plates without friction: the gusset plate cannot be directly connected with the beam or column, instead connecting the gusset plate with end plate which will be connected with the flange of beam and column by bolts. The surface between the end plate and flange is slidable, It is “the gusset plate with slidable end plates”. Establish the finite element model of the gusset plate with slidable end plates and compare it with both its ideal model(no end plate) and the welded gusset plate. The results show that gusset plate with slidable end plates can realize most characteristics of its ideal model, and the Mises stress peak is obviously smaller than the welded gusset plate(For the gusset plate edge connected to the column, the Mises stress peak reduces about 1/4 when the displacement angle is 2%). At the same time, the gusset plate with slidable end plates has its own characteristics. Under positive and negative loading requirements for bolts are different. The effect of the free edge stiffeners is reducing.