Seismic Performance And Design Method Of Sliding Gusset Connections In Buckling-Restrained Braced Steel Frame

Brace-type hysteretic dampers,such as buckling-restrained brace(BRB),the most popular methods of seismic mitigation control,have been widely adopted to structural seismic retrofit and aseismic design of new structures around the world.The BRB gusset connections are usually welded to the steel frame members,and these kinds of connections are called welded gusset connections.Lots of tests results suggest that the welded gusset connections will sustain forces caused by BRB action and frame action(the opening and closing deformations of beamcolumn joint).The BRB gusset connections and their frames will fail under such complicated situations,the BRB will be forced to lose its function and can't dissipate seismic energy any more.Based on the thought of “conquering firmness with soft”,this paper proposed a novel sliding gusset connection to fix such problem caused by welded gusset connection.This novel sliding gusset conncetion,which is connected to beam and column flanges by high strength bolt,but allows sliding deformation at the frame-gusset interfaces via employment of butyl rubber layers,can minimize the plastic demage of beam-column-gusset joint.The proposal of such connection is important for better performances of brace-type-damper hysterestic dissipation and better seismic performances of structures.The main research contents and conclusions of this paper are as follow:(1)A novel sliding gusset connection is proposed in chapter 2.Cyclic tests of three BRB steel frame subassemblages,two with proposed sliding configuration and another with traditional weled gusset connection,were conducted to research the difference of seismic performance between theses two gusset connections.The results show that the proposed sliding gusset connection can minigate the frame action and improve the structural deformation capacity.In addition,the sliding deformations of the proposed connection will not have severe and negative effect on BRB axial behavior and cumulative plastic dissipation.(2)Based on the phenomenon observed on the subassemblage tests and the parameters which did not considered on the subassemblage tests in chapter 2,ABAQUS finite element software was adopted to analyze the stress state of high strength bolts and the effect of different sliding configurations.The stress state of high strength bolts on the sliding gusset connection is confirmed by comparing theoretical analysis with the finite element results.The effects on the seismic performances of BRB connections with different gusset configurations,such as beam-column joint configuration,the strength of beam-column panel zone and slab effects,are confirmed by 18 finite element models.Based on the results of finite element,the optimal sliding gusset configurations are determined.(3)The proposed sliding gusset connection will release the shear interaction on the framegusset interfaces and resist the BRB axial force by normal direction.The results of finite element on chapter 3 also show that the high strength bolts can be seen as bearing tensile force only.Theoretical analysis and finite element models are adopted to analyze the location of tensile force on frame-gusset interfaces and its calculation method is confirmed in chapter 4.Such method is adopted to calculate the bolts force and 27 finite element models are designed.The finite element results show that the siemics performance of sliding gusset connection can be assured with such method.Based on the result above,a practical design method of sliding gusset connection is proposed.(4)The practical method of sliding gusset connection is adopted to design a one-bay twostory BRB steel frame with sliding gusset connection in chapter 5.The configurations of frame members,in which plastic hinges stiffeners are densely arranged along the 1.0 hight of beam or column section,are proposed to improve the frame ductility.The test results suggest that the practical method can ensure the seismic performance of sliding gusset connection under frequent,medium,rare and super rare earthquake,the gussets and high strength bolts are satisfied the design status.In addition,the test results also show that the local buckling of beamcolum flange under super rare earthquake can be avoided with the proposed configurations of frame members,and the coordinating deformations between BRB and the structures are effectively improved.