Experimental Analysis Of Lateral Resistance And Design Method Of Semi-Rigid Steel Frames With Knee Braces

With the rapid development of fabricated buildings in our country,semi-rigid connections are more and more widely used and diversified in steel structures due to their good ductility and convenient construction.However,compared with steel moment resisting frames,the lateral stiffness of semi-rigid steel frame is weaker.In order to improve the lateral resistance capacity of such frames effectively to meet the requirements of the seismic code or to repair such frames after the earthquake,this paper proposes a type of structure of the fabricated semi-rigid steel frame with knee braces,which does not need to add diagonal braces compared with the traditional knee braced steel frames to bring about the wider use space of the building.In addition,the knee brace can protect the beam-column connection from damage well and be replaced after damage conveniently.Not only does it combine the advantages of steel moment resisting frames and central braced steel frames,but also it overcomes the defects of difficult maintenance for the eccentric braced steel frame.In this paper,quasi-static cyclic loading tests and design methods are carried out to analyze the lateral resistance of the fabricated semi-rigid steel frame with knee braces,including the following work:(1)A semi-rigid steel frame and two semi-rigid steel frames with knee braces were designed to be tested under lateral monotonic loading respectively.Based on failure modes and force and displacement curves,lateral stiffness,bearing capacity,ductility and energy dissipation capacity of each specimen were investigated,and the effect of the installment of knee braces and the sectional area of knee brace were analyzed.(2)Based on the finite element simulation method verified by experiments,35 models were established by selecting parameters such as BRB knee brace,the sectional area of knee brace,the welding of the knee brace gusset and beam,the thickness of the angle,angle steel stiffener and web angle.By extracting the stress development curve and equivalent plastic deformation of the main members in the frames,the lateral resistance and failure mechanism of the top and seat angle frames with the knee braces were parameterized analyzed,and the key parameters about lateral resistance,failure modes and vulnerable section of such frames were summarized,providing engineering suggestions for the practical application of the semi-rigid steel frames with the knee braces.(3)Considering the corporate effect of semi-rigid connection and knee braces,through the analysis of its force distribution,yield mechanisms criterion method with considering gravity load and lateral stiffness and bearing capacity calculation method without considering gravity load under different yield mechanisms of this type of structural system are proposed,which were verified by the results of finite element modeling and experiment and provided a reference for the performance-based design of this kind of structure.