Hysteretic Behavior Research Of Buckling-restrained Reduce Beam Section Connections For Steel Frame

Reduce beam section(RBS)connection of steel frame is one of the typical forms to move plastic hinge outward from the beam and column interface.By trimming beam flanges,the plastic hinge will form away form the welds that have much fracture proneness due to stress concentration and welding sensitivity,reducing the possibility of brittle fracture of connections and improving the ductility of the structure with RBS connections.But with the increase of load and cyclic times,region of beam trimmed may produce the significant out-of-plane buckling when the flange and web is compressed.Joint’s strength and stiffness will degenerate as a result of this phenomenon.The weakened parts’ buckling will affect the energy dissipation ability of the joints,reduce the low cycle fatigue life,and lead to the early failure of the joints.The buckling-restrained brace(BRB)is an axially stressed member that external restraint components can limit the core plate’s buckling.The core plate’s hysteretic behavior can be brought into full play under strong earthquake,so the purpose of dissipating seismic energy can be achieved.Inspired by the principle that restraint member can restrain the core plate’s buckling when it is compressed,similar measures should be taken to limit local buckling of the weakened part’s flanges and web.In this paper,a buckling restraint device installed on the periphery of the weakeed part of RBS connection was put forward to limit the local buckling of the weakened part and improve the seismic performance of RBS connection.In view of the new RBS joint with buckling restraint member,the design method of this type of joint was firstly presented in this paper according to three aspects: the selection of weakening parameters,the stiffness demand analysis of the buckling constraint component,and the calculation of the clearance between the weakened part and the constraint plate.For the purpose of investigating the mechanical behavior of the new type connection,two specimens are designed,including a buckling restrained RBS connection and an ordinary RBS connection that has same weakening parameters.The cyclic loading tests of these specimens were carried out in this paper.The failure process and feature of each specimen were described and load-carrying capacity,ductility,energy dissipation capacity were analyzed.The results show that the local buckling of the weakened part could be limited effectively by the buckling restrained member.Compared with the ordinary RBS conncection,there was no decrease in bearing capacity before the failure,and the hysteretic curve was more full.This new type RBS joint has excellent plastic deformation capacity and energy dissipation capacity.Based on the large finite element analysis program ABAQUS,these two connections were numerical simulated,and the results of failure modes,hysteretic behavior,ultimate load,stress and stain distribution were compared with experimental results,which showed that the ABAQUS results were consistent with the experimental results.Though the analysis of the stess and stain distribution of weakened part and root of steel flange,it can be found the for the buckling restraint RBS joint,by limiting the local buckling,the excessive stress state at the weakened part can be reduced.This constraint member can improve the ductility and low cycle fatigue of the RBS connection.Connection’s carrying capacity can also be guaranteed.In view of the buckling phenomenon at the root of RBS connection in late-stage test,further improvement measures were proposed.