Studies On Properties Of Buckling-restrained Braces With Multi-constraint

Buckling-restrained brace(BRB)is a kind of metal-yield energy dissipation device,which is mainly composed of the core member,the restraint member and the unbonded materials.The core member may be multi-waves buckled under the axial pressure and be contacted with the restraint member,which causes the friction on the interaction surface.The friction between the core member and restraint member may decrease the low-cycle fatigue performance of BRB.This paper introduces the reason of the friction,and discusses the relationship between the length of core member and the magnitude of the friction.The transformation law of the total friction is discussed combined with the experimental result,and the loading process of the BRB core member is simulated by the computational procedure.Then the law of the adverse effects of friction force on the mechanical properties of BRB core components are summarized.The concept of buckling-restrained brace with multi-constraint is proposed in this paper,which divide the core member into a plurality of yield parts to reduce excessive friction of every part to improve the low cycle fatigue performance of the core plate.The stoppers are set on the middle of each yield segment and the restraint member are also divided into several segments.This new type of BRB could largely improve the low-cycle fatigue performance.The reasonable length of each yield segment of the buckling-restrained brace with multi-constraint is presented according to the relationship between friction and low cycle fatigue performance,and the finite element model is proposed to verify the rational of the relationship.The main contents of this paper are as follows:(1)The reason of friction in BRB and the influence of friction on the performance of BRB are analyzed theoretically.The stress process of BRB core components is simulated by the computational program.The result shows that the presence of friction has an important influence on the performance of BRB.The existence of friction force makes the stress and strain distribution in the core components of BRB is uneven,which results in the uneven distribution of energy consumption of the core components with the middle energy consumption more and the two ends less,and the fracture occurs at the central part and the real capacity could not be effectively ultilized.This phenomenon may be much more serious when the friction is larger.(2)The low-cycle fatigue cycle number of the core member under different frictions under the average strain in the vicinity of 0.5%,1%and 2%are calculated by using the computational program written in this paper.The low cycle fatigue cycles core plate under different friction forces yield,friction force is obtained at low strain effects on low cycle fatigue properties of high strain rate,the friction force is larger under the same strain,and the low-cycle fatigue of the performance decreases with the increase of friction force of the slow pace of the phenomenon,and analyzes its reason.(3)The calculation method of friction is verified by using the software ABAQUS The nonuniform coefficient of tension and compression and the strain change of the nearby of the stoppers on the core member are also verified,and the positioning bolt yield is calculated by a formula of damage degree,which proves the correctness of these results.(4)The core member is proposed to divide into several segments by considering the adverse effect of friction on low cycle fatigue properties of the core member based on the simulation computational program based on the conclusion,and the restraint member is also divided.The stoppers are set on the middle of each yield segment,and the friction on the core members are decreased.Furthermore,the research value and concrete construction of the multi section buckling-restrained brace are introduced in detail.(5)The total length of the yield segments of the core member is shorter than the traditional BRB of the same length,and the average strain of this new type of BRB is larger than the traditional one.The smaller the friction force is,the better the low cycle fatigue performance of the core plate,and the larger the strain is,which is detrimental to the low cycle fatigue performance.This paper gives the suggestion of the length of each yield section of the new BRB by analyzing the disadvantageous influence and the beneficial influence.