| Buckling-restrained braces(BRBs) are typical energy dissipation devices in anti-seismic structures. They have been widely used in recent years. In this study, a new kind of light-weight BRBs is proposed, which is composed of two chord members. Each chord member is a conventional single-core BRBs, and the two chord members are connected together by continuous web plates or several steel battens longitudinally. They are named as the solid core-separated buckling-restrained braces(solid CSBRBs) and battened core-separated buckling-restrained braces(battened CSBRBs) respectively. CSBRBs have the potential to be widely used as large-tonnage BRBs in practice due to their lightness and reliable brace-end connections.The elastic buckling loads of solid CSBRBs are firstly investigated by using the equilibrium method and verified by finite element(FE) buckling analysis. In the expression of elastic buckling loads, a performance parameter is proposed which reflects the effects of the distance between cores, the cross-sectional area of cores, the flexural rigidity of cores and restraining members. The buckling deformations of pin-ended solid CSBRBs with different sizes change from sinusoidal curves to cosine curves, and they can be obtained by the energy method. The two steel tubes and battens connecting them in battened CSBRBs are considered as an equivalent continuous restraining member. Then the elastic buckling loads of battened CSBRBs considering shear deformations are obtained theoretically.The moments in the middle span of CSBRBs under axial loads are deduced, considering the influence of overall initial geometric imperfections. Based on the principle that when the cores reaches to full sectional yielding, the maximum moment should not exceed the lateral bending bearing capacity of restraining members, a simplified method to determine the threshold of restrain ing ratios is proposed. The results of three elasto-plastic FE model of CSBRBs, namely the beam element model, the node-to-node contact model and the surface-to-surface model are compared. The comparison shows the reliability of simplified FE models in this study.Two design parameters, namely the normalized slenderness and the stability factor of CSBRBs are defined to develop a design procedure. The buckling behaviors of CSBRBs pin-ended in both directions, are investigated by FE buckling analysis, and the normalized slenderness of a chord member in battened CSBRBs is obtained by the equilibrium method. Then interaction formulas between the normalized slenderness and the stability factor are proposed based on FE elasto-plastic analysis, which can be used to predict the ultimate resistance of CSBRBs subjected to monotonically axial loads in full range of the normalized slenderness. Afterwards, the hysteresis performance of CSBRBs with different normalized slendernesses is discussed. Based on these research achievements, CSBRBs can be classified as three types, namely energy-dissipating buckling-prevented CSBRBs, load-bearing buckling-prevented CSBRBs and buckling-delayed CSBRBs. Moreover, influences of the yielding strength of restraining members, initial geometric imperfections, web height-to-thickness ratio and so on are studied. Then the strength design method of webs is discussed. Several recommendations are proposed to prevent the failure of a chord member before the overall failure of a battened CSBRB. Finally, a design method of battens in battened CSBRBs is established.Hysteresis experimental studies on CSBRBs are carried out. The reliability of theoretical and numerical results is verified by those experiments. Besides, different connection details are compared and verified by the experiments. Several recommendations related to the design and fabrication are also proposed based on failure modes in the experiments. These research achievements provide the foundation for further investigations and applications of CSBRBs. |
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