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Bracing Systems
Published in Suhasini Madhekar, Vasant Matsagar, Passive Vibration Control of Structures, 2022
Suhasini Madhekar, Vasant Matsagar
During severe earthquake events, the braces may be subjected to repeated cycles of lateral loading and stresses beyond their elastic limit. In such cases, the braces may yield in tension and buckle in compression. The buckling of braces in compression prevents the utilization of the full capacity of the braces in compression. Thus, the bracing ability of the conventional steel is greatly hampered. The tendency of buckling is influenced by the section property, the compressive force, and the unbraced length of the steel core. The buckling of the steel core results in a severe reduction in the capacity of the braces to resist the earthquake actions and dissipate the energy. To overcome this problem, the concept of buckling-resistant braces (BRBs) was proposed in order to obviate the buckling of the braces and to make the bracing system robust in both tension and compression. A BRB is a steel brace that does not buckle in compression but instead yields in tension as well as in compression. A buckling-restrained braced frame (BRBF) is a CBF that incorporates a buckling-restrained brace. Figures 3.2 and 3.3 illustrate the behavioral difference between the conventionally braced frame and buckling-restrained braced frame under lateral load.
Cyclic Behavior of All-steel BRBs with Bolted Angle Restrainers: Testing and Numerical Analysis
Published in Journal of Earthquake Engineering, 2023
Ahmad Fayeq Ghowsi, Dipti Ranjan Sahoo
Buckling-restrained braces (BRBs) are widely adopted as either lateral force-resisting systems or energy dissipation devices in structures located in the high-seismic regions. The main characteristics of BRBs are the higher energy dissipation capacity, better displacement ductility, and nearly symmetrical hysteretic behavior. Typically, a BRB consists of two elements, namely, an axial load-resisting element having a central yielding core segment with transition and elastic connection segments at both ends, and a restraining unit to prevent the buckling of the central core element under compression loading. A debonding material is used between the yielding core segment and the restraining unit to eliminate the load-sharing and to minimize the frictional resistance between them (Fahnestock, Ricles, and Sause 2007; Xie 2005). A clearance (i.e., air gap) is provided between the core segment and the restraining element to allow the core expansion due to Poisson’s effect at the elastic stage and to accommodate the higher mode buckling of core plates under axial compressive loading (Chen et al. 2016). The main goal is to absorb the input energy demand within the BRBs by plasticizing central core segments while keeping the beams and columns of a buckling-restrained braced frame (BRBF) in the nearly elastic stage when subjected to a seismic event (ASCE 7-16 2017).
Seismic Performance of Self-centering Steel Frames with SMA-viscoelastic Hybrid Braces
Published in Journal of Earthquake Engineering, 2022
Cheng Fang, Yiwei Ping, Yiyi Chen, M. C. H. Yam, Junbai Chen, Wei Wang
In the following discussions, two novel hybrid self-centering braces incorporating prestressed superelastic SMA elements and integrated viscoelastic damper (VEDs) are proposed, with the working principle presented in detail. Subsequently, seven basic prototype buildings, including a conventional buckling-restrained braced frame (BRBF), a “pure” self-centering braced frame (SCBF), and five hybrid self-centering steel-braced frames (HBFs) with different base shears and supplemental damping arrangements, are designed according to ASCE 7–16 (American Society of Civil Engineers (ASCE) 2016). These structures are then evaluated in terms of the peak/residual inter-story drift and peak floor acceleration demands with selected far-field and near-fault ground motions. The influence of the varying brace parameters on the key seismic demands is further discussed, and the reasons behind the observed trends are explained. Based on the available data, preliminary design recommendations for the proposed hybrid structures are provided, and a probability-based model for residual inter-story drift prediction is finally developed.
Stochastic optimisation of buckling restrained braced frames under seismic loading
Published in Structure and Infrastructure Engineering, 2018
Jiaqi Xu, Gaston A. Fermandois, Billie F. Spencer, Xilin Lu
The buckling restrained braced frame (BRBF) has superior energy dissipation capabilities compared with a conventional braced frame. During high-intensity ground motion, the BRBs dissipate seismically induced energy by metallic yielding, while other structural components are designed to remain elastic. BRBs can fully yield in both tension and compression without buckling, which results in symmetric hysteresis loops and stable energy dissipation (Black, Makris, & Aiken, 2004). A considerable amount of research has been published about the BRBF design, both analytically (Choi & Kim, 2006; Fahnestock, Sause, & Ricles, 2007) and experimentally (Khoo, Tsai, Tsai, Tsai, & Wang, 2016; Lin et al., 2012).