There has been an increasing interest in using residual deformation as a seismic performance indicator for earthquake resistant building design. Selfcentering braced structural systems are viable candidates for minimizing residual deformations following a major earthquake. Hence, this study proposes an alternative type of buckling restrained brace (BRB) with externally attached posttensioned (PT-BRB) carbon fiber composite cables (CFCCs). The steel core of the brace is used as an energy dissipator, whereas the CFCCs provide the self-centering force for minimizing residual story drifts. Three proofof-concept specimens are designed, fabricated, and cyclically tested at different posttensioning force levels. The CFCC behavior to obtain cyclic response, including the anchorage system, is examined closely. A parametric study is also conducted to show the effect of the different configurations of PT-BRBs on the inelastic response. Furthermore, optimal brace parameters are discussed to realize design recommendations. The results indicated that the implementation of partially self-centering BRBs in building frames can lead to the target residual displacements. A stable behavior is obtained for the proposed PT-BRBs when subjected to the loading protocol specified in the American Institute of Steel Construction (AISC) 2016 Seismic Provisions.
Conventional approach to earthquake resistant building design relies upon strength, stiffness, and inelastic deformation capacity, which are great enough to withstand a given level of design earthquake effects. However, modern approach in today's designs aims to mitigate seismic energy before the input energy reaches the structural elements. Dissipating seismic energy through the inelastic deformation of metallic dampers is one of the cost effective solutions. After appearing concept of dissipating energy through the inelastic deformation (mainly yielding and post yielding) of metallic dampers, numerous types of metallic dampers, such as X-shaped, J-shaped, U-shaped, shear panel, triangular plate dampers have been developed and their effectivenesses have been proved both theoretically and experimentally. Inelastic hysteretic behaviour of U-shaped devices is somewhat complex and varies with geometry of the damper. To address this issue and possibly attain some practical results, this present paper focuses on modelling hysteretic behaviour of Ushaped dampers. ABAQUS has been used as the computational tool in which a finite element model made of the C3DR8 solid element is adopted. Nonlinear kinematic and isotropic hardening material assumptions are considered to determine cyclic behaviour at 0º, 45º and 90º loading directions. For each analysis, effective stiffness, effective damping ratio, and maximum reaction forces (i.e. horizontal strengths) of the damper are calculated to evaluate performance. As an additional parameter, two different loading protocols are taken into consideration. Hysteretic curves and deformed shapes of a selected damper type taken from an existing experimental work and this numerical study show very good agreement proving that the modelling assumptions made during the analyses are appropriate and sufficient for a better prediction of behaviour. Additional numerical analyses on several dampers under various loading protocols reveal that effective damping ratio of the damper is more than ξeff =40% at the maximum displacement level due to significant energy dissipation through plastic deformation of the damper. A numerical example of mixed use of Ushaped steel dampers and rubber isolation bearings on a selected two story steel framed building is also discussed.
This paper proposes a new type of buckling-restrained braces with post-tensioned cables (PT-BRB). Such braces enable various hysteresis shapes between bilinear ( =2.0) and flag-shaped ( =1.0) behaviors. After a thorough numerical study for investigating the effect of post-yield stiffness ( ) and energy dissipation ( ) ratios, 1/3 scale specimens were tested for confirming expected hystereses. With the experimental data acquired, impact of the hysteresis on seismic response of various types of steel structures with PT-BRBs is sought. Seismic performances of structures equipped with PT-BRBs or conventional BRBs are compared.
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