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Conventional lateral force resisting systems, dissipate seismic energy through plastic deformation in primary structural members that results in significant damage in buildings. In most cases, repair of these induced damages are impossible from the structural viewpoint, or have not economic justification. Recent research works are to localize the induced damage to specific elements (as fuse, dampers and etc.) without plasticization of primary load-carrying elements that ensure the stability of structure. In steel structures, the self-centering rocking braced system is an innovative type of seismic lateral force resisting systems that is developed with aim to minimize structural damages, residual drifts and enable repair or replace of damaged elements with minor expense after experiencing earthquakes. Steel braced frame with controlled rocking system consists of three primary components: (1) steel braced frame with rigid joints and no connections to base foundation at the column bases that is free to rock cyclically during excitation; (2) post tensioning cables which are connected to the frame top and foundation base in order to provide retreat back or self-centering capability of the system. Expressed mechanism plays an important role in restoration of quake-imposed displacement into its initial position; and (3) the replaceable energy dissipating elements that act as structural fuses to absorb seismic energy through undergoing of inelastic deformations and provide the required ductility of the system prior to instability or collapse. In this type of lateral force resisting systems, the post tensioned cables and the members of the braced frame are design to remain elastic during excitation and provide high stiffness, strength and global stability of the structure with minor local deformations. In this design concept, post tensioned strands are the key members known in providing self-centering capability of the system and occurrence of any plastic deformation in these elements endangers overall stability of system. Probable exceedance of seismic force may result in yield of post-tensioned cables and consequent elimination of restoring functionality of self-centering mechanism. In current research work, the steel material is replaced by carbon fiber reinforced plastic (CFRP) fabric in post tensioning strands, and the consequent effects of proposed substitution is investigated on the behavior of braced frame and linked structural components. The research was conducted on two steel braced frames with controlled rocking system equipped with steel and CFRP cables and the models are analyzed using nonlinear dynamic time history analysis (NLTHA) procedure. The frames are subjected to JMA-Kobe ground motion record, that is scaled to 69%, 100% and 120% intensity groups which corresponds to unit, 1.45 and 1.74 times of maximum considered earthquake (MCE) ground motion level. Extracted results show that using CFRP post tensioned cable instead of steel cables, can protect the system against instability even under 100% Kobe ground motion record scale and leads to a more reliable type of controlled rocking systems. This study also revealed that remaining the CFRP cable on elastic region not only controls the frame lateral displacement, also prevents early failure in fuses under severe earthquakes and ensures the seismic energy dissipating capability of the structure.

Keywords: Self-Centering System, Post-Tensioned Cable, Energy Dissipating Fuse, CFRP, Controlled Rocking System

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