Parametric Study of Vertically Isolated Steel Braced Frames Controlled by Shape Memory Alloys

Abstract Vertical isolation has gained interest in recent years by incorporating the damping mechanism within the height and evading the concentration of isolation elements in the base. However, dividing the building into separate systems may be less practical in regular buildings. This study used a conventional steel-braced lateral load-resisting system inherently made up of two soft and stiff portions to compare the efficiency of the isolation technique. Shape memory alloys (SMAs) with flag-shaped hysteresis damping mechanisms are assigned among the two subsystems to elaborate the damping mechanism. Parametric coding in OpenSees investigates a large set of frames with altered stiffness of the stiff subsystem subjected to time histories of 40 records with 2 and 10 % probability of exceedance. Increasing the stiffness of the stiff subsystem reduces the interstory and roof drift by more than 30%. SMA employment is shown to be effective in reducing the interstory, and roof drift at the soft- subsystem. The maximum reduction happens on the 1st floor by 32% and the least on the roof by 8%. There was a mild rise in the stiff subsystem’s responses, however, this increase may be neglected as the performance level is governed by the soft- subsystem’s response. The SMA-equipped frame is then further assessed by incremental dynamic analysis. Fragility curves of the system damage states delineate a promising response from the system.