Impact of strongback on structure with varying damper and stiffness irregularity arrangements

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Structures susceptible to soft story mechanisms are particularly vulnerable to earthquakes because damage concentrated at a single story can lead to premature failure of the structure. The strongback, a stiff vertical spine pinned at the structure's base and running its height, has been proposed as a way to impose a more uniform pattern of floor displacements and prevent soft story mechanisms. However, changes in the impact of strongbacks on the performance of structures remain unclear when considering vertical stiffness irregularities at different positions along the height of a structure and different arrangements of energy dissipation devices in a structure. This study aims to address these gaps through an extensive parametric experimental investigation varying the location of vertical stiffness irregularities and the arrangement of dampers in a small-scale four-story elastic structure with and without a strongback. For this study, each configuration of the structure is loaded with shake table-produced seismic ground motion. The results of this study show that, regardless of which story a stiffness irregularity is located, the strongback significantly reduces the maximum story drift in the structure. Furthermore, with the strongback, the maximum story and roof drift are insensitive to damper position and distribution, whereas, without it, the damper position significantly impacts the structural performance. The strongback's ability to protect against soft story vertical irregularities, regardless of their locations, and the insensitivity of structural performance to damper arrangement when utilizing a strongback, presents promising new options for structural design, architectural design, and remediation efforts.