This paper focuses on vulnerability assessment of block-type restrained nonstructural component under sliding response. The general representation of restrained equipment considered in this study consists of a rigid block restrained by four post-tensioned, symmetrically arranged cables and subjected to both horizontal and vertical base excitations. The corresponding seismic vulnerability is assessed through fragility curves, which are developed for typical values of the parameters in the equation of motion. Two limit states are considered: breakage of the restraining cables and loss of functionality due to excessive absolute acceleration. In the case of the former, it is found that fragility curves depend strongly on the coefficient of friction at the block-surface interface and on the level of post-tension in cables. Vertical accelerations become relevant only for relatively large values of the coefficient of friction. The corresponding fragilities are always greater than that corresponding to the case of zero vertical acceleration. In the case of the excessive absolute acceleration limit state, it is found that fragility curves depend mainly on the coefficient of friction and only marginally on the other parameters. Besides, fragility curves are always very close to the absolute acceleration threshold. It is concluded that restraints are very effective in reducing horizontal displacements, but at the expense of peak absolute accelerations that are almost always equal to or greater than peak base accelerations.
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