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SYMBOLS
ρ = Redundancy factor
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Redundancy is an important property for structures designed with the expectation that damage will occur. Redundant structures have alternative load paths so that if some elements are severely damaged and lose load carrying capacity, other elements will be able to continue to provide a safe load path. Adequate redundancy is ensured when a large number of plastic hinges must form throughout the structure in a progressive manner before formation of a mechanism and when no one element is required to provide the full seismic resistance of the structure.
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C12.3.4 Redundancy
The standard introduces a revised redundancy factor, ρ, for structures assigned to Seismic Design Category D, E, or F to quantify redundancy. The value of this factor is either 1.0 or 1.3.This factor has the effect of reducing the response modification coefficient, R, for less redundant structures, thereby increasing the seismic demand. The factor is specified irecognition of the need to address the issue of redundancy in the design.
The desirability of redundancy, or multiple lateral force-resisting load paths, has long been recognized. The redundancy provisions of this section reflect the belief that an excessive loss of story shear strength or development of an extreme torsional irregularity (Type 1b) may lead to structural failure. The value of ρ determined for each direction may differ.
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