What Is the Redundancy Factor (ρ) in Seismic Design?
The redundancy factor (ρ — the 1.0 or the 1.3) penalizes the non-redundant seismic systems (the few — the single; the failure's — the catastrophic) by amplifying the design forces 30%. The determination: the ASCE 7 12.3.4's — the story's — the bays' count; the ρ=1.0 (the redundant — the perimeter's; the qualifying), the ρ=1.3 (the default — the non-). The redundancy's — the reliability rewarded.
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How ρ is determined
The story (the extreme — the bays'; the count's; the 12.3.4.2's — the two bays'), the plan (the perimeter's — the qualifying; the torsional's), the ρ=1.0 (the redundant — the met; the SDC D's — the required), and the ρ=1.3 (the default — the unmet; the penalty).
Effect on design
The forces (the 1.3x — the seismic's; the combinations'), the members (the sized — the larger; the connections'), the drift (the ρ's — the excluded; the 1.0's), and the diaphragms (the Fpx's — the excluded).
Achieving ρ=1.0
The bays (the two — the perimeter's; the each side's), the lengths (the qualifying — the 12.3.4.2's), the SDC D-F (the required — the 1.0's; the design's), and the documentation (the plans' — the noted; the calculations'). The ρ is the reliability's — the redundancy designed in.
The bottom line
Determine ρ per ASCE 7 12.3.4 (ρ=1.0 requires two qualifying perimeter bays per side; else ρ=1.3 amplifies seismic forces 30%) — SDC D-F effectively requires ρ=1.0.
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