What Is Soft Story Irregularity — and Seismic Retrofit?
Soft story (the ASCE 7 Table 12.3-1 — the Type 1; the stiffness's — the 70%/80%) exists where the story's stiffness (the open's — the parking's; the retail's) is <70% of the above (the 1a) or <80% average of three (the 1b — the extreme). The retrofit: the steel frames (the moment's — the added; the parking's — the preserved), the shear walls (the concrete's — the added), and the FEMA P-807 (the wood's — the guideline). The collapse's — the notorious.
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How soft story is determined
The stiffness (the 70% — the above's; the 1a), the 80% (the three's — the average; the 1b — the extreme), the strength (the weak's — the companion; the Type 5's), and the examples (the tuck-under — the parking's; the Northridge's — the collapsed).
Retrofit methods
The steel frames (the special moment — the added; the bays'; the parking's — the open), the shear walls (the plywood's — the wood's; the FEMA P-807's), the cantilevered (the columns' — the fixed; the proprietary's — the Simpson's), and the diaphragms (the strengthened — the tied; the continuous).
Programs and mandates
The ordinances (the LA's — the mandatory; the SF's; the Berkeley's), the FEMA (the P-807 — the wood's; the evaluated), the financing (the loans' — the PACE's; the grants'), and the tenants (the relocation's — the minimal; the phased). The soft story is the killer — the retrofit is the cure.
The bottom line
Identify soft story per ASCE 7 Table 12.3-1 (stiffness <70%/80%) — retrofit with steel moment frames or shear walls per FEMA P-807; comply with local mandatory ordinances.
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