Info

Structural stability or

Hazard level

Immediate occupancy

Life safety

collapse prevention

10%/50 years

a

b

c

5%/50 years

d

e

f

2%/50 years

g

h

i

possible to create dual or multiple performance objectives by selecting different performance levels and different hazard levels. An example of this would be achieving I-B performance level for a DE event but satisfying III-C for an ME earthquake (this would correspond to a and e in Table 21.2).

Both ATC-40 and FEMA-356 prescribe a basic safety objective (BSO), which comprises a dual-level performance objective. In ATC-40, this would entail satisfying III-C (LS performance level) for a DE and also achieving V-E (structural stability) for an ME event. In FEMA-356, the BSO criterion requires LS performance for a 10% in 50-year event and CP performance level for a 2% in 50-year earthquake. With reference to Table 21.2, the BSO in ATC-40 is b + f and in FEMA-356 it is b + i.

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