Straight Winds and Hurricanes

DOE-STD-1020-2002

3.2.2 Performance Category 2

Performance Category 2 SSCs are equivalent to essential facilities (Category IV), as defined

in ASCE 7 or model building codes. The structure shall not collapse at design wind speeds.

Complete integrity of the structure envelope is not required because no significant quantities

of toxic or radioactive materials are present. However, breach of the SSC containment is not

acceptable if the presence of wind or water interferes with the SSCs function.

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An annual wind speed exceedance probability of 1x10

is specified for this Performance

Category. The importance factor is 1.0.

Once the design wind speeds are established and the importance factors applied, the

determination of wind loads on Performance Category 2 SSCs is identical to that described

for Performance Category 1 SSCs. ASD or SD methods may be used as appropriate for the

material being used. The load combinations described for Performance Category 1 are the

same for Performance Category 2.

3.2.3 Performance Category 3

The performance goal for Performance Category 3 SSCs requires more rigorous criteria than

is provided by national standards or model building codes. In some geographic regions,

tornadoes must be considered.

Straight Winds and Hurricanes

For those sites where tornadoes are not a viable threat, the recommended basic wind speed

based on an annual exceedance probability of 1x10 ?3 . The importance factor is 1.0. Once

the design wind speeds are established and the importance factors applied, determination of

Performance Category 3 wind loads is identical to Performance Category 1, except as noted

below. SSCs in Performance Category 3 may be designed or evaluated by ASD or SD

methods, as appropriate for the material used in construction. Because the hazard

exceedance probability in Performance Category 3 contributes a larger percentage to the total

probabilistic performance goal than in Performance Categories 1 or 2, less conservatism is

needed in the Performance Category 3 design and evaluation criteria. This trend is different

for seismic design as discussed in Chapter 2 and Appendix C. (See Appendix D for further

explanation.) Thus, the load combinations given in the applicable material national

consensus design standard may be reduced by 10 percent. In combinations where gravity

load reduces wind uplift, the reduction in conservatism is achieved by modifying only the

gravity load factor.

When using ASD, allowable stresses shall be determined in accordance with applicable

codes and standards (e.g. see Reference 3-4 for steel). Load combinations shall be evaluated

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