Table 3-3 Recommended Straight Wind Missile Barriers for Performance Categories 3 and 4

DOE-STD-1020-2002

to determine the most unfavorable effect of wind on the SSCs being considered. The SD

load combinations shall be used along with nominal strength and strength reduction factors.

A minimum missile criteria is specified to account for objects or debris that could be picked

up by straight winds, hurricanes or weak tornadoes. A 2x4 timber plank weighing 15 lbs is

the specified missile. This missile represents a class of missiles transported by straight

winds, hurricanes and weak tornadoes. Recommended impact speed is 50 mph at a

maximum height of 30 ft above ground. The missile will break annealed glass; it will

perforate sheet metal siding, wood siding up to 3/4-in. thick, or form board. The missile

could pass through a window or weak exterior wall and cause personal injury or damage to

interior contents of a building. The specified missile will not perforate unreinforced concrete

masonry or brick veneer walls or other more substantial wall construction. See Table 3-3 for

recommended wall barriers (Ref. 3-7).

Table 3-3 Recommended Straight Wind Missile Barriers

for Performance Categories 3 and 4

Missile Criteria

Recommended Missile Barrier

2x4 timber plank 15 lb @ 50

8-in. CMU wall with trussed horizontal joint reinforced

mph (horiz.)

@ 16 in. on center

Single width brick veneer with stud wall

Max. height 30 ft.

above ground

Performance Category 3

4-in. concrete slab with #3 rebar @ 6 in. on center each way in middle of

Max. height 50 ft.

slab

above ground

Performance Category 4

Tornadoes

For those sites requiring design for tornadoes, the criteria are based on site-specific

studies, as presented in Reference 3-14. Other non-NNSA sites may utilize the same

methodology to develop their tornado hazard curves.. An annual exceedance probability of

1x10-3, which is the same for straight wind, could be justified. As explained in Appendix D,

a lower value is preferred because (1) the straight wind hazard curve gives wind speeds

larger than the tornado hazard curve and (2) a lower hazard probability can be specified

without placing undue hardship on the design. The basic tornado wind speed associated with

an annual exceedance probability of 2x10-5 is recommended for Performance Category 3.

The wind speed obtained from the tornado hazard curve are already converted from peak

gust to fastest quarter-mile; use importance factor of 1.0 for Performance Category 3. For

3-7