Effects of Wind

DOE-STD-1020-2002

components mounted within a structure, there are three additional considerations for earthquake

shaking. First, the input excitation for structure-supported components is the response motion of

the structure (which can be amplified from the ground motion) - not the earthquake ground

motion. Second, potential dynamic coupling between the component and the structure must be

taken into account if the component is massive enough to affect the seismic response of the

structure. Third, large differential seismic motions may be induced on components which are

supported at multiple locations on a structure or on adjacent structures.

E.2

Effects of Wind

In this document high winds capable of damaging SSCs are classified as 1) straight

winds, 2) hurricane winds or 3) tornado winds. Straight winds generally refer to winds in

thunderstorm gust fronts or mesocyclones. Winds circulating around high or low pressure

systems (mesocyclones) are rotational in a global sense, but are considered straight winds in the

context of this document. Tornadoes and hurricanes both have rotating winds. The diameter of

the rotating winds in a small hurricane is considerably larger than the diameter of a very large

tornado. However, most tornado wind diameters are large compared to the dimensions of typical

buildings or structures.

Although the three types of wind are produced by distinctly different meteorological

events, research has shown that their effects on SSCs are essentially the same. Wind effects

from straight winds are studied in boundary layer wind tunnels. The results of wind tunnel

studies are considered reliable because they have been verified by selected full-scale

measurements (Reference E-1). Investigations of damage produced by straight winds also tend

to support wind tunnel findings. Although the rotating nature of hurricane and tornado winds

cannot be precisely duplicated in the wind tunnel, wind damage investigations suggest that the

magnitudes and distribution of wind pressures on SSCs produced by hurricane and tornado

winds are essentially identical to those produced by straight winds, if the relative wind direction

is taken into account. Thus, the approach for determining wind pressures on SSCs proposed in

this document is considered to be independent of the type of windstorm.

Measurements of hurricane and straight wind speeds are obtained from anemometer

readings. Wind speeds must be cited within a consistent frame of reference. In this document

the frame of reference is "peak gust" wind speed (speed of air averaged over 3 seconds) at 33 ft

(10 meters) above ground in flat open terrain. Wind speeds measured relative to one frame of

reference can be converted to another frame of reference through the use of wind speed profiles

and relationships between averaging times. (Reference E-3)

Tornado wind speeds cannot be measured easily by conventional anemometers. Instead

tornado wind speeds are estimated from appearance of damage in the storm path. The Fujita

Scale (F-Scale) classification is generally accepted as the standard for estimating tornado wind

speeds (Reference E-2). Table E-1 lists the wind speed ranges and describes the damage

associated with each category. The wind speeds associated with the Fujita Scale are considered

to be peak gusts (2-3 second averaging time). The tornado hazard assessments used in this

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