Topography coefficient

(1)P The topography coefficient, q(z), accounts for the increase of mean wind speed over isolated hills and escarpments (not undulating and mountainous regions) It is related to the wind velocity at the base of the hili or escarpment It shall be considered for locations closer than half the length of the hill slope from the crest or

1.5 times the height of the cliff. It is defined by:


s factor to be obtained from Figure 8.1 or Figure 8.2 scaled to the length of the effective upwind slope length, L„

® upwind slope H/L in the wind direction (see Figure 8.2 and Figure 8.3)

/-e effective length of the upwind slope, defined in Table 8.2

Lu actual length of the upwind slope in the wind direction actual length of downwind slope in the wind direction

H effective height of the feature

* horizontal distance of the site from the top of the crest z vertical distance from the ground level of the site

Table 8.2: Values of Z^

Slope ($> = H/L)

Shallow (0,05 <0 <0,3):

Steep (d> > 0,3) = HI 0,3

(2)P In valleys, q(z) may be set to 1,0 if no speed up due to funnelling effects is to be expected. For structures situated within, or for bridges spanning steep-sided valleys care should be taken to account for any increase of wind speed caused by funnelling.

Design Values Actions Eurocode

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