When using the gap function for wind panels, the loading applied does not appear to change?
Environment
British Standard
Question
When using the gap function for wind panels, the loading applied does not appear to change.
I was led to believe the wall property 'gap' function was how we considered funnelling. Is this correct and if not, how would we look at loads due to funnelling?
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Answer
You need to make reference to BS6399-Part 2-1988 and Clause 2.4.1.4
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The Clause is best described by way of a worked example.
We will assume building dimensions of 24m width x 24m depth x 84m high
Funnelling effects the side elevations of a building where the wind flow is accelerated and hence increases the negative wind pressure coefficient (suction). It is a function of the scaling length, b which is taken as the smaller of B or 2H
B = 24m
2H = 2 x 84 = 168 m
b = 24 m
For the side elevation:
0.2b is the scaling length for Zone A = 0.2 x 24 = 4.8 m measured from the front edge.
b is the scaling length for the extent of Zone B = 24 m measured from the front edge.
There is no Zone C in this example as the building depth is 24 m.
Clause 2.4.1.4 states than funnelling needs to be considered if the gap between the adjacent buildings on the side elevation is greater than b/4 (6 m) and less that b (24 m). If it falls outside this range then funnelling is not applicable and you can use the isolated values from Table 5.
Hence funneling needs to be considered within the gap range of 6 m and 24 m.
Specifying gap values outside this range shows no change since the isolated values are being used from Table 5.
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When the gap values fall within the gap range of 6 m and 24 m then in accordance with Clause 4.2.1.4 b) - 2, linear interpolation is used between the funnelling value taken at b/2 (12m) and the isolated values taken at b/4 (6m) and b (24m).
For Zone A
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For Zone B
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Therefore for a gap value between 6 and 12 m:
For Zone A it will range linearily between -1.6 and -0.8
For Zone B it will range linearily between -0.9 and -0.8
i.e 9 m
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