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Home > Forums > Structural Engineers > Activities > Structural engineering other technical topics Forum

1997 UBC Wind Loads for Components

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Berniedog (Structural) (OP)

16 Oct 08 11:20

Has anyone ever compared the ASCE 7-02 component wind loads to the 1997 UBC wind loads for components? We started reviewing shop drawings for a project for claddding and girts for a transfer tower using the ASCE spec. and then found out we had to use the UBC. My calcs. show an increase in wind load of 50%. They are saying I am wrong but at this time won't review my calculations. It is costing the fabricator money.

It is exposure C at 105' high, 90 mph, 68 sf. area of cladding for the girt loading.

Thanks

JAE (Structural)

16 Oct 08 15:47

Here's what I get:

UBC 97
Wind - 90 mph
Exp C
Height - 105'
Area 68 sf

qs = 20.8 psf

Wall Elements not in areas of discontinuity - enclosed and unenclosed buildings
Area = 10 sf:  +/- 40.6 psf
Area = 100 sf:  +/- 30.4 psf

Wall Elements not in areas of discontinuity - partially enclosed buildings
Area = 10 sf:  - 54.1 psf
Area = 100 sf: - 43.9 psf

Wall Elements in areas of discontinuity
Area = 10 sf:  + 40.6 psf and -50.7 psf
Area = 100 sf:  + 30.4 psf and -40.6 psf

WAMRE (Structural)

16 Oct 08 19:40

Make sure you are using the correct/converted wind speeds between the two methods... then I believe they should be fairly close for the resultant pressures (not 50% difference).

UBC uses 'fastest mile' wind speed
ASCE uses '3 second gust' wind speed

90mph(3 second gust) converts to approximately a 76mph(fastest mile) wind speed.
or
90mph(fastest mile) converts to approximately a 105mph(3 second gust) wind speed.

Berniedog (Structural) (OP)

17 Oct 08 8:57

JAE WAMRE Thanks. Can you take a look at the following:

P=Ce*Cq*qs*Iw
Ce=1.62
Iw=1.15
Qs=20.8
Wall Elements not in areas of discontinuity - enclosed and unenclosed buildings
A=68sf. Cq:1.01
P=39.1 psf- inward & outward

Roof Elements not in areas of discontinuity - enclosed and unenclosed buildings
Cq=1.11
P=43.04 outward

Wall Elements in areas of discontinuity
Cq=1.01 inward
Cq=1.31 outward

p=39.1 psf inward
p= 50.8 psf outward

Roof Elements in areas of discontinuity - enclosed and unenclosed buildings
Cq=1.78

P=69.0 psf outward

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