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Re: minimum wind loads in the IBC

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minimum wind loads in the IBC> 1.      Section 1609.1.2 of the 2000 IBC
states the wind loads used in
> the design of the main wind-force-resisting system shall not be less
> then 10 psf multiplied by the area of the building or structure projected
> on a vertical plan normal to the wind direction (and similarly 10 psf is
> the minimum wind load for components and cladding and also for
> open structures).  However, footnote c in table 1609.6.2.1(1) states if
> the pressure is less than 0, use 0 for the horizontal roof loads for the
> end zone and the interior zone for MWFRS.  It seems to me there is a
> contradiction between them.  What do you use and why.

I don't see a contradiction, I see two load cases.  Check with higher loads
on the wall and low to zero load on the roof, then check with 10 psf
everywhere.  If the wall loads are fairly low, then the 10 psf everywhere
will likely control.

> 2.      When the forces are developed do you apply them uniformly
> across the building width and then the average plf is applied to the
> shear walls [if you calculate the end zone width and the interior zone
> width multiplied by the appropriate height (gives area) times value in
> the table (psf) gives the resultant force in #'s then sum the forces from
> both zones and divide by the building width to get average plf]  OR do
> you calculate the plf in the end zone and in the interior zone and then
> apply it to the tributary area and then distribute the force into the
> walls.

I pretend it's a horizontal beam: the wind is a varying load and the braced
panels are supports.  The end zone winds basically go into the shear walls
nearest to them.

> 3.      If it worked out that the calculated edge strip (a) is 3' and
> therefore the width of the end zone is 2a = 6', and the building is 50'
> wide would there be a 6' end zone on each end and the width of the
> interior zone be 38'?  See figure 1609.6(1) or would there be a 3' end
> zone on each end and the interior zone would be 54'?

The loading shown in Figure 1609.6(1) is intended to induce torsion similar
to accidental eccentricity in seismic design.  You have 8 load cases - two
for each corner of the building.  So in your example, you would have one 6'
strip on one end of the building with the extra load going into the braced
panels on that side.

Jason Kilgore
Leigh & O'Kane, L.L.C.

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