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Re: seaint Digest for 24 Sep 1999

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> From: "vicpeng" <vicpeng(--nospam--at)>
> That's true.  The uplift is as you described.  The lateral loads are the =
> one under discussion.  If the amount of "parapet" is very small then the =
> only loads that I can see are, in the limit, the horizontal vectors =
> calculated from the "perpendicular to member" coefficients acting on the =
> roof planes.  Different slopes give different resultants.  These may be =
> larger than the exposed "parapet" and column loads.  I concur with your =
> assessment but my associate still thinks that calculation is too small =
> and I'm trying to convince him that his fear is not justified. =20
> Thor A Tandy P.Eng, MCSCE
> Victoria BC
> Canada

Check out ASCE publication, Wind Loads and Anchor Bolt Design for
Petrochemical Facilities. They recommend that wind loads be considered
at an angle to horizontal (add 10% of width to the vertical face). This
actually covers two issue; wind with vertical component and deflected
roof alignment. This document is more specific to pipe, vessels and
racks but has some insight into design issues for open framing that
could be applied to other structures.

Although the NBCC defines the wind loading orthogonal to the major
horizontal axes of the structure, wind at, say, 45 deg can have a
significant effect on such a structure.

The above publication goes so far as to suggest 100% in one axis and 50%
in the perpendicular, combined. Again, this is for open framing and may
not be suitable for a roof.

Paul Ransom, P. Eng.
Burlington, Ontario, Canada
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