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• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: Wind Pressure Below Grade?
• From: Rick.Drake(--nospam--at)fluordaniel.com
• Date: Wed, 2 Sep 1998 16:33:19 -0400

```Brian A. Peterson wrote:

<<I am looking for information and/or opinions on wind pressures at the

We install temporary containment structures in graving docks to
blast/paint ship's structure.  The docks are 30 to 60 ft. deep adjacent to
the water's edge, and ~100 ft. wide by ~1000 ft. long.  A containment may
be installed in the base of the dock then rise above the "ground" level.

For design, at above dock height I use standard wind load calculations
from UBC and/or ASCE 7-95.  At dock height and below, for lack of other
criteria, I have used 10 psf based on ASCE 7-95 "minimum design wind
loading."  Depending on the depth below "ground" level, this may or may
not be conservative.  To add to the problem, any ship in dock will
undoubtedly have a channeling effect on the wind- but that's another
story.

Barring major wind tunnel testing (not justified for temporary
structures(?)), I would like an idea of whether or not I am on track with
these assumptions.  Any help is appreciated.>>

*************************

Another way to look at this problem is to consider what happens as the wind
stream hits the abrupt obstruction of a building.  The windward side
experiences a positive pressure and the other sides and roof experience a
negative pressure.  The wind going into your pit like a negative
obstruction and is going to put both positive and negative pressures on
your pit walls and any ship surfaces in the pit.

In this line of thinking, I would use the wall pressure coefficients from
Figure 6-3 of ASCE 7-95, Cp = +0.8 to -0.7.  I would calculate qz based on
60 feet and appropriate exposure category.  Running out the numbers will
give you close to 10 psf for Exposure Category C.

Your number of 10 psf as a minimum seems reasonable.  Make sure you apply
it both positive and negative.

Rick Drake, SE
Fluor Daniel, Irvine

```