Need a book? Engineering books recommendations...

# RE: Wind load on sloped roof with parapet

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Wind load on sloped roof with parapet
• Date: Fri, 5 Dec 2008 10:29:34 +1030

```Jeff,

>From a brief glance at ASCE07-05, B & D zones, appear to be the horizontal
pressures on the sloping roof surface, and may well be close to zero (though
not sure -- represents zero for interpolation purposes). Whilst A & C are
the wall pressures. I would assume the parapet is an extension of the wall
and apply the wall pressures the full height, from ground level to top of
parapet.

Irrespective of transverse or longitudinal directions the typical
distribution is:

Positive pressure to windward wall, suction to leeward wall, with side walls
experiencing suction which is highest at the windward edge and diminishes
(magnitude) towards the leeward edge. The roof pressure likewise experiences
suction which is typically highest at the wind ward edge and diminishes
towards the leeward edge. Depending on the roof pitch, for the transverse
direction, the windward face may become positive, with the leeward face
remaining with suction.

For whole building stability the appropriate pressures should be applied to
all surfaces at the same time. If designing a framed structure rather than
diaphragm box then can apply conservative pressure coefficients to
the parapet as a cantilever above the roof.

The parapet has a windward face, and a leeward face, and doesn't really have
a top or side faces. The windward face has the windward wall pressure, and
the leeward face has the roof pressure coefficient. That is the pressure
coefficient normal to the roof surface is experienced normal to the parapet
wall surface: not horizontal components there off. It is fluid pressure,
experienced at a surface. Typically pressure towards one face, and away from
the other: therefore net pressure sum of absolute magnitudes. (Transversely)

Longitudinally, the parapet experiences suction as a sidewall, and suction
on roof side face from roof surface. To pressures away from each other,
therefore net lower, therefore not critical condition.

Regards
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic(--nospam--at)bigpond.com
South Australia

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted