Need a book? Engineering books recommendations...

# RE: C &C wind load on parapets - really around 45 psf?

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: C &C wind load on parapets - really around 45 psf?
• Date: Tue, 13 Jan 2009 16:56:59 +1030

Another point which may help.

The MWFRS pressure coefficients are determined from the maximum coefficient
which occurs in a 45 degree sector either side of the wind direction
considered: transverse, longitudinal. These give an approximation of the
distribution of wind loading experienced by building as the wind blows in a
given direction. The C&C ignore direction.

ASCE7-05 Fig6-6 indicates that the side wall pressure coefficient is
Cp=-0.7, whilst AS1170.2 indicates the pressure is stepped (-0.65,
-0.5,-0.3,-0.2) in similar manner to that on roof for longitudinal. Note we
have one extra step of 3h.

As move away from windward edge the wall pressure coefficient and roof
the length of the building is reached where the transverse loading is
controlling. Also the windward edge, end frames only have half the load
width of typical frames: so higher pressures there tend not to be critical.

the longitudinal pressure coefficients, until reach a point along length of
roof where longitudinal have stepped lower. So in terms of AS1170.2 we could
be applying the local pressure factor to lower pressures (Use ASCE7 Fig6-6
has suction on both faces of parapet so not critical in terms of maximum
load: just important with respect to location of compression flange. Taking
Cp=+0.8 for windward wall (AS1170.2 has +0.7), then get Cpn=2*(0.8+0.4) =
2.4, smaller than the extreme Cpn=3.2 previously estimated.

Ok! To ASCE7-05 C&C pressures apply irrespective of direction. However what
ever the prescriptive requirements in our codes, the wind pressures are
still distributed across the surfaces. And ASCE7 commentary does indicate
permitted to use any rational methods in the literate: so seek texts and
research papers which identify the distribution.

Good luck.

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