NBCC Commentary I: Light tower wind loads
NBCC Commentary I: Light tower wind loads
(OP)
Greeting eng-tips forums,
I am working on designing a 18m cantilever pole light tower according the the National Building Code of Canada, using Commentary I and the dynamic procedures.
The details are as follows:
Wind pressure, q: 0.28 kPa
Height, H: 18.25 m
Width ave, w: 0.4 m
Natural Freq, fn: 0.045 Hz (EI~ 67*10^12 Nmm2, p~ 105 kg/m)
Critical Damping, B: 0.5%
Working through paragraphs 46 to 56 of Commentary I, I have come up with a Cg (gust factor) of 9.4. This value struck me as being very high, is anyone familiar with this piece of code and willing to chip in two cents?
Also, if you are familiar with the code, is figure I-24 of the Commentaries intended for this type of design and can you point out any recommended reading to understand their use of Cf and Cp separably?
Regards,
wadavis
I am working on designing a 18m cantilever pole light tower according the the National Building Code of Canada, using Commentary I and the dynamic procedures.
The details are as follows:
Wind pressure, q: 0.28 kPa
Height, H: 18.25 m
Width ave, w: 0.4 m
Natural Freq, fn: 0.045 Hz (EI~ 67*10^12 Nmm2, p~ 105 kg/m)
Critical Damping, B: 0.5%
Working through paragraphs 46 to 56 of Commentary I, I have come up with a Cg (gust factor) of 9.4. This value struck me as being very high, is anyone familiar with this piece of code and willing to chip in two cents?
Also, if you are familiar with the code, is figure I-24 of the Commentaries intended for this type of design and can you point out any recommended reading to understand their use of Cf and Cp separably?
Regards,
wadavis






RE: NBCC Commentary I: Light tower wind loads
Dik
RE: NBCC Commentary I: Light tower wind loads
RE: NBCC Commentary I: Light tower wind loads
Dik
RE: NBCC Commentary I: Light tower wind loads
RE: NBCC Commentary I: Light tower wind loads
Attached is the SMathStudio file with the numbers plugged.
For Y I'm using =39.2*SQRT(0.28 kPa)
wadavis
RE: NBCC Commentary I: Light tower wind loads
Dik
RE: NBCC Commentary I: Light tower wind loads
RE: NBCC Commentary I: Light tower wind loads
I see that CSA S6 recommends a Cg of 2.5 for lighter structures / slender structural elements / light standards. That looks like the similar approach Commentary I took with the static analysis of structural components.
It is a degree of confidence for using the less conservative method.