Glass Design to ASTM E1300 (wind load question)

[ivorm]

I'm wondering if someone familiar with ASTM E1300 can provide a little help with some double glazed sealed glass unit design (curtain wall). I'm in Canada and we typically design glass to CAN/CGSB 12.20. In Canada we use average hourly wind velocity while the US (ASTM) uses 3 second gust. I have unfactored wind pressures from a wind study for a building I'm working on which is based on average hourly windspeed at 10m. Typically I would use that wind pressure and compare it directly to the glass resistance with CAN-CGSB 12.20. However everything in ASTM E1300 references "3 second duration uniform load".

Can I use the unfactored pressures from my wind study and compare it to the unfactored glass resistance calculated using ASTM E1300? Or do I need to convert pressure to average hourly wind velocity, then to 3 second gust, then to a 3 second pressure to be used in ASTM E1300? For a given wind event the pressure is the pressure, it shouldn't matter how it's measured but obviously if you use the following equation to convert a 3 second gust velocity to a pressure versus an average hourly wind velocity to a pressure you're going to get different pressures. The equation below is the same one used in the Canadian code but we use different units which implies the equation is valid for average hourly wind. Would I use the equation below to convert a 3 second gust to a 3 second duration design pressure for ASTM E1300 or would that velocity need to be modified first?

p=0.00256(V^2)

where
p= pressure in psf
V=velocity in mph

Thanks,
Ivor

 

[Ron]

In most of Canada, like most of the US, ASCE 7 shows a wind speed of 90 mph. If you are in the maritimes, you might be looking at 120 mph.

Unfactored, you are using the correct equation. There are generally factors that would be applicable, particularly to components and cladding such as windows.

 

[dik]

As Ron noted, there is a 2.5 factor for cladding (and windows) and elements. Your approach is conservative because with the 3 second gust, the wind pressure is never uniform. Based on a short term spectra, your 3 second gust may only be affecting a few square feet.

Dik

 

[oldestguy]

A curious question. Noting the TV showing of a climber going up the outside of the Trump Towers in NYC recently, does the design for high wind presure at least equal the forces of a man hanging onto suction cups as he navigates up the glass enclosed building?

 

[hokie66]

oldestguy,
Yes, the wind design pressures are similar to those used for residential floor loading. Varies a lot by geographical location, but glass on high rise buildings is supposed to be strong. But saying that, I wouldn't trust it like that fool. Sometimes, glass falls of it own volition due to defects.

 

[ivorm]

So ASTM E1300 would be using a 3 second gust for calculating wind pressure? In that case I would need to convert my hourly wind pressure to a 3 second gust wind pressure in order to use the charts in ASTM E1300.