window failures: enclosed v. partial enclosed?

[seattlemike]

Windows are typically designed for a failure rate of 8 or 9 in 1000, that is less than 1%.

However, in modern buildings that are complete curtain walls, each side might have several thousand 2x4 windows in the curtain wall... and typically a few fail... so, that would make one think that ANY curtain wall building should be designed as partially enclosed, regardless of Wind-Debris area?

 

[CFSEng]

Windows are typically designed for a failure rate of 8 or 9 in 1000, that is less than 1%.

Can you please elaborate on what you mean by fail? Positive pressure failure, negative pressure failure, leaking, impact failure...?

 

[seattlemike]

By failure, I mean that they will be sucked off the building, or be blown inward. So, positive or negative pressure failure. I'm not sure which is more common:

Judging from ASCE-02, I'm guessing it's negative pressure, as the negative wall pressures are typically higher.

From SEAW-RSM method, windward (positive) pressure tends to be high, but sidewall (negative) pressure is nearly as high.

This has nothing to do with our structural code, but is more the level of quality the windows are designed to by the manufacturers. <1% can sound pretty good, but after windows have been in service for a time... that 8 or 9 in 1000 could possibly go up.

 

[CFSEng]

So you are assumming that the ~1% glazing failure will only occur on one side of the building, and that side also happens to be the positive pressure side. Hmmm...

 

[seattlemike]

well, after one failure occurs (anywhere), the increased internal pressure causes additional failures at the walls and the roof... it only takes one, then, it all goes to 'partial enclosed' and typically, roofs/ceilings, other windows, etc, get blown out.

the SEAW RSM seems to indicate high negative pressure on the sidewalls as well, so it could be anywhere. And the 3-second gust is indicative that wind is a fluttery beast, that does quickly change direction. Sure some areas have predominant wind directions, like Seattle 85% of high winds are from the S-SW, but...