Curtainwall deflections

[Galambos]

When dealing with curtain walls that bypass a steel framed floor, and are tied back laterally and supported for gravity by the spandrels, is it typical to denote the live load deflections in the plans?

I have a curtainwall manufacturer that has designed all of his joints to take 1/8" vertical movement from the structure over a 30 ft span, which turns out to be L/2880. He had made the 1/8" assumption because deflections were not listed. I have never had this issue come up, but it seems a little outrageous.

Thoughts?

 

[msquared48]

Kinda depends on the allowance provided between the glass pane and the mullion. Is that their normal standard to provide?

I would normally expect 1/8 to 1/4" play at ther glass/mullion interface with a lateral deflection allowance normal to the wall of at least L/600, maybe L/1000.

Mike McCann
MMC Engineering

 

[rapt]

Galambos,

If there has been no contact with curtain wall suppliers pre design, you need to define the design limits in the documentation/specs for the curtain wall so thatn they know what to base their design on.

Curtain wall manufacturers normally have very stringent deflection criteria, especially in a competitive pricing situation, so you need to make sure they are all quoting on the same limits. If no limit is specified, they will design the cheapest option, which allows the smallest vertical deflection!

There was once a curtain wall manufacturer in UK who reguired 0 deflection!

 

[SteelPE]

If the building is designed in accordance with the building code, I don't see how the curtainwall mfr could possibly end up with a deflection this small. In absence of specs on the drawings wouldn't the building code then be followed?

I have had conversations with GC's before about a similar situation. They asked what my deflection was to which I responded "within the limits of the building code" (yeah I was a jerk). They wanted to hold 1/4" on a roof member that was 30 feet long. My deflection was about 3x what they were requesting but well within the requirements of the code.