Cold Formed Backup Wall Design
Cold Formed Backup Wall Design
(OP)
I'm giving the architect estimate of size/gage for CF studs in a backup wall, eventually to be designed by others. The floor to floor is almost 15ft, so clear span of the studs is a little over 14ft. The jambs are about every 8.5ft on center.
- When looking at load path should I assume windows span vertically when sizing header and span horizontally when sizing jamb? i.e. take most conservative load path for each.
- At 14+ft the jambs appear to be very heavy. At what ga does it make sense to go to structural steel (say hss).
- When looking at load path should I assume windows span vertically when sizing header and span horizontally when sizing jamb? i.e. take most conservative load path for each.
- At 14+ft the jambs appear to be very heavy. At what ga does it make sense to go to structural steel (say hss).






RE: Cold Formed Backup Wall Design
I do the same as far as load paths go. Unless the windows are really tall, I always size the jambs using a distributed horizontal load based on the 1/2(center to center spacing + 16" to the next stud.).
You should be able to do "heavy" light gage for the jambs on something like that as long as the wind speed is not too high. I always try to do a single, heavy gage jamb rather than having them build up multiple studs and dealing with the eccentricity. 12ga or even 10ga is certainly reasonable if you want to stay out of structural steel.
RE: Cold Formed Backup Wall Design
RE: Cold Formed Backup Wall Design
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Cold Formed Backup Wall Design
RE: Cold Formed Backup Wall Design
RE: Cold Formed Backup Wall Design
I'm curious, what makes you say this? Certainly, I agree for most operable windows. I've often wondered how window suppliers themselves see their windows spanning.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Cold Formed Backup Wall Design
RE: Cold Formed Backup Wall Design
http://imgur.com/a/JjYBC
I sat through a lunch & learn a while back with a glazing guy who told us glass panes typically distribute load in a two-way fashion until the aspect ratio hits about 1.5:1. Beyond that it's still not a perfect one-way distribution because the corners are still anchored. Since it's less effort to distribute one-way, I've stuck with it for simplicity unless I believe it's clearly an incorrect assumption. I don't have a source on this but it was a local curtain wall rep and I was more interested in the free lunch...
jayrod12,
There can easily be a difference in what the window manufacturers assume and what we design for. If you have a glazing system that has square panes, each pane will distribute load in two directions, no argument there. But if this load is ultimately sent into vertical mullions, it'll end up in the head and sill, which is what matters to us in terms of design.
RE: Cold Formed Backup Wall Design
I always just worst case everything in my design.
RE: Cold Formed Backup Wall Design
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.