My contractor wants to hang stairs off my braced frame 1

[kkt5018]

I'm checking shop drawings for a particular project and have run into some conflicts with stair hangers and the building's braced frames, which rise up alongside the stair. The contractor originally intended to hang the stairs eccentrically off of a horizontal braced frame member that was not sized for that sort of torsion. I've been looking for some solutions to this issue, and a (much more experienced) coworker asked if it were possible to hang parts of the stair off of the diagonal members of the braced frame. Has anyone had experience with this? Where in the US codes can I find any references as to whether or not this is allowed?

 

[hokie66]

You just have to follow the forces. Don't depend on a code to solve this type of structural concept issue.

 

[kkt5018]

I'm more concerned about whether or not local building codes allow life safety stairs to be hung off of diagonal braces than the design. Are there any limitations?

 

[strucguy]

If you can think of other reasonable ways to support the stair please suggest the same in your review. We design stairs occasionally and find it next to impossible to get the support we want for some of the stair because apparently the A/E hasn't thought through. So, many a times I end up calling them before I make any assumption. Most of the times the issue is resolved by adding a hanger, a post or additional framing member. Sometimes the EOR is forced to resize some of the members, but many times there is enough meat in the structure to handle additional stair loads. So, feel free to make a quick phone call and always keep the Arch and GC in the loop. Good luck!

 

[kkt5018]

We are the EOR in this particular case. We proportioned the framing so that the stairs would be supported differently. In this instance, we are looking to see if anyone has had experience with detailing a hanger from seismic lateral bracing. The deformations between the life safety stair and the bracing will be quite different. Thoughts?

 

[CELinOttawa]

Bad idea.

 

[wannabeSE]

What kind of braced frame? In high seismic areas, it is probably a real bad idea if the brace is designed to buckle in compression or yield in tension. If the stair are needed for emergency egress, I would be very hesitant to attach them to a brace that could yield or buckle. Also, AISC 341 specifies protected zones on some of the high seismic braces.

 

[a2mfk]

Maybe post a snapshot of the drawings and maybe we can help you find a solution that does not involve the diagonal bracing?

I agree that this sounds like a bad idea due to the life safety and egress function of the stairs (if not particularly prohibited by code). I would like the redundancy of it not being tied into the lateral force system.

 

[rb1957]

my 2c would be to add extra diagonal bracing to support the pick-up points

Quando Omni Flunkus Moritati

 

[Bagman2524]

Hokie66 is correct. IBC/NFPA-101 don't tell you how to support a stair. Your structure just needs to be designed to support it with the stair loads included. Extra diagonal bracing or diagonal bracing and other supporting members sized to support the stair is acceptable.

“Faith is taking the first step even when you don’t see the whole staircase.” MLK

 

[dhengr]

Kkt5018:
You said.... “We are the EOR in this particular case. We proportioned the framing so that the stairs would be supported differently.” But then, you didn’t bother to show the support points and loads on your plans and say ‘stairs go here.’ How does that happen? How did the contractor know what part of the building to put the stair in? I suppose the BIM model showed places were a stair wouldn’t clash (new technical terminology) with the sewer. It would have saved even more engineering time and effort if you had just put a note on the blank sheet, something like, “20 columns, and 37 beams, contractor to select all sizes and locations, don’t forget bolts and footings.” And, stamped em.

 

[kylesito]

Dhengr...a little harsh, huh? BIM or no BIM, conflicts occur in drawings. I'm sure you pick up every piece of miscellaneous steel in your designs though, 100% of the time, right?

Hokie is correct. Although not desirable, it can be done as long as you account for the extra torsion/bending induced in your framing as a result. If your braces won't take the extra load (including P-Delta), then you need to work out another solution...maybe add a runner below your braces that's connected to the floor beams to pick up the stairs?



PE, SE
Eastern United States

"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi