Modifying windbracing

[Micah Davis]

Hello All,

I am a fire sprinkler designer and have a question about the ±1" windbracing welded to the bottom cord of the bar joists on a project we have recently completed. Due to an oversight on my part during the construction phase, we have installed some of our sprinklers directly above this bracing in several areas throughout the building. The sprinklers are Early Suppression Fast Response (ESFR) and as such have very stringent rules regarding obstructions. This windbracing qualifies as an obstruction to the discharge pattern of the sprinkler and we are analyzing the situation to determine the best fix for all involved.

Relocating our sprinkler piping is possible, but would be a pretty massive undertaking. I'm looking for some direction on whether it would be worth while for us to consider relocating the windbracing or replacing it with a material less than ¾" as possible solutions. I understand it would require the structural engineer analyzing any such plan and signing off on it, but from a practical standpoint am I right in thinking it could potentially be a workable solution.

Beyond this specific question, do any other possible solutions come to mind?

Thank you for your consideration!

 

[KootK]

Do you have a photo that you can share? I'm guessing that what you're calling wind bracing is really joist bridging. And that would probably be good news as bridging would be less critical and therefore easier to deal with.

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.

 

[Micah Davis]

I do not have a picture, but I looked again at the structural framing plans and it is indeed called out as bridging. The plan specifically says, "3 rows of continuous joist bridging typ w/ diagonal x-bridging where shown."

 

[mike20793]

Is this in a high wind area? The Steel Joist Institute allows for bottom chord and top chord bridging to be spaced independently of each other, but if this is a high wind zone, then the bottom chord bridging might be used to brace the bottom chord when it is compression from uplift forces. If that is the case, the bridging may not be able to be relocated. SJI gives some upper limits on spacing based on the slenderness of the briding, but this is probably a question the joist manufacturer should answer.

 

[KootK]

You generally need some bottom chord bracing, even if the bottom chord remains in tension under all load cases. That said, relocating the bridging line, perhaps in conjunction with adding another locally, should be entirely doable. Replacing the 1" bridging with 3/4" bridging may prove to be a solid idea as well.

If you're able, provide us with a scan of the relevant portion of that roof framing plan. Include the location of your sprinkler heads, the location of the bridging, and some indication of the zone over which obstructions are not allowed. You're still going to need a local structural engineer to sign off on it but we should be able to come up with a solution that has a very high probability of being accepted by whomever you wind up dealing with. It would also be good to know what kind of section has been used for the bridging. I'm guessing hot rolled, 1" angles.



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.

 

[Micah Davis]

mike20193
I would have to dig deeper to find out if we are in a high wind area. The snapshot of the of the framing plan below shows a note about the joist wind uplift if that clarifies anything.

KootK
I've attached an overlay of the structure and my sprinkler piping at one of the problem areas. I've also attached the same area of the structural plan itself. The no-go zone on the sprinkler for object ¾" to 1¼" is 12" in each direction and 16" vertically down from the sprinkler deflector. The bar joists are 24" and the sprinkler deflectors are approx. 12" down from the top of the joist. I can't confirm the kind of section for the bridging, but 1" angles sounds about right based on my visual inspections from the floor.

 

[EngineeringEric]

It should be more than doable to move the bridging or replace the bridging. I would recommend contacting the joist Manufacturer (Vulcraft or New Millennium or Other) and ask them. They may provide a repair that you can then send to the EOR for approval. And you better mention to the GC that you are willing to pay for the time required


EDIT:
I am only saying it should be do-able, not certain. Don't quote some stranger on the internet! Good luck!

 

[Micah Davis]

Thank you for the suggestions, EngineeringEric! I will track down the joist manufacturer and begin a discussion with them as well. We worked directly with the owner on this one. I have made it clear that this was our mistake and we will do whatever it takes to resolve it!

 

[KootK]

You could:

1) Delete the offending bridging line.

2) Add a similar bridging line one truss panel point to the right of original.

3) Add a similar bridging line one truss panel point to the left of original.

That should absolutely work and I would consider it the upper limit of what might be needed. The joist manufacturer or a local engineer can provably whittle that down to a single line of new bracing or maybe even nothing at all.

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.

 

[Micah Davis]

Good deal. That is what I was hoping to hear. I will start pursuing this with the owner and engineer and/or joist manufacturer. A much easier solution I believe than relocating the sprinkler branch lines. Thank you very much!!

 

[KootK]

You're welcome. On behalf of team structural, I applaud the responsible approach that you're taking with this.

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.