Steel joist roof - can I remove top chord bridging after deck installation? 1

[RichF2]

As the subject says, I'm curious if anyone can provide guidance on whether top chord bridging is required once the roof deck is installed.

I found an SJI webinar that discussed bridging at length, and seemed to suggest that the top chord bridging is only for erection and construction loads. It stops short of saying that the bracing can be removed once the deck is in place.

The Vulcraft manual provide similar information. They discuss how bridging needs to be designed for the lateral bracing loads when standing seam roofing is used, since the roofing can't be used to brace the top chord. That suggests to me that in typical circumstances, the deck is doing the work of lateral bracing. But there is a note in the Vulcraft joist manual, at the start of the bridging section, that says "Top and bottom chord bridging is required and shall consist of one or both of the following types..." Unfortunately, deck isn't discussed as one of those options.

I've got a situation where we are trying to reinforce existing joists to resist drifting snow. The method of reinforcing requires plates at the panel points that will interrupt the top chord bracing. I'd like to find a solid reference that says the top chord bracing is not needed. Otherwise, there will be a lot of additional work reestablishing this bracing.

I've searched the forums here, and seen discussion of the deck providing continuous lateral support, but haven't seen any references that discuss this in a way that makes clear that the deck is the only necessary top chord bracing. Any help is much appreciated!

 

[hokie66]

You probably won't find anything, but steel roof deck, adequately connected to the top chords, provides much more in terms of lateral bracing capacity than does a series of small angles. Roofing would not provide the same capacity, as the Vulcraft manual indicates.

 

[msquared48]

The Vulcraft manual does mention top and BOTTOM chord bridging for a reason - uplift due to wind affecting lateral buckling of the bottom chord member.

Check that load situation at least before removing any bridging.



Mike McCann, PE, SE (WA)

 

[RichF2]

msquared - I know we'll need to keep the bottom chord bridging in place. I'm just hoping we can eliminate the top chord. This will apply to a lot of joists, so any savings will add up.

Alternate solution - does bracing need to occur at panel points? It is located there on this building, but I haven't found anything in Vulcraft that says it needs to be. Maybe we reinstall continuous bracing just to the side of our reinforced panel point?

 

[JAE]

We had a drive through auto garage for a new dealership where we used T&G wood roof decking over the joists. The Owner wanted a "clean" look in that space and asked if we could remove all the bridging.

We checked with Vulcraft and found that the top chord bridging could be removed once the decking was in place.

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[RichF2]

JAE - thanks! That helps a lot. Our joists were manufactured by a company that is now out of business, so we won't be calling them up...but Vulcraft's answer is a good start.

 

[RickyTickyTavi]

That is an elegant look with the wood roof decking over the bar joist

 

[JAE]

Yes - it turned out pretty cool. The challenge was finding an appropriate fastener to go through the thicker decking and self-tap into the joist top chords.
Then a plywood layer on top to serve as a diaphragm.

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