WF Beams and Bridging Requirements

[SteelPE]

I am currently working on a project that, due to product shortages, is utilizing WF beams on the roof. Ideally we would have liked to use open-web steel joists but their lead time is out of control right now (supposedly out 11 months from date of order). Now that we are switching to WF beams I am having some questions in regards to bridging on these systems. Does anyone use bridging on WF framed roofs?

In particular, I am a bit concerned about roof uplift. Now, it's not an overly difficult calculation, however, my client is steaming mad that I am asking for a row of bridging at the roof to help with roof uplift. He sends me examples of projects showing similar WF beam framed roofs that do not require bridging..... however, while on the surface these systems appear to be the same, they are not... as we are spanning beams 52' @ 10'-0" o.c. using 3" roof deck. He is giving example projects with beams spanning 20' @ 5'-0" o.c. spacing. I have tried to calmly tell him that you are not comparing apples to apples but he just doesn't get what I am trying to tell him.

 

[jdcollins]

We've recently had to do a few projects with the exact same problem. A typical 5'-0" joist spacing with 1-1/2" deck becoming a 10'-0" beam spacing with 3" deck. I've always specified bridging angles. Bottom flange bridging for the in service uplift condition as well as top flange bridging for the stability during construction if I felt it was required. It's obviously dependent on your span/spacing/loading conditions, but I've never really gotten any complaints from it.

 

[OHIOMatt]

We always use bolt angle x-braces between wf joists. Usually at 8 to 10 feet on center.

 

[sbisteel]

I've had to do the same. We've analyzed for uplift and provided bridging as required for the bottom flange unbraced length. We've also analyzed the roof beams for a 20psf construction live load, considering the beam top flanges unbraced by the deck, adding bridging as required. It can get pricey depending on how you connect the bridging, especially X braces.

 

[SteelPE]

The argument has been made that the erector is responsibility of the beams during construction..... therefore the is no need for erection stability bridging. The argument comes from the fact that they install similar composite beam and deck systems all the time without they need for stability bridging during erection. However, I stopped the argument at roof uplift.

 

[jayrod12]

I was going to say, I'd bet their examples are of floor systems and therefore not subject to uplift.

Alternately, you could have said, "Sure, we can eliminate the bridging, however that causes the beam size to be increased to WXX x XX to accommodate the uplift and the unbraced length of the bottom flange." Once they see the new sizing I'd bet they feel a line or two of angle bridging and a couple of cross braces looks cheap in comparison.

 

[SteelPE]

jayrod,

No, they have plenty of examples of roof designs using WF beams, but unless all of the parameters are know then it's impossible to compare buildings.

Also, yes, I did tell him that putting concrete on the roof was possible..... but that would yield an increase in construction costs. I also told him that another option was to increase the beam size to get the beam to work with the unbraced length, but these beams are 52' long..... so I would think it would be easier to just add the bridging.

I am literally explaining this to a 30 something punk whos has so much success that he thinks his opinions are correct even though he doesn't have a clue what he is talking about..... and every time I explain the situation to him I swear he is singing the meow mix song in his head.

 

[jayrod12]

singing the meow mix song in his head.

Thanks for that, now I've got it stuck in my head.

Meow meow meow meow, meow meow meow meow, meow meow meow meow meow meow meow meow.