Roof deck bending 1

[CTSeng]

I have a steel deck (1.5") on bar joists 5' OC, narrow building with 2 bays steel beam running down the middle and masonry walls on exterior. Planning to slope joists 1/4" per foot to middle to roof drains. Architect wants to know if we can slope to outer steel beams that attach at the wall as well. I have concerns that the deck will not be able to step/bend as joist bearing elevations increase to outside wall. It does not seem reasonable to think the deck in the stiff direction will bend 1-1/4" between joists. Has anyone done this before? Is there a problem with the deck bending or kinking?

 

[jike]

As I understand your description, you would like the deck to warp in the strong direction, is that correct?

We have had similar requests from Architects over the years. One possible solution that we have used is to field cut the top of the deck directly over a structural supporting member so it can be bent down to the adjacent member. You should check the capacity of the deck, because you are creating a different span condition, thus weakening it.

 

[broekie]

Contact Vulcraft. They'll be able to tell you how much their deck can bend/kink.

 

[kvillebasser]

We occasionally get requests from architects like this.

I typically will not allow the metal deck to be "warped" or sloped in two directions at the same time. Occasionally I'm asked if the deck could be cut over the supports to provide a "warped" surface. I typically will not allow that to happen, as I am much more comfortable with my diaphragm knowing that its not cut at every support.

My reommendation to you would be to have the archtiect provide the warped surface with tapered insulation. Not only do I feel as though this is the best engineering solution, but I wouldnt be surprised if it was cheaper also.

 

[CTSeng]

I agree completely, thanks for the confirmation. Now the hard part ... beating into the architects head.

Thanks kvillebasser

 

[jike]

If the deck is fastened to the member on both sides of the cut, there should be no affect on the diaphragm strength. It is no different then a normal deck splice.

I see no reason that the deck would ever have to be cut over every joist. It would be only over one joist (where the deck slope changes drastically) and just for a short distance.

 

[jheidt2543]

I agree with kvillebasser!

Hey, CTSeng, I can lend you a maul if you need one, although with the price of steel right now, maybe a 2x4 would be cheeper and more enviornmentally "friendly"!