Metal Deck Diaphragm 1

[slickdeals]

Folks,
Please excuse my ignorance on the behavior of metal deck diaphragms. I have a few basic things that I am trying to get my head around.

Assume that I have a 1.5" metal deck spanning 5'-0" o.c between roof joists. The building is 100' wide and 50' long. There are shear walls at each end (one at 0' and one at 100'). The diaphragm spans 100' between these shear walls. The shear is perpendicular to the flutes of the deck.

For the deck to behave as a deep beam, sufficient side lap connectors must be provided. Are these side lap fasteners designed based on shear flow with highest number needed at mid depth of diaphragm? I am thinking of 3' wide pieces of deck connected by side lap fasteners that help to make it a 50' deep beam. I have searched online quite a bit but not found any answers that explain it.

The interior joist connections are required mainly to transmit uplift and no wind shear. However, the end connection to the shear walls will need to transfer a lot of shear and uplift.

The deck to chord connection will need to transfer diaphragm tension/compression to the chord member. This will be attained through side lap connections in the above case. Do you vary the number of side lap connections based on how much the tension/compression drops away near the supports?

I may have more questions based on your answers.

 

[SteelPE]

When we have run into problems like this before (not being able to get the decking shear diaphragm to work) we have added frames in the middle of the building.

Another option is to ignore the metal diaphragm and use a horizontal roof truss made out of 3/8" thick plate. The 3/8" plate can rest on top of the joists and can easily fit in-between the joists TC and the decking. However, you can't go much thicker than 3/8". The 3/8" straps act as tension only members and you must include the drag forces in the joist TC.

This is covered in the Fisher book Designing with Steel Joits, Joist Girders and Steel Deck. I just attended a seminar with Fisher where he covered the detailing and design procedure for this case.

Are you requiring a single 18ga or 16ga deck? or would it be a double 18ga or 16ga deck? I can't say that I have ever doubled up the deck to gain diaphragm strength. If you are looking at a double 22ga vs a sing 16 ga, I would just use the single 16ga decking.