metal deck diaphragm attachment

[vandede427]

For 1.5B roof deck on bar joists which do you think is the more economical way to increase shear strength, increase number of welds on supports or increase number of side lap fasteners?

 

[OHIOMatt]

Really, I doubt that you would see a quantifiable difference either way.

The only way that I have seen a significant cost change is to break the roof into zones based upon the required shear required in a specific area. Each zone could have a different number of welds, side laps and even deck gauge. From experience, I would only make one or two of the above variable with the gauge of material being the biggest potential cost savings. This is, of course based upon the size of the structure. I typically do not zone the roof unless the roof area is more than 40,000 square feet.

The above does make calculating seismic drift more complex as you have a variable deck stiffness, but it is not overwhelming.

As always, introducing variables into construction increases the potential for errors in installation. A simple phone call to the general contractor and the erector to make them aware of this can reduce this risk.