Diaphragm capacity

[sctiger07]

I'm trying to get some clarification on the design of diaphragm collector elements that are interior to a building (ie - deck on both sides) for a frame.

This is my understanding (sketch attached):

For the interior supports, there will be a shear on each side of a single brace (say v1 and v2). The diaphragm capacity from a manufacturers catalog must exceed the greater of v1 and v2.

The support fasteners (in my case, 5/8" diameter puddle welds), must be sized to transfer (v1 + v2) to the support. I'm having trouble figuring out the capacity of the support welds. Welds are at 36/5, and from the AISC spec (for plug welds - not sure that this applies for puddle welds), I end up with a capacity of 4021 plf (ASD), which is much greater than the diaphragm capacity of 1335 plf (ASD). This doesn't seem accurate at all.

Is there a different method for calculating puddle weld capacity? Also, when determining the length of collector elements required, would I use the capacity of the support fasteners (since that's what is transferring the load to the collector) or the published deck capacity?

Sorry for the long post, and thanks for your help!

 

[OHIOMatt]

To calculate the capacity of the weld connected to the deck use the procedures outlines in AWS D1.3.

I would use the published (or better yet code approval such as ICBO report) value. These values are based upon much more than weld capacity such as bucking.

One other idea to consider would be create a "break" in the diaphragm at the collector line. If the collector is wide enough, apply two lines of fasteners as boundary connections (1 from each side of the collector). This way you do not have to add the two shears together.

 

[DaveAtkins]

sctiger07,

You are looking at this correctly.

I believe the reason the puddle welds themselves have a higher capacity than the diaphragm is that the individual sheets of steel decking tend to rotate (in plan), causing two perpendicular components of shear on each puddle weld.

DaveAtkins

 

[ash060]

If it is light gauge deck you have to use the AISI Specification not AISC. Check AISI chapter E