Roof diaphragm action with horizontal steel bracing 3

[Waldoa]

We are designing a large commercial warehouse. The distance from the exteriors vertical bracing are large (around 300 ft.)
We have a large axial load in the roof steel deck diaphragm, the loads exceed the resistance of the connectors of the deck. We decide to use steel angle (2L) sections as horizontal bracing to withstand the large axial loads. I was wondering if we can share the loads between the deck diaphragm and the steel horizontal bracing sections, and we would consider the relative stiffness to share the loads between the two systems. Anyone have done this before? any literature is available to verify these assumptions?
Thanks!

 

[BAretired]

Perhaps you should consider a trussed system and forget about diaphragm action.

BA

 

[XR250]

could you go to a heavier deck?

 

[hokie66]

It should be one or the other. In order for a truss to work, the diaphragm connections would have to fail first.

 

[Istructeuk]

Yes, you can.

http://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=1246&context=isccss

 

[DaveAtkins]

We have a large axial load in the roof steel deck diaphragm

What kind of axial load are you talking about? Are you talking about the chord force? Because once the chord force is out of the deck and into the chord member, it no longer adds to the force on the deck welds.

DaveAtkins

 

[MotorCity]

Maybe I am not understanding the problem, but how can you share the load between the deck and the angles if the force exceeds the capacity of the connectors between them?

 

[Waldoa]

Thanks Istructeuk for the document, really helpful!!
Motorcity, my issue is that the seismic loads acting the steel deck exceed the connectors capacity of the deck, even with a spacing of 6 inches between the connectors. Then I will need to add horizontal x-braced to withstand the excessive loads and theses load will be transfert through their gusset plates.

 

[KootK]

You might consider using Hilti pins instead of welds to fasten the deck. They fail in a fairly ductile manner which, to some extent, may relieve you of having to be very accurate with your stiffness determinations.

I've looked as a couple of very long diaphragms. They warrant some extra consideration when it comes to p-delta effects. The tops of the columns in the middle of the diaphragm will lean the amount of drift in the vertical bracing plus the midspan deflection of the diaphragm. On a 300ft roof, the latter may be significant and add to the load on the diaphragm.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.