Steel Roof Deck - Propped Cantilever Diaphragm

[StrEng007]

Does anybody know of a reference for a steel deck roof diaphragm, analyzed as a propped cantilever?

For transverse loading (wind travelling north/south), my rectangular single story building has one full length shear wall at the west perimeter of the building. The other (3) perimeter walls (north, east, south) are open post & beam framing, supporting gravity and out-of-plane loading, and not assumed to be part of the LFRS. Longitudinal wind is braced by an adjacent, taller, structure.

For transverse loading, I'm looking to resolve my shear into the shear wall. Eccentric rotation of the diaphragm will be taken out into two joists (struts) at the north and south end of the diaphragm.

My approach is:
1. Qualify the roof diaphragm as rigid in order to perform a cantilever diaphragm analysis.
2. Determine shear requirements at origin of diaphragm.
3. Determine shear capacity. Are there any aspect ratio limitations or cantilever diaphragm restrictions similar to those in the SDPWS for wood diaphragms?
4. Resolve the eccentric diaphragm load into two joists (struts) that act as a force couple.

I've read through the examples presented in "THE ANALYSIS OF IRREGULAR SHAPED STRUCTURES". These design examples focus on wood diaphragms and do not present an example such as mine (1 load bearing perimeter shear wall, 3 non-lateral force resisting perimeter walls). This scenario isn't discussed in SDI's DDM04, either.

Thank you.

 

[jayrod12]

I would also be checking diaphragm deflection to see if the drift is more than tolerable.

 

[lexeng18]

I would imagine that as long as the north and south walls can transfer the chord forces as axial load into your adjacent structure, there should be no issue. It’s a three sided diaphragm.

As jayrod mentioned these usually have concerns with deflection. Every time I have designed a three sided diaphragm, I have ensured that it is oriented opposite of your situation. As in if your structure can be thought of as a channel in plan view, usually you want the longer building direction to make up the “web” of the channel.

 

[hokie66]

Diaphragm cantilevered off what? As you described it, you only have a shear resisting element on one side. Resolving the force couple into joists at the ends only works if the load in those joists has a way of getting to the ground. But maybe the taller adjacent structure resists these forces?