AISC Seismic Design Manual Diaphragm

[karthik_m]

Hello, please see the picture attached. A page from example 8.4 of AISC Seismic Design Manual Pg8-21. I'm trying to understand what does the statement below the calculation mean: "Note a mechanism needs to be provided to transfer the force from the slab reinforcement into the structure" ?

 

[phamENG]

Prior to this example, they select a steel beam as a collector - presumably over a large window opening or something of that nature - to span between shear walls. The slab (diaphragm) would be connected to this collector along its length and then the collector is connected to the shear walls at each end (or braced frame, or moment frame, or whatever other LFRS you're using).

If you use the slab itself as a collector, you don't have that continuous connection and you end up with a connection of the slab (specifically the collector portion of the slab) to the shear walls. All they're saying is that you can't just add reinforcement to the slab and be done with it. That reinforcement is carrying an axial load, and it needs a defined load path at its ends.

 

[JoshPlumSE]

What phamEng said.... It just means you have to check the load path from the diaphragm into main lateral force resisting system (shear wall, moment frame, braced frame). This could be studs on the top of a collector element, or it could be detailing of the slab to shear wall connection to take this force.