I have a multi story concrete structure that I am using RAM structural to model. The majority of the structure is post-tensioned slab, with a couple areas that are 1-way slabs with beams (at an elevated pool deck). I have seen in some posts that it is not recommended to mix 1-way and 2-way slab in RAM SS.
I am wondering if I should model the slabs as 1-way and 2-way slabs, or should I model all the slabs as 2-way and adjust as required? I am running the diaphragm as semi-rigid.
I am concerned that the 1-way slab is not distributing the lateral load properly through as a diaphragm, which results in larger story/building drift. If I have a 1-way slab on gravity beams with 2-way slab around the area, does the 1-way slab transfer the lateral load (contribute to the diaphragm) if run as semi-rigid?
If I model all the slab as 2-way, I am concerned the gravity load is not being distributed correctly to the gravity beams in the 1-way slab areas.
Any recommendations for how to model this type of condition in RAM SS and ensure that the loads are being transferred accurately?
Thanks is advance for any assistance you can provide.
The reason we caution against hybrid decks is that once any portion of the diaphragm is 2-way, the whole thing has to get meshed. If you are using a semi-rigid diaphragm anyway, that not an issue since it being meshed already. RAMSS Two Way Decks
The other thing that is tricky in hybrid decks is the determination of loads on the beams that straddle the two deck types. On the 1-way deck side, simple tributary loads are calculated and applied to the beam, on the 2-way deck side the deck is meshed and loads are applied to the nodes of the mesh (these loads are part of the meshing process and not shown in the external loads report for beams).
Various errors as noted in the RAMSS Common Framing Table Errors can occur when the area of one-way deck is not completely framed out (beams or walls along the perimeter and all interior polygons are closed).
Otherwise, it's fine to use hybrid decks. In a case where there is one area where 1-way load distribution is desired and not a natural result of the bay dimensions, then I would advise you to use one-way deck in that region. Just spot check the loads especially for the members between the two deck types.