Hello,
I've modeled some load bearing walls (CFMF stud walls in reality but modeled as concrete walls with an equivalent thickness to capture weight) which support a metal deck (concrete topped) for several typical levels. These load bearing walls are supported by a concrete podium level (level 3), which consists of a one way concrete slab and PT beam system supported by concrete columns. I've modeled this concrete slab as a one-way concrete deck.
I've fixed all errors but have numerous warnings (data check status) :
My understanding was that this warning type can be ignored as long as we intend to design the Level 3 concrete slab to support the load bearing walls.
I've done a column load take down manually for a typical interior column and compared that to the reaction at the bottom of the column for both dead and live load case (within RAM Frame) for that same column. The loads I calculate 2 to 3 times higher what RAM is showing which leads me to believe that the load bearing walls, and the associated LL and SDL for those levels, are being lost and not carried down to the foundation.
In fact, if I don't take into account the levels above the transfer concrete podium, my column load takedown calculations are almost identical to the reactions at the bottom of the column from RAM.
The load bearing walls have been copied up for every level, so they should be lining up correctly and tracking down.
Am I going wrong about how I am modeling these walls and deck? I will send over a zip file with the model.
Thank you!
If the supporting deck is 2-way, then it gets meshed with and will support the walls above. If the deck is one way then there needs to be a beam (or wall) below the walls above to work. See also: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/3262/ramss-two-way-decks-tn and https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/10202/modeling-podium-slabs
Thanks Seth. I have changed those transfer slabs to "two-way" and now the reactions at the column I was checking, match pretty close to my calculations. Regarding out of plane stiffness for a two-way slab. Note #3 under the one-way and two-way deck table (first link you provided) says
"The diaphragm will always be meshed, and out-of-plane stiffness will always be assumed under gravity loads."
This is fine for the gravity load cases, but when running lateral analysis (wind) in RAM Frame, and keeping all diaphragms as rigid, I would not want to include out of plate stiffness.
Your second link, mentions:
"For any transfer slab the out-of-plane stiffness should be considered when analyzing lateral load cases."
Though in RAM Frame, under Criteria>Diaphragm, I have purposely left the last box unchecked under "Include Out-of-Plane Stifness" so I would hope this stays true when the lateral analysis is run. Could you verify this?
That's consistent with what you want, and probably fine for gravity walls above. If the walls above that transfer are modeled as lateral walls, then the diaphragm out-of-plane stiffness for lateral loads ought to be considered too. See this: https://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/18616.ram-frame-criteria-diaphragms#two-way