I am trying to understand why the wall axial load (in a concrete wall) does not more closely match that of the applied load (using 1-way deck).
When I "view gravity loads" applied to the wall this matches the tributary load to the wall. This makes sense as RAM Concrete does not mesh 1-way decks. However, when I view the axial load in the bearing wall it is less than what I would get if I multiply the length of the wall by the applied load. My first thought was that this is because the walls are meshed and this wall ties into a perpendicular wall on end and butts into a different wall on the other end. I can see that the perpendicular (non-load bearing wall) is taking more load than it should. Therefore, I assume something is going on with the FEA. However, when I reduce my wall stiffness and/or apply extremely low cracked factors to the diaphragm and out-of-plane factors to the wall, I get no change in the axial forces in the wall. I'm wondering if this has something to do with boundary conditions (almost like when you pin both sides of a truss and you get compression in the bottom chord). Any ideas here?
Edit / Update:
I tried to break off part of the wall by putting two short dummy beams. The wall axial load (on the bearing wall) is now very close, but still off a little (even when considering the reaction of the short dummy beam). I would have thought it would matched perfectly, but this does seem to indicate that something is taking place in the wall mesh / FEA that I don't fully grasp.
Also tried to make the walls "tilt-up". No change.
Thanks again!
In Ram Concrete analysis, gravity walls are meshed finite elements. The axial force in the wall, reported at the bottom of the story, should match the applied loads on the wall top where there is a singular load path, i.e. no connected columns or walls or supporting beams (self weight also needs to be accounted for).
For any situation where there are connected columns, walls or beams with fixity that can potentially hold up the wall, then you can't assume that all the forces applied to the wall top are matching at the wall bottom.
See also: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/7578/ram-ss-walls-faq
Right. This is all expected I suppose. But maybe not to the extent that I was expecting. To me if the walls are broken up by a gravity beam, the loads in the wall should be pretty close to the applied load + the beam reaction. Unless the beam is acting like a tension member, but that shouldn't matter either because the perpendicular wall should be very flexible. Unless the that perpendicular wall is "pinned" to a global restraint or something. Maybe I will try modeling this separately in STAAD or Elements to get a better understanding and report back. Could be a relative stiffness thing. Sorry thinking out loud here.
My overall goal is to get these walls to carry the load "straight down".