I am having trouble understanding wall reactions (using Concept as rigid diaphragm distributing seismic loads to walls). The attached document discusses wall reactions from the
east direction seismic loading as well as a load combination that includes east direction seismic loading.
Thank-you.PDF
Is this reaction for walls below the slab only? Is it a single wall or part of a larger group? Is the lateral load case a Lateral Self Equilibrium (Lateral SE) type? If so were any stabilizing forces applied here (Check the calc log). Is this post-tensioned, i.e. what are the balanced load case reactions?
Checking deflections (vertical and lateral) is useful when checking signs.
Or send the file.
I will upload a file but my approach was: take the model used for the pt slab design and delete all pt and mild reinf along with all design strips. Increase in plane stiffness of slab elements to simulate rigid diaphragm. Create several lateral load combos (combo type single - analysis type linear). There are several walls in multiple directions (walls only below slab). Create seismic loading (uniform area loading) in addition to line loads that model the accidental eccentricity. The N1-N2 and E1-E2 load combinations were intended only to review drifts at slab corners to determine torsional irregularity.
Thank-you.
The first point to drive home is that the wall below reactions are the reactions at the top end of the wall (slab centroid = -6" elevation)). The reactions at the bottom of the walls below (which would account for the shear times the height) are not reported.
You have 339 kips of shear from load "Ult Seismic East" going into wall #19. Forces are applied in the positive X direction, wall reactions in the negative X direction as expected. The moment is small, -61 kip-ft, in part due to the loads being applied at the top surface (elevation 0) and in part due to complex frame action (this wall acts like a frame coupled with the wall group west of it).
Moment reactions in the wall due to unbalanced gravity loads, may be much larger. For example, All DL combination reactions are higher and opposite hand (Wall #, MS for All DL combo = +1810 kip-ft).
I see that I need to look at these numbers as wall "reactions" rather than wall "forces" and it makes sense from that viewpoint. Thank-you for looking at the model.