I am working on a building made in precast concrete elements. My goal is to extract “sectional forces” for each wall to proof stability and for the suppliers design. On top of that, I want to extract line load for dimensioning of the foundations.
The problems concerns the moment around an axis perpendicular to the plane of the wall. For a wall on story n, I would expect moment from horizontal (wind) forces to follow this rule:
M.n = M.n-1 + ∑V.n * h.n
Where:
M.n is the moment in the bottom of the wall at story “n”
M.n-1 is the moment in the bottom of the wall at the story above story “n”
∑V.n is the horizontal force, summarized from top story to story n and acting at the top of the wall in story “n” (The check is done using the distribution of vertical forces on the core walls as done by Robot)
h.n is the hight of the wall in story “n”
Hence, the moment should grow steadily down through the stories (giving that the layout of the stabilizing walls are identical on each story). Instead, I see that the moment jumps in what seem as an arbitrary way and the moment at the foundation is only a tenth of what is expected.
The vertical load has no significant eccentricity on the elements.
I have a feeling that the modeling of the deck slap could be the part problem. The deck is modeled as shell / stiffened diaphragm, partial stiffened (in XY) / simplified load transfer one-way. The only function of the deck should be to distribute forces vertically and horizontally. I have tried to alter the E-modolus of the deck down to 1/1000 of normal. This helps to some extend; the moment is now growing steadily, but the its still only 1/10th of the expected value.
What could be the reason why the moments are not as expected?
