zurch1818
Structural
- Feb 16, 2015
- 25
I've had some pretty good success modeling two way slabs in RAM Elements for flexure and shear. The one I'm working on now is from the 60's where everything is f'c=3,000psi concrete and fy=40ksi rebar. I find it interesting that the plans call out allowable steel tension and compression stresses...so this building's design predates LRFD (or at least what the engineer felt comfortable using).
Anyway, the one thing I've struggled to model accurately is boundary conditions. It seems may not be getting enough moment on the edge columns (modeled as pins as large as the column) and the stress concentrations for negative moments on interior spans is way too high.
In the past, I've basically just ignored the boundary elements (since they are on the column) and tried to add some rotational/translational springs to match delection/rotation behavior I would expect.
However, this process takes some iteration and I question if I am putting my "thumb on the scale" when I do this. I also question if I am missing something with punching shear because the two way slabs I've dealt with haven't had any issues. Maybe this is because it isn't as big of a deal as with post tensioned slabs (haven't designed on of these before)? I'm curious what other tips and tricks people have for modeling two way slabs.
Thanks!
Anyway, the one thing I've struggled to model accurately is boundary conditions. It seems may not be getting enough moment on the edge columns (modeled as pins as large as the column) and the stress concentrations for negative moments on interior spans is way too high.
In the past, I've basically just ignored the boundary elements (since they are on the column) and tried to add some rotational/translational springs to match delection/rotation behavior I would expect.
However, this process takes some iteration and I question if I am putting my "thumb on the scale" when I do this. I also question if I am missing something with punching shear because the two way slabs I've dealt with haven't had any issues. Maybe this is because it isn't as big of a deal as with post tensioned slabs (haven't designed on of these before)? I'm curious what other tips and tricks people have for modeling two way slabs.
Thanks!