I have two I-beams with full depth concrete sandwiched between them modeled in RAM Elements. The concrete is only supported by the beams; I am getting a moment of 458 k-ft. per beam from RAM Elements, while manual calculation indicates the moment is about 610 k-ft. per beam. This is part of a more complex model and I need to include the concrete in the model so the stiffness can be accounted for in deflection and load distribution computations. I tried modelling with STAAD pro and got similar results.
Moment from the lateral wind load also looks weird. Any ideas why the moment from RAM Elements is so far off the theoretical value? How do I model this to get the correct member forces? The model is attached.
I am having problems with the upload; this is how the model looks like - W44x262 beams, 80 ft. long and spaced at 2 ft. on centers.
We don't have composite sections in Ram Elements per se. Are you using 3 linear members that are somehow linked together frequently at the member centroids like a ladder? That might not work as intended unless the links were very stiff. Or are you building the whole thing out of plates?
Your model has some custom material for the shells, I substituted one of the default concrete. The shells and beams are deflecting together and I see a range of stress as expected.
The beams and slab work together to share the work. For vertical forces the beams and slabs are all at the same centroid so a summation of moments is simple enough, but for weak axis behavior the beams will form a couple and that is a big part of the total minor equilibrium moment.
The pair of end restraints likewise can form a couple when both are pinned in 3 directions.
Answer Verified By: Joe
Here's a way to model the left supports without making a rigid couple.
Thank you Seth. Since the concrete is not supported at the end supports, shouldn't all the moment be transferred to the beams (with the slab span being 2ft. instead of 80ft.)?
The actual model I'm working with is more complex than what is presented here, with several other members, load cases, and combinations. Manual summation of moments and manual member design doesn't seem feasible.
All of the shear ends up in the last segment of the beams, but the moments are partly resisted by the beams and partly by the shells.
Thank you!