Hi,
I'm trying to verify the drift of a one-story ware house with tilt-up concrete panels and steel deck roof.
I followed all the information that I found on the forum, but I still have a few questions:
First I calculated the properties and displacement as referenced here: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/18657/example-calculating-semirigid-diaphragm-e .
I used E' and the deck thickness on the properties, as can be seen here:
I'm using the same load from RAM on my hand calculation, and the same properties, so the results should at least be close. But unfortunately thats not the case.
From the hand calculation, I found a 1.3in displacement, while in RAM I found 0.55in.
I don't understand what I'm missing. Even though the results may be different, they are supposed to be similar, correct?
Appreciate any help!
Thanks,
Murilo Santos
I suspect that the walls are lateral members all around that make the deck stiffer than it would be without them (i.e. like chords of a truss). You could model up something like this to isolate the diaphragm displacements more completely.
Seth,
Thanks for your reply.
After I posted my question, I though something similar. But I believe the walls perpendicular to the load are making the diaphragm stiffer, so I created a model without those walls and just added some beams o stabilize the structure, like this:
And in fact, the displacement now is much closer than the hand calculation for the diapgragm only, with 1.2 in (in comparison with 1.3in from hand calc).
So assuming this is approach is ok, than it is possible to assume that the walls are actually making the diaphragm stiffer or I cant trust the result?
Murilo
The walls are making it stiffer, but I think you can still trust the results. The walls are really there and they are attached to the diaphragm acting like a chord or a flange, which seems even more realistic than a hand calculation, in my opinion.
I think I agree with you. And in fact, we also have a chord angle there that is not considered in the model.
The deflection considering only the chord angle is much higher than that, but now I believe it is over estimated. I'm leaning to assume the model results as the actual results for drift analysis.