Roof Diaphragm not analysing
Roof Diaphragm not analysing
(OP)
Hi all,
I've created a really simple model, as per the attached picture below. It has gravity and lateral frames and standard loadings. Nothing groundbreaking! I need the roof diaphragm to model as pseudo rigid however in order to get RAM to analyze the frame at all with this type of roof diaphragm I have to fix every single connection. (XXX - XXX everywhere!) This is incorrect as I need only the major axis to be fixed and torsional fixity. (XOX - XOX.) When I set this type of fixity though I get error messages about local instability at all the joints.
Another oddity which I have noticed, if I set the diaphragm to non rigid it doesn't like the lateral load cases (wind, seismic and notional)...
Does anyone know what is going on and how I can get the model to analyze as I want?!
I've created a really simple model, as per the attached picture below. It has gravity and lateral frames and standard loadings. Nothing groundbreaking! I need the roof diaphragm to model as pseudo rigid however in order to get RAM to analyze the frame at all with this type of roof diaphragm I have to fix every single connection. (XXX - XXX everywhere!) This is incorrect as I need only the major axis to be fixed and torsional fixity. (XOX - XOX.) When I set this type of fixity though I get error messages about local instability at all the joints.
Another oddity which I have noticed, if I set the diaphragm to non rigid it doesn't like the lateral load cases (wind, seismic and notional)...
Does anyone know what is going on and how I can get the model to analyze as I want?!

RE: Roof Diaphragm not analysing
When you choose a pseudo-flexible case, you need to have frame numbers assigned so you can assign the proper percentage of the lateral load. If you can, try modeling the diaphragm as semi-rigid. this Link and this Link may help you with that. The semi-rigid actually meshes a diaphragm which should help with stability of the model.