Pendulum Structure ETABS (Support Conditions)

[Rahal008]

Hi, im modelling a pendulum type structure and i am having problems with the analysis, im using ETABS. Could someone please help me to verify if this are the correct support conditions? Because deformed shapes are really not making sense. They are not behaving correctly to dead,live and wind demands. Just in case, the structure is symmetrically in shape and load. The only support condition that exists is on top a pinned support.

 

[driftLimiter]

What is your expected result? What type of analysis are you performing? Is it just the deformed shape or also the magnitudes of the displacement that is unexpected?

Its not clear to me what the loading is, or what the restraint to those loads would be. Have you verified the loads are being combined and applied the way that you think?

In the absence of some restraint or counter balancing force, a lateral load would cause excessive horizontal displacement because the pin support at the top provides no restraint to rotations due to lateral load.

If you are relying on the weight of the structure downward to restrain excessive horizontal displacements it seems to me that you need to consider a non-linear analysis technique.

 

[milkshakelake]

You know that you can't do this in ETABS, right?

 

[BulbTheBuilder]

I haven't done enough rigging to comment but hope this helps

Rigging and Bracing Stability: Considerations for Moving, Lifting and Placing a Non-Building Structural Module

 

[human909]

One the very few occasions I've turned to structural analysis packages for rigging analysis, I have found that it is generally better to put the constraints item being considered and the load on the lift point. The complicated stuff I've done hasn't been too different from what was in that paper (eg lifting 'thin shelled' items that require bracing for the lift).

If the OP is indeed trying to examine rigging then that is something to think about. But it isn't clear that is what the OP is indeed doing and if they are doing they they should be damn careful with their model to get sensible results.

 

[ThomasH]

The only support condition that exists is on top a pinned support.

I would say that destribes a model that is singular. To simplify it, say you have a beam with one end pinned (translations locked) and the other end free. That means that the beam can rotate around the free end.

Try performing a modal analysis. Do you get three modes with 0 Hz? That is the three free-body modes. Or have I misunderstood?

To be able to help, describe what you are trying to do. To me it looks like some kind of lifting arrangement. But the model looks, odd. If it is for lifting you may have one lifting location but that is not the only constraint.