Dynamic Analysis v.s. Equvalent Static load

[StrP88]

What are pros and cons of each method?
What you gain more from vibration/dynamic analysis that you cant get it from equivalent static load analysis/design?

My case is a vibration/rotating equipment on a structure?

Thank you

 

[WARose]

What you gain more from vibration/dynamic analysis that you cant get it from equivalent static load analysis/design?

My case is a vibration/rotating equipment on a structure?

A static analysis isn't going to tell you if you have a vibration issue or not. It's a different animal.

 

[StrP88]

WARose (Structural),
May I ask please explain it a little bit more detail?
There is a suggestion that convert the dynamic load to an equivalent static load, simile impact load. I want to know what we will be missing if we check structure this way rather than doing a vibration analysis when checking the structure

Thanks

 

[canwesteng]

If the structure deflects a bunch during vibration you'll miss this, although if you use a large equivalent static load and make sure your structure is sufficiently high tuned, you should have no problems. Obviously this requires some dynamic analysis.

 

[WARose]

[blue](Str88)[/blue]

There is a suggestion that convert the dynamic load to an equivalent static load, simile impact load. I want to know what we will be missing if we check structure this way rather than doing a vibration analysis when checking the structure

Since what you are describing (i.e. rotating equipment) does not produce a single (short-term) load (in fact, it produces a sinusoidal load that is continuous)....not having a time-history analysis could fail to miss some important displacements. (Especially if the supporting structure's natural frequencies are close to the operating frequency of the equipment).

 

[JoshPlumSE]

I've played around with this sort of situation a little. My experience:
1) When the applied load is small relative to the total supported weight of the beam or structure: The load amplification method (when based on the eigenmode that is closest to resonance) tends to be a pretty conservative when compared to the results you get from a Time History Analysis.

2) The larger the load is relative to the overall weight of the structure, the less this can be said.

Think about it this way, a relatively small dynamic force doesn't have all that much total energy to move a much larger amount of mass. Especially when damping is considered. But, the larger that force gets (relative to the mass it is exciting) the more important it is to run a true dynamic analysis.