Oscillating Load Supported by a beam 1

[Matthew Stevens]

Hello,

Was wondering if someone could help me. I'm trying to do calculations if a beam will fail when subjected to a certain load case.

The I-beam is supported at each end. It is subjected to 2 equal oscillating loads, one towards one side of the beam, and the other towards the center. Can anyone shine some light on how to determine if this will fail? I'm pretty sure I'm over-complicating this problem.

Thank you!

 

[rb1957]

research frequency, or harmonic, analysis; or time dependent loads.

you need to understand the difference between the natural frequency of your structure and the frequency of your load. If your load frequency is much lower than the natural frequency then a static analysis is adequate, if the load frequency is much higher then static analysis is conservative, if the load frequency is close to the natural frequency then you're in for a world of hurt.

I think the load near the support is not a problem (since I expect the beam and the support are very stiff).

another day in paradise, or is paradise one day closer ?

 

[JoshPlumSE]

When I re-wrote the RISA training course on dynamic analysis, I wrote up some notes on a problem like this. It's not really all that difficult, but I realize that this (i.e. dynamics) is something a lot of engineers fear. I'll dig up my course notes and post a snippet from them when I get home later today.

 

[Tmoose]

"I'm pretty sure I'm over-complicating this problem."

Hi Matthew Stevens,

For my feeble brain to understand, you are under-complicating the description and definition of the problem, in regards frequency(s) like rb1957 said, identifying location and characteristics of supports, what the gray (flanged?) component is, with dimensions, what the red outlined black component is, with dimensions, amplitude/force of "oscillating" load, phase of oscillating loads if they are of equal frequency.
Even the detail of how the forces are applied to the beam will have a huge impact on whether the beam will fail.
Cool looking welding is no defense.

http://i41.photobucket.com/albums/e289/kj790/001-1.jpg

If the black component is an infinitely rigid support, it would be pretty easy to dream up an oscillating load of the "right" amplitude and frequency in the very center that would have the welded connections at the ends of the gray flanged beam crack completely through by the end of the month.

regards,

Dan T

 

[WARose]

The first question is: what does the forcing function of the "oscillating" load look like? Is it something like a continuous sinusoidal load or is it a short-term impact load?

If it is indeed a sinusoidal load the next step becomes determining the response......that will have to be done with a dynamic analysis. (Preferably with some type of FEA software.) After that, you can get your stress range (for fatigue calculations) and displacements and compare them to allowable values.

 

[JoshPlumSE]

This is the excerpt that I was thinking about. Just a page or two about vibrating equipment in general. How to calculate a response amplification factor for near resonance conditions. Some rules of thumb for when you do and do not need to perform a more advanced analysis.