Wind induced vibration on steel truss

[Chris625]

Good evening all. I'm designing an equipment rack for an open area stage. The rack itself is 59 ft long (5 ft deep), and is moment connected to two columns at either end. The design itself is quite simple, a space-truss spanning the stage.

The rack will be exposed to wind but not snow. The design dead /live loads are relatively small, but the front part of the rack may be covered. For static loads, the forces are relatively small so the frame is pretty light.

I'm not an expert in dynamic analysis but i am trying to determine if a vibration analysis is required for this type of structure, moment connected at both ends? I am of course concerned about the wind exciting it.

Does anyone use any general rule of thumbs for span/depth or weight /span for a wind induced vibration analysis? In addition would someone be able to point out any reference design standards that may apply to this type of structure?

Any info would be appreciated.

Thanks

 

[Chris625]

sorry, typo: 39 ft, not 59.

 

[Ron]

Do a site search for aeolian vibration. You might find some help there. I know we've discussed it before.

I doubt that your application will see much affect from wind vibration, though you might want do check anyway. Keep in mind that you will be rigidly connected at the ends, so the entire spectrum of vibration frequencies will be cumulative with regard to fatigue stress. I've run into this issue with transmission tower cross-arms before.

Also, you mention a stage. If the rack is to hold speakers or if it holds lights that are excited by sound vibration, you might want to check as well.

 

[msquared48]

I'd be more worried about the teenagers getting excited than the truss. Galloping Gertie this is not.

Mike McCann
MMC Engineering