Dynamic load from mechanical unit

[Robvh1984]

I am a structural engineer and I would like to know if there is a calculation that translates the peak dynamic motion of a large HVAC unit to an equivalent static force for simplification. Or, do HVAC suppliers, such as Trane, have data available for the engineer's use?

-rob

 

[MiketheEngineer]

Most of them swear by how quiet and vibration free their units are --- so I would guess there would very little dynamic motion - maybe a bit at start and stop.

I have never heard of any with commercially available units. Check with the mfg. I think it wouldn't exceed 10% of the dead load...

 

[msquared48]

I usually use 30% of the gross unit weight, including any curbing, and put the force thru the horizontal and vertical location of the CG. Flies through the building department...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[JoshPlumSE]

I have been looking for a good reference on similar subject for a long time. My application is more for centrifugal or reciprocating machinery. But, the concept is essentially the same... convert a dynamic load into an "equivalent static" load.

Here is what I have been doing. This is based on the "deflection magnification factor" or "amplitude ratio" that I get from my old mechanical vibrations text books.

X_dyn/X_static = 1 / [sqrt (1-r^2)^2 + (2*zeta*r)^2 ]


where

r = w_equipment / w_structure = ratio between the operating frequency of the equipment and the natural frequency of the structure.

Zeta = fraction of critical damping