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Dynamic load from mechanical unit

Dynamic load from mechanical unit

Dynamic load from mechanical unit

(OP)
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  

RE: Dynamic load from mechanical unit

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...

RE: Dynamic load from mechanical unit

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

RE: Dynamic load from mechanical unit

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
 

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