Loading considerations for static seismic analysis 2

[IAS-Mech-Eng]

Should existing loads from o rings & preload in bolts be considered when carrying out a static seismic analysis?
Obviously compression of an o ring in a face seal requires a certain amount of force. Likewise a bolt tightened to a specific torque induces a tensile stress in the bolt. Should these pre-existing loads be taken into account when conducting a seismic analysis of the equipment? Previous calculations I have seen done by others have not taken these into account, but a calculation I have been asked to review does include the o ring loads.

 

[HTURKAK]

If you are looking for the global seismic analysis of the equipment ( with one part connected to equipment body with preloaded bolts ) , no..
Regarding the preloaded bolts, if the faying surface (joint is metal to metal and o-ring is located in double groove ), the bolts will not experience seismic loads if seismic loading stresses not greater than joint prestress..


Will you please provide a sketch showing the eq, preloaded connection etc . to get better responds ?

 

[IAS-Mech-Eng]

This is our equipment which is attached to the building structure similar to below:

Our equipment is a camera with pan-tilt unit. The purpose of the analysis is to provide evidence that it will not become a missile if a seismic event occurs. So essentially for the fixings shown not to fail...
If this was mounted upside down, then the seismic load would normally be applied on top of the equipment weight (dead load) i.e. if the equipment load was 70N and the seismic load were equivalent to 5g, the vertical Force on the fixings would be 70 x (5 x 9.81 x 1.5 + 9.81) = 5837N (where 1.5 = static coefficient).
So the question is, if the o-ring requires 500N to compress would this mean the force on the fixings would be 5837N + 500N = 6337N total?

 

[HTURKAK]

The hypothetical assumption (the seismic load were equivalent to 5g ) is not realistic and the seismic design load shall be applied at the CG of equipmnet in horizontal direction .

I do not know your local seismic code . If ASCE 7 applicable, you should look section 13 ( 13.3 SEISMIC DEMANDS ON NONSTRUCTURAL
COMPONENTS )

I will suggest you to look to the following doc. There are some worked examples for mech. eq. and components.

https://www.fema.gov/media-library-data/1474320077...

If you need further help, pls provide more information.