Seismic Restraint of Non Structural Components ( Mechanical Equipment) 2

[StrLamp]

Hi Everyone,

The consultant has provided the following specification (see attached) for the attachment of mechanical equipment: they said it must be limited to the lateral force-resisting elements only. For example, in a steel building with OWSJ and a steel deck, they do not allow components to be attached to them.
In my understanding, these gravity members should remain intact during an earthquake; therefore, connecting any units to them should be acceptable.
Also, they have mentioned that any unit resting on vibration isolation should include a snubber as well. Why is this a requirement? I assume that spring vibration isolators may resonate with seismic forces, which is why they are asking for a snubber to be installed. Is this an explicit requirement?
I was not sure where I should direct this question, as seismic restraints are typically handled by the mechanical engineer in most cases.

Thank you,

 

[KootK]

I think you start with a more explicit understanding of what the EOR is trying to accomplish:

1) Don't direct any secondary structure towards fragile things. This includes all column and light duty floor & roof framing.

2) Provide the snubbers so that there is a limit to the extent that the restrained items can shift without slipping their moorings altogether.

 

[KootK]

I think you start with a more explicit understanding of what the EOR is trying to accomplish:

1) Don't direct any secondary structure seismic demand towards fragile things. This includes all columns and light duty floor & roof framing.

2) Provide the snubbers so that there is a limit to the extent that the restrained items can shift without slipping their moorings altogether.

 

[DRa_C]

The 2nd part, about isolators, is for the mechanical engineer. In other words, any unit resting on springs needs to have snubbers. This is to avoid the unit bouncing around due to the lateral seismic load. It is the difference between the so called "free spring isolators" and the "seismically restrained isolators".

 

[ANE91]

Shake table tests and case history have shown that non-structural equipment damage from earthquakes is severe and can extend to other, important parts of the building frame. @KootK has the right of it.

 

[StrLamp]

The 2nd part, about isolators, is for the mechanical engineer. In other words, any unit resting on springs needs to have snubbers. This is to avoid the unit bouncing around due to the lateral seismic load. It is the difference between the so called "free spring isolators" and the "seismically restrained isolators".

Thank you, I understand. But vibration isolators come with housing around the spring, something like the one below. Doesn't that work as a snubber?"

 

[DRa_C]

This is correct. The isolator above is also called "restrained isolator" or "seismically rated isolator". Many manufacturers, same concept.
The one to the left, below, is the other option, called "free spring isolator", totally acceptable if you do not have lateral loads or you have some other type of snubbers or restraints. No anchors.
The one to the right is fully restrained, must be anchored to the floor, and does not need additional snubbers. If not anchored, it's almost the same as a free spring isolator.