Mechanical Units
Mechanical Units
(OP)
I work in a full service firm (Struct, Arch, Mech, Elec). The mechanical dept is reviewing their specs for attaching units (of all types) to the structure. ASCE 7, NFPA, and other codes have been reviewed as they pertain to seismic and wind loads.
How do other firms handle this issue?
Does the mechanical engineer include language in spec asking for the connection to the structure to be by the supplier and to include calcs?
Does the mechanical just ask for the connection by the supplier and no calcs or submittal?
Is it handled by a note on the drawings?
The structural drawings make reference to the required seismic and wind loads. The support framing is designed by structural.
How do other firms handle this issue?
Does the mechanical engineer include language in spec asking for the connection to the structure to be by the supplier and to include calcs?
Does the mechanical just ask for the connection by the supplier and no calcs or submittal?
Is it handled by a note on the drawings?
The structural drawings make reference to the required seismic and wind loads. The support framing is designed by structural.






RE: Mechanical Units
When this is requested, I provide the unit to curb attachment, curb to framing attachment, suplimental framing and justification that the existing framing is acceptable.
RE: Mechanical Units
We have not ever but we probably would design the connection of the unit to the curb and also the connection of the supplier's curb to the structure if asked to do so. But this would require information from the supplier and it is not in our typical scope of work.
How else is this handled?
RE: Mechanical Units
We've found it difficult to design these supports in the design phase as different suppliers have different, weights, bolt patterns, etc. We can only make general assumptions for our structure design.
RE: Mechanical Units
What states do you primarily work in?
I am asking because I am being told that asking the supplier to provide calculations for the connection will add excessive cost. Also, the suppliers won't hire an engineer to design the connection because they have the standard connection and they have a hurricane force connection. If required to provide and prove the design of the connection the supplier will just go to the hurricane force connection. The mechanical engineer's say this will add excessive cost.
I work primarily in the midwest/great plains area of the country. Low seismic generally and typical winds.
RE: Mechanical Units
We heard the same crap when we started enforcing this. Being close to California, we had an advantage. But once the suppliers miss one of these, they won't do it again. We would tell the contractor, if the supplier won't do the calculations, we will and we'll charge them. That really gets their attention.
And the final issue is; IT'S THE LAW. It's not optional. It's in the code.
RE: Mechanical Units
A lot of the specs I read are way outdated and do not comply with the current code for that state. Many still reference UBC. Sometimes they require a PE registered in that state and sometimes the specs require a PE seal from any state, which I think is reasonable. Some specs do not require a seal. Some specs have specific IBC wind and seismic load factors like what is required on the drawings and some specs have none.
Also, I never ever get to see the design drawings. I only get the specs. It is very difficult or impossible to get a mounting elevation and/or roof elevation above grade. The information request has to go through too many people and the answer is usually for a question that I didn't ask. Good specs will help.