Mechanical Units

[SperlingPE]

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.

 

[hawkaz]

From my experience (not saying that this is the correct way to do it), most architects/mechanical will submit without any structural. They come to us only when the municipality indicates that they need structural backup.

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.

 

[SperlingPE]

We will do the support for the mech units. We will provide a curb design if required due to circumstances.

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?

 

[JedClampett]

We provide sections in Division 1 of the specifications giving the seismic and wind parameters. For example; 90 mph wind, Exposure C, Importance Factor 1.0. In this section we say that anchorage is to be provided by the supplier with calculations provided and sealed by an engineer in the state of installation. The mechanical and electrical (they have gear that needs to be supported, too) engineers have the same statements regarding anchorage and providing calculations and referencing the Division 1 sections. It's very slightly redundant, but saying it twice is better than not saying it at all.
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.

 

[SperlingPE]

JedClampett
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.

 

[JedClampett]

You can tell the suppliers and your mechanical engineers that this is bull dookey. I work mostly in Arizona, but we have offices coast to coast. It adds the same cost to every supplier. An engineer to do seismic equipment calculations? $500? $1000? I don't know. But I've seen a lot of these, so someone does them. And if they were worth a lot of money, I'd be doing them! As far as the hurricane anchorage, if they want to supply them, fine. But they'll still have to provide calculations. And if the guy down the street provides an adequate anchorage and calculations for less, he'll win the bid. The engineers who do the calculations are quite efficient and good, too.
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.

 

[SteveGregory]

I do the anchorage calculations for an AHU manufacturer that supplies units all over the country. For a curb installation, we only submit calculations with reactions to be passed to the curb vendor. For a steel frame installation, we provide the same calcs with minimum bolting requirements for the EOR to review. For a concrete pad installation, we provide the calcs, a detail showing a post-installed anchor with minimum edge distances and concrete thickness required, and the minimum number of anchors required.

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.