Ontario Building Code- Seismic restraints

[Robbiee]

Hello,
We have a job that falls under part 11 of the Ontario Building Code. This part deals with renovations. We are adding a new mechanical unit on top of the roof of a hospital, a post-disaster building. Part 11 doesn't require the existing building checked for seismic. However, new building systems need to conform to the current code. A mechanical unit is a building system. So, do we need to provide seismic restraints for the unit and its ducts?
My understanding is yes, because, although the existing building is not built to the current code, it might possess a capacity to resist the next seismic event and therefore we should not assume it will fail.
Others see it differently; they say: the new unit is supported by the existing building, so if the building is not built per the current code, we should not ask for restraints required by the current code for systems attached to it.
Any help is appreciated. Thanks

 

[msquared48]

Don't know what the Ontario code says, but here in the Pacific Northwest, a high seismic zone region, regardless of the status of the building, the rooftop units do need to be secured to the roof for shear and overturning due to seismic.

Mike McCann
MMC Engineering

 

[Robbiee]

Thanks Mike. That is what I have done all the time. What do you do with the ducts? We have four branches of ducts connected to the unit with one being over 50ft. long. Do you support them on pipe hangers and secure the pipe hanger to the structure or just place the pipe hanger on the roof on some 2" insulation? The later is what my client wanted to do, then proposed to secure them to the typical 2ft x2ft patio stone.

 

[msquared48]

The building departments here focus on the units themselves and let the ducting on top of the roof rest on wood sleepers on the roof membrane. The ducting under the roof though must be strapped in place.

Mike McCann
MMC Engineering

 

[TDIengineer]

ducts less than 6 square feet in area suspended 12" or less from the structure need not be braced. some large ducts on the roof will require anchorage if the profile is tall and narrow. piping / conduit that are heavy with minimal profile may be on sleepers. Depending on pipe run, some lateral restraint may be needed at large intevals depending on pipe size and material. That's been my experience in west coast hospitals. CA CBC and AISC 7-05 for the above exemption noted.

 

[amecENG]

Robbie,
I'm not aware of any exemptions in NBCC for ducts as TDI mentioned above. The only clause I see bluntly states:

"Seismic restraint for suspended equipment, pipes, ducts, electrical cable trays, etc. shall be designed to meet the force and displacement requirements of this article and be constructed in a manner that will not subject hanger rods to bending".

I guess your main point is: "if the rest of the hospital is not designed as Post Disaster why does the new mechanical unit have to be?"

I run into this argument all the time in my province even with mechanical engineers. I can see their logic but we are suppose to adhere to the building code and the code is pretty clear. I know in the past we actually have written letters from the hospital authority to ignore Post Disaster requirements. This has happened on the M&E systems for two fairly significant hospital extensions. The justification was, as you said, the M&E systems that feed the new buildings are not restrained for seismic forces so therefore the new systems do not need to be either.

This has always been a contentious issue in our office and comes up every time we do work in a Post Disaster building. I would be interested to see the experiences/opinions of other forum members on this subject.

 

[Robbiee]

amecENG,
Agree. Here in Ontario, the controlling code is the Ontario Building Code, where its part 11 clearly states that new building systems need be designed per all other parts. I can't see how the hospital authority can make the decision to ignore the provision of a post disaster building.