Non-structural seismic criteria

[archeng59]

I have been working as a structural engineer for almost 25 years. During that time, I have helped mechanical engineers determine if their systems need seismic restraints based on the structural seismic criteria. Today, I was told by a mechanical subcontractor that my drawings are wrong because I did not specify the importance factor for non-structural systems. I have talked to several engineers who agree with me that my drawings show pertinent info regarding structural systems, but the seismic criteria for non-structural systems are to be determined by others using what is on the structural drawings. My drawings show the seismic information required per IBC 1603.1.5 (IBC 2015).

This started because the structural drawings show Risk Category III building, seismic importance factor 1.25, design category C. The mechanical subcontractor says the structural drawings need to show the non-structural component importance factor. I disagree and said it is the mechanical engineer's responsibility to determine the non-structural component importance factor.

Just curious what people in this forum think about it.

Thanks.

 

[Ron247]

I do not work in high seismic but as with most items like this, unless your local code states the Structural Engineer is responsible for this information, it is up to what your scope of work is. It is common for people to try to pin "anything they deem structural on us" when they do not want to pay someone else to do it.

I had an architect keep telling me I had to do the concrete steps that were on grade because "they are concrete and therefore they were mine to do". I told him site design did those items. I tried to tell him structural does not do everything in a building unless we contract for that item. We assume responsibility based on systems in a building or components in a building, not building materials. Since he claimed I was wrong, I had him confirm that if it was my duty to do anything steel, concrete or wood. At that point I changed his wood and steel doors to something that more suited an engineer. You know how utilitarian those tend to be.

 

[JAE]

I think you are referring to ASCE 7 section 13.1.3 where non-structural components importance factor is specified and varies depending on the nature of the actual component
Since you don't always know the full nature of non-structural components (they are NON-structural after all) you shouldn't be expected to sit down and classify every pipe, duct, machinery, etc. for all the NON-structural sub-contractors.

I think your mechanical subcontractor is fishing for free information.

The IBC even mentions the intent of 1603.1.5 in that it is to allow the building official to facilitate their plan review.
That information is not their to facilitate a mechanical contractor's separate design efforts.


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[EDub24]

Usually I show the component importance factor, Ip, as 1.0 on the dwgs with the note that it equals 1.5 if the component carries hazardous material, attached to a risk category iv structure etc per of ASCE 7 requirements. Ultimately it’s up to the contractor to determine the exact value.

 

[JAE]

EDub24 - probably a good idea. That, at least, provides some cover if someone else down the road doesn't use the 1.5 when they should have.

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[JStephen]

My take- those kinds of items should generally be specified by the owner or owner's consultants, not by equipment suppliers. That doesn't mean it should fall on the structural engineer- should be part of the mechanical or electrical specs or architectural if required.
My thinking: Those kinds of issues are more big-picture issues, whereas an equipment supplier may or may not have much information on the overall project.
For uniformity through the project, it would help to be specified by the owner. If the lights go out but the water stays on, where does that leave you?
For competitive bidding, it would help to be specified by the purchaser rather than the bidder.
And in looking through the criteria, it seems 90% would be clear-cut anyway, there'd just be a few items where people wound up wondering "Just how hazardous IS 'hazardous', anyway?"

As a side note, I find that in the vessel industry, nothing short of nerve gas seems to get classified as "lethal service", which makes one go "hmmm".

 

[JoshPlumSE]

I know OSHPD is very particular about what must be shown on their drawings. It's not necessarily required by code, but by OSHPD the authority reviewing the drawing and calc set. So, if they require it, we put it on.... Though we only do that for OSHPD. I'm guessing DSA may have similar requirements, but I haven't done enough DSA work to know.