Load Rating of Steel Mezzanine

[TRAK.Structural]

Considering taking on a project where I have been asked to determine the capacity (load rating) of a mezzanine that is used for storage in an existing facility. I'm comfortable with the field work and engineering to back out the numbers but my question is how far to take the checks. At face value my initial thoughts are that the components that need checking are the slab/deck, beams, girders, connections, and columns; and all of that is fairly straight forward. But what about foundations? These elements are buried and would take some selective demolition to uncover. I may be able to get drawings from the original construction but is that enough to hang my hat on when performing a load rating? Lastly is the question about lateral; obviously if there is no clear lateral system than I would address that concern with the client for safety reasons but is the standard of care here to run a full lateral analysis and check the capacity? The mezzanine is likely being braced (at least in part) by the building LFRS so if a complete analysis is required that becomes much more involved. Any experience here is appreciated.

 

[RPGs]

Personally, I don't think I would be worrying much about the lateral capacity if it's a low-seismic region AND you've established the building is providing at least SOME nominal lateral bracing.

For the foundation, if you don't have ANY drawings, then I'd most-likely be looking to verify the more-critical footings/piers/whatnot with selective demolition or GPR survey (if applicable).

If you actually have original drawings, I believe you are within the standard of care assuming they are accurate during your analysis of the structure. I'd probably be optimistic that another element of the system will control the capacity such that the foundations wouldn't need much of a closer look, but you could let your Client know that it may be the case.

 

[human909]

IMO unless the mezzanine is being completely repurposed with significantly higher loads than it has ever seen before then I wouldn't be chasing the foundations unless there is an indication that they are inadequate. If you have concerns then I would comment that footings were unable to be checked as such some unexpected settlement could occur. From the scenario described it doesn't sound like footings would ever be a catastrophic issue.

My thoughts anyway. Really depends on plenty of factors that we don't have on hand.

 

[JAE]

Usually industrial settings with mezzanines find they need a load capacity rating due to their insurance company insisting on it. This usually involves determination of the maximum live load.

In the several that I've done I have backed into the LL capacity after determining the framing and connection details (via drawings or via field work).

For lateral - I ditto what human909 suggests.

For foundations - the issue is public safety of course and if a foundation were to start failing under load it typically is a slow, gradual thing. I've not usually required local demolition to verify footings (if there are any - sometimes it's just set upon a slab-on-grade). I've usually communicated with the client that we can certainly verify the foundations if desired but the cost would be higher, disruption to ongoing activities would occur, etc. I give them a description of the types of failures that would be seen if there was a foundation/slab failure under the mezzanine columns. I include all that in my written report as well.

 

[lexpatrie]

Could you explore GPR or some other non destructive approach to assess a foundation, if desired, or try to find the "edge" with some small drilled holes in the slab?

As to standard of care, which is the standard, so to speak, it depends on local practice in your area, if you can assess what the average engineer would do, try to do a little more. Remember it's health and life safety, you're not on the hook for, not maximizing your liability by minimizing your fee or going "too far" without substantiation so the client is uniformed of the risks.

I would lean in the direction of doing everything possible on the finding drawings and the easy to collect data (some of these are a Nucor product, as I recall), trying to find information from suppliers.

To say "no" I think most engineers would not require coupons to determine yield stress of the beams versus the columns. Also unlikely (?) is any kind of NDT testing of the welds, if applicable.

Maybe rather than dig, you can estimate a footing size based on the loads and explain that to the client. I have seen a few engineers muck up EnerCalc so the footings have a punching shear deficiency, and that doesn't feel like a gradual issue, you could maybe advise they keep people out from under the mezzanine while they are dramatically changing the loads on top. Suggest bollards to keep the forklifts from hitting columns (too hard), etc.

While vibration may be a concern, heavy storage, as I recall, is less prone to vibration due to the superimposed dead load, and vibration isn't always a major concern for some engineers.

And always check the easy stuff....

Lateral you could at least consider notional loads from the gravity loads.

 

[human909]

A fair bit of difference in the responses here. I think a decent amount of responses come down to the interpretation that jumps into our heads of a 'storage mezzanine'.

But some of it probably comes down to our confidence and experience with dealing with such existing structures.

I deal with existing structures all the time (mostly less than 60 years old). So what a I imagine regarding a mezzanine would involve a site inspection and the the checks I'll do will mostly depends on what I find. I might find beams and joists that are very adequate but with some questionable connections. Potentially 95% of design checks I'll call suitable by inspection without any calculation at all.

(On the flipside earlier this year I was asked to certify a 20mx35mx7m light industrial structure that was less than a year old. My analysis and rectification specified was extensive. The structure was significantly undercooked for wind loads.)

Considering taking on a project where I have been asked to determine the capacity (load rating) of a mezzanine that is used for storage in an existing facility. I'm comfortable with the field work and engineering to back out the numbers but my question is how far to take the checks.

Ultimately go as far as your comfort level and confidence requires. As you have seen there is quite a range of responses here.

 

[XR250]

You have identified key components for checking during your load rating assessment namely slabs/decks, beams, girders, connections, columns—you must also give due consideration to foundations through documentation review and possibly selective demolition if warranted by findings. Additionally, addressing lateral stability through thorough analysis will ensure compliance with safety standards and best practices in engineering.

Given these considerations’ complexity and potential implications for safety and performance under loads, I would recommend proceeding with both foundation assessments and lateral system evaluations as part of your overall structural assessment strategy.

Chat GPT?

 

[TRAK.Structural]

Lots of good thoughts here.

As some have indicated, I think the final answer to this will depend on what I see in the field. I'm going to plan on (2) visits so that I can re-assess what information is missing after the 1st. I will try to space them out a little so if any selective demolition needs to occur than the time is already built in. Getting original drawings and comparing what I see in the field to those documents is another key task here that will inform how I proceed.

Thanks all!