Reverse Engineering Fabric Building

[cjowett]

I am looking for someone that could reverse engineer some structural drawings for me.
I bought a fabric shelter from a person off Facebook Market place but it didn't come with engineering diagrams or specs. In order to get a building permit the township is asking for drawings with an engineer's stamp so that they know it meets Ontario building code. Is there an engineer here that could reverse engineer the drawings for me, for a fee obviously and with a lot of support from me getting all the dimensions and details? The original manufacturer seems to have gone out of business so I am unable to get anything from them. Attached is a page from the assembly manual with as much detail as they provide.

TMG Industrial sell a similar building. Theirs uses 2" round 15 gauge tubing and they claim 60 lbs/sq. ft snow load. This one that I have uses 2 5/8" x 1 5/8" oval tubing and is 13 gauge so I am confident it will meet the code. I just need to prove it to the building department.

 

[cjowett]

Best solution I think is to re list it on FBM with the proviso that it needs to be put up somewhere where they don't need stamped engineered drawings.

That looks very much like a PEMB but with even dodgier shear walls or connections between the frames (Is it only the end two that have any sort of bracing?
PEMBS are pretty notorious for running over the limit, never mind at the limit of structural design.

What is the cost if you needed to buy a certified version from TMG? Then divide that number in two or three and that's the max you can spend on engineering before it becomes more expensive than just buying a new one. If someone is used to designing PEMBs or whatever they call them now adays (Modular buildings?), then you might stand a bit of a chance, but you've probably got to send samples of the frames away to get tested to find out what material properties are.

No material specs or docs, no welding details, no code design data, what you have really is a lump of scrap metal and some fabric. Sorry.

I see the same question posed loads of times when people have a Pressure vessel with no forms, no plate on the vessel just here's one we found out the back, can we use it? Answer - No.

Here is the attachment.

View attachment 15752

The diagram suggests that it is ony the end nits that have the diagonal cables. I think I would add the same to the centre sections.

 

[cjowett]

That's not a building. Why does it need to meet the building code.

It's a tent, at most a temporary structure.


From the TMG website.

It's funny you should say that, most local people I talk to about it have the same response. And frankly looking at the pieces in the boxes that is exactly what it looks like. The last page of the instruction manual has a little game and shows 4 different style structures that they sell and says "Congratulations Which one is the tent you have just set up?"

But on a serious note, a party tent is only intended for a day or two and if the weather was calling for a "significant snow event" as Environment Canada likes to call them, you would cancels your plans and not risk the tent collapsing on people. This building is intended to go up once and stay up until I no longer have horses or the fabric is starting to fray.

 

[cjowett]

These things are notorious for collapsing

They are but from what I understand it is often because people get lazy about tightening the straps and cables to take up the stretch.

 

[cjowett]

WhichTMG building?

This one looks similar and stated no engineering drawings available.

30' x 50' Straight Wall Peak Ceiling Storage Shelter with Heavy Duty 11 oz PE Cover & Drive Through Doors, TMG-ST3050E(Previously ST3050)

The TMG-ST3050E Fabric Peak Ceiling Storage Shelter provides an easy to assemble, durable outdoor storage solution or workshop for your farm, - TMG Industrial USA

www.tmgindustrial.com

Don't know where you found the snow load??

I don't recall offhand. It was a page that came up on a Google search of "307022T"

 

[Brad805]

These are imported from China. The design of most of these rely upon sliding snow factors. I doubt it will meet the NBC 2020.

If this is a agricultural use you could look at the farm code.

If you want to continue with the reverse engineering I would start by getting out your tape measure and calipers so you can create a drawing. The biggest task of revserse engineering is figuring out the geometry, and these silly things are far from simple. They usually use a lot of slip joints, and few of us like those much. I woudl not be surprised if revserse engineering something like this without any drawings could easily cost $5-10k.

 

[Ron247]

The list of tasks pointed out by canwesteng is close to what would have to occur. How much would a new building with design cost? It is best to have alternatives with real costs to compare to. The 60 psf snow advertised by TMG is what I was NOT CONFIDENT of.

Many "Sales" brochures and comments are playing numbers games. For USD, you factor up loads (1.7 multipler as an example) , design to failure as compared the old ASD method, use expected loads, design to a % of some "defined failure" like 67% as an example. To sales, an ASD design snow of 35 psf "could be sold" as 60 psf (1.7*35 rounded up).

I remember ears ago, an unethical salesman for a PEMB manufacturer stated their PEMB required smaller foundations than all other brands (33% cheaper). Regardless of brand, placing the same required building code loads on building with the same dimensions, layout and design concept, will yield somewhat the same magnitude of reactions for the foundation to be designed for. So what was their sales logic? At that time, it was widely accepted you could increase allowed stress 33% if it was caused by wind. Wind uplift tends to be the controlling factor in foundation size except is some cases of high snow, cranes etc. They decided it was ok to reduce the magnitude of the wind reactions they published by 33% and saw no difference. So, the normal uplift of 15k for one supplier is 10k. Add to that we use a FOS on uplift of about 1.5, it then becomes 22.5k and 15k (7.5 k difference over 5K). Problem was, the stress was the only thing allowed to be reduced, not the force. They boasted a 33% foundation savings, and some believed them.

 

[STpipe]

I looked at one of these recently and was skeptical the design worked for the snow load specified by the manufacturer from China.

The homeowner was able to get a calculation report from them, and when I looked at it, I found that their "design check" was based on the gross cross-section compressive strength with no consideration for buckling about the major axis between web panel points, or minor axis buckling between purlins, let alone the fact that the bottom truss chord did not have any purlins to reduce the out-of-plane buckling length.

 

[cjowett]

Probably not the best structure if you are looking for the "building permit" pathways. I would have thought you'd just build the thing?

I only went the fabric, prefab route because it was cheap. I'm not a big fan of them really. Their only redeeming feature is the available light inside during daylight hours. I would much rather have a wood structure with metal roof.

 

[cjowett]

I looked at one of these recently and was skeptical the design worked for the snow load specified by the manufacturer from China.

The homeowner was able to get a calculation report from them, and when I looked at it, I found that their "design check" was based on the gross cross-section compressive strength with no consideration for buckling about the major axis between web panel points, or minor axis buckling between purlins, let alone the fact that the bottom truss chord did not have any purlins to reduce the out-of-plane buckling length.

Not good.

 

[Aesur]

I woudl not be surprised if revserse engineering something like this without any drawings could easily cost $5-10k.

Only 5 to 10K? wow I need to start outsourcing to you The last project we did where an owner bought a PEMB online before realizing they needed to meet building code required us to reverse engineer the structure and strengthen significantly just to support lighting, fire suppression and finishes as it had zero collateral. The engineering cost for us to do this twice (they made changes, adding columns in middle, after the first strengthening costs came back) ended up around 90k (we actually, reluctantly, were paid this). The architect priced as if it was new and lost their butts on it however.

If half the engineers here knew what PEMB's get paid for engineering PEMB's you would choke at how much higher their engineering fees are than conventionally framed buildings that require significantly more work. This was part of the factor in pricing as we did, but also we knew without all their custom software/spreadsheets it would take a lot of work to reverse engineer a PEMB.

This all being said, this project appears simpler than a PEMB for the frames, being trusses moment frames one direction and braced frames the other with braced diaphragms. I would anticipate having to model this in RISA or other software and HOPE that all the frames are repeats, else that's a lot of work. The fabric would be tough to engineer as you would most likely know nothing of the properties of this, nor the forces required to tension it properly. Considering the amount of work, site visits etc, required for this, if were we to do something like this (we aren't licensed there, nor would I take this on), my fee would be a minimum of $100k USD + another 5 to 10k for foundation design.

I agree with others, it probably makes more sense to re-sale and get a new building that you know will meet your requirements, there are a few out there, I'm working with one out of Florida right now that does fabric tent hanger type structures all day and provide engineering and reactions for the foundation engineer to design foundations.

 

[cjowett]

This is what I see being needed to truly sign off on the building:
-A day or two with a tape as builting it
-A certified weld inspector to visually inspect the welds
-A couple coupons taken to determine steel strength
-A few weeks of analysis
-Probably more lateral bracing installed since these often rely on the fabric somehow, which is not something someone unrelated to the manufacturer will be able to sort out

Saying it's impossible and no one would do it isn't true, we do stuff like this on structures without drawings when needed. But the cheapest thing to do is buy a new fabric building.

I think that is a reasonable list of things to do (not that I know anything about certifying structures). Do you have any recommendations on how I find someone(s) to take it on?
As far as buying a new fabric building, that would be throwing good money after bad. Custom fabric buildings are way more expensive than wood structures with metal roofs.

 

[Brad805]

Aesur, I don't think this one would equate to the same level of headche as a long span pre-eng. Here I think one will not have to go too far down the path with one typical frame to have a good idea where you stand. When we have been asked to look at things like this many think these tasks are in the hundreds of dollars. It surely could be in the ten's of thousands of dollars. This job sounds like something Dik would be very good at.

 

[Ron247]

As far as buying a new fabric building, that would be throwing good money after bad. Custom fabric buildings are way more expensive than wood structures with metal roofs.

The "throwing good money after bad" fear, can be far more expensive than literally taking the loss and either use it "as is" or reselling it. Say I check your bldg for 4K and it does not work for 3 reasons but I have not researched all of it. You pay me to go further. I spend another $3k and get a complete list of booboos. You ask, "what will it take to fix them?" Finding the booboo and correcting it are 2 different things. That could be another $8K for the detailed repair. Now you are out $15k to me and then you get a price on the modifications. It is $20k. Now you say, I have $35k + initial cost tied up. Well, you need to continue on, to keep from throwing good money after bad.

Consider the wood structure cost seriously.

 

[Aesur]

Aesur, I don't think this one would equate to the same level of headche as a long span pre-eng. Here I think one will not have to go too far down the path with one typical frame to have a good idea where you stand. When we have been asked to look at things like this many think these tasks are in the hundreds of dollars. It surely could be in the ten's of thousands of dollars. This job sounds like something Dik would be very good at.

Maybe you are referring to reviewing the building only and giving a yes or no? My fee would have been all inclusive, site visit, size verification, analysis and strengthening as required, knowing there will be a few rounds of this to find the most efficient strengthening strategy. The only thing not included would be testing. I agree it could be done cheaper, however you are inheriting a lot of risk for little reward if only charging for what it takes to do such a project. I would estimate in the long run, including drafting new plans, you are 2 months time into such a project for one person. I don't think 100k for that is unreasonable when considering overheard and profit. Now if you didn't mind spending the owner money on retrofitting to a very conservative strengthening plan, sure I could do it for half that and the overall project will probably be more expensive.

 

[Aesur]

@Brad805 I think I misunderstood you there, I agree this is simpler for sure, expect for the fabric, I have no idea where to start there as I am not a fan of even shade sails. If I didn't have to touch the fabric I would think 35k to 40k is a reasonable engineering fee including strengthening, if doing fabric that alone is expensive to engineer for someone who doesn't do that every day. I once worked on a spreadsheet for a shade sail fabric and honestly gave up going after that work after that, will never pay for itself if you are trying to figure out the unique shapes yourself each time for the fees you get.

 

[Tex.Eng]

What happens when you spend ~$20,000 on an engineering opinion and they find the structure to be woefully inadequate? Are you prepared to spend another $20K + on the retrofit design of this building? Do you abandon the idea and eat the original 20K? The engineer would also now be responsible for the foundation design (add $).

If I were to take this project I'd want to be paid upfront. I'd be too worried that the homeowner would resist paying my bill if I came back to them with bad news.

My advice is to work with the building department on obtaining a variance or special exception to not have this building permitted. Think about your risk tolerance regarding a failure during a snow or wind event. Otherwise, I'd scrap this idea completely and design and build a real building.

 

[LittleInch]

I don't recall offhand. It was a page that came up on a Google search of "307022T"

Well the 3070V, 30' x 70' from TMG comes with an instruction book.

30' x 70' Straight Wall Peak Ceiling Storage Shelter with Heavy Duty 17 oz PVC Cover & Drive Through Doors, TMG-ST3070V

The TMG-ST3070V PVC Fabric Peak Ceiling Storage Shelter provides an easy to assemble, durable outdoor storage solution or workshop for your farm, - TMG Industrial USA

www.tmgindustrial.com

On the last page it has this to say about snow.



So one reputable vendor is telling you that EVERY SNOW FALL you somehow need to go out there and not only brush off the snow but also not let it pile up around the side.

And you're in Ontario!

That's a whole heap of brushing and shovelling....

 

[XR250]

I would think 35k to 40k is a reasonable engineering fee including strengthening,

That fee just seems crazy to me. If your rate is $250 per hour that is 160 hours of design and site time. C'mon seriously?
You would find out pretty early on in the process that the job is basically impossible anyway.

 

[Tomfh]

OP, just to be clear, reverse engineering a lightweight prefab defeats the point of a lean solution.

 

[Tomfh]

Looking at the knee details, 160 hours doesn’t sound too far off