Pre-Manufactured Building Evaluation 16

[ellas1]

Any tips on how to evaluate the structural integrity of an existing pre-manufactured steel building with unknown MNFR.

 

[dik]

Depends on how detailed... if just a cursory review, then you may check for bolt tensions, and x-bracing snugness... and general building envelope issues...

If very detailed, it is very difficult... you have to analyse the frames which may or may not have worked in the first place. Many PEMB's are designed for some other place and an owner picks one up cheap for his locale... different wind, snow and live loads...

Have fun...

Dik

 

[BAretired]

I wouldn't touch it with a ten foot pole. Without knowing the manufacturer, you can't even establish the grade of steel used. And if you conclude the structure is safe, guess who becomes totally responsible for it...you do, that's who.

BA

 

[haynewp]

BA makes a good point, but I would like to know more about the goal of your evaluation. When we make an alteration to any existing building, say adding a parapet, we are essentially taking over responsibility. We don't turn down this kind of work just because we are afraid of the liability. Not knowing anything about the prefab bldg is a pain and you would have to as-built the structure. The liability and the analysis required for a typical structural engineering company doesn't make it a very desirable project in my opinion. Foundations are another big problem if you don't have any info on them either.

 

[msquared48]

Unless you can find the original calculations and drawings for the structure to compare with what is actually in the field, I wouldn't touch it either. Chances are though that this information does not exist anymore.

Just say no here, politely.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JedClampett]

I took a webinar by ASCE on this. It was taught by Alezander Newman. It was pretty good.
But there's no magic involved. You measure all the flanges and webs and calculate section properties. They're normally tapered, so that adds another complication. Then you rent a lift and measure the girders, purlins and bracing.
Then do your calculations. You're likely to find that the building doesn't work for current loads, nor did it work for its original design loads. So now you wonder if you made an analysis mistake, a loading mistake, a measuring mistake or maybe the materials were stronger than you assumed. So you start over with different assumptions. Or maybe you go out to the field and remeasure everything.
Meanwhile, the hours are piling up. You will literally have to put more time into this than the building is worth. And you will have to tell the client that the building that's been standing for many years is a disaster about to happen. Maybe if you warn the client that these tasks are usually expensive, you'll either be given an adequate budget or they'll give the job to one of your competitors. Either way, you win.
I agree with the posters above. These are the ultimate in no win projects.

 

[bpstruct]

I also wouldn't do it. I have always had a tough time trying to justify the sizes of framing for metal buildings....without modifying it. You would have a lot of upfront legwork, but like Jed stated, far more scratching your head as to why the original building didn't work for the design loads. Always tough to relay that info to a client.

 

[SteelPE]

I agree with Jed,

I recently worked on a project that required metal building modifications. I took the project because I needed the work. I knew it was a metal building and tried to budget accordingly. Well this metal building had frames that were done out of trusses (didn't know that going in). Every single truss member need to be measured. I think there were 40 web members and chords that changed size all over the place. It took a 2 hour measuring job and turned it into a full day. I advised the client 5 times that demolishing the building would be better as he would get wish list vs settling for something else.

Turns out the building was a VP building and I knew the EOR who worked at VP at the time. He gave me some advice on how to look at the building. Spent 2-3x as long as I originally estimated only to have the project scrapped and now the client is refusing to pay his full bill.... so add that to the list. This project was not worth it at all.

There are guys who specialize in these things who can do these buildings in 1/2 the time. I hate to refuse work in this economy but sometimes you just have to.

 

[MiketheEngineer]

These have been discussed numerous times in these forums. You would think the steel they were using was gold - they cut it right to the bone and most times it hard for the average engineer to justify. I beleive they do a lot of in-house testing to justify.

RUN - do not walk from these !!

 

[spats]

I have to speak up in defense of "pre-engineered" metal buildings. No Mike, they DO NOT base design on testing. They follow the code just like you and me. The real problem I have with metal buildings is that, once the building envelope is breached in a windstorm, they tend to fall apart... but so do conventional buildings. Why their envelope seems easier to breach is somewhat of a mystery to me, even though they are light gauge, but it probably has a lot to do with the quality of construction (i.e. the right size and number of fasteners), not the design. YES, they DO design for ecomomy, which is mostly accomplished by using their own built-up and tapered plate sections for primary framing, and light gauge sections for secondary framing. Just because you don't know how to design a "pre-engineered" building doesn't mean they are wrong and you are right.

 

[WARose]

Then do your calculations. You're likely to find that the building doesn't work for current loads, nor did it work for its original design loads. So now you wonder if you made an analysis mistake, a loading mistake, a measuring mistake or maybe the materials were stronger than you assumed.

Ha! Glad to know I'm not the only one that has run into this. I remember some years back I got forced into this because my company put something near one of these house of cards and (as a result) was adding [snow] drift load to it. I remember at one point telling my boss: "...forget what we are doing to it...I don’t know what is keeping it up in the first place". We wound up doing something independent to the pre-engineered building to keep the load away from it.

I sympathize with anyone having to mess with it. You have to wonder if they are using plastic design and/or high grade steel to make those girders work.