Modify manufactured metal building frame 2

[Larryhd2]

We have a project where we are dealing with an older, 1980's or so, manufactured metal building.

The developer wants to add a cupola down the ridge and we also need to qualify it for current Code loading and flood loading.

Does anyone have a reference manual as to how to analyze and modify these frames?

Any help is appreciated.

Larry

 

[msquared48]

Changes to PEMB frames are well commented on in these forums, and generally a problem.

If your codes for local load requirements have decreased, it may be possible, but also tempered with code changes, in this instance, around 30 years or so of them.

Most PEMB manufacturers have written their own programs to design these structures, and many of them are no longer around. I realize that this is probably not what you want to hear, but if the original manufacturer is still in business, in all likelihood, it would be cheaper in the long run for the client to go thru them for the change.

Mike McCann
MMC Engineering

 

[Larryhd2]

Thanks for your input Mike.

I deal with this all the time, and I have yet to run across a MBM that is willing to engineer revisions to their buildings. It really makes no sense to me, but they seem to wash their hands of a project once it has been erected. In this case, the MBM is no longer around....

This means that we take on the task of basically re-engineering the frames which I'm sure will require modification to the connections and maybe beefing up the x-section in some areas. but where do I start is the question... I need some references get my head around it...

 

[msquared48]

I assume you have the MBMA manual and associated publications?

The things I would be really concerned about is the extra wind load from the cupola, plus snow drifting at the ridge from the wind due to the cupola, if you have snow in the equation.

Are the frames plate girders or open web trusses?

Mike McCann
MMC Engineering

 

[JedClampett]

ASCE has a seiminar on doing retrofit work to PEMB frames. Unfortunately, it doesn't look like it is available in the near future. It was taught by Alexander Newman.

https://secure.asce.org/ASCEWebSite/ESTORE/ProductListing.aspx?prodClass=SS.

I took the course and it basically just said, follow common sense. Measure all the member sizes, set up a model, analyze it for the load cases applicable, etc. The major complications are two:
One is that these structures are optimzed. Member sizes vary continuously. Plate thicknesses vary, widths, etc. as well as depths. So your properties are constantly varying. This makes your modeling and measuring complicated and tedious.
The second major complication is that once you start digging into the design, you're likely to find out that you can't make the structure work for current loads or even the code that applied during the design. These guys were (and are) masters at using every last ounce of capacity in ways that might not be obvious. So now you have a choice of reinforcing the entire building for a small change or just the frames you're impacting.
Good luck and prepare to be aggraved. You're lucky the building is not more current. All the stuff I said above applies double now that the frames can be computer optimized.

 

[Larryhd2]

Thanks Mike....

I will dig further into the MBMA publications to see what I can find.

It's just wind and seismic I would need to deal with, no snow. And the frames are tapered plate girders and the roof is Z-girts spanning between.

I appreciate your time.

Larry

 

[MiketheEngineer]

My investigation of existing PEMB buildings is that there is NOTHING left in them - usually. They are maxed out. Any changes are almost impossible. Search these threads for similar questions.

 

[JoshPlumSE]

On a related note, AISC just released Design Guide #25 which covers recommended analysis and design procedures for web tapered members and frames. Essentially, this replaces the older design procedures found in the ASD Green Book.

You may not be required to comply with these requirements (because this is a retrofit, not new construction). However, the Design Guide promises to be a good reference on the subject.... I am most of the way done wading through it and it seems a bit more rational than that was done in the past.

 

[Larryhd2]

Looks like we have convinced the owner to accept a column at the middle of the frame, at the ridge.

This will make things much easier and relieve loads at the joints.

Thank you all for your input.