Prefab Metal Building Design Help 1

[Shaylon]

Hello all,

I have come across a bit of a unique situation and I was wondering if anyone could help me out a bit. If I am correct, prefab metal building suppliers do not design their structures according to AISC standards. I am faced with the task of designing a sizable addition to an existing prefab metal building structure. Not only is the client wanting to extend it horizontally, but vertically as well. Therefore, I need to know how prefab metal buildings are designed so I can perform an accurate analysis of the existing structure to determine what I have available to work with and what needs to be done to bring it up to current code when all said is done. As usual, any and all input is greatly appreciated.

Thanks,
Shaylon

 

[Lion06]

I'll save you a lot of time. You can't extend it vertically. Not without substantially reinforcing it.

The way PEMB suppliers get business is through the economy of their system. That economy requires them to be as lean as possible on the load side and as liberal as possible on the capacity side.

I recently did a roof eval for an old un-named PEMB supplier's roof system. The stress ratios for the original loads had almost all member stressed between 1.01 and 1.06. This was also being extremely liberal with some k-factors per one of their reps.

I was quite shocked, honestly, to see how far some engineers/companies push the envelope.

There is no way that you will be able to add axial load and moment to the columns without them being significantly overstressed.

That's not even touching on the footings.

 

[Brad805]

I agree with Lion. The PEMB business is all about pounds of steel. These guys know how to squeeze out every pound. Some of the older PEMB had more reserve capacity since they did not have CAD/CAM systems, but not the new ones. Even the field work to complete such a task is considerable since the shop drawings for these buildings are not typically accurate enough for your analysis.

You need to sit down with the client and get an understanding how far they are willing to go to complete these. I typically start with high estimates to see how serious they are. Maybe toss out a cost for re-building new frames in situ at each bayline and see how that goes over. If that does not scare them, it is a great engineering project and is totally possible. Lots of channels, plating and field welding. Most of the significant part of the cost is in the field welding, and prep work.

Brad

 

[ToadJones]

Design the addition as if it were structurally independent of the PEMB and make sure it actually is. Drift snow load will be an issue here most likely.

 

[msquared48]

I agree with Toad and the others here. It's your only really viable option.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[MiketheEngineer]

This has been discussed a number of times and virtually all responses just follow what you have read. Sorry and good luck!

 

[Shaylon]

Was I wrong in stating that PEMB suppliers do not design according to AISC standards? If this is true, does anyone know what they use in order to do their design?

I have been searching around the web all day and everything keeps pointing me back to one website (

http://www.mbma.com)

and a manual they produce (2006 Metal Building Systems Manual). I was able to find a copy of this manual online and it did not look as if it helped with the design at all. Any input?

Thanks.

Shaylon

 

[ajh1]

All PEMB designs in the US, or at least all done by members of the MBMA (trade association), are done to the applicable building code and the AISC and AISI steel specifications. There is an accreditation program for metal buildings run by IAS, a subsidiary of ICC, that reviews both manufacturing and design conformance. If you are looking for a manufacturer be sure you get one who is accredited.

 

[StructuralHokie08]

As AJH1 stated. PEMBs design all their buildings to the applicable building code and in turn the related AISC and AISI steel specs.

 

[mbullism]

I agree with everything above, just wanted to add that we recently investigated a PEMB for added solar panels... we had access to a PE who came up in the family PEMB business, before going out on his own. One thing he said that really caught my ear was that apparently the fight for reducing pounds of steel was so competitive that larger companies that could stockpile material would actually shop for material that conformed to the bottom end of the tolerance for gage steel because they were buying by the pound as well... they could still call it 18ga, for example, but it was as skinny as 18ga gets-

Not sure how true it is, but just another insight how skinny skinny can be-