CA for PEMB

[masterthenight]

Our firm is designing the foundation for a new PEMB. The Architect has asked us to provide CA phase services including reviewing shop drawings and observing steel erection for the PEMB. Is this typical? Or would an Engineer from the PEMB shop perform those tasks?

 

[spats]

Reviewing shop drawings for design you perform is more than typical... it's really a must on all jobs, as far as I;m concerned. Observing steel erection is definitely not typical. What are they expecting to gain? You're not going to "certify" the erection. If anything you could perform a site visit when they're essentially complete. Just don't call it an "inspection"... you don't want to be liable.

 

[jgailla]

Before I went to engineering school, I worked for a while as an erector for a PEMB company.
Most buildings did not have any engineering oversight. Maybe about 20% had a structural engineer visit the site a few times during construction.
These buildings go up so quick that there aren't many site visits.
On one project, we had the wrong bolts (not enough exposed thread past the nut) delivered and the engineer caught it immediately when very few had been used. It saved us a lot of time on the construction side and it may never have been caught if the engineer wasn't there.
I think a couple of site visits by an engineer is a good thing for the contractor and the owner. You just have to be careful with the liability issue and be specific with the scope.

 

[JedClampett]

If high strength bolting is being used, the building is subject to Special Inspection. Also fillet field welds over 5/16 inch are required to be special inspected. The PEMB Industry seems to skate on this, although I'm not sure how (no high strength bolting?, no field welding?, never been challenged?). It's definitely a gray area. But I don't think they've (PEMB) ever had any field special inspectors on a project I've done.
I'd say, in general, if you're the Engineer of Record on a project you should be glad to be paid for as much construction involvement as possible, Review the language with your lawyer and keep an eye on things.

 

[ron9876]

I think it depends on where you are. Some of the areas where I am require special inspections of all structural steel connections.

I have never seen a PEMB supplier do anything at the site.

 

[MiketheEngineer]

I hate PEMB - there is "NO" give on them. They are generally designed down to the nat's A$$. Have the PEBM mfg take responsibility!!

 

[ajh1]

Inspections:
One of the beauties of the PEMB world is that they are intended to go together without any field welding requirements. Yes, I know there is the occasional weld to be made, but the basic structure is 100% field bolted. The manufacturers typically specify turn-of-the-nut method for pretensioned bolts. Keep in mind that the erector is not normally directly associated with the manufacturer so what they do or don't do in terms of inspections of bolt tensioning in the field is not the fault of the manufacturer. For shop welding, all members of the MBMA (Metal Building Manufacturers Association) have IAS AC472 accreditation. Just like the various AISC fabricator programs, this accreditation replaces per project special inspections in the plant per IBC 1704.2.5.2 (2012 ref).

The manufacturer is typically a vendor to either the GC or the structural steel subcontractor. The way the codes read, special inspections are usually intended to be performed by the owner's representative. This is not the manufacturer, and would present a conflict of interest if the manufacturer did it given who their contract is with. That said, the major manufacturers have erection consultants available for larger structures to insure that the erector understands how the parts need to go together and answer nuances about the particular part arrangements. It is in the manufacturer's best interest that the buildings are erected properly and competently and that they are structurally sound upon completion. An unhappy owner is going to look elsewhere the next time they need a building.

 

[JedClampett]

ajh1, yes the owner can provide special inspectors. But they almost always defer to their designee (third party CM) or the Engineer of Record (as allowed in Chapter 17 of IBC). And just because bolt tightening is turn of the nut, does not mean it's not required to be specially inspected. The fact that it is poor marketing to have their buildings incorrectly assembled might influence the big guys, who want to stay in business long term. It doesn't bother the lowest end PEMB suppliers, who want to make their money and get out of Dodge.
It would be nice for the PEMB providers, as an industry, to acknowledge that Special Inspection and other code mandated requirements, do exist even for them. If they would indicate, as part of their design, that someone needs to witness bolt tightening, welding, etc. so that it's not a mystery during assembly, that would be a start.

 

[Ron]

As jgailla noted, the most common thing we see with PEMB's is bolting issues. We also see issues with the buildings being designed as enclosed structures when they have large openings (air space around roll-up/sliding doors) that would exceed the requirements for enclosed consideration. Another issue is misplaced parts, such as improperly installed/missing wind girts, missing bolts, wrong bolts, poor erection fitup, etc.

As for turn-of-nut method, those should be clearly marked. If not, I assume they have not been done. I prefer to have bolt tensioning observed by me or by an independent testing lab.

Keep in mind that many erectors use the electrical conductivity method of quality control...if it touches, it is properly connected.