metal building versus conventional steel framing

[archeng59]

What is anyone's experience with cost comparisons between a conventional steel framed structure versus metal building framing. Not pre-engineered metal building, but a custom building using metal building components. Conventional steel framed building is hot-rolled wide-flanged beams and columns, bar joist and metal deck roof, cold-formed stud walls. Custom metal building is one that does not utilize the metal wall and roof panels, but a different veneer system such as brick and a standing-seam roof with rigid insulation. I work with several architects who believe that as long as the structural framing is metal building components, the building costs must be significanly less. I contend that as long as the owner uses an off-the-shelf pre-engineered metal building with no modifications, that is the most economical. When either system is custom designed, there really is not a signifant difference in cost between a custom metal building and a conventional steel framed structure. Assuming the foundation is essentially the same regardless of framing system. I know there are alot of variables involved, but wondering if in general terms, am I off base here? Looking at the RS Means data, I believe I am correct.

 

[msquared48]

"I contend that as long as the owner uses an off-the-shelf pre-engineered metal building with no modifications, that is the most economical."

For smaller metal buildings, what you say is more than likely true.

However, for large metal buildings, throw off-the-shelf out-the-window. Each of these buildings is one of a kind in structure, orientation, foundation, and load application.

That being said, I still feel that a PEMB will be cheaper.

Mike McCann
MMC Engineering

 

[mtu1972]

As much as I hate to say this, I doubt that we (structural engineers) can compete with a building using metal building component framing. Maybe a joist/joist girder building could be cheaper, or as cheap.

We had a case where we were designing a paper manufacturing facility and had started the conventional steel framing analysis as had been successfully done several times before.

The contractor was chosen and "value engineered" the switch to a metal building. This was a 2-story structure with a 3rd level of equipment access mezzanines and two building cranes running the full length for production and maintenance lifts.

Just remember that you are not comparing apples to apples.

They use the MBMA standards rather than AISC and do some things that do not necessarily make total sense. The shell and the crane support were done as a "metal building frame". The 2nd floor and equipment mezzanine were done with conventional steel framing, but beams were not on the frame lines. Two conventional columns straddled the frame columns, but shared common footings. In addition, beam spacings were varied so that the same structural shape could be used to carry differing or specialized loads throughout the structure. This played havoc with the process and electrical designs being done simultaneously for installation after the floors were poured.

Their approach saved money and expedited the schedule which proved to be a no-brainer to the Contractor and the Owner.

GJC

 

[271828]

"They use the MBMA standards rather than AISC and do some things that do not necessarily make total sense."

This is only partially true. They do have MBMA documents, but follow the AISC Spec. and AISI Spec. to the letter.

 

[271828]

archeng59, you asked if your thinking is off. I think the classifications of types of MBs are off. I used to work for a MBMA member and have done consulting for one for years. To my knowledge, practically all metal building systems are custom designed at this point. There might be some specialized application that uses "off-the-shelf," but that wouldn't be what we'd think of in 2009 as a metal building system. A MB system can have metal panels, brick, CMU, etc. as the cladding--it's still a metal building system.

I'm pretty confident that for the vast majority of low-rise designs, the MB system's *strutural system* will be cheaper than the conventional system. Their in-house design programs and design aids optimize the structure to an extent that EORs would never dream of for a conventional bldg. When's the last time you used a build-up member for a floor beam and changed the flange and web plate sizes multiple times in 30 ft? Never, I know, because it wouldn't make sense with a conventional fabricator. It does for MB companies, however. I've seen this in a MB mezzanine. Like MTU pointed out, there are situations in which their products are awkward.

 

[archeng59]

I'm unconvinced that 100% of all MB's are custom, but I believe that because architects are trying to use MB systems in buildings that are not rectilinear boxes that many MB's are custom. So is the term "pre-engineered" is really obsolete for the most part?

For buildings where the owner will be hanging things from the roof structure and those suspended items will be moved around and changed several times per year, is a conventional system (joists and metal deck roof framing) more suited to that functionality versus a metal building system? It seems that attaching wires or other hangers from bar joists would be easier than attaching hangers from z-purlins.

 

[mtu1972]

Yes - the Z pulins were another area of contention. We knew we had some areas with roof top equipment where conventional steel sections would be more vesatile - but that did not fit their normal way of construction.

GJC

 

[spats]

Metal building companies might follow AISC & AISI, but they sure have their own deflection criteria. That way you can create high strength steel tapered frames with webs so thin they can't even properly keep the flanges from buckling, and you can let the frame deflect H/60, or whatever other number is convenient, so that deflection never controls the design.

 

[dik]

PEMB's are generally less costly.

There are several issues with the cost savings (these are general and not necessarily applicable to your installation).

You cannot get after sales service. Any modifications you are strictly on your own.

As noted above, they often do not follow the same standards of most steel buildings. They are an entity unto themselves.

Any modifications will likely void any warranty you might have had.

They are difficult to modify and substantial cost can be expected from both engineering as well as fabrication.

They do not accommodate future loading easily, unless stipulated in the design requirements. Design check is costly.

Consider them as 25 year 'throw away' items.

In earlier threads, I've posted my standard notes for PEMB's. Tightening up the requirements bumps the cost up significantly.

Experiences from several years ago:
A 3psf added load for sprinklers resulted in a $12,000 extra.
A lower girt to provide lateral support for a 4' high masonry wall was designed for an L/90 deflection. I don't recall if the span was 25' or 30'... also, an extra.
A buiding that was used for a chemical process had roof deck corrosion that necessitated substantial re-roofing. The cost was in excess of $280,000 and the firm packed up its tent and left the town.
Removing an end support required reinforcing the structure two bays distant in addition to the end bay.

Dik

 

[271828]

"I'm unconvinced that 100% of all MB's are custom, but I believe that because architects are trying to use MB systems in buildings that are not rectilinear boxes that many MB's are custom. So is the term "pre-engineered" is really obsolete for the most part? "

LOL, you can be unconvinced and wrong at the same time! Just joking and some ribbing there.

If you design a building that is a single gable box, every MB company I know will run that through their programs and design it to death in a custom kind of way. It's impossible to prove non-existence, so I don't know if someone out there would have these "off the shelf," but I doubt it.

When you're referring to MBMA type bldgs, I'd say "pre-engineered" is indeed an obsolete term.

"For buildings where the owner will be hanging things from the roof structure and those suspended items will be moved around and changed several times per year, is a conventional system (joists and metal deck roof framing) more suited to that functionality versus a metal building system? It seems that attaching wires or other hangers from bar joists would be easier than attaching hangers from z-purlins."

I'd agree with that. Heck, I'd put bar joists into the "less than desirable" category for that type of application also. So if a guy wants to move an 800 lb load to another location, he has to reinforce the joist accoringly.

 

[271828]

Spats wrote "Metal building companies might follow AISC & AISI, but they sure have their own deflection criteria."

This is supposed to be some kind of evidence of what? Deflections are not usually codified and conventional engineering offices often use different values. They just happen to have studied, in detail, what they really need for their types of buildings. Some kind of problem with that?! They use tighter limits when they need to, such as when they have brick cladding.

"That way you can create high strength steel tapered frames with webs so thin they can't even properly keep the flanges from buckling"

Come one now. Not to sound harsh, but this seems to illustrate a lack of understanding of slender plate girder design by the AISC Spec. So bridge engineers who use slender plate girders operate in a similar cowboy-ish manner, LOL?

 

[archeng59]

Thanks for all the input.

 

[271828]

Dik: "As noted above, they often do not follow the same standards of most steel buildings. They are an entity unto themselves."

I don't know what you guys mean by "different standards." They design their bldgs to specifications adopted by the building code, period. This means the AISC Spec. and AISI Spec. They have MBMA specific guidelines also, but those are the "specs" that are used.

Can't argue with the rest of your post. MBs definitely have their limitations. *IF* one is in the position to shell out the dough for a building within those limits, then he's *thankful* that MBMA folks operate the way they do. The economy makes it possible for some folks to go into business to do their thing.

 

[271828]

Guys, sorry to sound combative. I have a soft spot for MBMA types because I've worked with them. These discussions usually end up in a bash-fest from folks outside their industry. I know guys from 4 of these companies and they are great guys who really like to do a good job. Their products are great for some kinds of projects and awful for others, but I think we could say that about any system. They know this, but if the project is borderline and the GC wants to push for a MB, they ain't gonna turn them down, LOL.

 

[spats]

Sorry, I didn't mean to sound so jaded, but facts are facts. By the way, I worked for a metal building company for 8 years, about half of that time in their product development department.

271828 wrote "They just happen to have studied, in detail, what they really need for their types of buildings. Some kind of problem with that?!". I am currently working on a metal building project with (2) 20T bridge cranes, and their "studied need" called for H/60 deflection on the main frames and portal frames (their "standard"). I also have masonry walls to 10' high all around. I don't think anybody other than PEMB folks would think that kind of deflection is appropriate.

With metal buildings being used more-and-more with conventional wall systems and unusual loadings, it's about time they reconsider their standard deflection criteria, among other things. Of course, they don't want to compete by the same rules as the rest of us, because then they wouldn't be able to steal as much work from us conventional designers. They convince owners and contractors that they get the same quality of building, because it "meets code", but this is not true in my book. As mtu1972 said earlier, we "are not comparing apples to apples".

 

[archeng59]

My question started with a discussion between me and an architect. We are working on a project where the owner will have various events in the building that will require signs, marquees and various displays suspended from the roof framing. Most of the suspended weights will be less than 500 lbs per hanger. The architect wants to use a metal building to reduce costs. Both his fees to consultants and final construction costs. In my opinion, a metal building does not offer the owner the flexibility to hang things inside the building wherever he wants to based on the events he has discussed. I recommended a conventional steel braced frame system with bar joists and metal deck roof framing. The architect said metal building framing is always more economical. I agree to a point, but not for this building. When all is said and done, the rigid frames, portal frames and roof purlins will be the only metal building components in the building. The architect does not want girts even though I explained that the girts serve as lateral bracing for the columns. I lost the battle on this job.

Anyway, thanks for the input.

 

[JedClampett]

I wouldn't blame the PEMB industry exclusively, except for the fact that they throw away their calculations minutes after being paid for the project.
You can't tell me that when owners are pushing for the cheapest product out there, that they don't know that they're getting a less durable building. These aren't stupid people. They want to make budget and let the next guy worry about the lifespan, dings, recoating, swaying fixtures and fact that you can't hang a 500 lb. lifting eye from the structure.
When you pay Yugo prices, you get a Yugo.

 

[FLCraneBuilder]

Great set of comments!!!! - I completely agree with both sides on this. Being a crane guy, I would caution against excessive deflections in any part of the structure. This could lead to premature crane wheel & bearing problems; that nobody will think is the building's fault. Also, it's nearly impossible to prove, if the building becomes an item of discussion.

 

[271828]

Whose fault is it when the MB is designed to deflection limits that are too loose? I've worked on MB projects from both sides. The EOR's structural notes should indicate the appropriate deflection limits when soemthing other than MB typical values are not OK. I've done this lots of times and they've complied without any issue every time.

Do you guys not do this? If not, then I'd suggest that the fault is not only the MB engineer's, LOL.

 

[mtu1972]

Lots of great comments since I made my earlier posting. I should have been more specific when I mentioned standards as I was not questioning strength, but was concerned about lateral stiffness. And yes those may not be codified standards but we all know and try to comply with them.

The Contractor had considerable problems with getting the crane runway girders aligned and indicated that regardless of what future Metal Building guys say, he would never put up another industrial facility without grouting the column base plates to help with squaring and aligning the structure. They had ridiculously thin base plates and no grout to our foundation piers.

JedClampett is totally correct when he says the Owner made the choice to help insure staying On-Time and Under Budget, so it's on him when the future inevitable changes become difficult and costly.

The Contractor pushed for this decision because it took all of the shop drawing review, siding, and roofing submittal time factors off of his plate and out of the project schedule.

From our standpoint, we were on a T & E Not-to-Exceed contract and we lost out on about 2 people's billing time for the steel design. One senior designer was still required full time to interface process requirements and keep our CAD model up to date with the structural framing.

GJC