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Re: seaint Digest for 16 Apr 2010

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Mr. Shahid:

In a sense, any steel building is pre-engineered, since it is rare to have the steel all fabricated in the field instead of being designed, detailed and then fabricated in a shop. However, the term is more specifically used for buildings that are provided in a "kit", along with engineering by the manufacturer of the kit. There is usually additional engineering required for a project with a pre-engineered building. The manufacturer's engineer designs the building and takes responsibility for it, but the architect or engineer of record for the project does the site design, interiors, electrical, mechanical and plumbing design, and usually the foundations.

Most pre-engineered buildings have welded three plate moment frames supporting cold formed purlins in the roof and girts in the walls. The building skin is commonly pre-finished corrugated steel, although just about any material can be used over the basic structural system. Lateral loads at right angles to the frames are commonly resisted by rod bracing in the plane of the roof and rod or portal braces or frames in the plane of the walls.

There are also pre-engineered masonry, fiberglass, aluminum and concrete buildings, but they tend to be smaller. Pre-engineered steel buildings can be quite large, although generally only single story, perhaps with a mezzanine. The big three of pre-engineered steel buildings in the US are American, Butler and Varco-Pruden. They all have good websites. I have built all of these over the years and they are all good systems. There are many good regional manufacturers and other smaller national firms. The more substantial ones are members of the MBMA, which is like the AISC, only for metal building firms. The AISC used to have a certification process for pre-engineered buildings, but they dropped it, (although many engineers continue to specify it).

The rationale for using a pre-engineered steel building instead of a conventional hot-rolled or tube steel structure is usually cost and sometimes schedule. Right now, you can get a pre-engineered building of just about any size in somewhere between four and ten weeks, including engineering for the structure. Pre-engineered buildings usually cost more per pound of steel than a hot-rolled or tube steel building but use less steel by using tapered beams and columns and light gauge secondaries.

Pre-manufactured buildings are usually factory built in modules and trucked to the site, set with a crane or lift, and bolted together. The size of the modules is limited by the "over the rad" clearance requirements, which is usually about 10 feet wide x 60 feet long x 16 feet high, including the lowboy trailer. Pre-manufactured buildings are often used for temporary facilities and in this case are often not installed on permanent foundations. Modular buildings can be assembled into quite large structures by combining modules. Many jurisdictions have a separate building code for manufactured housing which is less restrictive than the code for site built structures.

Hope that helps. As you can tell, I am a fan of pre-engineered steel buildings. / Eric Cox, RSE


From: "Shiraz Shahid" <sshahid(--nospam--at)engineering-solutions.biz>
To: <seaint(--nospam--at)seaint.org>
Subject: Preengineered - Prefabricated

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Hi

Please if the list can tell me the difference between pre-engineered and
pre-fabricated buildings. Or are they one and the same thing?

Best regards,

Shiraz Shahid.

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