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Re: Cantilevered Steel Beam Contruction

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Blake :

AISC Marketing published a study in 1994, called "Cantilever Roof Framing Using
Rolled Beams". They were promoting it's use as an alternate to joist girders
which I believe at that time we were experiencing long delivery times. I have
used this system for the last 30 years when I could justify it. It might be
easier to justify today with Grade 50 being the commonly available steel. I
suggest that you check with several fabricators in the area where your project
is being constructed to find out about prices for stiffeners. Use fitted
stiffeners only where required. If it doesn't have to be fitted tight between
the flanges, it is obviously less costly for the fabricator.

Some other advantages of the cantilevered system (also known as Gerber Framing)
are:

1. Less (depth) headroom required than joist girders or simple beams. Architect
could possibly lower the building and save on wall height.
2. Less deflection than simple span beams.
3. Can utilize frame action with cantilevered beams to resist lateral loads.
4. Shorter delivery time.
5. Can bid more joist manufacturers if only K-series are used on the project.

This system, however, is more difficult to evaluate for ponding.

 I  hope these comments help.


Jim Kestner, P.E.
Green Bay, Wi.


Blake Haley wrote:

> Does anyone know of any studies or information on the cost differences
> between cantilevered steel beam roof construction and typical beam-to-column
> simple span construction?  I am wondering if by the time stiffeners are
> placed
> over the columns and any intermediate bracing of the bottom flange offsets
> the savings in pure beam weight in the cantilevered option?  Is
> constructability an issue?
>
> I personally prefer a simple steel beam spanning from column to column with
> a simple framing connection, but I want to be open to use the cantilevers if
> it is the best option for the owner/client/contractor.
>
> Any comments would be greatly appreciated!
>
> Thanks,
>
> Blake Haley, P.E.
> White Engineering Associates, Inc.
>