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Re: Structural System Determination

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Tom,

As Jim pointed out, there is not really a simple answer to your question.
He did a good job of pointing out many of the factors that can effect the
decision process.

I will offer my own experience from the Southeastern Michigan area.
Around here, one of the biggest factors is the economics (or in reality
the perceived economics) of the structural system.  Since this area is
heavily unionized, systems that utilize less labor but more potentially
more expensive materials have a perceived advantage.  This results in the
fact that virtually ALL buildings in this area are structural steel,
because they are peceived to be less expensive to building.  This is
largely due to the lower labor costs of erecting steel as opposed to
busting bars, buildings forms, and placing concrete.

While the cost of labor is a major factor, there are certainly other
contributing factors as to why steel is so predominate in this area.  One
is the cold weather environment.  It is much easier and less costly (don't
have to have special requirements in cold weather like concrete does) to
erect steel in this area during the winter.  As a result, the construction
industry can still essentially have a 12 month work period as long as they
have the foundations in before freezing as they can erect steel in the
winter and can certainly work on many non-structural elements once they
get the building enclosed (either temporarily or permanently).

The availablility of steel also has a hand in the situation in this area.
Since we are smack dab in the middle of steel country, it is realtively
easy and cheap to get steel here.  Also, considering that there are many
auto manufacturing plants in the area, there is already a high amount of
steel flowing into the area.

The availability of quality contractors also plays a role of selection of
which material is used in this area.  Since this area is overwhelmingly
steel, there are few quality concrete contracts that do concrete work
other than flatwork (i.e. slabs on grade or supported slabs on metal deck)
or simple formed work for foundation walls and foundations.  In
otherwords, there are not too many good contractors for doing serious
formwork necessary for cast-in-place concrete structures.

And finally, the type of structures largely play into the use of steel in
this area.  Most structures built now in this area are low rise
structures, that are typically 3 stories or less.  And many are one story
buildings for development companies that want quick, down-and-dirty
buildings.  The result is that MANY of the one story building are what
some affectionately refer to as "Wal-Mart" construction (WF columns that
have WF girders that cantilever over the top of the columns with the
"filler" members being open-web joists).  This type of construction is
even commonly used for one story office buildings in office space
development sites.  And also keep in mind that many of the buildings
built in this area are "industrial" buildings (i.e. plants) for the auto
industry and other such industries.  This building type in virtually all
areas are typically structural steel with truss roof framing systems.

That is not to say that we don't get some variation to the theme.  Most
parking decks in the area are precast concrete (double tees, inverted T
beams, L beams, etc).  Low rise hotels tend to be either wood (more
common these days for what I observe) or masonry bearing walls with precast
planks.  Many churches are wood structures (LVL or glulam).  There are
also occasional flat-plate, post-tensioned cast-in-place concrete parking
decks and occasional buildings built with masonry bearing walls with with
structural steel interior framing or precast planks.  Thus, the type of
building can greatly effect which type of structural system is used.

Now to step outside of my local area, I know that it can vary widely from
location to location.  I know that the Chicago area uses a lot more
concrete framing even though they face many of the same issues that we do
(steel is readily available, unionized labor, etc).  As I understand it,
the Washington D.C. area is largely a flat-plat cast-in-place area due to
the high restrictions on buildings (as I understand it nothing can be
built that goes higher than the Capitol dome), but I am sure that Gail
Kelley can offer more insight to that area.  I know that many areas of
Texas use cast-in-place concrete on a much more regular basis as they have
skilled, cheap, non-unionized labor AND lots of quality concrete
contractors (I have a buddy that work for a major contractor down there).

Thus, while in theory the general reasons that Jim gave are good overall
guides, it is also important to realize that local perceptions and
traditions can LARGELY influence which of those factors influence the
decision more or less in a particular area.

As far as specialization in structural systems by companies or
individuals, I would say that the answer is a yes and no kind of thing.
Firms tend to more specialize in the "use types" of structures as opposed
to structural systems.  That is some companies get a reputation for long
span structures (i.e. domed stadiums) or sports facilities or high rises
or medical facilities or manufacturing plants.  This can then lead to them
essentially specializing in a structural system by default (i.e. long span
structures are usually steel as are manufacturinng plants).  But many
companies work in multiple fields.  It largely becomes a business decision
for the individual company.  One guy that I know in the area specializes
in erection issues and typically works for contractors on dealing with
erection and other structural issues beyond the design phase.  He is
nationally reconized in this area and gets a lot of work since it is such
a specialty.  As a result, his company virtually does ALL steel stuff.

BTW, as a side note, I find it highly entertaining that ACI is
headquartered in an area that is virtually all steel while AISC is
headquartered in an area that uses significant cast-in-place concrete (at
least relative to this area).  Highly ironic to me!!!

HTH,

Scott
Ypsilanti, MI


On Wed, 8 Jan 2003, Tom Bodkin wrote:

> Who typically selects the structural system that will be used for a building
> structure?  Does it come from the Architect, CM or owner?
>
> I know it varies based on several factors but I just wondering who typically
> specifies it.
>
> Also, I'm picking a thesis topic at Villanova and the answere to this
> question will help me out alot.  Do consultants generally specialize in one
> type of sytem when it comes to building and industrial structures ie. steel
> frame, prescast concrete, cast in place concrete floor systems and frames,
> masonry?
>
> What usually governs the selection of a structural sytem and what is usually
> used in the Northeastern part of the country and in the rest of the country
> for that matter.  I know (or think) concrete fairs better in the drier, non
> freezing areas, CMU does not so well in the wet freezing areas, and steel
> has fire proofing requirements.
>
> I would appreciate input based on your experiences.
>
> Thanks,
>
> Thomas W. Bodkin, E.I.T.
> Carroll Engineering Corporation
>
> tbodkin(--nospam--at)carrollengineering.com <mailto:tbodkin(--nospam--at)carrollengineering.com>
>
> Phone: 215-343-5700 x360
> Fax: 215-343-0875
>
>



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