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Re: using existing structures

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>         I don't know why you have to reject your first concept because of
the
> restriction on W21 beams.  I expect you could design your own steel beams
using
> three plates 18 or 19 inches deep that are just as strong as, or stronger
than
> any W21 in the book.  I think that is what I would prefer.

One thing I didn't mention is that the architect now wants to use the space
between the penthouse floor and the existing roof to run mechanical ducts.
Small residential sized stuff, of course, but they still take up space.  So
in reality I'm limited to about 12", or I'm going to have to cut and
reinforce holes in the webs, or design custom steel trusses.

I contacted a local testing agency this morning, and they're familiar with
this type of work.  They do testing and analysis on existing roofs for the
addition of cell towers.  The *very* rough quote I was given consisted of a
couple of guys x-raying select beams, performing selective demolition to get
bar sizes, and drilling some cores in the slab for concrete strength.  All
this for about $2000.  If this results in the ability to use the existing
roof, this could pay for itself many times over.


----
Jason Kilgore
Leigh & O'Kane, L.L.C.
jkilgore(--nospam--at)leok.com
816-444-3144
816-444-9655 (FAX)
----- Original Message ----- 
From: "Daryl Richardson" <h.d.richardson(--nospam--at)shaw.ca>
To: <seaint(--nospam--at)seaint.org>
Sent: Monday, July 07, 2003 7:22 PM
Subject: Re: using existing structures


> Jason,
>
>
>         To answer your questions:
>
> 1.)    I understand that you can get reinforcing sizing and spacing from
X-Ray
> photos; but ask about cost.  Every time I have contemplated this cost had
ruled
> it out.
>
> 2.)    Yes, you can do this (scientifically speaking, at any rate).  If
you're
> using LRFD the ultimate load distribution should be basically as you
describe.
> If you're using an elastic analysis then he deflections of the two beams
will be
> the same and the actual distribution of loading between the two beams will
be a
> bit of a bitch to calculate (assuming the concrete beam is continuous and
the
> steel beam is simple span).  If they are both continuous or both simple
span the
> distribution will be as you describe.  You can also connect them in such a
way
> as to make them react as a composite beam; but that will probably be quite
> difficult and not especially beneficial.
>
> Regards,
>
> H. Daryl Richardson
>
> Jason Kilgore wrote:
>
> > I'm working with the renovation of an existing structure.  In general,
it's
> > a 2-story concrete joist-beam-column building, constructed about 50
years
> > ago.  It is obvious that the building was originally designed for the
> > addition of at least one more floor.  I do not have any original
drawings on
> > this building.
> >
> > After finalizing all design drawings, the owner and architect have
decided
> > that it would be "neat" to add light-frame 2-story penthouses to the
roof.
> > I admit that it will look awesome after construction, however, the
design
> > has now become a nightmare.
> >
> > Setting aside all lateral upgrade problems (there will be several), my
> > current concern is supporting the gravity load from the new penthouses.
The
> > bearing walls cannot line up with the beams/joists, and one area has 34'
> > joist spans.  Because of the lack on information on the existing
structure,
> > I was trying to avoid using the existing roof and relying completely on
new
> > structure built on top of the existing columns.
> >
> > The first floors of the penthouses have to be raised above the concrete
deck
> > so the residents can see over the existing 8' parapets from their living
> > rooms.  The first plan was to build a new steel platform to both brace
the
> > parapets and to support the penthouse floors.  The platform was
supported
> > entirely by steel columns centered over the existing concrete columns.
Now
> > this will not work because the top of steel can't be higher than 1'-10"
> > above the top of concrete for various reasons (the residential floor
level
> > is 2'-0" higher than this).  Some of the steel beams needed to be W21's
to
> > span 34' with two stories of wall load, which obviously won't fit in
20".
> > I'm now looking at supporting the new structures entirely with the
existing
> > concrete roof, with some possible reinforcing.
> >
> > Finally, the questions:
> >
> > 1. Is it possible to accurately determine the existing reinforcing in a
> > concrete beam?  I know concrete strength can be determined easily, but I
> > need the steel.
> >
> > 2. Is it possible to reinforce an existing concrete beam from ABOVE?
There
> > is very limited headroom from the 2nd floor to the existing roof.  I was
> > thinking along the lines of adding a steel beam along the top of the
> > concrete beam and sharing the load based on relative stiffness.  Another
> > option would be to use epoxy/FRP reinforcing strips along the bottom of
the
> > exposed roof beams, but this would be "ugly".
> >
> > Any help would be greatly appreciated.  I'm going to call my contacts at
a
> > few local testing agencies tomorrow.
> >
> > ----
> > Jason Kilgore
> > Leigh & O'Kane, L.L.C.
> > jkilgore(--nospam--at)leok.com
> > 816-444-3144
> > 816-444-9655 (FAX)
> >
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