Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: using existing structures

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Jason,

        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.

        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)
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********



******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********