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Re: 75 PSF Equipment on 50 PSF Floor

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I have followed this thread with interest, and nobody has suggested what it
seems to me the natural way to proceed.

Some time ago I found myself in a similar situation. What I did was a
finite-elements model of the entire floor consisting of the steel beams and
concrete slab, and I applied also the distributed and concentrated loads. Of
course the results showed that the concentrated load spreads among the
beams. The thicker the slab the more beams contribute. In an infinitely
rigid slab, all the beams take the same portion of the total load. Without
slab only the beams under the load actively support it.

In summary, I would recommend you to model your floor conditions with a good
FE program and find out the actual performance of your system.

Javier Encinas
ASDIP Structural Software
www.asdipsoft.com
----- Original Message -----
From: "Sherman, William" <ShermanWC(--nospam--at)cdm.com>
To: "SeaInt Listserver (E-mail)" <seaint(--nospam--at)seaint.org>
Sent: Monday, March 24, 2003 11:40 AM
Subject: RE: 75 PSF Equipment on 50 PSF Floor


> I am currently working on a similar problem, except that it is a 12,000 lb
> electrical transformer on an existing equipment slab that was designed for
> about 300 psf. The effective pressure immediately below the equipment base
> is about 700 psf, but it is not realistic to assume this pressure on the
> entire floor. Portions of the transformer extend beyond the equipment base
> and there are two such transformers in the equipment room. I am assuming
> that the transformers could be moved around the room during installation
or
> future maintenance, and that one transformer may be moved past the other
> transformer such that both will load the support beams at the same time.
> There is also other electrical equipment in the room which weighs about
150
> psf. Looking at the equipment projections and assuming 12" between any
> adjacent equipment during transporting, I can justify an effective 300 psf
> uniform load for design.
>
> I am reviewing the existing floor supports to confirm that they can
support
> 300 psf. I am also noting on the drawings that the Contractor must shore
> other floors as required, which may be loaded during installation of the
> equipment.
>
> Each such loading situation must be looked at individually, but I
recommend
> considering a slightly expanded area below such heavy equipment where
> reasonable. Adding 6" to 12" at the edges of the footprint can make a
> significant difference in effective uniform load. (However, electrical
> panels are often set side-by-side, so extra area may only be practical on
> two sides of the equipment.)
>
> We have also considered directing the Contractor to shore the existing
floor
> during installation and then only consider the equipment load in its final
> fixed location, with a reduced uniform load on the adjacent floor area.
> However, this would limit the Owner's ability to move such equipment in
the
> future and increases risk of overload if the equipment is moved in the
> future without reviewing the design documents.
>
> Bill Sherman
>
> -----Original Message-----
> From: Chris Banbury
> To: seaint(--nospam--at)seaint.org
> Sent: 3/20/2003 4:22 PM
> Subject: 75 PSF Equipment on 50 PSF Floor
>
> I've been asked to determine if a 1200 lb medical intrument can be
> placed on the third floor of a hospital office building.  The instrument
> is 30"D x 74"W.  The building was constructed in 1989 and I've obtained
> the original plans from county records.  The design live loads listed on
> the plans include 50 psf for office and higher loads for corridors etc.
> However, the entire third floor was originally designed, permitted, and
> constructed as an empty shell with no corridors, partitions, or offices
> so it seems I'm forced to use the lowest uniform load given.
> Non-bearing walls, hallways, offices, laboratories, etc. were added
> later as the hospital found doctors who wanted custom rental space.
> Since the equipment exceeds the minimum uniform live load I am
> considering the following:
> 1. frame a platform to span several floor beams
> 2. place a steel bearing plate to distribute load over a larger area
> 3. paint or demarcate an area on the floor around the instrument where
> no additional equipment can be located such that the painted area
> satisfies the allowable superimposed live load
> 4. modify the floor beams in order to increase the load rating of the
> floor
> 5. calculate the actual allowable superimposed live load of the concrete
> slab and steel beams from the structural drawings.  Since the corridor
> locations were unknown at design stage, it is possible that 100 psf was
> used for the entire floor.
>
> Obviously there are concerns with all these solutions.  I would
> appreciate any additional thoughts or advice on this problem.
>
> Christopher A. Banbury, PE
> Vice President
> Nicholson Engineering Associates, Inc.
> PO Box 12230, Brooksville, FL 34603
> 7468 Horse Lake RD, Brooksville, FL 34601
> (352) 799-0170 (o)
> (352) 754-9167 (f)
> www.nicholson-engineering.com <http://www.nicholson-engineering.com>
>
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