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RE: 75 PSF Equipment on 50 PSF Floor

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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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