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Re: Heavy line loads on thin slabs on grade

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It's more than the 750 lbs vertical load, it's also the tipping load where the load goes to one side of the rack as it travels or experiences a seismic event.   Does the track have to be connected to the slab?

I've analyzed a number of these units but never got involved in the foundation as that was by someone else.  If these units a stored at one end of the room, then it becomes a fairly large loaded area.

If the slab cracks and settles, then the system may not work and an attorney may be contacting you about that.

Neil Moore, SE, SECB



At 11:54 AM 8/30/2006, you wrote:
That's the type. It has several 9'x2' sections which stack together and allow access by moving the sections over a rail to create an aisle - say 25' of filing in a 30' track. This is the second attempt for the owner to locate the file system; the first attempt was to put it on the second floor of a (barely) composite slab. They decided to change the location to the first floor, as the second floor would have needed new columns to support the existing beams.

That's the kind of answer I was looking for, but hate going to an owner with an "it won't work" answer without analytical backup. Like I said, the numbers appear to calc, but it doesn't "feel" right if you think of the actual mechanics (resilient foundation).  These owners don't have any idea of what constitutes structural loads. I was originally asked to review new HVAC roof unit placement, and checking the loads for this HDFS was an afterthought.

I'm thinking about sawcutting the existing slab where the unit will go and _not_ doweling the thickened slab back into the existing floor. If/when they take this system out (this is a tenant), they can gypcrete the area if it sinks a bit. I don't want the adjacent lessees complaining about cracks in two years.

Jordan


David Topete wrote:
Jordan,
Is that filing system one of those automated, secured filing system that stands about 7 ' tall?  I'm looking for more info, but the 750 plf may be a good start for me.  As for your situation, RHK summed it up best by stating "caveat emptor."  The owner can't reasonably expect a very lightly reinforced 4" slab to support a high density filing system.
DT

"Jordan Truesdell, PE" <seaint1(--nospam--at)truesdellengineering.com> wrote:
Has anyone here done an analysis of existing slabs on grade (4" thick,
minimal WWR) to support high density filing systems? I've got a unit
with a pair of 750plf loads about 7' o/c and reading ACI 360 has clouded
the issue more than helping. Using the plain concrete formulas for
shear in ch22 of ACI 318 and looking at the allowable subgrade bearing
all look good (Vu/phi-Vn=0.4, q/q-all=0.35). If this were new
construction I'd put a thickened slab in an skip the calcs and hand
wringing, but the building is in service and we are trying to minimize
the amount of "dirty" work in the area. Suggestions?

--
Jordan


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