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Re: Soil-Structure Interaction

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I agree with Javier.  You have to include the weight of the slab and design
it as a one/two way r.c. slab.  Unless the owner is perfectly comfortable
with the risks associated with using a slab on grade in this situation,
which could, in extreme cases, leave a very useless and expensive building

Alden Manipula
Structural E.I.T.

----- Original Message -----
From: "Javier Encinas" <jencinas(--nospam--at)>
To: <seaint(--nospam--at)>
Sent: Thursday, January 04, 2001 2:59 PM
Subject: Re: Soil-Structure Interaction

> Of course you have to include the slab weight in your calcs. Your
> is founded on piles precisely because of the low bearing capacity of the
> underlaying soil, otherwise it would be a mat foundation, and the piles
> would be useless. Not only that, the slab itself has to be designed as if
> was an elevated slab (not a slab on grade).
> Javier Encinas
> ASDIP Structural Software
>  ----- Original Message -----
> From: Gunnar Hafsteinn Isleifsson <gunnarhi(--nospam--at)>
> To: <seaint(--nospam--at)>
> Sent: Wednesday, January 03, 2001 11:16 PM
> Subject: Soil-Structure Interaction
> > Hi
> >
> > I have a sort of a geotechnical question:
> >
> > A steel structure stands on a thick concrete slab, which in turn stands
> pile footings. When evaluating lateral seismic forces acting on the piles,
> do I include the weight of the slab, or does it just "move with the
> as an integral part of it.
> >
> > My first impression is that one has to include the weight of the slab,
> when determining the base shear at the top of the piles, because that
> although the slab will also be ground supported (cast on ground), any soil
> settlement will cause the slab to rest solely on the piles, and then one
> can't rely on any friction (sliding resistance) between the slab and the
> ground.
> >
> > Our client wants to know if anything can be done to exclude the slab
> weight, since it has great effect on the pile foundation costs.
> investigations have not been undertaken yet, apart from some rough
> estimates, so I don't know if any liquefaction potential exists on the
> >
> > Any thoughts on the subject are appreciated.
> >
> > Regards
> > Gunnar Hafsteinn Isleifsson
> > Denmark
> >
> >
> >
> >