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RE: Soil-Structure Interaction

[Subject Prev][Subject Next][Thread Prev][Thread Next]         Sorry Paul, I have to agree with Javier. (Could we have more comments on this?).  If the building is supported on the SOG and the SOG rests on piles, the columns loads are transfered to piles through the SOG, which now forms a part of the system.  (if this load could be taken by the soil, we'd have a raft here).  Now, you must include SOG load for pile calculations and also design it as suspended slab with column loads and pile supports.  Altrnately, you could support each column directly on pile groups and leave the disconnected SOG to settle on its own.
        Theoretically, you could model soil springs under the SOG, but its usually not much help in weak soils.


From: Paul Crocker <paulc(--nospam--at)>
To: "'seaint(--nospam--at)'" <seaint(--nospam--at)>
Subject: RE: Soil-Structure Interaction

"Not only that, the slab itself has to be designed as if it was an elevated
slab (not a slab on grade)."

That is a matter to discuss with the soils engineer.  Some structures have
sufficiently larger column gravity loads to induce undesirable settlement
and require piles, but do not have problems with slab on grade settlement
due to the much lighter and more dispersed loads the s.o.g. presents.  In
others, the soil under the slab on grade will settle, too, but not so much
as to require a structural slab if some local cracking and uneveness can be
tolerated.  In much the same way, the degree to which the slab seismic loads
will go to the piles can also vary.  Check and see what kind of soil
condition you are dealing with, this will determine your course of action.

Paul Crocker

 ----- 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 on
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 ground"
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
> 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. Geotechnical
investigations have not been undertaken yet, apart from some rough
estimates, so I don't know if any liquefaction potential exists on the site.
> Any thoughts on the subject are appreciated.
> Regards
> Gunnar Hafsteinn Isleifsson
> Denmark