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RE: SOIL PROFILE TYPE FOR STRUCTURE OVER WATER

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The UBC soil types are based on the relative stiffness of the underlying
soil. The underlying soil has an "effective period". If the soil is very
rigid, the periods of the soil and the building are very different and
amplification of the seismic forces is not required. As the soil becomes
softer and its period starts to increase and approach the buildings period
the seismic loads are amplified. Based on this, one could possiblly argue
that in your case, it is not just the soil type that is important. The
flexibility of the pile system supporting the building should be taken into
account. If your seismic model begins at the top of the piles, the
flexibility of the piles is not taken into account. One possible model would
be to model the pile system along with the building in a 3-D model and use
the Sf soil type at the base. (base is where piles penetrate into soil) If
the piles are long, your building period would increase and perhaps reduce
the base shear. However, the drift and moment in the piles may be
substantial.


-----Original Message-----
From: Dir: David Carolan [mailto:david_carolan(--nospam--at)ttw.net.au]
Sent: Thursday, June 01, 2000 6:54 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: SOIL PROFILE TYPE FOR STRUCTURE OVER WATER


My question relates more to the building being over water which the UBC
makes no mention of. Without the water the site would be class Sf.


-----Original Message-----
From: seaint(--nospam--at)seaint.org [mailto:seaint(--nospam--at)seaint.org]
Sent: Thursday, 1 June 2000 1:53
To: seaint(--nospam--at)seaint.org; Dir: David Carolan
Subject: RE: SOIL PROFILE TYPE FOR STRUCTURE OVER WATER
Importance: High


 
97 UBC provides 6 soil types Sa, Sb, Sc, Sd, Se and Sf.  Soil type Sf
requires a site specific geotechnical investigation and dynamic site
response analysis to determine the seismic coefficients Ca and Cv (see
1629.3) Division V (section 1636) specifies the procedure to be used to
determine the soil profile type.

Nick Blackburn, PE