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RE: Piles and Seismic Forces

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Gary,

"Seismic loading" is an inertial response force in the structure to the earthquake ground motion. In an earthquake the rock shakes at the epicenter. At the building site, the movement from the rock is transfered to the soil to the building foundations to the building superstructure and then to your crane.

The piles will be like noodles and not reduce the lateral eathquake ground motions. The type of soill "site class" WILL have an effect on the inertial response of the building structure. For Puerto Rico, with a site class E, and an Ss of 1, the soil will actually work kind of like a base isolator and will reduce the lateral earthquake ground motion accelerations for short period ground motions. However, the site class E will amplify the long period ground motons.

Bottom line - LATERAL earthquake in structure inertial response forces will not change by using piles.

Regards,
Harold Sprague

From: "Gary Hodgson & Associates" <ghodgson(--nospam--at)bellnet.ca>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: Piles and Seismic Forces
Date: Mon, 22 Aug 2005 11:02:13 -0400

List,

I've been designing a crane runway for Puerto Rico (first designed in
'99 and then postponed).  The soil is a Type SE.  Consequently, the
seismic forces are quite high.

The end customer has said that the foundation will be placed on
piles.  How will this affect seismic loading?  As we are not relying
on the soil, can we reduce the seismic loading and what can be used
in lieu of SE?

thanks muchly,
Gary


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