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Re: combined seismic load with creep load

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>Third, be aware when combining loads that the creep is downhill but the 
>seismic is up or down.  For small fill depths and large seismic loads, 
>don't forget the uphill case if you are providing more reinforcing on 
>one side of the cage than the other.  Our office standard is to use a 
>circular rebar pattern in our piles so this is not a problem for us.

Your comments as to considering stiffness considerations are o.k., but I
don't usually design for vertical acceleration.  Most earthquakes I know of
make the ground go back and forth horizontally, unless you are in a thrust
fault area.

Also, if this is a side hill project, the piles may be extending to
underneath the structure - making a grade beam difficult.  In some cases,
we've used timber poles.  

Another topic, marginally related:


Have a communication pole, 45 feet high, fairly light.  This pole is
supported by a 60" diameter caisson, in a Zone 4 location.  The geotech
says the site has a liquifacation problem - 17' deep.  Therefore, I design
the pole and pier using UBC Sections 1628.3.2, par 2 and 1809.5.1.  The
geotech has provided me with a depth using the LPile program of which I
know very little.  For the program we provided an increase factor for a
factor of safety relationship.

My real question is:  When the pier portion, which is anchored to good
material below 17 feet, is being moved back and forth during a seismic
event, is there any additional load caused by the drag through the
liquified soil above the minus 17 feet level?

Neil Moore, S.E.