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Re: combined seismic load with creep load[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: Re: combined seismic load with creep load
- From: Neil Moore <nmoore(--nospam--at)spider.lloyd.com>
- Date: Thu, 18 Sep 1997 09:07:30 -0700 (PDT)
Bruce: >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: Problem: 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.
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