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Re: Landslide[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: Re: Landslide
- From: John Buchanan <jjb(--nospam--at)scruznet.com>
- Date: Wed, 11 Mar 1998 18:38:32 -0800
At 07:54 PM 3/11/98 EST, you wrote: >We do lots of hillside homes. You need a good soils report, and then design >accordingly. 36" diamter piles with lots of reinforcing is not uncommon. The >largest piles we have designed so far were 48" diameter with about 30-#11 bars >going about 72' total length! (It's only money.) Beyond 48" diameter piles, >it's usually time to sit down and rethink the project. > >Bruce Resnick, SE >Parker Resnick Str. Eng. In Santa Cruz the geotechnical engineers seem to favor putting houses on drilled cast in place concrete piers interconnected with concrete grade beams. The reasons vary from steep hillsides, ridge top craking during an earth quake, and clay soil conditions. Generally the soils engineers recommend a minimum of a twelve inch diameter pier with four number four bars and #3 ties at varied spacing. Most of the piers on the load bearing walls are spaced at approximately eight feet center to center. Non load bearing walls can see pier spacings as high as 16 foot center to center spacing. >From the plans I have reviewed I have seen every thing from 24" piers with the minimum of 1% reinforcing and greater to a twelve inch diameter pier with one #6 bar in the center. For residential structures generally the axial load is very small and the member approaches pure bending if one were to plot out the column curves. So - I have argued with the geotechs that a twelve inch pier with four bars in a square pattern does not make sense with a three inch steel to earth clearance, but they do not seem to listen and still spec this. Does one consider the member a confined column and provide the minimum of 1% or greater for reinforcing steel? Does one consider using a reduced col. area as allowed in the ACI to compute the minimum required steel area and check the bending of the piers? There used to be a provision on the ACI where the steel area could be reduced to .05% if certain criteria were met. Any comments? Most of the time the lateral load at the top of the piers is around five hundred pounds. and the connection from the top of the pier to the grade beam consists of 4 #5 bars embedded in the pier and tied to the grade beam reinforcing steel. How does this sound for a connection? A new twist in the equation is now the geologists have entered the equation and require the foundation to with stand a six inch drop in the soil with in a ten foot dia circle placed any where in the building envelope. Any suggestions or comments on design?
- Re: Landslide
- From: Parkerres
- Re: Landslide
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