Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Landslide

[Subject Prev][Subject Next][Thread Prev][Thread Next]
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?