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Re: pier design

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MarthaAlic wrote:

> I am currently designing a roof platform. The lateral resisting system is
> composed of moment frames running in both directions. This platform is exposed
> and due to space limitations, I have no other choice than using drilled piers
> for foundations.  For the embendement length, I divided the moment by the
> shear at the base and found an equivalent height for the shear load (ie.
> M/V=h'). My questions are:
>
> 1. What is the minimum reinf. required.



> 2. Do I have to design the pier as if it were a column with and axial and
> amoment (eventhough it is lateraly braced by the soil) or should I justconsider
> the moment.

I  develope an interaction diagram for the piers to determine reinforcing steel
requirements using ACI 318-95.

> 3. Is there a source I can use as a guideline for my design.
>

The simplest method I've found, in a uniform soil, to determine the moments and
shear is Brom's theory from 1964.  It is describe by Poulos & Davis in their text
published in 1980.

If the situation is critical, I'd consider using one of the finite difference
solutions with P-Y data.  If your not familiar with P-Y curves there is some
guidance in Poulos & Davis.

Also check out Bowle Fifth Edition of his text.  It is usually straight forward
and has alternative methods.

If this is a layered soil site it might be a good idea to get assistance from a
geotech engineer with experience in designing laterally loaded piles using
computer aids such as L-Pile or PileDG.

Arvel L. Williams, P.E.