Foundation piles in seismic areas

[Mccoy]

A discussion arised with Italian colleaugues about the subject.

Some say piles in seismic areas are highly unreliable and slab foundations are preferable.

I retort those are purely qualitative remarks and the problem is more one of adequate structural design, since flexural stresses along the shaft and at the pile cap may be very significant. But, provided enough steel of the right thickness and shape has been placed in the concrete, I see no overwhelming probs. Of course, some types of piles (i.e., the slender ones, the inclined ones) may be more vulnerable then others...
But we rule out the blatantly weak designs.

Any thoughts/experiences/references ???????

 

[JAE]

In the U.S., Piles used in seismic areas are required to be tied together at the top and the codes provide a minimum lateral force to use in the design of the ties. The ties are usually some form of foundation grade beam linking the pile caps to each other. Away from the office right now so I can't cite the code or section.

 

[GeoPaveTraffic]

I agree with JAE, reinforce the caps and tie them together. Also, don't use battered piles as they have a tendency to tear the pile caps appart.

 

[SlideRuleEra]

In some seismic areas, because of soil properties, slab foundations are not an economic option. We have areas where a structural slab would require the removal of 80 feet, or more of "unsuitable" material and replacement with "suitable" backfill (if you can find it). That pretty much leaves piles or drilled-piers as real choices - just use lots-and-lots of rebar, as JAE & GeoPaveTraffic have said.

http://www.SlideRuleEra.net