Limit State Design for friction piles

[harpoon]

How would one calculate the ULS, SLS for a friction pile? The method I use is I calculate the Allowable capacity based on working stress design, then use the factors in the Canadian Foundation Engineering Manual to calculate the ULS. But how would one get the SLS?

Will appreciate any input on this.

 

[jdonville]

There are several limit states for strength and serviceability, to wit:

Ultimate structural strength
Ultimate geotechnical strength
Capacity at maximum allowable settlement, lateral deflection (often much less than ultimate capacity values)

Jeff

 

[Panars]

Service limit states for foundations are usually based on settlement. So for a pile foundation, you would determine the load that corresponds with the maximum allowable settlement. (This sounds a lot easier than it is).

 

[Mccoy]

I do not know about the North american practice (LRFD) which appears to be focused on ultimate limit states.

Here in 'ole Europe, the practical procedure to calculate a SLS would be the following:

1) define the maximum allowable settlement, the treshold beyond which movements in the soil will cause unacceptable damage to the structure, serviceability-wise. The serviceability concept may be a relative one: In example, a very wealthy owner may define as serviceability treshold the onset of a very little crack on the wall. He has the money, he defines an arbitrarily low treshold as allowable structure settlement or tilt, which corresponds to an estimated maximum settlement treshold. In a few words, he only allows a very little settlement. As far as I know, the passage from soil settlement to structure movements is experience-based and a strong factor of the foundations and structures types. In the literature you can find only general examples.

2)Define the structural loads. SLS Load combinations are different from ULS combinations, the latter being more pessimistic. Loads are statistically represented by some high percentile of the pertinent distribution

3)Define the soil parameters of interest (Ey, Ed, Mv, Cc...)as a cautious estimate of its average value. Very cautious in particular conditions.

4)Apply formulas. Global and partial FOS' are equal to one.

5)If calculated settlement is lesser than the treshold settlement as previously defined, then SLS are satisfied.

One interesting aspect is that load used to calculate bearing capacity is different from the load used as an input for settlements calcs...