What load combination used for pile uplift capacity check?

[szleok]

In IBC2003 or newer, there are load combinations: 0.6D+1.0W and 0.6D+0.7H to account the safety factor. 1.5 for wind and 1.0 for seismic.

But I remember in UBC97, there is no 0.6D in the combination. The 1.5 safety factor is specified in other chapters such as retaining wall, spread footing design, etc.

However, I don't see any words saying you need 1.5 SF to check pile uplift capacity in UBC97. Is that mean in IBC2003 or IBC2006, the 0.6D+1.0W is not required for pile uplift capacity check?

 

[Teguci]

Try using the load combos under 1605.3.2 in lieu of 1605.3.1 as allowed by the code.

As for piles, there is a safety factor of 2 required for tested piles. This includes uplift and, pending special circumstances, uplift piles should be tested in uplift. 1808.2.8.3. If you don't want to test the piles, higher safety factors have been used (try the FHWA publications for pile foundations if you need additional info).

 

[szleok]

Thanks.

But load combo in 1605.3.2 requires 1.0D+1.3W. That's almost same as 0.6D+1.0W in 1605.3.1 if testing the uplift capacity. I am a little confused here.

 

[Teguci]

The uplift capacity of the piles is 1/2 of the maximum tested load on the pile. This has nothing to do with load factors. This is what resists your factored (allowable)loads from 1605.3.2.

In other words, you have two sides of the equation - The loads coming down the structure (these get factored). And the reactions from those loads such as pile reactions and footing reactions. Do not get them confused or you will get a headache.

As for safety factors for retaining walls we use the proscribed 1.5 safety factor method for the soil interaction and the LRFD approach for the concrete design. Next year the manuals will be even bigger! I think the Chinese call this the "Fat belly disease"