ASCE 7 LRFD Load Combination Interpretation

[craigmcg]

I have a few questions concerning ASCE 7 Clause 2.3.2 - Exception (2). It states: "The load factor on H shall be set equal to zero in combinations (6) and (7) if the structural action due to H counteracts that due to W or E. Where lateral earth pressure provides resistance to structural actions from other forces, it shall not be included in H but shall be included in the design resistance."

Ok, now say I'm designing a laterally loaded concrete pile and the lateral load is due to wind forces. According to the first part of the above statement, the soil does not provide any resistance to the lateral loads, therefore the pile experiences zero resistance (floating)??? This makes no sense. And for the second part of the statement, how is the lateral soil resistance included in the design if not through H? Does it become a dead load? Again, I'm lost here.

Moving on, assuming I neglect my interpretation of this statement for logical reasons, would the p-y curves modelling the soil resistance on the pile be multiplied by 1.6 so that the design moment for the concrete pile can be determined? This correlates to the fact that soils are designed with allowable stress combinations and concrete with LRFD. Obviously the concrete stress varies greatly if ultimate soil strength is used instead of allowable.

Thanks!

 

[kslee1000]

I personally do not believe all these building code covers anything below building foundation. I would pick and choose the load combinations are truely critical for the task at hand. Ultimately that's the code meant for - provide baseline for safety.