LRFD Deep Foundations on Rock
Hey everyone! We have an ongoing conflict in our office regarding compressive resistance of piles in rock. It seems that when piles are driven or drilled to rock, most of the time, the structural compressive resistance of the pile dictates the factored resistance of the pile. So Factored Resistance = Minimum (Factored Compressive Resistance, Factored Geotechnical Resistance) = Factored Compressive Resistance (aka pile structural capacity).
It appears that typically in driven H-Piles for example, Factored Compressive Resistance = factor(compression) * fy *A = 0.5 * fy * A
Or if drivability is applied it is 0.9*factor(compression)*fy*A
Now, here is the tricky thing. All the structural engineers we talk to say Factored Compressive Resistance for the same H-Pile driven to rock is 0.5*0.5*fy*A
Where is this extra factor coming from? Are they applying the geotechnical factor to the compressive resistance or something else? Why?