When we calculate the dimension of a foundation we always use the allowable SERVICE bearing capacity (lets call it qs) and all the necessary checks are based on this value qs.
My question is why does the geotechnical report calculates the ultimate bearing capacity (lets call it qu)?
In my own research I stepped upon an article that says that when the geotechnical engineer calculates the ultimate bearing capacity it calculates the ultimate load by multiplying the service loads with a safety factor (lets call it Fs) now for a structural engineer (such as i am) we use different load combinations to calculate the ultimate load (especially when we have seismic and wind) in a simple case for example the most famous load combination in the ACI Code is 1.2D + 1.6L if in a certain case the Live Load is >>>> than the Dead Load the use of a simple Fs will not work to calculate the ultimate load combination.
Is that Explanation for this topic is feasible ? and what do you have other suggestion to the difference of qs and qu ? and where do we use each one?
Thank You in Advance.