Applies To
	Product(s):	STAAD Foundation Advanced
	Version(s):	ALL
	Environment:	ALL
	Area:	General
	Subarea:	N/A
	Original Author:	Sye Chakraborty, Bentley Technical Support Group

I am not able to match the Cs calculation being provided by SFA. When I look at the calculation sheet for my vessel foundation job, I see the following 

As per Equation 12.8-2 of ASCE7-10, my calculation shows Cs= 0.185/(3/1) = 0.06. However SFA reports the Cs value as 0.01. Why is that?

Answer:

It is true that the Cs calculated as per 12.8-2 would come out as 0.185/3 = 0.06 but there are limits to the calculated value of Cs which are applied on top of this calculated value. The equation 12.8-3 puts an upper limit to the Cs = 0.102/(6x3) = 0.006. However as per the Eq 15.4-3, Cs cannot be considered as lesser than 0.01. Therefore Cs is considered as 0.01 by the software. There is a note that is included as part of the calculation sheet (highlighted in the screenshot below) indicating that these limits are applied on the values of Cs.