I'm working in Staad Foundation Advanced connect Edition version 08.00.00.00 and am having some confusion about reinforcement and how it's calculated.
1) In the design parameters, the value for bottom cover appears to be from the top of the pile. However, in at least one instance in the GA drawing, this distance was shown from the bottom of foundation. We found it difficult to determine which d was actually used for the calculation of the required reinforcement. Is there a place where we can confirm which d value is used?
2) In the verification manual, you have the calculation used for the reinforcement ratio as follows:
So Resisting Moment = Mnz= Muz/ϕ = 744.44 ft·kip
Rn = Mnz/b·d2 = 0.147 Ksi
2·m·Rn/fy = 0.0864 <1 , Hence OK
ρ = 1/m· (1-√1-2m·Rn/fy) = 0.0025
In your calculation sheet, you have the governing moment Mtl (which I assume to be the same as the verification Mnz), and then the reinforcement criteria "calculated Reinforcement Ratio (R)" and Rmax. Then compare R to Rmax and 0.0018 and say that "R is accepted". I created a spreadsheet to perform this calculation and have been unable to get the rho to equal "R". Should the value listed as R be equal to rho in the verification manual?
3) If so, the calculated reinforcement ratio was 0.0025 for a 7' wide by 27" deep foundation with a moment of 148.6 k-ft (fy 60, f'c 4ksi). In my calculation, this value should have been closer to 0.0009 to 0.0011 in which case Asmin (0.0018) would have controlled. And the program accepted #7@12 which is just above the Asmin. Why is the reinforcement provided below what is required by the "calculated reinforcement Ratio"?
Thanks in advance.
Ryan