Hi,

I am trying to use SMath to do a calculation using an empirical formula. This formula is used to initially estimate the bending strength of a concrete shaft. For this equation the variable "D" (diameter of the concrete shaft) must be in feet. The answer will be in kip*ft. I have:

D:= 4 ft
M:= 27 * D^3 = 1,728 kip*ft

27 is an empirical constant. Is there a way to ensure that SMath uses "D" in feet for this calculation? Obviously this is a simple equation to check by hand, but I want to use this as part of a more complex calculation sheet. I would like to have confidence that SMath is consistently doing the calculation with "D" in feet.

The alternative case, which I am concerned about is:

D:= 4 ft
M:= 27 * D^3 = 2,985,984 kip*ft
In this scenario the calculation is made using "D" as 48 inches.

Thanks for the help

-Dale

When I've come across similar circumstances with empirical formulas, I'll assign units or modify units as needed.

For instance, M:= 27 ksf * D^3 = 1728 ft-kips.

Divide "D" by the desired input unit, multiply everything for the output unit

M27*(D/'ft)^3)*'kip*'ft

What Davide said or understand where the constant comes from. You'd be surprised how many people "forget" how the constant is derived. SMath carries the units and modifies as needed internally... Derive Constant.sm (3 KiB) downloaded 47 time(s).