You need to write the expression dividing f'c (and / or any other terms) by their units to render them dimensionless, and then multiply the solution back by the desired units to get the expression to work.
Either way - this is one of the best error-trapping features of Mathcad in my opinion.
#Force system mathcad code
If you try to code the expression exactly as written, Mathcad will return incorrect units of (stress)^0.5 for the flexural tensile strength - which is a surefire sign that you have either made an error in entering your expression, or that the expression is dimensionally inconsistent. This expression only works when the tensile strength and compressive strength are in units of MPa, it won't work when you are using Pa, psi, ksf, etc. the Australian Concrete code defines the characteristic flexural tensile strength of concrete in terms of the compressive strength as being:
Dividing out the various terms by the units used is an error-free means of creating a dimensionless expression when required to not do so risks gross error if you happen to be using incorrect units for any of your variables.Į.g. because you are using an empirical Code expression which is dimensionally inconsistent, and assumes a particular set of units is being used for all terms in the expression), then you need to be VERY careful that you are using the correct units when you "strip" the expression.