Concrete is unable to withstand such forces. Steel, on the other hand, resists tensile forces well, so concrete workers reinforce concrete with steel rebar.
-
Decide on the percentage of steel to concrete. Structural concrete needs to be professionally engineered, so these calculations are just a general guideline. Typical values for continuously reinforced concrete pavement, for instance, are between 0.6 and 0.7 percent.
-
Find the rebar-to-spacing multiplier with the formula M = 0.9_sqrt(Pt), with "P" representing the percentage of steel required and "t" representing the thickness of the slab. For example, if the percentage is 0.65 and the thickness of the slab is 6 inches, M = 0.9_sqrt(0.65*6) = 1.78.
-
Insert common spacing distances into the formula n = M_sqrt(s), with "s" being the spacing in inches. Round up the value of "n" to the next whole number to find the nominal rebar size required for that spacing. You can use any value of "s" you want, but for easier installation, "s" usually is a value that is a factor of 12, such as 3, 4, 6 or 12. For example, with spacing at four inches on center, n = 1.78_sqrt(4) = 3.56, so No. 4 rebar would be required. A layout with six inches on center calls for No. 5, and 12 inches on center requires No. 7.