• Ultimate compressive strain in concrete is identical to 0.003.
  • Tensile strength of concrete is not considered.
  • Strain differs linearly over the depth of the cross section.
  • Steel stress differs linearly unless yielding and stays constant beyond yielding.
  • Compressive force in the concrete is obtained from Whitney's equivalent stress block.


Several values should chosen for the calculator. The effective depth d is obtained from the centroid of tension reinforcement up to the top-edge of beam. If two layers of tension rebar exist, divide them with a clear distance and other criteria according to ACI 318. The user of this calculator is should abide by the ACI guidelines for beam thickness, rebar spacing and cover etc.