### Cracking Moment Equation

Cracking moment equation is a famous formula that gives you the value of tensile bending stress at which the concrete of the beam starts to crack. This concept is important to understand the stress distribution of the beam across the depth. It will also help you to determine the deflection in the concrete at the point of failure. But for deflection calculation you can’t use the gross moment of Inertia (Ig) because of cracking effect. So, instead you have to use the effective moment of inertia (Ie) which provides transition between the upper and lower bounds of Ig and Icr. However, for Ie you have to determine the Mcr which is the cracking moment. Establishing the Cracking moment Equation Let’s now derive its formula Step No. 1 – finding modulus of rupture But first you have to establish an equation for the modulus of rupture (MOR) of concrete. Modulus of rupture is the tensile flexural strength of the beam and it shows the amount of stress and force an unreinforced concrete