Internal Couple Method

Consider a relatively long simply supported beam shown below. Assume the load w_o to be increasing progressively until the beam fails. The beam will go into the following three stages:

1. Uncrack Concrete Stage – at this stage, the gross section of the concrete will resist the bending which means that the beam will behave like a solid beam made entirely of concrete.
2. Crack Concrete Stage – Elastic Stress range
3. Ultimate Stress Stage – Beam Failure