Flexural collapse in over reinforcement beams refers to the failure of a beam due to excessive compression on the top fiber of the beam. This failure mode is known as secondary compression failure.

Primary compression failure occurs when the ultimate compressive strength of the concrete is reached, resulting in crushing of the concrete in the compression zone. This failure mode typically occurs in under-reinforced beams, where the amount of reinforcement is not sufficient to resist the compressive forces.

Primary tension failure occurs when the ultimate tensile strength of the steel reinforcement is reached, resulting in the rupture of the steel reinforcement. This failure mode typically occurs in under-reinforced beams, where the amount of reinforcement is not sufficient to resist the tensile forces.

Bond failure occurs when the bond between the steel reinforcement and the surrounding concrete is lost, resulting in the separation of the reinforcement from the concrete. This failure mode can occur in both under-reinforced and over-reinforced beams, depending on the adequacy of the bond strength.

Secondary compression failure, on the other hand, occurs in over-reinforced beams where the amount of steel reinforcement is excessive. In these beams, the steel reinforcement is able to resist the tensile forces, but the excessive reinforcement leads to a significant increase in the compressive forces on the top fiber of the beam. As a result, the concrete in the compression zone crushes and fails, leading to flexural collapse.

In summary, flexural collapse in over reinforcement beams is a form of secondary compression failure. It occurs when the excessive steel reinforcement in a beam leads to excessive compressive forces on the top fiber of the beam, causing the concrete to crush and fail.