Bridge-Ultimate Moment Design

When a prestressed beam is subjected to bending, one extreme fiber of the section is compressed while the another is subjected to tension.

Concrete is weak in resisting tension, therefore cracking will occur and the forces are now transferred to reinforcement instead.

The moment capacity of a section is determined by comparing the balance of the tensile force in reinforcement with the compressive force in concrete.

A section is considered failure under moment when the compressive strain of concrete exceeds its limit e.g. 0.0035, or the stress in reinforcement exceeds its yield stress.