The behaviour of a girder under an increasing shear load may be divided into the three phases:
- Unbuckled. The situation prior to buckling when equal tensile and compressive principal stresses are developed in the plate.
2. Post-buckled. The development of a tension field.
3. Collapsed. Failure occurs when the web yields and four plastic hinges form in the flanges to allow the development of a sway collapse mechanism.
