Stiffeners are the members which are connected to the thin webs to prevent loss of strength due to web buckling.
It is usually necessary to stiffen the webs of plate girders to prevent loss of strength due to web buckling. For riveted or bolted girders, angles are connected to the webs while for welded girders, plates are connected to the webs.
Image taken from John Brandon’s ‘Fly Safe!’ tutorials
These are divided into two groups:
Bearing stiffeners are provided just above the reactions or just below the heavy concentrated loads. These transfer heavy reactions or concentrated loads to the full depth of the web providing a uniform shear transfer. Bearing stiffeners are always provided in pairs, i.e., on both sides of the web.
Intermediate stiffeners are also called as non-bearing or stability stiffeners. These are placed at various intervals along the web to counteract against the buckling due to diagonal compression.
These are provided in pairs on both sides of the web or as a single unit alternatively on each side of the web.
Tension field action
The intermediate may also provide post-buckling shear strength by the development of mechanism called Tension field action.