For greatest resistance to bending, as much of a plate girder cross section as practicable should be concentrated in the flanges, at the greatest distance from the neutral axis. This might require, however, a web so thin that the girder would fail by web buckling before it reached its bending capacity.

To preclude this, the AISC specification limits h/t.

For an unstiffened web, this ratio should not exceed.

where F_{y} = yield strength of compression flange,ksi (MPa).

Larger values of h/t may be used, however, if the web is stiffened at appropriate intervals.

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