Span is a section between two intermediate supports, e.g. of a beam or a bridge.

The span is a significant factor in finding the strength and size of a beam as it determines the maximum bending moment and deflection. The maximum bending moment and deflection in the pictured beam is found using:

moment:   M_max = 1/8 · q · L²

deflection: f_max = 5/48 · M_max· L² / (E · I)

From this it follows that if the span is doubled, the maximum moment (and with it the stress) will increase four times, and deflection will increase sixteen times.

Building engineering | Structural engineering