Span is the distance between two intermediate supports for a structure, e.g. a beam or a bridge. A span can be closed by a solid beam or of a rope. The first kind is used for bridges, the second one for power lines, overhead telecommunication lines, some type of antennas or for aerial tramways.
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:
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.
For long-distance rope spans, used as power line, antenna or for aerial tramways, see list of spans.