Span (architecture)

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Span is a section between two intermediate supports, e.g. of a beam or a bridge. A span can be made of a solid beam or of a rope. The first kind of spans is used for bridges, the second one used for power lines, overhead telecommunication lines, some type of antennas of for aerial tramways.

Side view of a simply supported beam (top) bending under an evenly distributed load q (bottom).

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.

For remarkable long-distance rope spans, used as power line, antenna of for aerial tramways, see List of spans.