Span (engineering)

In engineering, span is the distance between two adjacent structural supports of a structural member. Span is measured in the horizontal direction either between the faces of the supports or between the centers of the bearing surfaces. For a bridge, the total span is the distance between the faces of the abutments:
A span can be closed by a solid beam or by 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.
Image:Bending.svg|frame|right|Side view of a simply supported beam bending under an evenly distributed load.
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:
where
The maximum bending moment and deflection occur midway between the two supports. From this it follows that if the span is doubled, the maximum moment will quadruple, and deflection will increase by a factor of sixteen.