Span is the distance between two intermediate supports for a structure, e.g. a beam or a

bridge A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...

. 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 line An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-p ...

s, overhead telecommunication lines, some type of antennas or for

aerial tramway An aerial tramway, sky tram, cable car, ropeway, aerial tram, telepherique, or seilbahn is a type of aerial lift which uses one or two stationary ropes for support while a third moving rope provides propulsion. With this form of lift, the grip ...

s. 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

M_

and deflection

\delta_

in the pictured beam is found using: :

M_ = \frac

\delta_ = \frac   = \frac

where :

q

= Uniformly distributed load :

L

= Length of the beam between two supports (span) :

E

= Modulus of elasticity :

I

= Area moment of inertia Note that 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 (and with it the stress) will quadruple, and deflection will increase by a factor of sixteen. For long-distance rope spans, used as power line, antenna or for aerial tramways, see list of spans.

References

{{DEFAULTSORT:Span (Architecture) Architectural elements Structural engineering Bridge components