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

beam Beam may refer to: Streams of particles or energy *Light beam, or beam of light, a directional projection of light energy **Laser beam *Particle beam, a stream of charged or neutral particles **Charged particle beam, a spatially localized grou ...

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 In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies a ...

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 In solid mechanics, a bending moment is the reaction induced in a structural element when an external force or moment is applied to the element, causing the element to bend. The most common or simplest structural element subjected to bending mome ...

and

deflection Deflection or deflexion may refer to: Board games * Deflection (chess), a tactic that forces an opposing chess piece to leave a square * Khet (game), formerly ''Deflexion'', an Egyptian-themed chess-like game using lasers Mechanics * 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 An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is ...

I

Area moment of inertia The second moment of area, or second area moment, or quadratic moment of area and also known as the area moment of inertia, is a geometrical property of an area which reflects how its points are distributed with regard to an arbitrary axis. The ...

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 Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

) 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 The following is a list of spans, either used for overhead line crossings of rivers, sea straits or valleys, as antenna or for aerial tramways. Powerline spans in flat areas with high pylons At these spans the sag of the conductors is less t ...

References

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