In
engineering
Engineering is the practice of using natural science, mathematics, and the engineering design process to Problem solving#Engineering, solve problems within technology, increase efficiency and productivity, and improve Systems engineering, s ...
, span is the distance between two adjacent
structural support
A structural support is a part of a building or structure that provides the necessary stiffness and strength in order to resist the internal forces (vertical forces of gravity and lateral forces due to wind and earthquakes) and guide them safely to ...
s (e.g., two
piers Piers may refer to:
* Pier, a raised structure over a body of water
* Pier (architecture), an architectural support
* Piers (name), a given name and surname (including lists of people with the name)
* Piers baronets, two titles, in the baronetages ...
) of a
structural member
In structural engineering, structural elements are used in structural analysis to split a complex structure into simple elements (each bearing a structural load). Within a structure, an element cannot be broken down (decomposed) into parts of dif ...
(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
*Radio beam
*Particle beam, a stream of charged or neutral particles
**Charged particle beam, a spatially lo ...
). Span is measured in the horizontal direction either between the faces of the supports (clear span) or between the centers of the
bearing surface
A bearing surface in mechanical engineering is the area of contact between two objects. It usually is used in reference to bolted joints and bearing (mechanical), bearings, but can be applied to a wide variety of engineering applications. The choic ...
s (effective span):
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 Electric power distribution, distribution to transmit electrical energy along large distances. It consists of one or more electrical conductor, conductors (commonly mu ...
s, overhead telecommunication lines, some type of
antennas
In radio-frequency engineering, an antenna (American English) or aerial (British English) is an electronic device that converts an alternating electric current into radio waves (transmitting), or radio waves into an electric current (receivi ...
or for
aerial tramway
An aerial tramway, aerial tram, sky tram, cable car or aerial cablecar, aerial cableway, ropeway, téléphérique (French), or Seilbahn (German) is a type of aerial lift which uses one or two stationary cables for support, with a third movin ...
s.
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 (physics), reaction induced in a structural element when an external force or Moment of force, moment is applied to the element, causing the element to bending, bend. The most common or simplest ...
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
and deflection
in the pictured beam is found using:
:
:
where
:
= Uniformly distributed load
:
= Length of the beam between two supports (span)
:
=
Modulus of elasticity
An elastic modulus (also known as modulus of elasticity (MOE)) is a quantity that describes an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it.
Definition
The elastic modu ...
:
=
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. Th ...
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.
See also
*
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 th ...
— longest spans of ropes used as power lines, antennas or aerial tramways.
*
List of longest suspension bridge spans
The world's longest suspension bridges are listed according to the length of their main span (i.e., the length of suspended roadway between the bridge's towers). The length of the main span is the most common method of comparing the sizes of ...
*
List of longest cantilever bridge spans
This list of cantilever bridges ranks the world's cantilever bridges by the length of their main span. A cantilever bridge is a bridge built using cantilevers: structures that project horizontally into space, supported on only one end.
Completed ...
References
Sources
*
Architectural elements
Structural engineering
Bridge components
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