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 supports (e.g., two
piers) of a
structural member (e.g., a
beam). 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 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 and
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
:
=
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
*
List of longest cantilever bridge spans
References
Sources
*
Architectural elements
Structural engineering
Bridge components
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