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Span (engineering)

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Distance between supports of an arch, bridge, etc.

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"Clear span" redirects here. For type of steel building, seeSteel building § Types.

Inengineering,span is the distance between two adjacentstructural supports (e.g., twopiers) of astructural member (e.g., abeam). Span is measured in the horizontal direction either between the faces of the supports (clear span) or between the centers of thebearing surfaces (effective span):^[1]

A span can be closed by a solid beam or by a rope. The first kind is used for bridges, the second one forpower lines, overhead telecommunication lines, some type ofantennas or foraerial tramways.^{[citation needed]}

Side view of asimply supported beam (top) bending under an evenly distributed load (bottom).

Span is a significant factor in finding the strength and size of a beam as it determines the maximumbending moment anddeflection. The maximum bending moment $M_{max}$ and deflection $\delta _{max}$ in the pictured beam is found using:^[2]

M_{max}={\frac {qL^{2}}{8}}

\delta _{max}={\frac {5M_{max}L^{2}}{48EI}}={\frac {5qL^{4}}{384EI}}

where

q {\displaystyle q}

= Uniformly distributed load

L {\displaystyle L}

= Length of the beam between two supports (span)

E {\displaystyle E}

=Modulus of elasticity

I {\displaystyle I}

=Area moment of inertia

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 thestress) will quadruple, and deflection will increase by a factor of sixteen.