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In engineering, 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 surfaces (effective span): [1] A span can be closed by a solid beam or by ...
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 suspension bridges, often correlating with the height of the towers and the engineering complexity involved in designing and constructing the bridge. [4]
The length of the main span is the most common way to rank bridges as it usually correlates with the engineering complexity involved in designing and constructing the bridge. [1] If one bridge has a longer span than another it does not necessarily mean that the bridge is longer from shore to shore or from abutment to abutment.
The further apart its supports, the weaker a beam bridge gets. As a result, beam bridges rarely span more than 250 feet (80 m). This does not mean that beam bridges are not used to cross great distances; it only means that a series of beam bridges must be joined together, creating what is known as a continuous span.
The definition of cable-stayed bridge deck length used here is: A continuous part of the bridge deck that is supported only by stay-cables and pylons, or are free spans. This means that columns supporting the side span as for example found in Pont de Normandie , excludes most of the side span decks from the cable-stayed deck length.
A swing bridge (or swing span bridge) is a movable bridge that can be rotated horizontally around a vertical axis. It has as its primary structural support a vertical locating pin and support ring, usually at or near to its center of gravity, about which the swing span (turning span) can then pivot horizontally as shown in the animated illustration to the right.
A bascule bridge (also referred to as a drawbridge or a lifting bridge) is a moveable bridge with a counterweight that continuously balances a span, or leaf, throughout its upward swing to provide clearance for boat traffic. It may be single- or double-leafed.
Until 1964, the Golden Gate Bridge had the longest suspension bridge main span in the world, at 4,200 feet (1,280 m). Since 1964 its main span length has been surpassed by eighteen bridges; it now has the second-longest main span in the Americas, after the Verrazzano-Narrows Bridge in New York City.