Editing Suspension bridge (section)

== Forces ==
Three kinds of forces operate on any bridge: the [[Structural load#Dead load|dead]] load, the [[Structural load#Live load, imposed loads, transient load|live]] load, and the [[structural load#Environmental loads|dynamic]] load. Dead load refers to the weight of the bridge itself. Like any other structure, a bridge has a tendency to collapse simply because of the gravitational forces acting on the materials of which the bridge is made. Live load refers to traffic that moves across the bridge as well as normal environmental factors such as changes in temperature, precipitation, and winds. Dynamic load refers to environmental factors that go beyond normal weather conditions, factors such as sudden gusts of wind and earthquakes. All three factors must be taken into consideration when building a bridge.

===Use other than road and rail===
[[File:Cable-suspended footbridge at DFW terminal D.JPG|thumb|Cable-suspended footbridge at [[Dallas/Fort Worth International Airport|Dallas Fort Worth Airport]] Terminal D]]

The principles of suspension used on a large scale also appear in contexts less dramatic than road or rail bridges. Light cable suspension may prove less expensive and seem more elegant for a cycle or footbridge than strong girder supports. An example of this is the [[Nescio Bridge]] in the Netherlands, and the Roebling designed 1904 Riegelsville suspension pedestrian bridge across the Delaware River in Pennsylvania.<ref>As exists with signage re the history.</ref> The longest pedestrian suspension bridge, which spans the River Paiva, [[Arouca, Portugal|Arouca]] [[Geopark]], Portugal, opened in April 2021. The 516 metres bridge hangs 175 meters above the river.<ref>{{Cite web|last=|first=|date=29 April 2021|title=World's longest pedestrian suspension bridge opens in Portugal|url=http://www.theguardian.com/world/2021/apr/29/worlds-longest-pedestrian-suspension-bridge-opens-in-portugal|access-date=29 April 2021|website=The Guardian|language=en}}</ref>

Where such a bridge spans a gap between two buildings, there is no need to construct towers, as the buildings can anchor the cables. Cable suspension may also be augmented by the inherent stiffness of a structure that has much in common with a [[tubular bridge]].