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7 Different Types of Bridges - Coggle Diagram
7 Different Types of Bridges
Arch Bridge
This bridge design dates back more than 3,000 years. Concrete is now also used to build modern arch bridges.
Arch bridges work by transferring the downward pressure of gravity inward toward the center of the structure—toward a central stone called the keystone—rather than directly downward.
Fixed arch bridges can be unstable due to temperature fluctuations, so the design of the arch is sometimes modified by installing hinges at each base or even in the center of the span.
Beam Bridge
The simplicity of a beam bridge made it the first type of bridge ever built. It is still the cheapest bridge to build. Only one beam is needed to cover the span, supported by an abutment at each end.
Gravity is a bigger challenge when building a bridge because, unlike a building, most of the space beneath a bridge is empty space. A beam bridge may be supported by only two abutments, one at each end, to counteract gravity and carry its full load.
In a beam bridge, compression forces push the load inward toward the piers in the middle of the bridge. At the same time, tension, or tensile forces, pull the load outward toward the abutments at each end of the bridge.
Cantilever Bridge
This type of bridge uses pillars anchored vertically in the ground to support a horizontal deck extending from one or both sides of the span. Loads are usually supported from above and below. A diving board or platform is a good example of a cantilever structure.
The world's longest cantilever span belongs to Canada's Quebec Bridge, which was built in 1919 and is 1,800 feet long. It exceeds the length of Scotland's Forth Bridge, which was built in 1890.
Cantilever bridges are usually supported by trusses. The bridge trusses move loads away from the deck and transfer them to the supporting piers and abutments, helping the cantilever to withstand the tension of the upper supports and the compression of the lower supports.
Suspension Bridge
Suspension bridges are perhaps the most recognizable type of bridge in the United States, thanks to San Francisco's iconic Golden Gate Bridge. Completed in 1937, the bridge attracts more than 10 million visitors each year to admire its 746-foot-tall orange twin towers and stunning Art Deco effects.
As the name implies, suspension bridges are stabilized by vertical struts, or pylons, connected by cables. Attached to these main cables are smaller vertical hangers, which support the bridge deck using tension, the primary force that supports a suspension bridge.
Suspension bridges are also subject to torsion, which is often caused by environmental factors such as wind and can produce dangerous movements. If the deck twists enough while pedestrians are on it, they could be thrown off the bridge.
Cable-Stayed Bridge
A cable-stayed bridge is a variation of a suspension bridge that connects the beams or deck directly to the pillars or towers. Cable-stayed bridges have no main cables, only a large number of vertical hangers attached to the tops of the towers. These hangers use tension to help keep the deck stable and in place.
Sweden's Strömsund Bridge is considered the first modern cable-stayed bridge. The three-span structure was completed in 1956. Its reinforced concrete deck is suspended by diagonal cables from two towers.
Tied-Arch Bridge
A tied arch bridge combines features of an arch bridge and a suspension bridge. It uses horizontal thrust from both sides to support the arched structure, just like a normal arch bridge. But instead of supporting the structure from below, the arch is raised above the road and vertical ties are lowered to add support to the bridge deck.
They are also called bowstring bridges because they look like a bow from the side. The bow uses the tension of the vertical cables, as well as the compression of the arch, to support the load and keep the bridge stable.
The wooden decked Blackfriars Street Bridge in London, Ontario, Canada is an example of this style. It carried vehicle traffic from the year it was built until it was permanently closed in 2013.
Truss Bridge
A truss bridge spreads its load across a series of small components that fit together. Small bridges are made up of structural beams, and large bridges are made up of box beams. The bridge trusses are usually held together by a series of triangular welded or riveted joints.
Vertical steel or wooden supports help support the bridge in tension, while diagonal truss supports add stability in compression, directing the load toward the center, similar to an arch.
This fairly inexpensive truss design has been around for a long time. Most truss bridges were built with wood in the 1800s, before switching to steel. The familiar Pratt truss design features diagonal segments that slope toward the center of the bridge. It was introduced by Thomas Willis Pratt in 1844.