Truss arch bridge

A truss arch bridge combines the elements of the truss bridge and the arch bridge. The actual resolution of forces will depend upon the bridge' design. If no horizontal thrusting forces are generated, this becomes an arch-shaped truss which is essentially a bent beam – see moon bridge for an example. If horizontal thrust is generated but the apex of the arch is a pin joint, this is termed as a three-hinged arch. If no hinge exists at the apex, it will normally be a two-hinged arch. In the Iron Bridge shown below, the structure of each frame emulates the kind of structure that previously had been made of wood. Such a wood structure uses closely fitted beams pinned together, so the members within the frames are not free to move relative to one another, as they are in a pin-jointed truss structure that allows rotation at the pin joint. Such rigid structures (which impose bending stresses upon the elements) were further developed in the 20th century as the Vierendeel truss.

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  Garabit Viaduct, a thrust arch type employing a catenary shape
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  The steel Stoney Creek Bridge carries the Canadian Pacific Railway
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  Illustration of a Truss arch bridge, showing the Honeymoon Bridge over the Niagara River (1917)

Truss arch bridge

New River Gorge Bridge, in Fayetteville, West Virginia
Ancestor	Truss bridge, arch bridge
Related	None
Descendant	Through arch bridge
Carries	Pedestrians, vehicles, light rail, heavy rail
Span range	Medium
Material	structural steel
Movable	No
Design effort	Medium
Falsework required	Sometimes, but long spans are often built using temporary cantilevers

Some bridges of this type

• Maria Pia Bridge (1877), Gustave Eiffel's pioneering two-hinge arch.
• Hurricane Deck Bridge (1936), the last remaining truss-type bridge on Lake of the Ozarks in central Missouri.
• I-35W Mississippi River bridge (1967) bridge that collapsed in 2007 in Minneapolis, Minnesota, USA.
• Navajo Bridge and newer (1995) bridge of the same general construction, each built as unsupported cantilevers joined with a central pin.