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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.
The Iron Bridge, a two-hinged arch, the first cast-iron bridge and the oldest still standing on its original site
New River Gorge Bridge, in Fayetteville, West Virginia
The Iron Bridge, a two-hinged arch, the first cast-iron bridge and the oldest still standing on its original site
Garabit Viaduct, a thrust arch type employing a catenary shape
The steel Stoney Creek Bridge carries the Canadian Pacific Railway
Illustration of a Truss arch bridge, showing the Honeymoon Bridge over the Niagara River (1917)
