Types of Bridges That Use Inverted Catenary Arches

The Math

• The catenary arch is one fixed shape, while parabola defines a whole family of curves. To a mathematician the catenary is defined by a hyperbolic cosine function. During the 17th century, the catenary arch was discovered by accident, when Galileo predicted a hanging chain of cable of equal thickness would form a parabolic curve, when supported at each end and subjected to the forces of gravity. What ensued was a scientific investigation, which determined that this shape, described by Galileo, was actually a new kind of curve determined by a different set of mathematical principles than the parabola.

Masonry Arches

• Masonry arch bridges have been around long before the catenary curve was discovered in the late 17th century. Before this unique curve was incorporated into a masonry bridge support system, designers used other similar curved shapes such as the semi-circle, ellipse and parabola to support a road when it traversed a river or canal. The use of the inverted catenary curve allowed construction of longer masonry bridges, according to the Webster's Dictionary website.

Truss Arch Bridges

• Train routes across gigantic river gorges provide examples of some of the highest bridges in the world. Many of these structures owe their strength to large arch and truss network, which hold the top platform in place. Sometimes designers and bridge architects will use an inverted catenary curve as the main support for the bridge. The new Ulla Viaduct across the Ulla River in Spain is a classic example of an inverted catenary curve incorporated into a modern railroad bridge.

Tilt Swing Bridge

• The tilt swing bridge is a new, sophisticated design incorporated into a few pedestrian bridge structures. Prime example is the Gateshead Millennium Bridge, which crosses the Tyne River in the United Kingdom between Newcastle and Gateshead. In this innovative structure cables from an overhead metal arch support a level, curved pedestrian walkway across the Tyne. The overhead metal arch is actually an inverted catenary curve. When boats approach the structure, both the walkway and overhead arch tilt as a unit, to allow river traffic to pass underneath the raised walkway. Tension between the walkway and overhead curve remains constant at all times.