How do Cantilever bridges function? Ten longest cantilever bridges around the world

Articles > How do Cantilever bridges function? Ten longest cantilever bridges around the world

Cantilever Bridges:

The cantilever is a non-elastic structure which is projected straight (horizontally) into space (above the water/ obstacle) with a dorsal end, which supports it. Cantilever bridges are built using cantilevers. One end of the cantilever bridges is suspended in the air, while the other end is attached with abutments for support. If the bridge is a small footbridge, the cantilever is a projection of a small beam. On the other hand, if the span of the bridge is very large, the cantilever is made up of a truss of structural steel and metallic girder. The larger the span of the bridge is, the stronger the material is used.

Origin of the Cantilever Bridges:

The 19th-century engineers found out that the load on a bridge will be distributed among multiple supports, on which the bridge span is placed. Resulting in lower stresses in the girders/truss lead to bridges of a longer span. In the 19th-century, the bridges with hinge points at mid-span evolved.

The use of hinges in the multi-spans of a bridge presented the significance of a statically determinate system and of differential settlement of the foundations of a bridge. Calculation of forces and stresses with a hinge in the girder became easier.

Heinrich Gerber (1866) is among the engineers who gave the concept of a hinged girder and is recognized to be the founder of a Cantilever bridge. The German Hassfurt Bridge (completed in 1867) has a central span of 38 meters and is recognized as the first modern cantilever bridge.

From 1867 onward, several Cantilever bridges like High Bridge of Kentucky, Niagara Cantilever Bridge, and Poughkeepsie started being constructed. Now cantilever bridges are considered to be among the most successful bridges.

How do the Cantilevers function?

The structure of a Cantilever has two extended portions; one is extended ahead in the space over the water body, while the other remains behind the abutment. The dorsal portion of the cantilever acts as anchorage for sustaining the projected portion of the cantilever. The structure is balanced on the abutment.  A simple cantilever consists of two arms projecting from opposite sides of the obstacle. Both the suspended arms do not meet with each other at the ends. But rather both ends support a central suspended truss. The truss is assumed as the central part of the bridge. The truss rests on the ends of cantilever arms. The cantilever bridges are independent of the central vertical support. We don’t need to install vertical pillars, piers, or abutments within the obstacle (water/ ridge). These bridges sustain the truss on the doctrine of equilibrium.

Structural Elements of Cantilever Bridges:

A cantilever bridge consists of four parts:

1. Abutments:

Abutments are an optional element in a Cantilever bridge. The Abutments which are also called piers or pillars are constructed on both of the opposite sides of the water body or whatever the obstacle is. These pillars are deep-rooted and resistant to shaking. These pillars strongly hold the outer beams or the dorsal side of the cantilever.

2. Outer Beams:

The back-part or the dorsal side of the cantilever is called the Outer beam. The outer beam is either attached to piers or grounded concrete foundation. The purpose of the outer beam is to sustain the burden of the cantilever (the ventral part of the cantilever).

3. Cantilever:

The cantilever is the front arm of the bridge, which is extended in the space above the water or obstacle. This part of the bridge is suspended with the help of the gravitational pull of the outer beam. The weight of the outer beam must be greater than that of the cantilever, so as to sustain the cantilever in space.

4. Central Beam or Truss:

The projected ends of the cantilever are not directly attached to each other, but rather they are attached to a central beam or a truss. The truss sits on the ends of the cantilevers. The truss does not need any vertical support from the downside. The truss is hung with the ends of the cantilevers. The truss is the central part of the bridge.

Longest Cantilever Bridges around the World:

The world’s longest cantilever bridge was constructed in 1917, between Quebec and Levis cities of Canada. This bridge was named "Pont de Québec", which, ever since, has been the longest cantilever bridge in the world. There are hundreds of wonderful cantilever bridges in the world, which are listed in the following table.

 Bridge City/Country Main Span Year constructed Pont de Québec Quebec City and Lévis, Canada 549 (1,800) 1917 Forth Bridge Lothian/Fife, Scotland, United Kingdom 521 (1,710) x2 1890 Minato Bridge Osaka, Japan 510 (1,673) 1973 Commodore Barry Bridge Chester, Pennsylvania, to Bridgeport, New Jersey, United States 501 (1,644) 1974 Crescent City Connection New Orleans, Louisiana, United States 480 (1,575) 1958 (eastbound) 1988   (westbound) Howrah Bridge Kolkata, West Bengal, India 457 (1,500) 1943 Veterans Memorial Bridge Gramercy, Louisiana, United States 445 (1,460) 1995 Tokyo-Gate Bridge Tokyo, Japan 440 (1,443) 2012 San Francisco–Oakland Bay Bridge (east Bay span) San Francisco, California, United States 427 (1,400) 1936 (demolished 2016) J. C. Van Horne Bridge Campbellton, New Brunswick, to Pointe-à-la-Croix, Quebec, Canada 380 (1,247) 1961

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