CHENAB BRIDGE MAP
Crossing Chenab River, Jammu and Kashmir, India Designer/Engineer WSP Expected completion 2020 Span 1,532 feet (467 meters)
Material Steel Type Arch
Structural history is being made high in the Himalayas.
When completed, the Chenab Bridge will be the world’s tallest railway bridge, and one of the longest as well. These statistics alone would distinguish the steel arch span, but where and how it was designed and built make it more remarkable still. It is now under construction in the high mountains of northern India, an area that is under constant threatfrom wind, earthquakes, and potential terrorists. Moreover, the area is undeveloped, with no electricity and narrow roads. Despite all, the heroic rail bridge continues to rise, piece by piece.
India’s Ministry of Railways undertook the megaproject, part of a new railway line across the rugged terrain of the state of Jammu and Kashmir. With a total length of 4,314 feet (1,315 meters), the crossing is formed by the 2,575-foot (785-meter)-long arch bridge and a 1,739-foot (530-meter)-long approach span. Two rail tracks run on a deck that hovers 1,050 feet (320 meters) above the Chenab River. Piers with heights up to 394 feet (120 meters) support the superstructure; to put their height into perspective, the George Washington Bridge (see here) towers are a mere 213 feet (65 meters) tall.
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The Chenab Bridge’s many technical innovations include, most notably, its alignment. Typically, bridges are launched incrementally on either a straight or curved alignment with a uniform radius. However, the Chenab viaduct combines straight, curved, and transitional alignments with varying radii. This is one of the first times an incremental launching on a transitional curve has been attempted. WSP led the effort; subconsultant Leonhardt, Andra & Partner participated in the arch design; and Afcons Infrastructure, an Indian contractor, built it.
The biggest challenges are courtesy of Mother Nature. Every tall structure has to resist wind forces, which increase with height, but the bridge’s deep gorge location also guarantees periodic blasts of gusting wind, a different kind of load. To limit wind resistance, the bridge is a steel truss that air can pass through. It is located in an active seismic zone; those loads, along with wind loads, are constantly monitored.
Other hurdles combine topographic and economic realities. The constricted site requires that every component be manufactured on the ground and lifted. Because the river water is not suitable for manufacturing concrete, water has to be brought to the site, as were electrical generators. Some 25,000 tons (22,680 tonnes) of steel are being transported via roads that are no wider than 16 feet (4.9 meters) and often jammed with villagers and livestock. Steel is transported plate by plate because parts longer than 39 feet (12 meters) cannot be delivered. Cutting, welding, and painting, as well as state-of-the-art 3-D computer modeling, are done in temporary sheds built nearby. Some 1,300 people work there daily. Once manufactured, the steel components are lifted by the cable crane that moves between the pylon towers on either side. The crane can lift only 34 tons (31 tonnes) at a time.
Some threats are human. The bridge was considered a potential terrorist target from day one, given previous insurgencies of Kashmiri militants. Engineers designed it so that even if one of its seventeen piers is blown up, it won’t collapse. For security reasons, the exact amount of blast load that it can absorb has not been disclosed.
Approximately 1 million cubic meters of rock247 acres or almost 200 football fields’ worthhad to be excavated.
In this isolated area, where some children must walk 12 miles (20 kilometers) to school, the bridge has brought economic benefits, growth that will be sustained once rail operations begin. As one driver told the Economic Times, people once “had to go all the way to Jammu and Katra looking for work. Now, the work has come to our doorstep, thanks to this project.”
Lifted by a cable crane, the largest ever used, a suspended steel column floats in the air before being installed in the pier below.
Narrow road networks determined construction methods. Here, a truck transports a single steel deck section for the bridge approach.