What goes into running a train: Bridges and Viaducts

A viaduct is a long bridge-like structure carrying a road or railway across a valley or other low ground.

Bridges are built across rivers or arms of the sea, whereas viaducts tend to cross valleys and low lying areas where there may or may not be a river.

Rail bridges and viaducts are as old as the railway itself.

The oldest bridges that were built were arch bridges. These are based on the principle that an arch is a very stable structure. The span in Mumbai over which the first train ran in our country, the Dhapoorie viaduct, was an arch bridge.

The arch bridge design reached its pinnacle on the Kalka-Shimla narrow gauge section where you can see a 4-tiered arch bridge, reminiscent of similar bridges built by the ancient Romans as aqueducts.

An interesting feature of the Kalka - Shimla Railway line was complete absence of girder bridges initially.

The Nilgiri Mountain Railway line also features 205 bridges that come between Udagamandalam and Mettupalayam stations, which are only 45 kms apart.

An artist's rendition shows the amazing steel arch bridge, which is being constructed on the line from Jammu to Srinagar across the Chenab.

When completed, it will be the tallest bridge in the world, with a height of 359 meters from the river bed level to the centre of the arch.

The Chenab bridge will also have the widest span in the Indian broad gauge railway network.

The screw pile bridge was another type of bridge the early engineers adopted, particularly while bridging estuaries and backwaters, where the current was not too severe. While these bridges served the purpose at the time they were built, they had a short life and other limitations.

The Indian Railways, as a policy, decided in 2001, to replace all such bridges. Railway bridges are some of the ‘Mega Structures’ that have been created by railway engineers over the last 160 years. Many of these bridges are now over 100 years old.

In the last three decades, there has been much greater use of pre-stressed concrete slab girders and many of the new bridges built over major rivers have been with pre-stressed concrete slab girders.

This bridge is a bascule bridge or a Scherzer span, which is a movable bridge with a counterweight that continuously balances a span/leaf. The Scherzer span can be opened and closed by cranking wheels, which in turn rolls the curved structure on the horizontal platform.

It is the first sea bridge in India and the 4th longest bridge in the country (with the length of 2057 meters).

An engineering marvel of yesteryear, Pamban Bridge is more than 103 years old.