Wednesday 20 February 2013

The bridge without nuts and bolts

Bridges are very common and they rarely make news unless they have something extraordinary to reveal. However, there are a few bridges that have become landmarks and they are even known by the name of the city in which they are built.
One such bridge has not only the name of the city in which it is situated but it has been the scene of shooting of films in almost all languages in India and even in English. It also has a film named after it.
Built by the British as a link between two areas separated by one of India’s greatest river, it has today attained the status of a monument that is visited by every person who comes to the City.
By the way, what sets out this bridge from others is that it has no nuts and bolts and it has been playing host to one of the densest traffic volume in the world.
When it was under construction, it collapsed triggering such a strong wave that it demolished a nearby temple and also led to a seismic station nearby recording it as an earthquake.
The bridge is in operation even today and it is counted as among the busiest in the world. It has defied all odds to stand tall even seventy years after its construction.
This is the Howrah Bridge and it is located across the Ganges in Kolkata. The Ganga or Ganges in Bengal is called as the Hoogly and  the bridge was opened to traffic in 1943. It is a cantilever bridge  and is the sixth longest of  such a type.
                             The bridge on a misty December morning
There are no nuts and bolts on the bridge and it is constructed entirely by riveting Cantilever truss.
Over period of time, Kolkata has embraced the bridge as its own and today it is as much known for the bridge as for the Victoria Memorial and its tram,
The construction of the bridge started in 1937 and it took almost ten years to complete. The bridge has remained one of the most outstanding landmarks of Kolkata and more than 150,000 vehicles and 4,000,000 pedestrians cross over the bridge every day.
The bridge is the lifeline of Kolkata and its is exposed to traffic throughout the day, except for Inter-State transport buses, goods vehicles, and all India tourist buses. At night, only three wheelers and goods vehicles are allowed to pass.
Steel truss cantilever (STC) was one of the newer technologies in the 1930s which was used for constructing the bridge.This is the first link to this city, as you approach it from Howrah railway station.
There are three more bridges connecting the city of  Howrah and Kolkata- Vidyasagar Setu, Vivekananda Setu and Nivedita Setu. This is the Rabindra Setu-named after Rabindranath Tagore.
When Howrah bridge was constructed, it consumed 26,500 tons of steel, out of which 23,000 were high-tensile alloy steel, known as Tiscrom. This was supplied by Tata Steel.
The main tower was founded with single monolith caissons of dimensions 55.31 x 24.8 m with 21 shafts, each 6.25 metre square. The fabrication was undertaken by Braithwaithe, Burn and others   at four different shops in Kolkata.
The central span is 1500 feet and the Anchor arms are 325ft. and the Cantilever arms 468 ft. long at both ends. While the middle suspended span is 564 ft., main towers are 280 ft. high above the monoliths and 76 ft. apart at the top Bridge deck width is 71 ft. with two footpaths of 15 feet on either side.
The bridge stands on two anchorage caissons which are each 16.4 m by 8.2 m, with two wells 4.9 m square. The caissons were so designed that the working chambers within the shafts could be temporarily enclosed by steel diaphragms to allow work under compressed air if required. The caisson at Kolkata side was founded at 31.41 m and that at Howrah side at 26.53 m below ground level.
One night, during the process of  removing the muck to enable the caisson to move, the ground below it yielded, and the entire mass plunged two feet, shaking the ground. The impact of this was so intense that the seismograph at Kidderpore registered it as an earthquake and a Hindu temple on the shore of the Hooghly was destroyed. This was rebuilt later.
When the muck was being cleared from the waters below the to be built bridge, all kinds of objects were brought up, including anchors, grappling irons, cannons, cannon balls, brass vessels, variety of coins dating back to the East India Company.
Then the sinking the caissons was carried out round-the-clock at a rate of a foot or more per day. The caissons were sunk through soft river deposits to a stiff yellow clay 26.5 m below ground level. The foundation for the bridge was completed on November 1938. By the end of 1940, the erection of the cantilevered arms was commenced and was completed in mid-summer of 1941. The two halves of the suspended span, each 282 feet (86 m) long and weighing 2,000 tons, were built in December 1941.
The entire project cost 25 million ( Pounds 2,463,887). The bridge did not have any pompous opening ceremony as the British were afraid of air attacks from the Japanese.
The first vehicle to use the bridge was a solitary tram.
This perhaps could be one of the few bridges to have a poem written about it.   
Howrah Bridge: Rabindra Setu by Catherine Daly
I drew in to Howrah Station along the river
to the city rising from the swamp.
Amid the muck and refugees, I saw a white bridge
cantilevered over the flat land and flat water,
improbable technology,
truss and girder like buttress and clerestory arch
spanning the Hooghly, thrust
into Calcutta. The bridge
is a new mathematical prayer
performed by clerks and reams of carbon paper,
clocked and numbered as if doves fly across daily at 2:00 p.m.
Horse carts and chickens wander over its asphalt.

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