Howrah Bridge

                     Today as I was having my first walk on the only suspension bridge in our city ie,”THE HOWRAH BRIDGE”aslo known as “Rabindra Setu” with one of my close friend Aritra da,I was fascinated by this wonderful mighty structure. 

                      Its not that I have seen this monumental structure for the 1st time,but its excellence and utilty to the kolkata’s life is of utmost importance is what I felt today.

         Howrah Bridge is the undisputed link of life between Kolkata and Howrah.

 

 

 

The vital statistics of the howrah bridge are::::

Built                     1937—1943

Location               Kolkata, West Bengal, India

Current status       In use

Crosses                Hooghly river

TypeBalanced        Cantilever Suspension

Usage                    Road bridge

Daily Traffic           80,000 vehicles, possibly more than 1,000,000 pedestrians

Builders                 Rendel Palmer & Tritton                                                                             Cleveland Bridge & Engineering Co. Ltd

Material                 Steel

Tower height          82 m

Number of spans     3

Length of spans       99.125 m    457.50 m      99.125 m

Length of drop-in span  172.08 m

                         Howrah Bridge is the gateway to Kolkata. Built on the Hooghly River, its original purpose was to facilitate military transportation between Kolkata and the industrial town of Howrah during World War II. It remains a cantilever bridge connecting the city to its main railway station, the Howrah Station, one of the busiest railway stations of the world.

History

Early plans

By the 19th century AD, Calcutta and Howrah on the opposite banks of the Hooghly River had grown to be the most important economic and cultural centers of British India, and a need for bridging the Hooghly River arose.

In 1862, the Government of Bengal asked George Turnbull, Chief Engineer of the East India Railway Company to study the feasibility of bridging the Hooghly River — he had recently established the company's rail terminus in Howrah. He reported on 29 March with large-scale drawings and estimates that:

1. The foundations for a bridge at Calcutta would be at a considerable depth and cost because of the depth of the mud there.
2. "The impediment to shipping would be considerable".
3. A good place for the bridge was at Pulta Ghat "about a dozen miles north of Calcutta" where a "bed of stiff clay existed at no great depth under the river bed".
4. He recommended and designed a suspended-girder bridge of five spans of 400 feet and two spans of 200 feet.

The bridge was not built.

The pontoon bridge

The famous Floating Pontoon Bridge was built in 1874 by Sir Bradford Leslie.

           The Old Howrah Bridge - The Floating Pontoon Bridge.

            The Floating Pontoon Bridge was built using timber on pontoon. The bridge was opened to let river traffic through. The bridge had hinged shore spans since Hooghly River is subjected to tides. During high tides these became very steep and bullock carts were not able to negotiate their way, which resulted in traffic jams. It was also feared that the floating bridge could affect river currents and cause silting problems. With time the bridge became too inadequate for the ever increasing traffic.

                               Due to all these reasons Government of Bengal in 1933 decided to replace the Floating Pontoon Bridge. The Floating Pontoon Bridge which was originally commissioned to service for 25 years, was decommissioned on February 1943, after its long service of 69 years.

The modern bridge

                                Construction of the New Howrah Bridge was started on 1937. The Cantilever Era was prevailing at that time, and engineers felts that cantilever bridges were more rigid than suspension bridges. This bridge is one of the finest cantilever bridges in the world - left to India by the British engineers.

 

View of Howrah Bridge (1945).

                                Considering various aspects like navigational, hydraulics, tidal conditions of the river and the projected traffic conditions, Rendel Palmer & Tritton came up with a design for a cantilever bridge of 1500 feet, with a 71 feet wide roadway and two 15 feet wide cantilever footways. Considering the quotation from various firms, the contract was awarded to Cleveland Bridge & Engineering Co. Ltd of Darlington, with a strong recommendation that they use Indian-made steel, which they agreed to do. Out of the total 26,500 tons of steel used, Tata Iron and Steel Company supplied 23,500 tons of steel and fabrication was done by Braithwaite, Burn and Jessop Co. at four different shops in Calcutta.

                                The two huge caissons which was sunk (on the first stage of construction) is still the biggest ever sunk caisson on land. It is told that while clearing the muck, all kinds of curious things was brought up, which included anchors, grappling irons, cannons, cannon balls, brass vessels, variety of coins. 40 Indian crane drivers were trained on the job and worked in three shifts of 8 hours each. The job of sinking the caisson were carried out round-the-clock at a rate of a foot or more per day.

                                One night, while grabbing out the muck to enable the caisson to move, the ground below it yielded and the entire mass plunged down two feet, shaking the ground. The impact of this shake was so intense that the seismograph at Khidirpore had registered as earthquake and a Hindu temple on the shore was destroyed; which was subsequently rebuilt. In spite of these challenging situations the caissons were placed true to position.

                               To keep the water out at depth of 103 feet (31 m) around the foundations so that construction can be done, around 500 people were employed on the compressed air operation.The air pressure maintained was about 40 lbs per square inch (2.8 bar). The work on the foundation was completed on November 1938. By the end of 1940 the erection of the cantilever 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. 16 hydraulic jacks, each of 800 ton capacity were pressed in to service for joining the two halves of the suspended span.

 

The Howrah Bridge

                        After completing the steel work of the deck and concreting of roadway. the New Howrah Bridge was finally opened to traffic on February 1943. The old Floating Pontoon Bridge was decommissioned. In May 1946, census of the daily traffic on the bridge was taken and it was found to be 27,400 vehicles, 121,100 pedestrians and 2,997 cattle. The rate of only vehicle traffic over the bridge was 20% more than that on the London Bridge, in the same period, which was till then the busiest bridge in the metropolis.

                          The final cost of the bridge amounted to ₤2,500,000.

Sources & Images: http://en.wikipedia.org/wiki/Howrah_Bridge                                                    Howrah Bridge-WikiPedia