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British Industrial History

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Hooghly Bridge

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In 1887 the first railway bridge was built over the Hooghly River but at a point 28 miles front Howrah.

The work on the bridge was begun in 1883.

The bridge is approached from both sides by masonry viaducts of 3,278 feet and 441 feet respectively consisting of 141 brick arches of spans varying from 10 to 48 feet. The total length of the bridge proper is 1,213 feet. The length of the entire structure is approximately a mile. The bridge was originally constructed for a double line of railway, but as the present day moving dimensions do not permit double line traffic on the bridge, the tracks have been interlaced on the bridge to pass trains as a single line.

At the site of the bridge the Hooghly channel is 1,200 feet wide, being the narrowest over several miles up to Calcutta. In places the bed is 66 feet deep below mean sea level, and the height of the tide varies from a little below mean sea level to 20 feet above, with a maximum velocity of four and a half miles an hour on the ebb tide in freshets. The river is largely used for navigation, and provision had to be made for allowing big country sailing boats, inland steamers and fiats of 500 to 600 ton capacity to pass under the bridge. The bridge provides for two large openings each of 525 feet clear span, with a central smaller opening of 106 feet 6 inches between two piers, supporting a span of central cantilever girders. The central girder section of 360 feet is carried on two piers placed only 120 feet 6 inches apart front centre to centre. Resting on the overhanging projecting end of the central cantilever girders, the two land girders each 420 feet long stretch to the bank abutments. The object of this somewhat unusual arrangement giving two very wide land spars end a small one in the centre was partly to locate the piers in comparatively shallow water and partly to leave the widest opening on each land side for navigation.

Some very unusual methods had to be adopted in the construction of the bridge. The girders of the land spans for example, were each erected on lines of rails carried on the surface of the two approaching viaducts. A complete span, composed of two connected girders weighing 1,000 tons, was then mounted on rails, and the whole mass was run forward by the aid of steam tackle, until the outer end of the girders projected over the water for some distance beyond the face line of the abutment. At this stage two floating pontoons fitted with a suitable staging were brought into position beneath the projecting ends of the girders which were wedged in and supported on the pontoon staging. The pontoons were them moved across with the current, until the ends were brought into position and deposited on the projecting extremities of the cantilever girders. All these operations of extraordinary magnitude and difficulty required the most exact calculations, ingenious adaptation of basic principles to local conditions, and utmost precision and timing.

The total cost of the bridge inclusive of the approaching viaducts came to nearly Rs 39 lakhs.

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