Holkar-Narmada Bridge

From FIBIwiki
Jump to navigation Jump to search

The Holkar-Narmada Bridge opened in 1876 and carried the ‘Holkar State Railway’ metre gauge(MG) line from Khandwa running northward to Indore.
The railway was absorbed into the ‘Rajputana-Malwa State Railway’ from 1881-82 and the into the Bombay, Baroda and Central India Railway(BB&CIR) from 1900 onwards.

The following description of the ‘Nerbudda Bridge’(see spelling Note ), written after its erection, is from a report submitted in June 1878 by the Engineer-in-Chief, and given in the ‘Administration Report of the Holkar State Railway from commencement to close of 1878-79’. The ‘Nerbudda Bridge’ opened on the 5 Oct 1876 and the whole line was completed on the 1 Jan 1878 [1].

Spelling Note
Nerbudda River is the spelling used in this Report. The Narmada River is the later name. The’ Imperial Gazetteer’ uses both [2]

Nerbudda Bridge

"The bridge consists of 14 spans of 60 metres from centre to centre of piers. The width of each pier at girder bed level is 4 feet, and the length of its square part is 16 feet 6 inches. It has an up-stream and a down-stream cutwater, with an angle of 90°. The square part of the pier has a batter of 1 in 20, and the cutwater a batter of 1 in 17. A sketch of the pier is given in the margin. The highest known flood-level at the site of the bridge is 66 feet. Between this and the girder bed level a clearance of 10 feet. Considering also the possibility of damage from heavy trees impinging against the girders when carried by floods running with a velocity of over 15 miles an hour, it was decided to raise the bridge 5 feet higher, thus giving a clearance of 15 feet between the highest known flood-level and bottom of the girders."
"The iron-work of the Nerbudda bridge was finished by Messrs. Handyside and Co. and reflects the greatest credit upon them. The girders are of the Warren type and rest on the upper boom, one end being fixed and the other placed on expansion rollers. The length of the girder from outside to outside is 191 feet 3 inches. Their depth is 15 feet, and the extreme width from outside to outside of both girders is 14 feet."

Girder Design

The following is the detailed description of the girders and of the additions made for stiffening them:-
"The girders are divided into 23 equilateral triangles, 11 with apices pointing downward and 12 with apices pointing upwards. The base of the former is 15 feet 91/16 inches, that of the latter 15 feet 8 9/10 inches.
The top and lower flanges of each girder are alike in character, and measure 2 feet 6½ inches from outside to outside. They are each in the centre of eight angle irons 5"x5”x5/8” , arranged as per sketch, which towards the ends are reduced 5"x5”x5/8” At, the end the girder there are only four angle irons 5"x5”x5/8”. Between the apices the triangles these angle irons are tied together vertically in the top flange by three distinct; pieces of bar iron 4"x7/8”, and in the lower boom by two pieces of bar iron 4"x 7/8”and cross wire, above and below by two pieces of bar iron 4" 3/8". The struts and ties of the web forwards the end of the girder are of solid plates, but in the centre are attached to the angle iron of top and bottom boom by gusset the centre are plates to which they are riveted.
The top flanges of the two girders are tied together at the apex of each triangle by two cross girders of solid plates which carry the, rail-bearers of the roadway, and each bay is stiffened by a, bar of angle iron 3x3x3/8 laid diagonally and riveted to the main girders and the rail-bearers. The lower flanges of the girder are tied together by two lattice girders at the apex of the top and lower flanges of these lattice girders are composed of a 3”x3”x 3/8” They carry a longitudinal plate girder to support the lower roadway.”

From the above description it will be noticed that the top flange of the girders is of quite a novel design, being composed of what may practically be said to be a number of detached angle-irons. This peculiarity was noticed by Mr. Molesworth, the Consulting Engineer to the Government, who called the attention of Government to it. It was further very practical and forcibly brought to notice by the buckling and twisting of some 30 metres of girders of the same type when being lifted on this railway, and by the collapse of three of these girders after they had been lifted and placed into position.

Government therefore ordered that, before the iron-work of the bridge was commenced, one span of girders should be temporarily erected on the bank of the river, so that it could be easily and carefully examined; and Mr. Molesworth was deputed to report on it.

The apparent want of stiffness and rigidity in the compressive member of the girder was very marked; and Mr. Molesworth suggested that each set of four angle iron composing it should be tied together with a lattice web composed of 3" bar iron, so as to unite them into one strong girder, and that the two girders thus made should be tied together, top and bottom, transversely and diagonally, by bars of angle iron x 3" x 1", and thus formed into a stiff and rigid box-shaped boom. Mr. Molesworth also recommended that the top members of both girders should be further tied together to the rail-bearers by two angle iron bars 3”x 3" in each bay, and that the lower roadway should be braced diagonally in a similar manner to the upper roadway.

Staging

The girders of the Nerbudda Bridge were erected upon wooden staging. The plan adopted is described as follows:- In designing it the principle of having a rigid support under each apex of the triangles in the girder was adhered to. It consists of eight trestles, arranged in pairs, each pair being so tied and braced together as to form a strong wooden pier 15 feet 9 inches wide. The space between each pair of trestles was 31 feet 6 inches, which was spanned by trussed timber beams. The trestles rested on masonry pillars carefully levelled off to the required height.
In the span over the deep-water channel the trestles were supported on wooden cribs. These were floated into position, filled up with dry stones, and then levelled off with masonry.
The top of the staging was covered over with 6 inch planking. The vertical supports of the trestles were composed of three lengths of timber. This admitted of their adaptation to almost any height required and made the staging as suitable for the low-land spans and those with steep shelving banks as for the high spans in the bed of the river. Owing to the raising of the bridge, 5 feet extra had to be added to the height of the trestles after they were made.
“The amount of timber in the staging for each span was about 10,000 cubic feet. This was nearly all required for the roadways of the bridge. Three sets of stagings were used in erecting the girders. This enabled two spans of girders to be in progress at the same time, whilst the third set of staging was being taken down and re-erected. The time occupied in pulling down one span of staging was usually occupied three days, and its erection usually occupied seven days.”
The cost of making, fitting up, and removing the stagings for the 14 spans of the bridge, exclusive of the cost of the timber and iron work in them, was Rs. 18,000; and as the total weight of girders erected was 2,352 tons, this gives a rate of about Its. 7-12 per ton.

Construction

The fitting up of the girders in position was begun about the middle of January 1876 in span No. 3, and the whole of the 14 spans, weighing 2,352 tons, were erected and in place by the middle of July 1876. They were built on wedges, on the staging the wedges being so arranged as to give a camber of 4 inches to each girder. Each span weighs 168 tons, and was sent out from England in pieces, which were easily handled.

All the iron-work was taken in trolleys to the bed of river and was hoisted piece-by-piece to the top of the staging by gangs of men working sets of tackle, consisting of double and single rope pulley blocks suspended from derricks. Two derricks and two sets of tackle were used for each span. For fixing the web struts and ties, two sets of shear legs were used. These, with one or two spare sets of tackle for moving heavy pieces on the staging, comprised the whole plant employed in hoisting and fitting the girders. The rails are carried on longitudinal timbers 12"x6", bolted down to cross sleepers 8"x4”. The lower or cart roadway consists of 3-inch planks covered with a grating of teak laths 12" x 1"

References

  1. British Library ‘India Office Records’ V/24/3590 ; "Public Works Department: Railways, 1876-79" which contains the ‘Administration Report of the Holkar State Railway from commencement to close of 1878-79’ Para. 6, pages 3-4
  2. “Imperial Gazetteer of India”, v. 2, p. 220; Retrieved 22 Dec 2017