80 



BRIDGES. 



Railway Bridge at India Point, Providence. 

 Soundings for this bridge were made to ascer- 

 tain the nature of the river-bed, the depth of 

 water, etc., in June, 1868. A good solid bottom 

 was found, consisting of gravel, covered with 

 a layer of mud, on top of which is a crust of 

 oyster-shells, forming the river-bed. In the 

 places where the piles were to be sunk, no 

 obstructions were discovered, with the excep- 

 tion of the stump of an old pile, which was 

 removed by the divers. On account of the 

 soft, muddy layer of several feet in thickness, 

 which covers the solid bottom, the piles were 

 driven from temporary platforms. They were 

 constructed of piles driven in four rows, about 20 

 feet into the bed of the river, and about 9 feet 

 apart ; these piles were capped with hard pine, 

 about 13 inches square, and then covered with 

 spruce plank. The permanent piles are arranged 

 in clusters of 12 for the 2 piers west of the 

 draw, and also 2 groups under the draw con- 

 tain the same number. The other groups, five in 

 number, contain 9 piles each. The piles were 

 driven in the following manner : the first pile 

 driven in was sharpened on all sides, the bevel 

 commencing about 18 inches above the lower 

 end, and the end left about 4 inches square ; 

 all the remaining piles, that presented only one 

 side to those already driven, were sharpened 

 only on one side, and the corner piles and those 

 that were in contact with other piles were 

 sharpened upon the two opposite sides. They 

 are encased in cast-iron cylinders driven over 

 them, the space between the piles and cylin- 

 ders being firmly packed with concrete; the 

 diameter of the cylinders west of the draw is 

 6 feet; the other 5 feet. The castings were 

 made four and a half feet long, one and an 

 eighth inches thick, having a flange four and 

 five-eighths inches wide. The weight of the 

 sections, as they came from the moulds, was, 

 for those six feet in diameter, 5,459 pounds, 

 and those five feet in diameter, 4,360 pounds. 

 The rough castings were covered with a coat- 

 ing of cement, which attached itself firmly to 

 the rough scale, thus forming a solid, durable 

 covering ; the sections were then firmly bolted 

 together and carried by a scow to the platform, 

 upon which they were hoisted, and from there 

 forced down over the piles by means of a pow- 

 erful screw-press. Notwithstanding the im- 

 mense pressure brought to bear upon the cyl- 

 inders, they were unable to penetrate the solid 

 crust of oyster shells at the river-bed ; the crust 

 was then broken up by driving piles all around, 

 and the cylinder again lowered; its weight 

 alone, this time, carried it about four feet into 

 the crust, and upon piling about ten tons of 

 iron together, with continued rocking (accom- 



ished by means of levers), the cylinder was 

 finally forced home ; all the others were sunk 

 in a similar manner. 



The capping of the piers west of the draw 

 consists of yellow pine, that of the draw is 

 formed of oak ; the pier upon which the east 

 end of the draw rests consists of granite, 



twenty-two feet long, and six feet thick, resting 

 on piles driven to a depth of thirty feet below 

 the river-bed. The superstructure is of the 

 ordinary form of Howe truss. 



Bridge over the AllegJiany. The bridge 

 of the Pittsburg, Fort Wayne, and Chicago 

 Eailroad, over the Alleghany River, is now 

 completed. An interesting account of its con- 

 struction we extract from the Pittsburg Ga- 

 zette:' The original superstructure for double 

 track was of wood, on the Howe-truss plan, 

 with arches for additional strength, and con- 

 sisted of seven spans of various lengths, being 

 in all 1,172 feet long. On account of the pecu- 

 liar form and location of the company's freight- 

 yard at Pittsburg, an additional pier 101 feet 

 long was built on the wharf, under the first 

 span on the Pittsburg side, and the abutment 

 extended parallel with the river, along Du- 

 quesne Way, to 148 feet in length. By this 

 arrangement the bridge opens gradually like a 

 fan toward the Pittsburg freight-yard, being 

 at the narrowest part, next to the main span, 

 55 feet in width, and extending out for 176 feet 

 in length, to the point where it connects with 

 the yard, where the width is 138 feet. For 

 symmetry and economy in the construction, 

 another pier was also built on the wharf at the 

 Alleghany City end span of the bridge. At 

 both of these end spans the tracks are now 

 supported from below by girders, made en- 

 tirely of plate and angle iron. The two west- 

 ern spans have each three girders 89 feet in 

 length and 6 feet 6 inches deep, to support the 

 double line of railway, the middle one being 

 made proportionately stronger. On the two 

 eastern spans, which form the above-mentioned 

 addition to the yard, eighteen iron-plate girders, 

 varying in length from 86 to 93 feet, all 6 feet 

 1 inch deep, are placed, distributed according 

 to the tracks they are intended to support. The 

 five large spans over the main part of the Alle- 

 ghany River are built for a double line of rail- 

 way, with one projecting footpath on the out- 

 side, consisting of three main girders, one on 

 each side and one in the centre, between the 

 ways. The average length of the spans is 153^- 

 feet in the clear, with a bearing of 5 feet on 

 each pier. The depth of the girders is 19 feet. 

 The clear width between the outside and the 

 central girders is 14 feet, except the south part 

 of the first main span, where it widens from 

 14 feet at one end to 32 feet at the other. The 

 top and bottom sections of the girders are in 

 the form of the letter T; the cross-sectional 

 area of the top chord consists of 4 thicknesses 

 of iron laid one over the other, well riveted, 

 and forming together a plate 2 inches thick, 

 and 24 inches wide in the centre part of the 

 girder, and diminishing gradually to about two- 

 thirds its cross-section al the ends, where it 

 rests on the piers. In addition to which there 

 are 2 large angle-irons 5 inches by 31 x | inch 

 to i inch thick, and two vertical bars 12 inches 

 by -^ inch on the inside between the angle-iron, 

 running along the centre of the horizontal 



