ENGINEERING. 



313 



five feet were added to the clear elevation 

 proposed in the plans. This requirement, 

 together with an increase of five feet in the 

 breadth, added 8 per cent, to the original esti- 

 mates. Other changes in the designs, which 

 swelled the actual cost to nearly $15,000,000, 

 were the adoption of solid masonry for the 

 approaches, instead of light iron trusses, and 

 the sinking of caissons for the towers, instead 

 of erecting them on a foundation of piles. 



There were many hindrances and delays in 

 the work of construction. In addition to the 

 enormous and to a considerable extent unex- 

 pected technical difficulties, differences fre- 

 quently occurred between the two municipali- 

 ties, and occasionally appropriations were not 

 granted in time, so that the work had to be 

 suspended for long periods. The piers were 

 built up by the aid of caissons of unprecedent- 

 ed size. The dimensions of the towers at the 

 base are 140 by 59 feet. The New York tower 

 was founded on the bed-rock, 78J feet below 

 the surface of the water. The Brooklyn tower 

 was built up from the clay, 44 feet below the 

 surface. The lowering of the Brooklyn cais- 

 son began in May, 1870, and was completed in 

 March, 1871. The New York caisson was 

 towed into position in October, 1871, and sunk 

 to the rock by the May following. The erec- 

 tion of the enormous towers was a work of 

 time. The Brooklyn tower was finished in 

 May, 1875, and the New York tower in July, 

 1876. The towers are each pierced by two 

 archways 31^- feet wide at the height of 118 

 feet above high -water mark. Through these 

 openings passes the floor of the bridge. Above 

 the arches, which are 120| feet high, the par- 

 titions reunite, and the towers rise 30 feet 

 higher, to support the saddles which sustain 

 the cables. The total height of the towers 

 above the surface of the water is 276 feet. 

 The height of the bridge-floor over high-water 

 mark is 118 feet at the towers, and 135 feet in 

 the center of the span. 



The four cables are .16 inches in diameter, 

 and contain about 5,000 single wires each. 

 The wire is of -$-inch size ; 278 single wires 

 were grouped into a rope and 19 ropes bunched 

 to form a cable. The wires were carried for- 

 ward and back from anchorage to anchorage 

 over the towers. The sun, expanding the more 

 exposed wires, and the wind, rendered the nice 

 work of forming the ropes with mathematical 

 exactness exceedingly difficult. The work of 

 stringing the wires began in June, 1877, and 

 was completed in October, 1878. On one oc- 

 casion a bundle of wires broke away from the 

 anchorage and shot across the tower, falling 

 into the river. The iron saddles on which the 

 cables rest are made movable, to permit of 

 expansion and compression on a saddle-plate 

 of iron firmly imbedded and anchored in the 

 towers. The saddles are 13 feet long, 4 broad, 

 and 4 thick. They glide through minute dis- 

 tances in response to strains and changes of 

 temperature, upon 40 iron rollers. 



The anchorages are 930 feet from the tow- 

 ers on each side ; they are solid masses of ma- 

 sonry, each 132 by 119 feet at base and top, 

 89 feet high, and weighing 60,000 tons. 



During the construction of the bridge 20 

 fatal and many disabling accidents occurred. 

 The compressed air of the caissons caused over 

 100 cases of caisson- disease. The victim of the 

 first accident was Engineer Roebling, who died 

 from lockjaw resulting from a crushed foot, 

 received when laying the foundations of one of 

 the shore-piers, July 22, 1869. His son, Wash- 

 ington A. Roebling, took charge of the work, 

 but in 1871 he was prostrated with a peculiar 

 form of caisson-disease which destroyed the 

 nerves of motion, the result of a fire in the 

 Brooklyn caisson in 1870. This fire necessi- 

 tated the flooding of the caisson, and delayed 

 the work two months. After his accident Mr. 

 Roebling never was capable of active work. 

 His intellectual faculties, however, were unim- 

 paired, and he was able to make the plans and 

 calculations, and to superintend the construc- 

 tion, through the mediation of his wife. It was 

 not until 1876 that he was sufficiently restored 

 to be removed, after which he remained in view 

 of the bridge, directing the work, though for a 

 long time after that he was still incapable of 

 locomotion. 



The total length of the bridge and approaches 

 is 5,989 feet. Of this the middle span takes up 

 1,595 feet, the distance between the towers and 

 the anchorages on each side 930 feet, and the 

 approaches 1,562^ feet on the New York and 

 972^ feet on the Brooklyn side. The length 

 of the suspended structure, from anchorage to 

 anchorage, is 3,454 feet. Its total weight is 

 6,470 tons. The maximum load which it is 

 designed to bear is 1,740 tons. The ultimate 

 resistance is calculated at 49,200 tons. (For 

 other measurements see u Annual Cyclopedia " 

 for 1882.) 



The bridge is divided into five avenues. The 

 central one, 15^ feet in w r idth, is the path for 

 foot-passengers. The two outer ones, 19 feet 

 wide, are for vehicles. The others are laid 

 with the rails for the cars, which are drawn by 

 an endless chain. They are attached and de- 

 tached by means of a " grip " arrangement. 



Niagara Cantilever Bridge. A double-track rail- 

 road-bridge over Niagara river, about 300 feet 

 above the railroad suspension-bridge, complet- 

 ed in November for the New York Central and 

 Michigan Central Railroads, is constructed on 

 the new cantilever principle, which is that of a 

 balanced beam. In the perfect cantilever, rep- 

 resented by the bridge now building over the 

 Forth, in Scotland, of which a description is 

 given below, the diagonally-braced frame of 

 the cantilever is exactly poised on the upright 

 iron columns in the center. In the Niagara 

 bridge, designed by C. 0. Schneider and Ed- 

 mund Hayes, the abutting banks are made 

 use of to attach the shore ends to a mass of 

 masonry which counterpoises the extra weight 

 of the river arms, and stays and anchors the 



