Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/387

Rh EXAMPLES.] collectively to an area of 69 square inches. They are secured to a cast-iron anchor plate, by a pin 3^ inches diameter. From the fourth link the chain curves, and the section is gradually increased to an area of 93 square inches. There are two towers at each end of the bridge, based upon a mass of masonry 60 feet by 20 feet, which is pierced by an arch 19 feet wide, forming the entrance to the lower roadway. The towers are GO feet high, 1 5 feet square at the base, and 8 feet square at the top. &quot; Above the floors are 64 diagonal stays, extending from the saddles to the suspenders, amongst which they are equally distributed; they are formed of wire-rope Ifth inches diameter. There are also 56 stays attached at their upper extremities to the soffit of the bridge, and at their other ends well anchored to the rocks below. The super structure is thus tied down as well as suspended, and all undulations directly resisted. The bridge was commenced in September 1852, and opened for traffic in March 1855. The total cost was 80,000.&quot; The use of two chains of different versed sines is certainly a defect in this design. 339 There are several other suspension bridges in the United States of great span, e.g., Cincinnati, 1057 feet; Brooklyn 1600 feet. 81. Saltash, Victoria, and Coblentz Bridges. Fink Truss. Saltash. Fig. 131 shows one span of Saltash Bridge erected by FIG. 131. Span of Saltash Bridge. Brunei. The span is 455 feet. The pier is a column or circular pillar of solid masonry, 35 feet diameter and 96 feet high from the rock foundation to above higli- Fia. 132. Fink Truss. water mark. Upon this are placed four octagonal columns of cast-iron, 10 feet diameter, carried up to the level of the roadway, which is 100 feet above high-water mark. The Victoria Bridge over the St Lawrence at Montreal is a tubular bridge of great length (7000 feet), chiefly remarkable for its ice breakers, shown in fig. 93. Fig. 132 shows some details of a Fink truss as used in America. The mode of computing the stresses on this truss has already been explained in 59. All the struts are cast-iron tubes. Fig. 133 shows one of the wrought iron arches of a Coblentz. bridge over the Khine at Coblentz. The bridge consists of three spans of about 315 feet each. 82. St Louis and Illinois Bridge, The St Louis and St Louis Bridge. Fro. 133. Arcli of Bridge at Coblentz. Illinois bridge over the Mississippi (fig. 5, Plate XVIII.) is the finest example of a metal arch yet erected. It is described as follows by Sir Charles A. Hartley who visited it in 1873 : &quot;The Mississippi at St Louis is confined to a single channel 1GOO feet wide and 8 feet deep at extreme low water by an embank ment or levee on the Illinois side, which is carried up to the level of extreme high water, at which time the width is augmented to 2200 feet. Both shores are revetted below the low water, soine with nibble stones, and protected by the wharf pavements above that line. The extreme range between high and low water is 41 feet. Owing to the narrow gorge through which the whole volume of the Mis sissippi flows the variations in the bed of the river are rery great. Captain James B. Eads, M. Inat. C.E., the distinguished engineer who designed the bridge and superintended its construction, informed the author that a rise of 13 feet less than high -water mark caused a scour of 18 feet, and that in the freshet of 1870 the scour reached a depth of 51 feet below lew-water mark alongside the east pier. These facts induced him to believe it possible that the scour, at times of extraordinary high flood, might extend even to the rock itself. He therefore determined to establish the piers and abut ments on the rock ; and this was done by means of caissons provided with air chambers and locks at depths for the east pier and east abutment reaching 136 feet below high-water mark, or 110 feet from the surface of the water where the foundation work was actually performed. This feat, which was satisfactorily executed in 1870-71, is finite unprecedented in the annals of engineering. The piers and abutments are composed of coursed rubble masonry up to low-water mark. Above this level they are faced