244 



ENGINEERING. 



eters, elongate 12 per cent, of their length, 

 and sustain a pulling strain of 80,000 pounds. 

 The tests disclosed the same superior strength 

 in bars of small section as compared with 

 larger ones which is observable in wrought- 

 iron bars. The chief engineer was George S. 

 Morrison. Tbe floor of the bridge, which is 

 uniform throughout, is constructed with iron 

 guards of angle-iron, within oak guard-tim- 

 bers. These angle-bars with the broad side 

 flat will, it is expected, carry a derailed car or 

 train for any distance. 



A railroad- bridge over the Ohio Eiver at 

 Beaver, Pennsylvania, consists of six spans 

 over the river and an iron viaduct across the 

 flats on the north side of the river, 1,000 feet 

 long. The first span on the south side is a 

 plate deck-girder, 30 feet long; the second 

 span over the channel is 446 feet, crossed by a 

 double-intersection Pratt through truss; the 

 next truss, 260 feet long, is of the same pat- 

 tern; the third, 180 feet long, is a Pratt deck- 

 truss, as are also the fifth and sixth, 230 feet 

 each. The bridge is for a single track. The 

 bridge proper has a length of 1,376 feet, and 

 the iron viaduct of 1,080 feet, divided into thir- 

 ty-six spans of 30 feet each. The piers for 

 the channel-span were built up from the solid 

 rock, in coffer-dams. They are 90 feet high 

 from the low-water mark, and are 12 feet 

 thick, and 30 feet long under the coping, slop- 

 ing outward one in 24 to the foundation 

 courses. The next pier, at the north end of 

 the 260-foot span, has the same height. The 

 next two piers, supporting the first 230-foot 

 truss, are 60 feet high above low water, and 

 eight wide by 24 feet long at the top. The 

 channel-span is formed by two trusses, 18 feet 

 apart and 42 feet high. The end-posts are in- 

 clined, and the intermediate posts, which are 

 double, each half being formed of an eight- 

 inch beam with plates riveted on the flanges, 

 are stiffened by a longitudinal strut, formed 

 of two channel-bars, fastened to them at their 

 centers, and running the whole length of the 

 bridge. The trusses are divided into 21 panels 

 of 2l feet two inches each. The channel-span 

 was erected in the river upon a temporary 

 bridge of three spans, 135 feet each, of Howe 

 trusses, resting on timber piers, 55 feet high, 

 and these upon columns of rough masonry, ten 

 feet high above low water. Under these tem- 

 porary spans the river-traffic was conducted 

 without interruption. The shorter span of 

 double-intersection trusses was raised upon a 

 wooden trestle-work. The viaduct rests upon 

 iron trestles, each formed by two legs inclined 

 one in eight, and braced by four panels of cross- 

 struts and diagonals. The height of the via- 

 duct is 60 feet from the ground. Each leg of 

 the iron columns is anchored in a masonry 

 foundation. The longitudinal bracing is a line 

 of struts composed of two channel-bars, fast- 

 ened to each leg at its center, and strength- 

 ened by diagonals. Every third span was left 

 unbraced to allow of expansion. 



The Tay Bridge disaster led to a long Par- 

 liamentary investigation. This resulted in the 

 adoption of plans for an entirely new bridge by 

 the side of the old one, which is still standing 

 unimpaired, except the thirteen long spans over 

 the main current. This number was adopted by 

 Sir Thomas Bouch, in place of fourteen spans 

 of shorter breadth, in order to hasten the com- 

 pletion of the bridge. This broke down in a 

 high gale of wind on the 28th of December, 

 1879, while a passenger train was passing over, 

 causing a terrible loss of life. (For description of 

 the bridge see ENGINEEEING in "Annual Cyclo- 

 paedia" for 1877.) In the report submitted to 

 Parliament the commissioners say : " The con- 

 clusion to which we have come is that the 

 bridge was badly designed, badly constructed, 

 and badly maintained, and that its downfall was 

 owing to inherent defects in the structure, 

 which must sooner or later have brought it 

 down." The engineers stated that 20 pounds on 

 the square foot of wind-pressure had been allow- 

 ed for, although maximum pressures of 40 to 50 

 pounds have been observed, and the locality of 

 the bridge is subject to storms of extreme vio- 

 lence. French engineers usually allow for 50 or 

 55 pounds per square foot of lateral wind-press- 

 ure, or more. It transpired that the customary 

 allowance for wind-pressure made by English 

 bridge - builders is much less than observed 

 maximum pressures, though invariably greater 

 than the allowance made in the iron piers of 

 the Tay Bridge, cind that the only reason why 

 such disasters had not before occurred was that 

 a far greater lateral stability is usually secured 

 than is nominally held in view. 



The new Thames Dock in London, which was 

 called while building an extension of the Vic- 

 toria Docks, but was opened on the 24th of 

 June, under the name of the Royal Albert 

 Dock, is the largest in the world. It was built 

 to provide for the greatly enlarged shipping 

 traffic of London, and to furnish accommoda- 

 tions for the steamships of colossal size which 

 are replacing the smaller vessels for which the 

 existing dock facilities were intended . The 

 improvements were commenced in 1875, with 

 the channel which was begun between the old 

 dock and Galleon's Reach, a work which was 

 only intended originally as a new entrance be- 

 low two troublesome bends in the river. This 

 plan was abandoned in favor of a new dock, 

 which it was foreseen would have to be con- 

 structed before very long, and which would 

 render the expenditure upon the canal in a large 

 measure superfluous. Instead of the depth of 

 27 feet, as was intended for the canal, the 

 depth of 30 feet was seen to be necessary in 

 the new dock to accommodate such vessels as 

 the Orient. The new dock is connected with 

 the Victoria Dock by a channel 80 feet wide. 

 At its lower end it has another entrance, com- 

 municating with the Thames through a largo 

 basin, connected with it by a lock, and con- 

 nected by another with the river. The new 

 dock and the old one run in one straight line, 



