The Viaduct Works' Handbook
Forfatter: Henry N. Maynard
År: 1868
Forlag: E. And F. N. Spon
Sted: London
Sider: 108
UDK: 624.3
Being A Collection Of Examples From Actual Practice Of Viaducts, Bridges, Roofs, And Other Structures In Iron; Together With Tables Of Prices, Weights, And Other Information Useful To Engineers In Design And Estimating Wrought And Cast-Iron Work
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37
turned by two men walking round upon the centre of the bridge,
thereby setting in motion the pinion which acts upon the fixed teeth
of the lower ring, and causing the bridge to revolve. This bridge
was put together complete before leaving the works, and it was
found that two men could quite easily turn it and cause it to revolve
in a few minutes. It has obvious advantage over the old system of
swing bridges, in which only one span is made to open, and where
a large amount of counterpoise must be added to the weight required
to move.
The total weight of ironwork in this bridge, exclusive of the
cylindrical iron piles, is 874 tons, and taking the price at £19 per
ton f. o. b. an English port, brings the price to £1662 10s., or about
£14 14s. 6Æ per foot run.
A swing bridge of single opening, on the counterpoise prin-
ciple, to carry a single line of railway over a 30 feet opening,
with two main girders, 51 feet long, placed 14 feet 6 inches apart,
with cross girders and roadway at the bottom, weighs 34 tons,
requires 46 tons of cast-iron balance weights, which have to be put
in motion, in addition to the 34 tons of girders and platform, when-
ever the bridge is opened.
A bridge recently made at Crumlin, and erected in England,
by Messrs. Kennard, on the telescopic principle, merits attention in
point of economy of material. It carries a double line of railway
over two spans of 45 feet each, and gives a clear opening of
water-way, when open for river traffic, of 45 feet. The road
is at bottom of the main girders, which are three in number,
the centre girder being strongest, are continuous for 104 feet, and
sufficiently long to reach over two spans ; rest upon rollers, 3 feet
diameter, fixed upon the central pier and upon the edge of the
abutment. To open the bridge, it is drawn back upon the abutment
by means of a chain and suitable crab gear, fixed on the central pier
beneath the bridge; the chain is attached one end at each extremity
of the girder, and takes one turn round the crab barrel, so that any
motion in the crab causes the bridge to move in or out from the
abutment corresponding. It will be seen that before the bridge can
be drawn in upon the abutment, it is necessary to remove a portion
of the rails, in order to allow the bridge to come in; this is done by
the rails over the abutment, and for a distance corresponding to the