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154 REPORT—1857. 
On the Adaptation of Suspension Bridges to sustain the passage of 
Railway Trains. By C. Vienours, C.E., F.R.S. 
Tue following observations are submitted to the British Association as ap- 
pearing to possess sufficient interest for discussion, from the circumstance 
of differences of opinion amongst civil engineers having thrown doubt upon 
the feasibility of applying the principle of suspension to the purpose of 
railway transit. , 
But the practical success in America of this principle on a large scale 
may be quoted as an example in its favour, and is a striking set-off against 
the failure in this country, which occurred upwards of five-and-tweuty years 
ago, under circumstances which have militated against any attempt to 
repeat the experiment. Some debate on this question took place in the 
Institution of Civil Engineers of London, at a meeting last spring, from which 
many engineers were absent ; and as the subject was on the intended appli- 
cation of a suspension bridge to carry a railway across a navigable river 
in the North of Ireland, a further inquiry may not be wholly uninteresting 
at a meeting held in the Irish capital, where many engineers and other 
practical and scientific men may be present, and who, not having had a pre- 
vious opportunity of joining in the inquiry, may be disposed to propound 
their opinions. 
A further reason for bringing the subject forward, and one which will 
naturally create a more extended interest in the discussion, is, that the recent 
events in India cannot fail to produce, among the remedial measures to be 
applied, a general and a more rapid extension of railways, even to the most 
remote parts of our Asiatic dominions, and in the course of this extension 
many rivers of great breadth must be bridged. 
It is desirable to condense the matter into a few salient and important 
points, and it may be generally assumed that the whole inquiry is comprised 
under the following heads, viz— 
Ist. The maximum load to pass the bridge. 
Qnd. The velocity of the train. And these being given, there are then 
to be determined— 
3rd. The strength of the chains. 
4th. The rigidity of the platform ; which having been duly provided for, 
the additional considerations will be as to— 
5th. Prevention of undulation, vibration, and oscillation. 
lst. Maximum load to pass the Bridge.—This load may be taken as equal 
to the weight of the locomotive engine and tender, and of as many carriages 
as will extend on a single line of railway along the platform of one whole 
opening between the suspension piers ; to the consideration of such a single 
line the inquiry may be confined. 
The length of the train, and consequently the weight on the platform of 
the bridge, will therefore be in proportion to the span or opening. The 
weight of an engine and tender may be taken, speaking roundly, at one ton 
per lineal foot of the railway over which they pass, and the weight of loaded 
carriages at half a ton per lineal foot. For a bridge with a clear opening 
of 400 feet, the weight of a train extending the whole length of the platform 
would average little more than half a ton per lineal foot ; but as it has been 
generally customary to compute the insistent load on railway bridges at one 
ton per lineal foot of single line, this weight will be the one assumed. 
Qnd. Velocity of the Train.—It would be opening too wide a field upon 
the present occasion to inquire into or to attempt to solve the complex 
problem of what additional gravitating effect is produced upon railway 
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