Vermont phÅ“nix. [volume] (Brattleboro, Vt.) 1834-1955, 1858-09-11

ritory for the purpose of future immigration,
and by connecting the settled provinces of Wes-
tern Carala with the seaboard States of the
American Union, calculated to afford full scope
for the development of the industrial resources
of that magnificent colony. Without the Vic
toria Bridge the system of communication would
have been maniiestly incomplete. The extern
sive series of Canadian railways on the north
side Of the st. Lawrence, terminating opposite
Montreal, would, for all purposes of through
traffic, be virtually sealed up during the six
month, of the year that the st. Lawrence is
closed against navigation hy the ice and the
Grand Trunk system must necessarily have re-
mained to great extent nugatory, in conSe-
qucnce of the province being cut off from the
coast, to which the commerce Of Canada natu-
rally tends.
The particular kind cf structure to be adopt
ed formed the subject of considerable prelimi-
nary discussion Even after the design of n
tubular bridge had been adopted, and the piers
were commenced, the plan was made the sub
ject of severe criticism, on the ground of its al
legged excessive cost. 1t therefore became nee
cssary for Mr.. Stephenson to vindicatc the pro-
pricty of his design in report to the directors
of the railway. in which he satisfactorily proved
that as respects strength, efficiency, and ccono-
my, with view to pcrmancncy, the plan Of the
Victoria Bridge is unimpeachablc Various
modes were proposed for spanning The st. Law
renee. The suspension bridge, such as that ov-
or the Niagra, was found inapplicablc for 5, ycr-
al reasons but chiefly because of It's defective
rigidity, which greatly limits the speed and weight
of trains, and consequently the amount of traf-
iic which can be passed over such a bridge
Thus, taking the length of the Victoria Bridge
into account, il was found rlat not more than
20 tr5ans could pass within the "A hours, a num-
har insufficient fnr hp accommodation Of fl,
anticipated traffic. To introduce such an amount
of material into the suspension bridge as would
supply increased rigidity. would only be approx
mating to the original beam, and neutralizing
any advantages in point of cheapness which
might be derivable from this form of structure,
without securing the essential stiffness and
strength. Iron arches were also considered in
applicable, because of the large hcadway rcquir-
ed for the passage Of the ice in winter, and the
necessity which existed for keeping the SPRING
ing of the arches clear of the water line. This
would have involved the raising of the entire
road, and largely increased expenditure on the
upper works. The question was therefore re-
duced to the consideration of the kind of ho,i-
so"td beGms or girier to be employed.
Horizontal girders are of three kinds The
1ubuiar is constructed of riveted rectangular
boiler plates Where the span is large, the road
passes within the tube where the span is com
paratiyely small. the roadway is supported by
two or more rectangular beams. Next there is
the Ldtt'ce glrdcr, borrowed from the loose
rough timber bridges ofthe American engineers.
consisting OF a top and bottom tange connected
by number of Hat iron bars riyited across
each other at a certain angle, the roadway rest
ing on the top, or being suspended at the bot
tom between the lattice on either side. One of
the best known specimens of this bridge is the
fine work erected by Sir John Macnei ON the
line of the Doublin and Drogheda Railway, oy-
er the river Boync near the town of Drogheda
its centre span being of 264 feet. Bridges on
uiacitufed in this Gc,oiGGntry fSteRFivaraR Hi
India, and are specially designed with view to
their easy transport and erection. The TrcliiS
or Warren girder is modification of the same
plan, consisting Of atop and bottom flange, with
a connecting web Of diagonal fiat bars, forming
a complete system of tranguaton-hence the
name of Triangular girder, by which it is gen
orally known. The merit of this form consists
in its comparative rigidity, strength, lightness,
and economy Of material These bridges are
also extensively employed in spanning the broad
rivers of India. One of the best specimens in
this country is the Crumlin yiaduct, 200 feet
high at one point, which spans the river and val
le, of the Ebbw near the village of Crumlin in
South Wales. The viadust is about third of
Il lnllt lOilH, ulNlutu ll4lO lNO pdlAS ny llhSN
of hills which runs through the centre of the
valey-each part forming separate viaduct,
the one of seven equal spans of 100 feet, the
other of three spans of the same diameter
This bridge has been very skilfully designed and
constructed by Mr.. T. W. Kennard, and, by
reason of its great dimensions and novel ar
rangements, is entitled to be regarded as one
of the most remarkable engineering works of
the day.
In calculating the strength of these different
classes OF girders,' Mr.. Stephenson observes,
'one ruling principle appertains and is common
to all of them. Primarily and essentially, the
ultimate strength is considered to exist in the
top and bottom-tho former being exposed to a
compression force by The action of the load, and
the latter to force of tension; therefore, what
ever be the class or denomination of girders
they must all be alike in amount of effective
material in these members, If their spans and
depths are the same, and they have to sustain
the same amount of load. Hence, the question
of comparative merit amongst the different
classes of construction of beams or girlcrs, is
really narrowed to the method of connecting the
top and bottom webs SO called In the tubu
lar system the connexon is effected by continu
Gus boiler plates ryited together; and in the
lattice and trellis bridges by flat iron bars, more
or less numerous, forming series of struts ant
ltS. lHcSt cllSIlStIS wiz atNONd AilS WI
ployment of the latter form of construction, SCI
forth as its principal advantage the saving o
material which is effected by employing bars i'll
stead of iron plates whereas Mr.. Stephenson
and his followers urge, that in point of econo
my the boiler plate side is equal to the bars
whilst in point of effective strength andrigidit.
it is decidedly superior 70 show the compare
tive economy Of material, he contrasts the lat
tice grder bridge over the river Trent, on tn
Great Northern Railway near Newark, with tn
tubes of the Victoria Bridge which are now il
course of construction. In the former case
where the span is 240 1-2 feet, and the bridg
l3 feet wide, the weight, including bearing,
232 tons in the latter, where the span is "a
feet, the width of the tube l6 feet, the weight
including bearings, is 275 tons, showing bal
apce in favor of the Victoria Tube OF II tons
The comparison between the Newark Dyk
Bridge and the Tubular Bridge over the rive
Aire is equally favorable to the latter and n
one can have travelled over the Great Norther
t line to York without noting as respects rigidit
under the passing train, the Tubular Bridge
f decidedly superior. 1t is ascertained that tn
DETECTION caused by passing load is considers
q Il