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THE BRIDGES of
THE TYNE
The Science of
the Bridge
The arch takes
the form of a lattice framework. It is therefore exactly like a
curved beam, is nearly as strong as a solid curved beam of the
same dimensions and has the advantage that it is not so heavy in
itself. At each side of the river the arch is supported at the
bottom CIA oil two steel hinge-pins which rest in horizontal
half-bearings on the massive pier. These four pins have, between
them, to carry the weight of the arch-some 3,500 tons. So they
are very large in size (12 inches in diameter) and are made of
the finest Steel procurable They ensure that crushing forces in
the bridge-arch always pass to flip piers through two definite
points, namely the centres of the pins.
It is well known
that metal expands when heated and that, in building bridges
allowance has to be made for the change in file, temperature as
Winter passes into Summer. Sometimes this allowance is made by
means of sliding ends, but in the new Tyne Bridge the ends are
fixed, and it is the shape of tile arch which varies very
slightly to allow for the expansion and contraction as the
temperature changes. The topmost point of the file arch will be
several inches higher in Summer than in Winter.
The piers rest on
solid rock, are 84 half feet long and 28 feet wide, and are sunk
to about 75 feet below quay level
The roadway is suspended from
the centre of the arch by steel tie-rods (made to resist a
" pulling " force) and to the bottoms of these
tie-rods are fastened cross girders. These cross girders may
easily be seen from the Quayside. At the ends of the arch the
roadway is supported by cross girders held up by steel columns
(made to resist a " crushing " force) and fixed upon
the steel arch, The cross girders in this case are fastened to
the tops of the steel columns.
The approaches,
to the arch on both sides of the river consist of long
plate-spans resting on tall, steel supporting pillars. Cross
girders are secured to these plate girders and carry the roadway
at these parts of the bridge.
Electric lifts are
fitted on the Newcastle side of the bridge to transport
pedestrians from quay level to bridge height.
The following
statistics, relating to the size of the bridge may serve to show
the magnitude of the task undertaken in bridging the Tyne with a
single span, dimensions below :-
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