In determining upon the mode of construction, which was the same in the
four designs, Mr. Brunel acted upon the principle which guided him in
all his subsequent undertakings, which was, as he states in his report,
‘to make use of all that has been found good in similar works, and to
avail himself of the experience gained in them, and to combine with all
their advantages the precautions which time and experience had pointed
out.’
He dismissed in a few words the plan of breaking the span into two or
three lengths. This was in his opinion unnecessary, and he computed that
the cost of a pier built up from the water’s edge to sufficient height
above the bridge to carry the chains, would be at least 10,000_l._ For
this reason he recommended the adoption of spans, the smallest of which
far exceeded any up to that time constructed.
In designing the chains, he dispensed with the short connecting links,
which had been previously adopted in suspension bridges, introducing
instead the method now universally used, of connecting each set of links
directly with the adjoining one by means of a pin passed through the
holes of both. The number of joints and pins was thus reduced one half,
and a considerable saving of expense, as well as diminution of weight,
effected.
Another improvement, which diminished still further the weight of the
chains, was making the links in lengths of 16 feet, or nearly double
that of the longest links at the Menai bridge. The chief reason for this
alteration was to ensure a near approximation to equality in the strains
on the different links, should all the distances between the holes not
be exactly equal. This improvement was afterwards carried still further
in the Hungerford Suspension Bridge, the links of which were 24 feet
long.[27]
Mr. Brunel also intended to introduce equalising beams in the supports
of the floor, so that each chain should bear an equal share of the load.
By this arrangement, there would have been comparatively few points of
suspension, and ‘the view of the scenery would not be impeded from the
observer being surrounded by a forest of suspension rods.’
The disturbance of the strains on the links arising from the greater
expansion of the metal of the outer links by the direct heat of the sun,
he proposed to obviate by sheet-iron plates placed on each side of the
chains, but separated from them by a small interval, and thus screening
them from the heat. He did not, however, use this protecting covering at
the Hungerford bridge.
Public-domain text, read in full here on John Shaqi.
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