Page 18 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

FIRST DELIVERY IN 1942 tension, by means of a hand winch, to remove sag,

The result of the tests made in accordance with the and then secured, also by wedges, to the movable
requirements of the panel of the British Standards or jacking plate.
Institution, were studied by the authority
concerned, and a sleeper to give the required The final tensioning was carried out by four
strength for main-line load conditions was hydraulic jacks which were inserted between
designed and produced, using the same method the steel structures of the abutments and the
of pre-stressing, and was supplied to the L.M.S.R., jacking plate; the load applied was between 60 to
L.N.E.R., G.W.R., and Southern Railway. The first 90 tons depending on the number of wires used
delivery was to the L.M.S.R. in 1942 for installation for two lines of sleepers. When the tension was
in the fast down track at Cheddington. obtained, the last set of distance pieces was left
to support the tension while the sleeper moulds
The Colwall yard consisted of an open concrete were filled with concrete and during the time it set
apron 340 feet long and 30 feet wide with mass and hardened. The concrete was barrowed up to
concrete abutments at each end. The abutments the position of the sleeper moulds, where it was
supported the heavy steel structures, to which the poured and vibrated, using a pneumatic vibrator
reinforcement wires under tension were anchored applied at the top of the moulds.
during the pre-stressing process. High-tension steel
wire of 0.2 diameter, used in the reinforcement of The concrete was cured for a period of 10 to
the sleeper, was first passed through a combined 14 days, depending on weather conditions; the
cleaning and straightening machine. tension in the wires was constant for this period.

It was then threaded through the individual end The sleepers were then detensioned. In this
plates of the sleeper moulds. Each mould, which operation the hydraulic jacks were again inserted
consisted of an open steel trough, had at each end between the abutment, and the movable plate: the
a removable end-plate holed to suit the distribution latter was jacked out a short amount, so allowing
of the wires in the sleeper. the distance pieces to be removed and the jack
plate to return, thus freeing the tension existing in
After the wires had been threaded through the end the wires between the sleepers.
plates, the moulds were placed under the wires and
the end plates secured. During this operation the
wires were made off by wedges to a fixed anchor
plate at one end of the apron and passed through
a similar, but movable, plate at the other end of
the apron.

When the required number of wires had A view of the production lines showing the steel wire
been threaded, for two lines of sleepers to be on reels from which it is led off to the production lines
manufactured, they were subjected to preliminary prior to being stretched to a pre-determined tension.

The Indian Concrete Journal | November 2018 19