final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 111
versal column s standing on the permanent pile caps (the foundations) of the
bridge piers. The 33 in x 11 ½ in universal beams were at 3 ft 4 in centres and
their top flanges supported the outer legs of all the trestles. Inner trestle legs
were supported on numerous 8 in x 4 in x 17 in RSJs placed at intervals
between the beams.
Forkheads with 2i in diameter jacking screws were fitted to the top of the
trestles. The uprights of the trestles were of 4 in diameter tubes with telescopic
sections inserted at their bases and mid heights, perforated by l l in diameter
holes at approximately 4 in centres to receive 1 in diameter steel fixing pins.
Thus the height of the trestles was adjustable by means of the forkheads and
the perforated insert tubes within the main trestle members, which were actuated
by hydraulic jacks fitted on the outside of main members. Fine adjustments of
the trestle heights were generally made by means of tapered steel plate clamps
bearing against the fixing pins in the perforated legs.
In order to distribute the load carried by the 26 trusses over 16 pairs of forkheads, each end of the trusses rested on a two-layer grillage of steel beams
placed on top of the trestles. (See page 114). Each upper layer of this grillage consisted of header beams of 10 in x 10 in x 49 lb universal column sections,
with special bearing pads 12 in long x 12 in wide on the top flanges. the upper
surfaces of which mated with the rocker bearings of the trusses. These bearing
pads were either tack welded, or clipped by bolted steel flats, to the upper
universal column sections. The latter were supported on short lengths of 12 in
x 6½ in x 31 lb universal beams at right angles to the 10 in x 10 in x 49 lb
header beams, and spaced generally at intervals of approximately 3 ft 6 in
along the top of the trestles either side of the river and rested in the trestle
forkheads at 2 ft 4 in centres. Short lengths of 5 in x 2 i in rolled steel channels
were fitted inside the forkheads to centralise the 12 inx6½ inx31 lb universal
beams over the backing screws. Tapered timber packings were also used with
the centralising RS channel pieces, to fix the beams in position.
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Span which collapsed
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NOTE
Piers alongside river shown only
General Site Plan
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Approx 93' between piers
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112
Loddon
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