Page 28 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

of the bridge was investigated and found to be CONSTRUCTION
of a rather minor nature. This has been verified The bridge bearings at pier 11 are fixed so that
2
subsequently by Fransen . In most cases the thermal movements take place over three spans.
lane loading governs the design; however, in the Because of the method of construction, it was
regions of the inflection point a check using wheel necessary to fix the girder in stage 1 temporarily at
loadings was made. This condition was never pier 8. Upper bearing plates were offset from the
found to be significant. pier centre-line by the distance by which the girder

would shorten during construction. Once the centre
The two girder webs with top and bottom flanges pier was reached, the fixity was removed at pier 8.
comprise a large hollow box. Diaphragms 36-in With stressing of stage 3 the three-span bridge
(91.4-cm) thick over each pier are used to transmit moved towards the fixed bearing, and the offsets
the shear forces to the bearings. These are 800- at piers 8, 9 and 10 were cancelled. Subsequent
ton (813-tonne) Andre Rotaflon bearings located bearings on the south side of the centre-line were
at 6-ft (182.9-cm) centres. A nominal transverse adjusted for stressing movements.
prestress is supplied in each diaphragm to control
cracking. As shown in Fig 3 the piers are single 10-ft
(3.05-m) diameter shafts rising from a foundation The temperature was assumed to vary by ± 40°F
supported on 12BP 74 batter piles. The underlying (± 22.2°C) about a construction temperature
material is metamorphosed slate overlaid with of 60° F (15.5°C). This is less than the normal air
glacial till and graded sand, gravel and clay. temperature fluctuation in this region of Canada;
however, the thickness of members is such that the
response of the structure to diurnal temperatures
is quite slow.

The uniformity of the cross-section made
construction relatively simple. A check of cable
elongation, dynamometer readings and jack
pressures during stressing showed that the friction
factors used in design (µ = 0.20, K = 0.0005) were
apparently too large.

Fig 8 H25-S20 truck loads
Fig 7 Moments

The Indian Concrete Journal | November 2018 29