50 Years Ago
FROM
Using a principle of mechanics
centuries old this new bridge has
been described as a ‘shaduf in
steel’. This design however makes
use of the latest technology to
achieve operating efficiency
with considerable elegance in
appearance. Mr. R. E. West CEng,
MICE, of the Engineering Dept,
Port of London Authority here
briefly describes the structure
which was opened in 1969.
Until 1969 the South Dock Entrance of the
India and Millwall Docks group was spanned
by a double leaf cantilever bridge of Schertzer
pattern. This bridge carried Manchester Road
which is part of the perimeter road around the
Isle of Dogs. However, after forty years service
the bridge was in need of repair, partly from
deterioration of the bearing girders, partly from
damage caused by ships colliding with the
footway and main girders and also because
the motors and switchgear had reached the
end of their useful lives. Various design studies
were completed to examine the economics of
repairing the existing structure or building a
new bridge and the cost difference was so little
that the decision was made to go ahead with
a new installation at a cost of about £250,000.
The existence of massive concrete foundation
blocks for the double leaf bridge influenced the
choice of structure and enabled considerable
economy to be made in the civil works.
30 NSC
May 20
The selected design is of a counterbalanced
drawbridge type similar to those traditional to
Holland. However, Manchester Road bridge
is on a larger scale and is believed to be the
biggest bridge of its type anywhere. The line
of the road has been maintained and its new
slightly elevated profile has been graded down
to meet the existing levels. Manoeuvring a ship
through a lock entrance is not easy, particularly
when there are strong tides or high winds. For
this reason the towers have been sited on the
south side of the entrance as experience has
shown this to be the less vulnerable position.
The bridge span of 110ft is greater than the lock
entrance so that when it is raised sufficient width
remains on the quay to work ships through. The
roadway is 25ft wide, thus providing two lanes
of traffic and there are two 7ft 6in footways.
‘Verynyl’ PVC tiles are bonded to the steel deck
to provide the road surface and crash barriers
protect pedestrians from vehicular traffic.
The particular type of bridge consists of
a few large components and these were
assembled by site welding prefabricated
sections together in an erection yard at the lock
side. The towers are held down by anchor rods
which were grouted into holes drilled into the
existing concrete foundations. All parts of the
bridge were raised to the open position within
a few hours of erection so that no obstruction
was caused to ships using the dock.
The superstructure is welded throughout
and in general is fabricated from steel to
BS 2762 ‘Notch Ductile Steel for General
Structural Purposes’. Since the racks operate
on the sides of the deck structure they
impose considerable torsional loads which
are efficiently resisted by the closed cellular
structure. Local point loads are resisted by
Universal Beam stringers while the hangar,
rack and main trunnions are supported by
integral transverse boxes. The orthropic
Building
with Steel
May 1970
MANCHESTER ROAD BRIDGE
Main sections through structure