SSDA 2018 C O M M E N D A T I O N
26 NSC
October 18
Opened in August 2017, Transport Scotland’s Queensferry Crossing is both the
UK’s tallest bridge and the world’s longest three-tower, cable-stayed bridge.
FACT FILE
Structural engineer:
Ramboll
Steelwork
contractor:
Cleveland Bridge
UK Ltd
Main contractor:
Forth Crossing Bridge
Constructors
Client: Transport
Scotland
Approach Viaduct South,
Queensferry Crossing
Linking Edinburgh with Fife, the new
Crossing stands proud in a unique
bridgescape, alongside its illustrious
neighbours, the Forth Bridge and
Forth Road Bridge (FRB).
The bridge is strategically vital to
Scotland. It was commissioned following
revelations of potential structural
compromises to the aging FRB, which
were uneconomical to repair. The FRB was
susceptible to weather-related closures, with
a huge impact across the region.
On the south side of the crossing the
approach viaduct is 545m long, consisting
of twin parallel continuous composite decks
with steel box sections, supported on six
V-shaped piers.
The approach viaduct comprises two
composite steel box girders, set 21.75m
apart. These are directly connected to the
main span cable-stayed single box section of
the Crossing.
Steel offered the strength, lightness,
versatility, durability and speed, making it
an environmentally sustainable solution. Its
lightness allowed a delivery solution that
minimised any damaging impact on the
estuary banks.
“With steep terrain making way for
mud flats and shallow water on the south
approach, a launched steel viaduct solution
offered a number of environmental benefits,
allowing us to minimise reliance on marine
plant and negate the need for dredging or
temporary causeways that would harm the
environment,” explains Ramboll Director
Steve Thompson.
The viaduct was pre-assembled before
being progressively launched into place,
following the design philosophy for the
entire Crossing; completing complex
assembly offsite. Assembly took place in
an efficient and controlled environment,
keeping work out on the estuary to a
minimum.
The steel twin box girders of the viaduct
were fabricated and pre-assembled by
Cleveland Bridge. The completed girders
were transported by road in halves due to
the width of the boxes.
“Behind the southern approach, we
prepared a 160m long assembly platform
work area. This formed the assembly and
launch area for all stages,” says Cleveland
Bridge Site Services Manager Mike
Condren.
“As there was insufficient space to
assemble the entire length of the steelwork
prior to launching, we launched the east and
west girders independently and alternately
in six stages. This facilitated a rolling
programme of fabrication, segment delivery,
site assembly and a staged installation.”
The approach viaduct steel box weight
is 2,600t per girder with an additional 500t
for installed soffit concrete at pier support
locations for the double composite action in
the permanent installation.
With a further 100t for king post, stays
and associated temporary works stiffening,
the launch weight was approximately 3,200t
per box. Ancillary items such as inspection
gantry rails, internal access ways and MEP
were installed after launching.
Construction of the concrete deck slab
and cantilevers was undertaken in phases.
All main service lines and mainline drainage
are housed within the box. This offers
a cleaner aesthetic while ensuring vital
services can be maintained and repaired in a
controlled environment.
Summing up, the judges say in a
landscape comprising the Forth Bridge and
the Forth Road Bridge, the new Queensferry
Crossing, Britain’s tallest bridge, cannot fail
to impress. This scheme for the southern
approach viaduct embodies the knowledge
in design, fabrication and long‐term
maintenance, in the launching and finishing
the twin box viaducts, from some of the
world’s most accomplished bridge builders.
All images on this page © Transport Scotland
/Box_girder_bridges#Composite_box_girders
/Sustainable_steel_bridges#Lightweight_construction
/Sustainable_steel_bridges#Durability
/Design_for_steel_bridge_construction#Transportation
/Design_for_steel_bridge_construction#Launching
/Design_for_steel_bridge_construction#Fabricating_the_steelwork
/Design_for_steel_bridge_construction#Deck_construction