A W A R D SSDA 2019
NSC 19
October 19
and lean outwards to produce a dramatic
visual effect, opening up the views from
the bridge of the river and surrounding
landscape.
The arch geometry was devised to avoid
double curvature to facilitate fabrication from
sheet steel, and the triangular shape results in
a much greater transparency, emphasising the
slenderness of the design.
White was chosen as the colour of the
arch as it stands out within the natural
backdrop, while adding to the slender
appearance and giving an attractive profile
along the river.
“The arches support a remarkably slender
composite steel-concrete deck formed by a
steel tray comprising the edge beams and
bottom plate, which was filled with in-situ
concrete after the bridge was installed,” says
Ms Taylor.
“Transverse stiffeners are revealed below
and extend outwards to form the hangers.
This composite construction results in
improved structural behaviour, particularly
from the point of view of dynamic response
and acoustics, but also facilitated easy
construction.”
The flat plate hangers, with expressed
pinned joints at their ends, provide lateral
stability to the arch, enabling greater
slenderness than if wire strands had been
used.
The shortest hangers experience some
out-of-plane bending due to relative
longitudinal movement between deck
and arch. To keep the same thickness and
maintain the desired transparency, which was
a key architectural desire, the designers used
higher grades of steel for these hangers.
Offsite fabrication by S H Structures was
a key factor in the project as this enabled
a high-quality finish to be achieved and
allowed for a trial assembly to be carried out,
ensuring a more efficient on-site build.
“Installation was the most significant
challenge with limited access to the site. This
meant a conventional crane could not be
used and so the bridge had to be delivered
by river,” says S H Structures Sales Director
Tim Burton.
The structure was transported in three
parts by road to a laydown and assembly
yard a short distance downstream of the
bridge site.
The bridge was assembled on temporary
works, before the entire steel structure was
then lifted onto a pontoon, floated upriver
and installed using hydraulic jacks in a
single one-day operation.
The use of steel was key to permitting this
method of installation, which significantly
reduced the time, energy, cost, disruption and
environmental impact of more traditional
methods. All aspects of the project were
driven by the need to simplify installation as
much as possible. This included designing
the parapet to be installed with the offsite
steelwork to provide a safe environment for
all subsequent construction activities on the
bridge deck.
Durability was another important aspect
of the bridge’s design. The careful detailing
of the structure facilitates easy long-term
maintenance. The entire structure is also
painted to a high standard, including the
arches which were designed from the start as
a sealed, painted section.
The ends of the arches have a simple end
plate detail, with a knuckle arrangement,
which allowed rotation during concreting
of the deck to reduce bending effects and
minimise plate thicknesses. This was then
cast into the abutment on completion
to act as a fixed end for live load effects,
avoiding the use of a bearing at these points
for a maintenance-free solution, which is
particularly crucial as they are below flood
level.
The judges say, this elegant bridge
comprises twin steel arches, triangular
in section, with the deck suspended via
inclined steel plate hangers. The result is
a distinctive, slender structure providing
a valuable link between communities and
fitting in sensitively with its environment.
The steelwork is beautifully detailed, and
trial assembly helped ensure trouble-free
installation, using barges on the river,
despite challenging conditions.
FACT FILE
Architect: Knight Architects
Structural engineer: COWI
Steelwork contractor: S H Structures Ltd
Main contractor: Land & Water
Client: Berkeley Group
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/Steel_material_properties#Strength
/Accuracy_of_steel_fabrication#Trial_erection
/Design_for_steel_bridge_construction#Erection_using_cranes
/Design_for_steel_bridge_construction#Transportation
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/Sustainable_steel_bridges#Durability
/Paint_coatings
/Bridge_articulation_and_bearing_specification#Bearings
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