NSC
October 19
Numerous challenges were
overcome during the design
stage for the Chiswick Park
Footbridge; a new three-span
arched structure that connects a business
park with Chiswick Park Underground
Station.
The team had to incorporate a
dominant 45m-long span over Network
Rail Overground lines with the necessary
design constraints and approvals; allow
for a restricted landing site at one end of
the bridge that includes a 4.5m drop in
level; and include a minimum road height
clearance for double decker busses in the
central span.
Added to the above, the bridge had to
curve along its entire length and be built
in a complex urban environment, hemmed
in by train lines, roads and residences, as
well as the adjacent Gunnersbury Triangle
Nature Reserve.
According to Expedition Engineering
Project Manager George Oates, the use of
steel was instrumental in the successful
delivery of this bridge, as construction of
the scheme in an alternate material would
simply not have been possible.
The curved nature of the deck and
arches required parametric modelling to
create geometry and analysis models, in
turn creating the geometric definition of
every single steel plate in a format that was
passed directly to steelwork contractor
Severfield for the basis of its fabrication
model.
A lightweight solution was also needed
to ensure that the 45m-long Network Rail
span could be lifted into place from nearby
Chiswick Park. The span was fully fitted out
and incorporated a steel deck, which was
considered to be lighter than a concrete
alternative.
The arch was designed as a network arch
(close-centred crossed cables), as this is
said to produce a highly efficient structure,
one that acts as a stiff mesh to control
pedestrian dynamic effects and enables
the bridge to be slender. This is said to be
only the second network arch footbridge
constructed in Europe.
“The construction of network arch
bridges can be a complex undertaking
due to the numerous cables involved. At
Chiswick Park the stressing of the cables
was achieved via a self-stressing sequence
using the self-weight of the bridge, rather
than a more conventional multi-pass
stressing procedure using tensioning jacks.
This saved considerable time and effort,”
says Mr Oates.
The bridge is designed and built
around whole life costing. This lead to
all materials being chosen for maximum
lifespan and minimum maintenance
requirements.
Chiswick Park Footbridge
“Weathering steel was used as it offered
a 120-year life span for the structure,” says
Severfield Assistant Project Manager Stuart
Haslam.
“Steel provided the necessary strength,
while also satisfying the architect’s
vision for a slender footbridge that
blends perfectly into the business park
environment.”
Meanwhile, stainless steel was used
for the hanger cables due to the material
requiring less maintenance compared to
more standard zinc galvanized cables.
Stainless steel was also used for the
architectural metalwork to minimise
maintenance and for its visual appeal.
In summary, the judges say brilliantly
conceived, beautifully made and
ingeniously erected, this project provides
not only a much-needed physical link for
the community, but also a remarkable local
landmark.
25
C O M M E N D A T I O N SSDA 2019
© Jill Tate
FACT FILE
Architect:
Useful Studio
Structural engineer:
Expedition
Engineering
Steelwork
contractor:
Severfield
Main contractor:
Lendlease
Client: Blackstone
A three-span arched footbridge provides a key
pedestrian link between a west London business
park and a local underground station.
/Bridges
/Design_for_steel_bridge_construction
/Modelling_and_analysis
/Steel_construction_products#Flat_products_-_plates
/Design_for_steel_bridge_construction#Modelling_the_structure
/Design_for_steel_bridge_construction#Modelling_the_structure
/Bridges#Arch_bridges
/Design_of_steel_footbridges#Dynamic response
/Weathering_steel
/Design_of_steel_footbridges
/Steel_construction_products#Stainless_steel_products