Cathedral Green Footbridge
cranked back span
assistance, thermal assessment, and development of bridge
Green Footbridge is an award-winning pedestrian and cycle
cable-stayed swing bridge in the centre of Derby that spans the
River Derwent and an adjacent old silk mill race. It has a 30m
main span and an 18m cranked back-span that
counterbalances the main deck. The bridge rotates on a pintle
bearing, with a central wheel to support its weight and swings
to one side automatically when the river is in flood. Ramboll used LUSAS
bridge analysis software to assist with the design of the
structure on behalf of its client Derby City Council.
Rambollís competition-winning design
for the bridge is unique in the UK and a novel variation on the
cable-stayed swing bridge form. Its scissor-like shape was partly
inspired by a tailorís shears echoing the heritage of the nearby
silk mill. The end result is a single bridge that spans both the river
and the old mill race (that has now been re-interpreted as a piece of
dynamic modern art) in one economic structure.
The deck is a stiffened plated box
girder, tapering in two directions. Its closed section provides the
torsional properties needed to carry the out-of-balance forces induced
by the geometry of the cranked backspan. Three prestressed cables
support the deck and carry the load back to a 20m high raked
Ramboll used LUSAS finite element
modelling to assist with:
- Design of the deck, cables and mast.
- Thermal performance assessment
- Developing a bridge construction
Because of the riverís flow rate, and
the ability for its level to rise rapidly by up to 1m the bridge was
required to open during flooding so as not to restrict the flow. In a
flood condition, the 90 tonne bridge swings off the river and folds
back into the newly constructed waterfront to Cathedral Green. When in
either of its fixed positions the nose end of the bridge is supported
on end bearings.
In use, the bridge swings utilising a
pintle bearing that is always in uplift and a very large central wheel
which supports the whole weight of the bridge. The tail of the bridge
is held down using a wheel running in a concealed track rather than by
using kentledge as with traditional swing bridges. Despite its weight
but because of its design, the operation of the swing bridge mechanism
can be effortlessly controlled by one person using a specially
designed console, or even be winched to a closed position by hand in
around 20 minutes.
The bridge was officially opened in
A presentation entitled 'The Design of
Derby Cathedral Bridge, a Unique Cable Stayed Swing Bridge' was given
by Steven Wilson of Ramboll at IABSE-IASS 2011 Symposium "Taller,
Longer, Lighter, London, UK. 20-23 September 2011.
to the use of LUSAS on this project.
Other LUSAS Bridge case studies: