R G Carter Drayton »

Jarrold Bridge

Norwich

Introduction:

Jarrold Bridge was commissioned to provide a pedestrian and cycle link from the new St James development to the heart of historic Norwich city centre in Norfolk. The primary design concept was to create a bridge that traced a sweeping arc across the river, appearing to float over the water.

Details:

The project’s brief was to create a structure which enhanced the river, making the most of the views of historic Norwich while causing minimal impact to the natural environment.

The completed bridge is just over 80m in length and sweeps across the water in a dynamic curve, appearing to float with little visible means of support.

The curvilinear 3D geometry follows the most efficient path between the two landing points and simultaneously accommodates clearances for both river traffic and the riverside’s cycle way without ever being steeper than 1 in 20, thus meeting high standards of accessibility.

Features:

The bridge has been engineered around a curved primary box beam which carries cantilever supports for the decking.  The bending and torsion of the deck is resisted using a closed steel box beam.

The main structure is made from weathering steel which has been aged to reduce visual impact and to prevent any future run-off into the river. No applied finishes have been used anywhere on the bridge which reduces maintenance requirements and, therefore, lifetime cost.

The bulk of the deck was fabricated offsite and craned into position which reduced disruption to the river banks. The positioning of the bridge was timed so not to disrupt a local river cruise operator and was completed in a matter of hours over two days.

Our Commitment:

One of the major concerns with this project was protecting the river from contamination during construction and for the 120 year lifespan of the bridge. We worked closely with the Environment Agency and the Broads Authority to ensure we were doing everything possible to mitigate environmental risk.

The first stage of the construction involved installing the bridge abutment load-bearing pile foundations. Following extensive investigations we decided to carry out some temporary works to enable the use of a large 50 tonne CFA rig to reduce the number of piles.

Gabion baskets were placed in the river (held in place with scaffolding bars doubling up as hand rails) and back filled with suitable imported crush to create the required working platform.  These were removed on completion, returning the river bank to its former condition. While the piles were bored, sand bags were used to create a bund to prevent any overspill into the river.

A bolted splice connection was developed at mid-span to remove any need for temporary works within the river during installation and the oils used in the piling rig were changed to bio-degradable versions in case of any environmental incidents.

The decking is made with sustainably sourced hardwood and the lighting for the bridge was carefully designed to minimise disruption to the wildlife; the lights cast only onto the bridge to light the way, not into the water, and lux levels have been adjusted to make sure no more light is used than absolutely necessary.

At one point work was halted for a week to prevent disturbing spawning fish and bat boxes, made by a local cub group were placed in the trees surrounding the site.

Awards:

Civil Trust Awards – received the only award in the Eastern Region, which was given for its outstanding contribution to the quality and appearance of the built environment

Considerate Constructor National Site Awards – silver

Institution of Civil Engineers Awards – highly commended  in the Engineered in London category

Structural Steel Awards – highly commended

British Construction Industry Awards – shortlisted for Civil Engineering project of the year

Quotes:

“This bridge is a glorious addition to the many Norwich bridges constructed over the years. It is a sophisticated construction in wood and rusted steel with a very pleasing shape… I believe it will be the Best Bridge built in Britain this year ”

Peter Jarrold

“Careful consideration has been given to the specification of materials which are environmentally responsible, requiring minimal maintenance and should retain their appearance over time. These materials have been utilised in inventive ways to achieve a richly detailed, dynamic and unique bridge.”

Judges at the Civic Trust Awards