Infinity Bridge
Infinity Bridge or the North Shore Footbridge is a public pedestrian and cycle linkage across the River Tees in the borough of Stockton-on-Tees in northern England. Connecting the Teesdale Business Park and the University of Durham’s Queen’s Campus in Thornaby-on-Tees is built at a cost of £15 million with an estimated 4000 people/day usage. The name derives from the infinity symbol (∞) formed by the bridge and its reflection.
Design and Concept
With a 120 years design life, the superstructure consists of a continuous asymmetrical ‘double arch’ with two spans, the north at 120 m and the south at 60 m. It has a pair of continuous, differently-sized structural steel arches with suspended precast concrete decking and one asymmetrically placed river pier. The tapering arches with a trapezoidal box section are fabricated from weathering steel plate. The arches’ box sections bifurcate on plan over the central pier and are supported by four steel arms. The arms in turn land on two 3-tonne solid machined pieces of high grade steel, forming the central nodes. The deck is made from 7.5 m long precast concrete units, suspended by 30 mm diameter high strength steel cables from the arch. The PC deck units are longitudinally
pre-stressed to form a stiff in plane structural system, which resists lateral wind and translational effects at deck level. A stainless steel and stressed wire enclosure system is used.
The main arch of the bridge is 120 m long, weighing 300 tonnes, and 32 m tall, with its top 40 m above the Tees. The short arch is 60 m long and 16 m tall. The hangers are spaced 7.5 m apart and are made from 30 mm diameter, high-strength, and locked-coil steel cable. Four exposed, high-strength post-tensioned, locked-coil steel-tie cables run alongside the deck and tie the bases of the arches together, pre-stressing the concrete deck sections. The tie cables are 90 mm diameter on the large arch and 65 mm on the smaller. The aggregate concrete deck sections are 7.5 m long and down to 125 mm thick in places, making it one of the thinnest bridge walking surfaces.
The handrails and parapet are stainless steel while the guardrail is made from stainless steel wire. To ensure any bridge oscillation is controlled, the deck is fitted to the underside with seven tuned mass dampers – one on the short arch, and six on the larger weighing 5 tonnes in all. The mass dampers control horizontal as well as vertical oscillations— a feature only required on very slender bridges.
The clearance below the decking on the navigable part of the river is 8 m.
Construction
Constructed within 18 months between June 2007 and December 2008, the Bridge was managed by Balfour Beatty Regional Civil Engineering and steel fabricator Cleveland Bridge & Engineering Company with White Young Green.
At the start of construction, a temporary jetty was built on the south bank to enable the building of a cofferdam for the safe construction of the central pier. In April 2008, the supporting legs were added to the central pier. Steel falsework was constructed in the cofferdam by Dorman Long to support the ends of both incomplete arches as they cantilevered over the river during construction. The first steel arch, made from four pieces of fabricated steel welded together was put in place in June 2008 and was later used to stabilise the cantilevering lower portions of the main arch using a strand-jack and tie cable between the top of the small arch and the large arch and then to reduce sway stress during the progressive construction of the large arch. The final section of the main arch came in four pieces which were welded together on site and all 170 tonnes of it was lifted into place by a 1,500-tonne mobile crane Gottwald AK680, the largest in the country.
The concrete deck panels were cast on site using three steel moulds in temporary sheds in a construction compound on the north bank of the river. Using a short temporary jetty on the north bank the deck, panels were floated out on a small barge and jacked into position, working progressively away from the river pier. The concrete deck sections are held together by steel welds and adhesive.
The footbridge was completed on time and to budget in December 2008 with 530 workers and uses in total some 450 tonnes of Corus steel, 1.5 km of locked coil steel cable, 780 lights and 5,472 bolts and weighs 1040 tons. Almost all labour, materials and components were sourced regionally.
The phenomenon of pedestrian induced vibrations on footbridges is well known, hence extensive analytical analysis was undertaken to identify the structure’s natural frequencies and expected behaviour under a variety of cases. This led to the inclusion of seven tuned mass dampers which were discreetly hung within the soffit of the deck units. Following extensive onsite testing of the final structure the analytical model proved highly accurate and the dampers, once released, were seen to perform as predicted.
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Arch Bridge
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Bicycle and Pedestrian Bridge
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Weathering Steel, Stainless Steel and Reinforced Concrete
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Asymmetric Double Tied-Arch and Suspended Deck
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120 Years
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2007-2008; 2009
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£15 Million
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240 m (787 ft)
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8 m (26 ft)
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1
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Expedition Engineering
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Stockton-On-Tees Borough Council
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River Tees, Teesdale Way
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4000 People/Day (approx.)
Awards
Supreme Award from Institution of Structural Engineers for Structural Excellence 2009, the premier structural engineering award in the UK.
It also won in its own category of Pedestrian Bridges.
The Structural Steel Design Award 2010
The Concrete Society Civil Engineering Award 2009
The ICE Robert Stephenson Award 2009
The North East Constructing Excellence Awards ‘Project of the Year’
Green Apple Award for the environment
Reference
https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.729.8486&rep=rep1&typ e=pdf
https://www.steelconstruction.info/Infinity_Footbridge,_Stockton
https://expedition.uk.com/projects/infinity-bridge-stockton-on-tees/
https://www.oasys-software.com/case-studies/infinity-bridge/
By -
Tuhina Chatterjee, Associate Editor - Civil Engineering and Construction Review
