the gateshead millennium bridge

P A P E R : C l a r k / E y r e

G. M. Clark, BSc (Eng), ACCI, CEng, FlCE Gifford & Partners

J. Eyre, BA (Hons), AA Dip Arch, RIBA Wilkinson Eyre Architects

Keywords: footbridges, innovations, case studies, curved, site investigation, design, construction work, parabolic arches, foundations, moveable, steel

Fig 1. Tyne Bridqe

Fig 3. Location plan

Evening Meeting An invited paper to be presented and discussed at a joint meeting of the Institution of Structural Engineers and the Royal Institute of British Architects at RIBA, 6 6 Portland Place, London W7, on Tuesday 2 0 February 200 7 at 6pm.

The Gateshead Millennium Bridge

Synopsis The Gateshead Millennium Bridge is a unique tilting opening bridge fvrpedestriuns and cyclists, spanning some loont a c m s the River !@ne in the northeast of E n g M close to the famous Bridge.

collaboration in a design competition, wd the planning andpnxurementpnxess is outlined

!&?paper describes the design from concept through development and analysis and explains the design criteriacuhptedfvrstaticananddynumikcorulitions. Consfmciion of the various elements of the bridge is explainecE, as are the proposals fir emtiom

Introduction and context Anthony Gormlefs majestic ‘Angel of the North’ sculpture has sparked public awareness and strengthened Gateshead’s iden- tity as being distinct from that of its more famous neighbour a m the Tyne. Newcastle is perhaps best symbolised by the &e quently seen view of the iconic Tyne bridge, instantly mgnis- able as a form, later seen again spanning Sydney Harbour (Fig 1). Historically, Gatahead has been an industrial area and is only now beginning to shed its junior status, the focus for the intended transformation is on the quayside on the south bank of the Tyne. Here Gateshead Metropolitan Borough Council is putting imaginative plans into action to create the dehitive cultural centre for the whole Tyneside conurbation. Central to these proposals is the new Gateshead Millennium Footbridge.

The River Tyne has six major bridges in the central city area, many of which have major historical roots.

The Tyne Bridge itself, opened in 1928, was designed by Mott, Hay &Anderson. At the same time, the Sydney Harbour Bridge was built to an almost identical design. Armstrong‘s Swing

It was the result of an mhitectlenginer

Bridge @ig 21, the only existing low level bridge, was opened in 1876. The high level bridge (Fig 2), a doubledeck rail and road bridge designed by Robert Stephenson, was opened in 1849. ”his illustrates just some ofthe signiscant engineerjngpedigree of the Tyne Bridges.

In the mid-1990s Gateshead Metropolitan Borough Council conceived plans to regenerate the riverside and what had become derelict and disused areas of adjacent land (Fig 3). The north bank in Newcastle had already begun to regenerate, and a vibrant riverside was emerging with bars, cafks, offices, and apartments. With the opporhmities offered by the prooeeds of the

I Fig 2. High level bidge and S w i n g Bridge 1

I”,

Natiod Lottery to fund deserving project proposals, the Council conceived the idea of a new low-level opening bridge across the river, for pedestrians and cyclists. The bridge would form a fun- damental part of the p h e d Gateshead riverside developments by providing a link at a low level, a function crucially missing from the existing high level bridges, apart from the swing bridge some 60Om upstream.

The Council was aware that the UK Government had established the Millennium Commission with funding from the National httery. Its main aim was to provide hancial assis- tance to projects in the UK designed specifically to celebrate the Millennium Year 2000.

The types of project suggested by the Commission as being suitable for consideration were diverse, ranging from arts, local funding for village halls, national projects such as the Millennium Dome at Greenwich, science and study centres and exhibitions, and a number of bridge proposals.

To be considered for funding or support, the projects had to have something special, and many proposals were rejected. Common themes predominatd the proposed bridges were innovative and more adventurous than just the result of an exami- nation of pure function; many were the result of collaboration between architects and engineers, producing designs that, through competitions, were more elaborate and visually exciting than might otherwise have been cons idd . Cost, as always, was an issue but always to be considered in the light of the greater value that higher quality designs offer to the environment.

With the use of public money, it was generally a requirement that the design of Millennium Commission-funded projects were open to competition. In the case of the Gateshead Millennium Bridge an open call for firms to register and express interest in

30 The Structural Engineer . Volume 79/No 3 6 February 2007

the project permitted a prequali6cation process whereby teams with proven experience were shortlisted to participate in a design competition.

The design competition and concept design Gateshead Metropolitan Borough Council invited six prequdi- fied teams to submit design proposals in response to a specific design brief for a low level opening bridge about 400m down- stream of the Tyne Bridge. The briefwas demand&. It required a bridge to open to shipping to provide 25m of headroom over a notional 30m wide ~ ~ i g a t i ~ n a l channel, yet link the quaysides at only about 4-5m above river level and not include any construction on the quays themselves.

The new bridge would provide cross-river access for pedestrians and cyclists between the regenerated Newcastle Quayside and the proposed redevelopment on the south side in Gateshead. Here there were ambitious plans for a new arts centre (as in London, at the "ate Modern, also a conversion of a disused build- ing, in this case a former flour mill) and a brand-new music centre, together valued at over da12Om. "he music centre was sub- sequently put out to international competition, and the winner's proposals are under development.

The proposals for the new bridge by the six teams were scru- tinised by the judging panel, and the chcsen winner, after public consultation, was the design by engineers Gifford & Parhers and architects Wilkinson Eyre (Figs 4 -7).

The site requires a span of over loom, and the design provides

..y J. Image

Control barriers

3 K ?l e Bridge

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1 Plan Fig 5.

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n n W

The Structural Engineer Volume 79/No 3 6 February 2001


a simple but innovative and adventurous solution in the form of a tilting bridge formed of a pair of steel arches, pivoting from a common springing point within concrete pilecaps. It can be com- pared in the way it operates, with the raising visor of a motor- cyclists helmet, or the opening of an eyelid. The whole 80Ot bridge rotates and opens to allow passage of ships underneath. In this respect it is unique but simple. The operating system has hydraulic jacks which push on a steel paddle from underneath a pivot point and rotate the bridge as a whole (Fig 8). In the open position the connecting suspension cables are horizontal and hold the pair of arches together.

Initially, the concept was developed from the idea of curved deck, the elongated ~ t u r e of which would improve gradients, but also make for a more interesting passage across the bridge. The idea had been that the curved deck would be countered and supported by structure leaning back the other wax perhaps of a suspension type. "his was soon found to be impracticable, and the clearer concept of a curved deck tied to, and balanced by, a naturally curved arch was pursued. Apart h m the potential for drama and spectacle in the opening operation, the attraction of the form is also in the vast space that the con6guration of deck, arch and cables would enclose, engaging with its surroundings in a wholly new way.

There is a s h n g logic for the curved footway of the bridge, since the maximum gradient specified would not have achieved enough headroom over the river if it were a straight crossing deck, without reducing the thickness to virtually nothing.

The context of historical bridges idormed the choice of an arch structure of a visibly simple form, refined using high strength steel and spanning the river as elegantly and lightly as it could. "apering of sections was intrcduced to enhance the elegance.

The in-plan curvature of the deck provides a functional solution to obtaining the required headroom under the bridge when in use by pedestrians and also responds to a circular route for pedestrians to walk the Newcastle Quayside, cross to Gateshead, and return to Newcastle by the only other low level bridge: the Swing Bridge just upstream of the Tyne Bridge.

The resulting form of an opening eyelid or visor is orientated to welcome river vessels into the city riverside.

Site investigations and planning Following announcement of the winning design in February 1997, the proposals were presented to the Millennium Commission for consideration of fun-, this was successful, and the bridge was chosen to be a Millennium Commission Funded Project, in this case achieving a 50% award of 59.3m.

Site geotechnical investigations were put in hand. Geotechnical desk studies had anticipated that foundations would need to penetrate riverbed silt, sands and gravels, and weathered mudstones, before reaching suitable foundation strata within the coal measures rock strata, comprising mudstones, siltstones, and sandstone.

The site drilling revealed strata largely as expected, but the position of some coal seams would innuence chosen depth of pile founding levels. Choice of foundation type would be discussed with the contractor who was to be brought 'on board' into the team for delivery of the project following a competitive procurement process (Fig 9). In parallel, the Council made the necessary representations

and consultations to achieve planning approval for the projwt and discussed further the fund& and technical requirements of interested local statutory authorities. The Port of Tyne Authority became key to this in that a requirement to prevent potential shipping impact with the bridge outside the 3Om-wide ~ ~ i g & i ~ ~ l channel emerged.

The unique and complex nature of the project led to a desire to appoint a ' p r e f d contrado? at an early stage, to enable and benefit from their input into the development of the design. It was decided to adopt a NEC target cost contract and, following prequali6cation and second-stage interviews with conhctnrs, Harbour & General WorWolker Stevin was appointed. Design development then brought into play preferred subantractors for steelwork and M&E (Watson Steel and Kvaerner Markham) following similar quali6cation processes in conjunction with the -

31


Fig 6. Elevation A-A

Y/AT

Approx. bed level

E Bearing

Elevation A-A

Fig 7. East elevation

Parabolic fabricated steel arch

Outline of parabolic steel

Reinforced concrete

Piled foundation

East elevation

main preferred contractor. Over a period of about 12 months the design was developed

and target cost established. A partnership joint management team ~JIVIT) was established, comprising Diredors from client, contractor, engines, and architect, and agreement was made that all key project decisions would be referred to the JMT Trial piling was carried out, and the preferred contracto?s costs were paid. Finally, in April 1999, a formal construction contract was agreed following approval of a Transport & Works Act Order by the Secretary of State.

Fig 8. Structural design Opening AnalysiSldesigncrite?.iu

32

The unique form of the proposed bridge, as a supporting arch and flat deck section, which would transform on opening into a pair of arches, needed very careful analysis. Key issues identikl at an early stage were the dynamic behaviour in wind and pedestrian conditions and response of the structure during opening operations. Investigations were put in hand for wind tunnel testing at the University of Western Ontario under several different wind directions and bridge opening positions, and a pro- gram of analysis for the potential interaction of hydraulic systems with the bridge structure was commenced by Kvaerner

The aerodynamic testing was comprehensive and quite con- clusive that the structure should prove to be stable in design wind speeds up to 6 W s in service.

"he hydraulic interaction analysis has not yet been totally concluded but is aimed at prwing satisfactory operation at 4min to open in wind speeds up to 14ds with emergency operation in wind speeds up to 25ds. Acheck on pedestxian comfort has been &ed out for wind speeds up to 20 d s .

Requirements of the Port of Tyne emerged late in the design process, and criteria were imposed such that a vessel collision protection system WCPS) comprising floating booms had to be designed and installed to cater for impact from 400Ot vessels. This had significant cost and visual implications which the proj-

The Structural Engineer Volume 79/No 3 6 February 200 7

Markham (Fig 10).

P A P E R : C l a r k / E v r e

North South ,Newcastle quay wall Gateshead quay wall

5

0

ii -10 0 E v

Coal measures

Fig 9. Cross-section ectteamtriedhardto~elioratebutcouldnot,inthefaceof~ch harsh requirements (Fig 11).

The design conditions for the d&arch structure proposed by GifFord allow for accidental severance of a cable, for whatever reason, perhaps h m vandalism or undetected corrosion, in that it should not precipitate ultimate collapse. This is a significant design condition for arch and deck.

The detailed analysis of the global structure was carried out on a h i t e element model, and local analyses included shell models of cable attachments (Fig 12).

Foundations The geotechnical investigations had revealed the presence of several coal seams and, because of the potential for mining fissures and voids, a decision was taken to carry out probing and grouting prior to the construction of bored piles.

(in consultation with the preferred contractor) as being the most Wind tunnel suitable technique to penetrate potential obstructions and provide the leaskisk option. Large floated-in caissons were considered, to be founded on

the gravels, but were rejected for cost reasons. Driven piles were rejected because of potential vibration problems which might have affected the emtmg quayside structures.

The main foundation structures were to be positioned in the river, and the resulting short linking spans to the quayside were designed to cantilever from them in order to minimise loading onto the old quay walls.

Arch, stuys, and deck Theparabolicarchsectioncomprisesa~~shapedsectiontaper- ing in both plan and elevation. It is fabricated h m steel plate up to 35- thick and is internally stiffened both longitudinal- ly and transversely. The section also contains the upper anchorages for the staycables which are hemispherical inserts orientated into the plane of the staycables @'g 13). W d to the arch, the connection of the spiral strand stay-

cables is by traditional open-forkended sockets. Attachment lugs on the arch are seated in the hemispherical recesses and connect through onto diaphragm plates and stiffeners within the arch. The 18 staycables are formed h m galvanised wire and have an adjustable anchorage at the connection to the deck where they pass through a cylindrical hole within which the anchorage plate is bedded.

The deck is also parabolic in elevation and, being curved in plan, presents a most complex, geometricaly warped shape (Fig 14).

The main element is of steel box construction, tapering in plan h m the quayside towards the centre of the river. The box section accommodates the staycable anchorages in elliptical recesses accessed from the soffit, and is sized to enable any stressing of the cables to take place h m this location. The upper surface of the box will be coated with a non-slip epoxy coating. Fromthesteelboxarecantileveredtransversesteelbeamsat

about 3m spacing which radiate outwards mund the curve and

Large diameter bored piles were chosen for the foundations Fig 10.

Fig 11. VC PS

Fia 12.

cycleway is of constant width over the length of the bridge and is about 3OOmm lower than the adjacent footwax thus enabling

' the different required parapet heights to be accommodated uni- formly across the section.

The two elements, cycleway and footwax are co~ected at intervals by a series of steps and separated between by an integral seating arrangement, so that bridge users can pause to enjoy the spectacle of the views of the riverside.

Lighting Lighting is incorporated into the deck within purpose-made recesses, and computerantrolled spotlighting of features of the bridge is proposed. Deck lighting makes use of long- life U D luminaires, deployed such that the deck is lit at low level. The controlled lighting makes use of Trideon' fittings which incop rate motordriven dichroic filters, combining to emit strikingly pure colours that can be changed rapidly. It is envisaged that the new bridge, together with the regenerated quaysides on both sides of the river, will become a focal point for cultural activity

Newcastle bank /

I F =

Gateshead bank

4.5m

I I Lzz# MLWS -1.8m

Low tide (at LAT) High tide (at HAT)

support a lightweight aluminium deck to cany the cycleway. The FE midel


P A P E R : C l a r k / E v r e

Fig 13. Arch

Fig 14. Deck

Fig 15. Paddlehams

and gatherings; hence the ability to make use of light to enhance the sculptural forms of the structure is seen to be an important opportuni@.

Mechanical and electrical The arch and the deck unite at each end where they converge about a transverse cylindrical trunnion sh&, supported at each end by spherical bearings. From this cylinder extends down- wards a substantial fabricated steel paddle to which the hydraulic rams are conneded (Fig 15).

To open the bridge, the groups of double-acting hydraulic cylinders mounted horizontally in each pilecap, below deck level, thrust against this paddle, forcing the whole structure through

of the riverbed to provide a flat, relatively silt-free area at each of the two main foundations. Plans to dredge the material and take it out to sea were frustrated by refusal of a license from the Ministry OfAgnculture, Food & Fisheries on the basis that some contamination existed as revealed by the site sampling. The project team had anticipated that disposal at sea would be accepted and were surprised that levels of contamination low enough for the material to be accepted for domestic gardens was rejected. The need to take the dredged material to landfill caused some delay and additional cost.

F’iled foundation construction followed. Some 14 large diameter bored piles (1.5m diameter) were constructed, formed of a rock socket into the coal measures. Construction required sub-

the required angle of about 40 of rotation and imposing forces stantial chiselling of hard layers. The piles were formed within of about lOOOt at each end. temporary steel casings h m floating piling plant.

Since the structure is only partially balanced, static cylinder At the same time, construction of steel fendering piles for the loads change from compressive, at commencement of opening, VCPS was progressed. These were designed to cany floating to tensile as the centre of mass of the bridge passes through the booms, collared to the fixed steel piles in a sand socket which vertical plane to the fully open position. Acceleration forces and would yield at a design level just below river bed. wind forces on the structure produce additional positive or neg- ative loads on the cylinders. Substructure and temporary works

Each group of cylinders is operated by an independent, hydraulic powerplant housed in machine moms located within the pilecap, and separate rooms are provided for electrical switchgear. For each opening and closing movement, the elec- tronic control system produces a programmed sequence of acceleration, controlled speed, and deceleration, initiated from a remote operating console and accurately synchronised between each of the two pilecaps to avoid twist of the bridge.

Construction Foundations and VCPS Preparatory work for foundation construction required dredging

On completion of bored pile construction, large sheet-piled cofferdams were installed, followed by installation of internal prop ping, bracing and then cleaning of the bed by airlift and pour- ing of a 2m-deep underwater concrete plug. Once these 2000m3 pours were cured, dewatering was carried out and the pile tops were revealed for cutting down. Following this the foundation cap reinforcement was fixed and the first main structural concrete pours were placed.

The two main reinforced concrete foundation structures are deceptive in their enormity and complexity Within the sheet piled cofferdams each concrete pour gradually progressed upwards with curved, tapering fair-faced concrete surfaces on the outside, and the inside formed to accommodate plant rooms, stairway access, sumps and the main hydraulic ram facility beneath the trunnion bearing housings.

The casting-in of the main holding-down bolts for these required accuracy to within 3mm over the width of the river, to match the superstructure steelwork being fabricated and avoid locking in excessive distortion.

Within the various concrete pours, carried out over a period of about 12 months, all the various ducting, box outs, access holes, doorways, recesses, etc., were formed, for installation of the services for mechanical & electrical operation equipment.

Steelwork fabrication Meanwhile, the contract for the steelwork fabrication and erection had been awarded to Watson Steel, based in Bolton. The developmental nature of the procurement process, and the contract on a partnering basis, facilitated discussions with Watson

7 Bearing . \ P End support

34 The Structural Engineer Volume 79/No 3 6 February 2001


Steel to improve the design details to minimise cost. No one underestimated the complexities of the warped, tapering sections, and this had been a key issue in the JMT partners’ choice of Watson Steel as steelwork subcontractor. During the negotia- tion stage they presented a scaled section of the arch steelwork to demonstrate their understanding.

Planning and production of fabrication drawings progressed, and the arch was to be made in 9 segments, each proportioned to be handled in the works and able to be transported by road. Similarly, the main bridge deck section was to be fabricated in 13 parts, to be later joined by welding, and the cycleway cantilever section added on installation.

Welding of the deck proved to be very intricate. Viial ly all parts are extensively stiffened, and the small available spaces were a real challenge to the welders. Geometrical fitting of the various segments of the bridge had been computer calculated and translated into detailed fabrication drawings.

Mechanical & electrical As part of the package for mechanical & electrical services, it had been decided to adopt a procurement process to require the contractor to subcontract detailed design and manufacture. The project partnering board ( J M T ) considered several offers advised by Bennett Associates and chose Kvaerner Markham (KVM) to provide these services.

The design was contracted by Gateshead Metropolitan Borough Council as a separate contract direct with KVM which included the requirement to carry out detailed dynamic computer-modelling of the systems to prove satisfactory interaction. The structural design team were anxious to ensure that the hydraulic systems would not cause any resonance or impose unacceptable dynamic stresses on the structure.

The bridge requires systems to open it that could push and pull, because the centre of mass passes over the pivot point during opening. Ram loads could change h m 10 000 kN push to 4500k.N puU during this sequence, in fully operational wind conditions. Various emergency procedures and requirements were stipulated to allow for system failures or adverse conditions.

Synchronisation of the ram systems on each side of the river was vital to ensure that the structure was not adversely twist- ed, and control devices keep the two sets within 15mm of each other.

All the necessary plant and equipment, including pumps, control panels and emergency generators , are housed within the end supports of the structure. Main power is supplied fhm a sub- station on the south bank and passes through the deck to sup ply the systems on the north side.

Erection Initial plans were that the erection sequence would be as follows: - transport steelwork segments to local work area for joining - weld arch into one piece and attach bearing trunnion hous-

ings and install with floating cranes and temporary guying - join deck segments into three parts and install side ‘thirds’ fol-

lowed by central part supported temporarily on VCPS piles - make site connections, install stays - install and commission mechanical & electrical services.

Design development and enquiries over crane availability led to a revised proposal (which had been considered at concept stage) to assemble the bridge on the quayside and lift it into position as one piece. This plan would remove a great deal of the risk of working over water and shorten the programme for installation by largely completing steelwork fabrication prior to erection.

The various sections of steelwork were delivered by road to the AMEC works at Hadrian Yard on the banks of the River Tyne and the arch segments painted and welded in flat position on a carefully set out support system. On completion, the arch was lifted up into elevational position and the deck segments were moved under it to be joined. The stay-cables hung surreally from the arch, looking for something to support (Fig 16).

The cycleway cantilever beams were welded on, and nosing added. At this stage the sheer scale and elegance of the structure began to be realised, and preparations were in hand for meeting the proposed Wing date of 6 November 2000.

320Ot, is the largest inshore floating crane in the world. The plans to erect the bridge in one piece focused on an available ‘slot’ within its booking schedule and emerged as an option during summer 2000.

Erection methodology proposed needed reanalysis of the bridge structure to ensure that it could accommodate the stresses of this alternative, and conclusions were positive. A 9km trip up river would be involved, and wind, wave and tidal conditions had to be carefidly considered (Fig 17).

Commitment to this erection option was made by the JMT in mid-summer 2000, accepting that the main risk to the client was weather conditions.

Finishes Apart h m the general form of the bridge which impads on the user in a visual way, the hishes of the bridge are the part that the user comes into direct contact with most. These comprise, k t , the deck. For the cycle path this is made up &om a series of aluminium extrusions with integral linking bars. The deck panels are secretly fked down to the steel p u r h below. This surface offers god grip for cycles but is of light construction which is important for the outermost cantilevered part of the deck. With the lightness, the deck also provides a degree of transparency that will be perceived best when the bridge is tilted open and the underside of the deck is fuUy exposed. The main pedestrian deck surfacing consists of an epoxy-bound aggregate system which provides the necessary grip for pedestrians.

Between the two decks,which are at Wering levels, are located a series of benches and metal ‘hedges’. The benches offer the opportunity to pause and reflect on the bridge, admiring views back up to the Tyne Bridge, while the hedges, which consist of formed perforated stainless steel sheet on an internal &ame, offer a degree of protection h m the wind. The parapets are metal and are all-purpose designed. At the ends of the bridge a series of gates are incorporated to control access to permit opening, The two concrete supports to the bridge, built into the river, provide all-glass enclosures, one to be used as a control m m and the other expected to be fitted out in the hture to house events or possibly exhibitions.

Statistics Foundations: 150Omm0 piles #Om Substructure: concrete 7051m3

reinforcement 683t Superstructure: steel 80Ot

180km of equivalent +6mm fillet weld

cost: overall 6i16m per m2 of deck S17 000 of electricity to open 6i3.60

Conclusion The unique design of the Gateshead Millennium Bridge has been a fascinating challenge. The project was chosen to feature on a Royal Mail first class stamp issued on 6 June 2000, which is perhaps indicative that it may itself one day become an icon of the River Tyne.

The design concept is the result of a successll collaboration between architect and engineer, neither of whom would have realised the project without the other.

Gordon Clark is a Director of Gifford & Partners and has been in the bridge business for around 25 years. He has recently been involved in several Millennium bridges. He graduated from Imperial College and gained initial experience with contractors before joining Gifford & Partners. He is Deputy Chairman of fib Commission 1 ‘Bridges’ and is active in much of the national and international development work on grouting of post- tensioning. One of his previous challenges was the new Jackfield Bridge in the Iron Bridge Gorge World Heritage Site.

J im Eyre has been a PartnerlDirector of Wilkinson Eyre Architects since 1987, responsible for managing the practice$ increasing workload of transportation, bridge and infrastructure projects. He has over 18 years experience in architectural practice, including 6 years with Michael Hopkins . Architects. (Photo by James Cant)


the gateshead millennium bridge

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