Design Awards: 2001

The Wellcome Wing, The Science Museum, London

The Welcome Wing, The Science Museum, London

Architect

MacCormac Jamieson Prichard

Structural Engineer

Ove Arup & Partners

Steelwork Contractor

William Hare Ltd

Main Contractor

Kier Build Ltd

Client

National Museum of Science & Industry

In 1995 the Trustees of the Science Museum decided to extend the museum to provide additional exhibition space and a 3D Imax cinema. A design competition was held, which was won by a team comprising: MacCormac Jamieson Prichard, Ove Arup & Partners, and Davis Langdon and Everest. The winning entry offered a building with spectacular internal spaces which occupied a little over half of the available site and left space for a further building on the Queens Gate frontage.

Funding has been provided by the Wellcome Trust and the Heritage Lottery Fund.

The competition concept was for a building supported by two rows of columns, 30m apart, about which were pivoted gerberettes – double cantilevered steel beams, which supported steel floor trusses at their inner ends, and were restrained by tie downs to the ground at their outer ends. The museum’s brief required a 5.5m clear height on the exhibition floors, and this system reduces the effective span of the main trusses from 30m to 25m with a corresponding reduction in depth.

The structure has a basement constructed in watertight reinforced concrete supported on bored piles founded in the london clay.

In the four corners of the building are reinforced concrete stair and lift cores which provide horizontal stability. Between the cores are the main building columns, 110 x 750 reinforced concrete, which carry the marjority of the building load. There are six pairs of columns, 30m apart, on an 8.5m grid in a east/west direction. They sit 5.5m inboard of the facades on the north and south sides of the building. These main columns span vertically from ground floor to roof level, and the roof slab acts as a beam carrying wind loads and stability loads back to the cores.

The gerberettes extend to the north and south faces of the building where they are held by a vertical “tiedown”. The tiedown connects each gerberette on a column down to ground floor level, where the tie force is transferred into reinforcement bars cast into the retaining wall and thence to the foundations. CHS sections are used for the ties, rather than rods, as they are in compression in the temporary condition during erection.

Gerberettes are positioned at the same levels on each column, at a constant dimension below each exhibition floor. The main exhibition trays are supported by 25m long trusses, which span directly between pairs of gerberettes. Gerberettes are pinned to the columns and to the ends of the main trusses, so that this basic framework is statically determinate.

The floors comprise 150mm dense concrete on Holorib decking acting compositely with cellform secondary beams at 2.54m centres. The cellform beams span 8.5m between the main trusses and at the front and rear edges of the floors they cantilever 3m beyond the trusses to enhance the impression of the floors floating in the space. The upper exhibition floors only connect to the rest of the building on their north and south edges. On their west side, they stop 3m short of the west wall. On their east sides they stop 6 to 10m short of the underside of the Imax structure, providing a diagonal slot from the ground floor 32m up to the roof which enables the visitor to see the floors and Imax within the overall internal space of the building.

The regular spacing of the gerberettes which support the exhibition trays is maintained for the Imax gerberettes. However the Imax cinema has a more complex arrangement of floors, with floor trusses required both a various levels and beween main column lines. In order to connect the trusses to the gerberettes, the inner ends of the Imax gerberettes on each grid line are connected together by steel column sections. Load is therefore shared between these gerberettes, and trusses can be supported at any level. This section of the structure is not statically determinate and the effect of the construction sequence on loadsharing between gerberettes had to be investigated.

The floors in the Imax comprise 130mm concrete on Holorib decking generally, except for the base of the auditorium area where it is increased to 200mm thick to provide acoustic separation. The floors are supported by steel beams, at approximately 2.5m centres, spanning between the main trusses.

The roof structure is similar to the exhibition floors, with a concrete slab on Holorib decking acting compositely with cellcore beams spanning between main trusses supported from the inner tips of the gerberettes. The roof is designed for normal loads on top and the same suspended exhibit loads as the floors.

The West Wall fills the 30m wide by 30m high space between the west cores. It is supported by a structural steel frame, which hangs from the tops of the two cores and obtains horizontal support at floor levels from the core walls. It is glazed internally with blue glass, blue light being a theme of the internal space.

The primary structure comprises tubular steel trusses at main floor levels, which span horizontally between, and transmit wind loads to, the cores. The trusses are supported vertically near their ends and at mid point by a system of vertical and diagonal hangers, which take the vertical load to the top of each core at the end connection of the roof level truss. All other trusses have connections to the cores which slide vertically to allow for temperature effects. Connections to the core are also able to slide in the north/south direction, in order to allow the trusses both to act as simply supported, and to avoid stresses generated by changes in temperature. One connection in each truss does not slide in the north/south direction to ensure positional fixity.

The design assumed a specific erection sequence, which was provided in detail to the contractor, who elected to follow it rather than justify an alternative. The side aisles were erected first, and needed temporary bracing in the north/south direction until the roof slab was case and provided the permanent support to the top of the main columns. At this point the north and south aisles formed stable independent structures, and the main trusses and secondary beams were erected from east to west by crawler cranes running on the ground floor slab, which was provided with additional temporary propping to the foundations.

Judges’ Comment

The multi-level space is organised and defined by a masterly combination of structure and light to create a series of wide span unobstructed floors. These provide a superb environment for the enjoyment of the exhibited material.

The Eden Project, Bodelva, Cornwall

The Eden Project, Bodelva, Cornwall

Architect

Nicholas Grimshaw & Partners Ltd

Structural Engineer

Anthony Hunt Associates Ltd

Steelwork Contractor

Biomes – Mero (UK) plc
Link Building – Pring & St Hill Ltd
Visitor Centre –
Snashall Steel Fabrications Co Ltd

Main Contractor

Sir Robert Mc Alpine Ltd /
Alfred Mc Alpine Construction Ltd
Joint Venture

Client

The Eden Project Ltd

The Eden Project, a showcase for global bio-diversity, is one of the most innovative and high profile Millennium Projects. Its network of “biomes”, a sequence of great transparent domes that encapsulate vast humid tropic and warm temperature regions, make it the largest plant enclosure in the world built in the lightest and most ecological way possible.

The Biomes

The design, inspired by the Buckminster Fuller geodesic principle, evolved as a collaborative series of adjustments to a working 3-Dimensional computer model passed digitally between the architects, engineers and contractors. The final structure, the perfect fulfilment of Fuller’s vision of the maximum enclosed volume within the minimal surface area, emerged as a sinuous sequence of eight inter-linked geodesic domes threading around 2.2 hectares of the site: a worked-out Cornish clay pit. These “Bucky balls” (named after Fuller) range in size from 18m to 65m radius in order to accommodate the varying heights of the plant life. Form follows function, a tangible expression of the client’s aim to draw global attention to human dependence upon plants.

The biomes are an exercise in efficiency, both of space and of material. Structurally, each dome is a space frame reliant on two layers. The first, an icosahedral geodesic skin, is made up of hexagonal modules that range in diameter from 5m to 11m. Each comprises six straight, compressive, galvanised steel tubes that are light, relatively small and easily transportable. This makes it possible for each hexagon to be pre-assembled on the ground before it is craned into position and simply bolted to its neighbour by a standard cast steel node.

The primary layer is joined to a secondary one by diagonal Circular Hollow Section members at the node points. Structural stability is guaranteed by the “shell action” of the intersecting domes, that is, meeting of inner and outer structural members to form pinned connections. These are anchored to reinforced concrete strip foundations at the perimeter.

The exact location of the biomes on site has been determined by Solar Modelling, a sophisticated technique that indicates where structures will benefit most from passive solar gain. The architects have capitalised upon this gain by cladding the biomes with ETFE (Ethylene Tetra Fluoro Ethylene) foil.

ETFE represents less than one percent of the dead weight of equivalent glass. It is also strong, anti-static and recyclable, contributing to the overall realisation of the Eden biomes as tangible examples of energy-awareness in action. Elsewhere on the site, energy-awareness is manifest in both the Biome Link building and the Visitors’ Centre.

Biome Link

The Biome Link primarily functions as the entry to the biome complex, and has thus been designed with the ease of visitor movement in mind. It is essentially two structures within one: a front-facing public facility and a two-storey service area to the rear.

The front-of-house element, incorporating a raised steel and timber walkway into the biomes, is of a sloping convex truss system. The trusses consist of curved top and bottom booms with pinned jointed internal strut and tie members. They are supported by raking columns at the front that have expressed pinned joints top and bottom and are stabilised by the building to the rear, a two-storey braced steel-framed structure. The main cellular beams are set out on a radial grid, which can accommodate variations in the span between columns. The secondary beams are at 2.75m centres.

The roof plane is “warped” at both ends, and its profile steel decking supports a green roof system that allows the Biome Link to seemingly melt into the “cool temperature zone” of its surrounding environment. Access is by way of a path that winds down through this zone from the Visitors’ Centre.

Visitors’ Centre

The Visitors’ Centre is primarily an educational facility, with multimedia exhibits serving to introduce the aims and objectives of the project. The structure itself is equally informative. Dramatically curving to complement the contours of the quarry, it consists of two single-storey buildings linked by a partially covered courtyard. While the smaller (service) building nestles into the quarry, the main building thrusts outwards, offering a panoramic view of the biomes.

The main building is steel framed, with the roof beams spanning up to 20m between columns. The beams are set out on a radial grid and slope down at approximately 5° towards the service building at the rear. The roof structure, a steel deck capped with aluminium, forms part of the shallow cone resulting in a radial beam spacing of approximately 5m at the rear of the building and 6m at the front. To the south of the main building, it forms an overhang that shelters a rammed earth elevation. The use of rammed earth walling as a construction technique is local to Cornwall. It is also very much in keeping with The Eden Project’s emphasis on recycling. The material used is the excess from excavation work carried out elsewhere on the site, geologically identified as containing the required range of particle sizes.

The building is stabilised at each end by columns that cantilever from pad foundations. The central section is loaded laterally by the fabric roof, in addition to the wind load. In this section, a truss system in the plane of the roof transfers the lateral loads to braced frames. The truss members are generally sized to limit the deflection of the horizontal truss where it cantilevers at each end.

Judges’ Comment

The size and scale of this complex and visionary engineering project is truly breathtaking. Its success has the hallmark of dedicated and committed teamwork.

Underbridge 278 Railway Bridge Reconstruction, East Coast Main Line, Newark Dyke

Underbridge 278 Railway Bridge Reconstruction, East Coast Main Line, Newark Dyke

Structural Engineer

Cass Hayward & Partners

Steelwork Contractor

Cleveland Bridge UK Ltd

Main Contractor

Skanska Constrction Ltd

Client

Railtrack plc

The Newark Dyke rail bridge reconstruction demanded a high profile solution at a strategic river crossing on the East Coast Main Line. Railtrack demanded an aesthetically pleasing solution whilst specifying new high speed design criteria with demanding safety requirements so as not to disturb the live railway.

Steel was chosen by the design and construction team as the ideal structural material on which to base their proposals to secure the Contract. Steel was used not only for the primary features of the new main span, but also for the special substructures and the extensive temporary works, including piling, needed for launching and slide-in operations. Steel’s high strength/weight ratio, shallow construction depth, flexibility, durability and robust qualities were essential ingredients in the success of this project.

Two previous bridges had carried the railway on a skewed alignment over the River Trent – the original wrought iron and cast iron trusses constructed in 1852 being replaced by the all steel Whipple Murphy trusses in 1890, one beneath each track, which survived until now. After a series of short-term strengthenings, Railtrack decided to replace the structure and, at the same time, take the opportunity to seek a solution that met their future aspirations for higher speed trains, by increase of the line speed from 100mph to 140mph. The existing double truss bridge involved reverse track curves and hence limited speeds at the site.

The new 77m span bowstring half through bridge is carried on new outboard foundations to avoid uncertainties associated with re-use of the existing abutments. The necessarily heavier new superstructure, with its ballasted track and greater dynamic effects from higher speed trains, was considered likely to give long term safety risks if the existing abutments on timber piles were retained. The bridge itself is square spanning (and not skewed as the existing) so as to eliminate potential problems with track maintenance and dynamic behaviour. Main bowstring trusses are diagonally braced so as to minimise deformations and are spaced at 11.25m centres to allow the tracks to be re-spaced for higher speed running. The top chord is of open “H” steel plated section offering the maximum lateral inertia for stability whilst eliminating the need for overhead bracings between the trusses and is 1.5m wide and 1.0m deep. Flanges and web are up to 60mm plate thickness and the chord is straight between node points coinciding with a circular arc in elevation giving the best aesthetic appearance.

Water run-off from the top chord is ensured by elimination of stiffening on the top surface of the web. Diagonals consist of fabricated “I” sections measuring 500mm transverse to the bridge with flanges typically 325mm wide. Members of this form facilitate practicable and fatigue resistant welded end connections by elegantly shaped integral gussets to the chords and offer robustness against damage. Screwed rods, wire ropes, strand or hollow sections have been used in bowstring bridges, but were, in this case, rejected due to potential difficulties with compressive capability, durability, fatigue, creep or excessive maintenance of pinned connections. Spacing of node joints is generally 8.46m, but is decreased at the ends for aesthetic reasons and to facilitate rigid U-frame connection to the end three cross girders where the diagonals are of deeper section.

The bottom chord consists of a fabricated plate girder 1.5m deep with its top flange level with top of the floor slab upstand robust kerb. Shear connectors are provided full length of the bottom chord to achieve composite behaviour. At bridge ends the top and bottom chords converge to form a combined stiffened fabrication with downstand to bearing level. Main bearings are of fabricated steelwork and eliminated the necessity for limited life low friction materials. Fixed end bearings are of linear rocker type with roller type bearings at the free end. These bearing types also assist in stability of the bowstring top chords.

The floor is of minimum depth to maintain headroom over the river and is supported by composite cross girders 550mm deep at 2.82m spacing, cranked at the ends to form rigid HSFG bolted end plate connections with the bowstring bottom chord. The floor slab is 250mm thick cast onto GRP permanent formwork and incorporates edge upstands containing the ballast and forming a robust kerb at least 400mm above rail level to meet Railtrack standards.

Two continuous longitudinal steel stringers at 4.0m spacing interconnect the cross girders and serve to distribute concentrated live loadings effectively between cross girders, forming virtually an isotropic floor which fully participates as part of the bowstring bottom chord. This floor configuration enables the calculated acceleration levels to be controlled to the specified limits as demanded by new criteria for dynamic response under higher speed trains.

The solution for the substructures completely eliminated risks involved in excavation beneath the live railway. During a railway possession at Christmas 1999 mined openings were formed through each of the existing abutments which otherwise remained intact to support the existing superstructures. New independent foundations were constructed outside the hazard zone of the railway to receive the ends of prefabricated steel box girder needle beams which were installed through each opening.

Main bowstring girders manufactured and trial-assembled in Darlington were welded up to full length standing upright at site before launching out individually over the river immediately adjacent to the existing live bridge. Transverse slides enabled the girders to be positioned at the correct spacing to receive cross girders which were erected using a purpose-made steel gantry employing the permanent runway beams suspended beneath. Following completion of the deck slab and waterproofing the bridge was ready to be slid into place during the August 2000 Bank Holiday railway possession, which was successfully achieved along with re-alignment of the tracks and erection of new steel overhead electrification masts well within the 72 hours allocated.

Notable features of the temporary works included braced steel plate girder launching beams, one section of which was mounted on a steel barge and fitted into place only during limited blockages of the waterway which otherwise remained open for vessels during the works. The old bridges were slid out on parallel staggered slide paths extending to the opposite bank of the river where demolition took place. These employed the same plate girders which had been used to launch the new trusses across the river. The novel use of steel needle beams as part of the substructures will at a future date assist in removal of the new bridge, thus fulfilling aspirations for sustainable construction.

The new bridge is the first to be completed in the UK which is designed to counteract the dynamic effects of high speed 140mph trains under European based criteria.

Judges’ Comment

Railtrack and the Train Operating companies should be proud of the dedication and commitment that the design and construction teams gave to this classic piece of infrastructure renewal. Completed on time and on cost, Victorian and heroic in spirit, contemporary and innovative in execution and design.

DC170 High-Capacity Switch Tower

DC170 High-Capacity Switch Tower

Designer

Dynamic Concepts

Structural Engineer

Woolgar Hunter

Steelwork Contractor

M & S Engineering Ltd

Main Contractor

Dynamic Concept Ltd

Client

One 2 One

The proliferation of unattractive lattice structures in both urban and rural areas has led to severe criticism from planning authorities, environmental groups and the general public.

The DC170 is a fabricated steel tower with a unique identity and a strong visual code. Its elegant and distinctive form is combined with strength and practicality to make a versatile structure suitable for many different applications. The tower is circular in plan, limiting the envelope size while ensuring best practice in terms of safety. The three CHS legs form a strong vertical element, linked every three metres with a circular beam and internal connecting beams. This modular arrangement means that circular cantilevered headframes for equipment mounting can be added at any level. The result silhouette is exceptionally slim and visually transparent, despite its strength and capacity. The footprint of the tower is kept to a minimum, reducing both land-take and foundation size.

Available in a range of standard heights from 15 metres to 51 metres, the modular form the DC170 makes it ideal for site-sharing and expansion (essential in the fast changing telecommunications industry). A typical tower is capable of supporting in the region of 50 to 100 dishes while operating within industry standard design limits. The circular plan provides flexibility for equipment mounting, ensuring that 360 degrees coverage is obtained.

The structural form of the DC17 switch tower is a rigid Vierendeel frame acting as a vertical cantilever. The three CHS legs are linked horizontally by ring beams and internal connecting beams at three metre centres throughout the height of the tower. Therefore the tower is able to act as a frame in three planes and, being triangular in plan, provides stability in any wind direction. This configuration of stiff structural elements means that the footprint of the tower is limited to less than three metres in diameter. It has no diagonal members, resulting in clean vertical lines.

The cost of the DC170 may, on first inspection, appear higher than the equivalent lattice tower. However, it must be taken into account that the DC170 is a bespoke tower, designed for the highest standards of safety, flexibility and practicality. The superior design of the DC170 also means that lead time, particularly the time spent gaining planning permission, is greatly reduced. Typically a DC170 tower takes only seven to eight weeks going through the planning process, the cost benefits of which can be considerable. Furthermore, because the tower is delivered to site as a small number of pre-fabricated components, the on-site time required for erection and on-going maintenance is minimal. The modular form of the DC170 also means that it is a relatively simple operation to extend an existing tower.

The simple, elegant and aesthetically pleasing DC170 switch tower should set new industry standards for high-capacity structures.

Judges’ Comment

Radio coverage affects the whole of the UK, from areas of outstanding beauty to brownfield sites and industrial estates. These two structures and their associated family of masts give operations and planning authorities a wide choice for each situation. These two examples are beautifully fabricated, practical in operation and use as little as 20% of the footprint of a conventional lattice mast.

DC140 Guyed Monopole

DC140 Guyed Monopole

Designer

Dynamic Concepts

Structural Engineer

Woolgar Hunter

Steelwork Contractor

M & S Engineering Ltd

Main Contractor

Dynamic Concept (International) Ltd

Client

Crown Castle International Ltd

The DC140 guyed monopole is a most elegant and distinctive design. Available in a range of five standard heights, it is equally suited for greenfield sites, rooftops and urban settings. It resolves the visual problems of lattice towers by eliminating a large number of bracing components – its unique structure consists of a single CHS spine, with a series of cast steel arms linking this spine to three tensioned guy-rods (the number of “tiers” of cast arms depending on the height of the tower). This hierarchy of components produces an unusual and graceful form – the resulting silhouette is visually akin to that of a monopole, yet the structure is capable of reaching a height of 40 metres. The cast steel arms fulfil both structural and aesthetic functions as their sculptural forms, with cutouts to allow light to pass through, give the mast its distinctive visual identity.

The concept of the guyed monopole originally evolved from combining aesthetic simplicity of the traditional monopole with guyed lattice technology; however the way its structure performs is quite unique. Unlike guyed lattice towers, the central CHS spine of the DC140 has a fixed base that attracts bending moments, and horizontal cast steel arms at frequent intervals connecting the spine to the tensioned Macalloy tie-rods. The end of each horizontal cast arm is restrained by the guy rod, thus bending moments are attracted through to the central spine and distributed throughout the structure. The result is a base moment considerably less than that of a simple monopole structure. This fixed base moment imparts a high level of stability to the tower allowing the angle of the guys to be reduced from the normal 30 to 40 degrees to a mere 3.5 degrees from vertical on the DC140. With this, the footprint of the guyed monopole is reduced to an absolute minimum.

The DC140 is designed to provide for up to five telecoms operators, each using a full compliment of cellular panel antennae and microwave link. The monopole is cost-efficient and has advantages over more traditional towers in terms of speed of assembly. The central spine is formed from standard sizes of circular hollow section, and Macalloy bars provide an appropriate and readily available component for tie rods. Steel casting has proved to be an economical method of producing the structural arms, once the price of the initial moulds is absorbed the costs are far less than the equivalent fabricated component. While the DC140 weighs more than a lattice tower, its small number of components means that time spent on-site during construction and maintenance is dramatically reduced – for example, a 25 metre tower can easily be assembled within a few hours.

The guyed monopole has already proved to be extremely successful for sites where planning consent for more traditional towers has been refused, thanks to its distinctive architectural form.

Judges’ Comment

Radio coverage affects the whole of the UK, from areas of outstanding beauty to brownfield sites and industrial estates. These two structures and their associated family of masts give operations and planning authorities a wide choice for each situation. These two examples are beautifully fabricated, practical in operation and use as little as 20% of the footprint of a conventional lattice mast.

Wessex Water New Operations Centre, Bath

Wessex Water New Operations Centre, Bath

Architects

Bennetts Associates Architects

Structural Engineer

Buro Happold

Steelwork Contractor

Wescol Glosford plc

Constructor Manager

Mace

Client

Wessex Water

Situated on a brownfield site just outside Bath, the £23M bespoke headquarters building overlooks an area of outstanding natural beauty. It incorporates a host of environmental features such as greywater recycling and passive climate control.

Placing sustainability at the heart of the design concept provided impetus for fresh thinking and approaches to the problem of finely-detailed exposed structure.

The office spaces have been designed to facilitate natural cross-ventilation and passive cooling. They feature a soffit formed of exposed sculpted precast concrete coffer units on slender steel beams. The exposed structure provides thermal mass to control temperatures within the spaces. A subtly curved rib is a feature of each coffer, providing strength as well as increasing the surface area available for heat exchange.

The steel frame has enabled a very light appearance. Only the bottom flanges of the secondary beams are visible, as slender dove-grey strips supporting the precast coffer units.

To express the lightness of the structure through the façade, a study was performed with the architect to establish the optimum column spacings.

Whilst the central columns are at 6m centres along each wing, reducing the edge column centres to 3m (one for every secondary beam) meant that the edge beam functions purely as a tie. A small PFC section sits below the edge coffer unit, framing the BMS-operated high-level windows which provide night-time cooling. The shape of the coffer is expressed externally through the glazing.

The primary “spine” beam was designed as a box-section, perforated to maintain the flow of natural cross-ventilation below the soffit.

The internal faces of the spine beam can be seen from the office space. It was decided to fabricate the beam from a pair of PFCs toe-to-toe, to allow shop application of paint to these faces.

Particular attention has been paid to the detailing of exposed steelwork connections. Machined pins are used to provide interest where the spine-beam-to-column connection is expressed.

It was recommended that the steelwork, precast units and painting to both should be procured as one package, under the leadership of a steelwork contractor.

Fire engineering studies carried out by Buro Happold FEDRA demonstrated that the secondary beams did not require applied fire protection, and that only the external faces of the primary beams required intumescent paint.

Whilst undoubtedly not the cheapest structural solution in capital cost terms (steel, precast floors and topping, painting and erection together cost around £220/m² in a typical bay), the system offered numerous holistic cost and environmental advantages:

  • The optimal integration of the natural ventilation solution considerably reduces the amount of area required for mechanical plant, saving an estimated £50/m². It removes the cost and programme implications of supplying and installing ductwork (estimated saving £20/m²) as well as yielding a saving in running costs (estimated saving £50K per year).
  • Saving in materials embodied energy: used half as much concrete as a coffered concrete naturally-ventilated design (or a third as much as a flat slab), with the same total weight of steel.
  • In providing a first-quality exposed soffit with attractive details, the cost of a suspended ceiling was removed.
  • The coffers integrate the lighting within the structural zone and maximise the sense of height and space within the storey height.
  • The excellent quality of the working environment, developed around the integrated structure/M+E/architecture solution, offers potentially significant benefits in terms of increased staff productivity, and reduced absenteeism and staff turnover.

Judges’ Comment

Carefully engineered modular design, creating a high quality office environment with a simple, but well crafted, frame solution. Thermal mass of this steel-framed structure is successfully utilised for internal climate control. A significant step towards the development of fully integrated building design, with good environmental credentials.

Shanks Millennium Bridge, Near Peterborough

Shanks Millennium Bridge, near Peterborough

Structural Engineer

Whitby Bird & Partners

Steelwork Contractor

Fairfield-Mabey Ltd

Main Contractor

May Gurney

Commissioner

Peterborough Environment City Trust

The Shanks Millennium Bridge forms part of the Peterborough Environment City Trust Project funded by the Millennium Commission. It provides a new equine/pedestrian footbridge across the River Nene, and is sited at an ancient forded crossing. Following the construction of nearby sluice gates, the river became non tidal and the forded crossing impassable. The Shanks Millennium Bridge recreates a crossing at this location and links the north and south banks of the River Nene.

The structure is located 2.5km from the eastern edge of Peterborough. At this point the River Nene is contained by raised flood defence embankments, known as the North and South banks, and is above the general level of the surrounding drained farmland. It is open to a range of river traffic and contains a designated navigation channel.

The architect-designed bridge comprises a five span structure, approximately 120m long. It consists of a curved, slender steel box section, to which is bolted a cantilever walkway and handrail. The northern half of the bridge turns through approximately 90° in plan. The bridge deck comprises segregated footpath and bridle path areas at two levels. The footpath at the higher level is surfaced with hardwood. The lower bridge path deck consists of non-structural reinforced concrete. The parapets were constructed using a steel frame with hardwood slats set into the frame. This gives the horse and rider more space and, should any horses be startled, will prevent them climbing the parapet.

The shaped deck and the intermediate piers were constructed from weathering steel to reduce whole life maintenance costs and provide an architectural feature. Concrete abutments tie the bridge into the existing ground levels at the north and south ends. Two abutments were constructed on either bank of the River, and two intermediate piers located on the flood meadows.

Close working relationships that developed between all parties involved permitted drawings to be completed and approved in sufficient time to allow fabrication of the structure to proceed with minimal delay. The use of CAD/CAM provided a 3-D model, which gave virtual views of the bridge at every elevation and linked directly into automated fabrication facilities, including plate profiling and plate marking for assembly, minimising cost. The complex structure meant that all the steelwork was hand welded either in the steelwork contractor’s workshop or on site. The weathering steel was blasted at the works during the fabrication process prior to delivery to site.

Due to the complexity of the geometry, partial trial erection of box joints of the box sections was carried out at the steelwork contractor’s works.

The five span box girder sections were delivered to site in 12 individual box lengths. Each box section was supported by trestle towers and butt welded in the air to the adjacent box section. A crane was positioned on the flood plane adjacent to the River to enable the three box girders above the River to be erected. Closure of the River Nene was required during erection. Ancillary steelwork was then fixed to the bridge and then the decking and surfacing was added.

The complex design and the use of weathering steel has resulted in a bridge which is simple in its purpose to accommodate bridle path users and pedestrians whilst remaining aesthetically pleasing and architecturally challenging.

Judges’ Comment

This is a most beautifully designed curved box girder bridge in weathering steel that fits the Fens landscape as if it were a natural part of it. It is a pity that land restrictions necessitated stepping of the decking on the approach to the south bank.

The Lowry, Salford Quays, Manchester

The Lowry, Salford Quays, Manchester

Architect

Michael Wilford & Partners Ltd

Structural Engineer

Buro Happold

Steelwork Contractor

William Hare Ltd

Main Contractor

Bovis Lend Lease

Client

The Lowrie Centre Trust

The Lowry project on Salford Quays has been designated the Nation’s Landmark Millennium Project for the Arts. The Lowry consists of two theatres, two galleries and various facilities for conferences and general hospitality.

In the Lyric Theatre two rows of columns based approximately 3m apart set out on an oval grid as defined by sight lines and linked back to shear walls by curved steel beams were used to provide the transverse stability. These columns were used to support cantilevered trusses which in turn supported the seating. The central core columns and beams were painted with intumescent paint to satisfy the one-hour fire rating requirements.

Set on the outside perimeter of the leaning concrete wall, the Lyric Foyer provides access from the theatre entrances to the galleries and exits. The roof beam consists of a plated 610 deep beam cut to suit the architect’s requirements. The difficulty of connecting this to the cruciform column which was made up from a 356 UC with Ts welded to the web was overcome by means of a tubular insert welded to the top of the column.

This Adaptable Foyer comprises four cruciform columns made from four 120 x 120 SHS welded together. These in turn support a tree top configuration made from tapered beams out of 610 UCs. The tapered beams supported 165 UC purlins which in turn supported the metal decking roof. A curved 152 RSC formed the edge support.

The two Galleries comprise longitudinal trusses supported on 322 x 25 CHS columns with the bottom boom supporting first floor cell beams and the top boom supporting similar transverse roof trusses. The connections had to be kept as clean as possible to satisfy the architect’s requirements for clear uncomplicated lines as the steelwork is visible both internally and externally.

The Diagrid Tower is used to house the artwork when not in use the architect required this to be the highest visible feature using symmetrical steel beams to form a cylindrical shape with no connections visible on the perimeter. Four beams connected together formed a facetted diamond shape and this pattern was repeated around the cylinder and from bottom to top.

Set at the entrance to the Lowry, the Canopy was designed as an imposing architectural feature as well as a functional structural item. Supported on two sets of A-frame legs with six smaller CHS supports the structure consists of a central toblerone shaped truss on which are supported frames with a sloping top boom and curved bottom boom to give the architect’s required shape. This structure was covered in perforated cladding.

Why Steel? The design team recognised from the outset that the structure had to satisfy both structural and architectural requirements. The geometry of the structure with its various leaning walls, cylindrical shapes and large spans meant that for the majority of the structural framing, steel was the only logical choice.

Despite its complex nature the engineers could design the structure confident that the steelwork would achieve their requirements within the tolerances required.

From an installation perspective steelwork was the only logical choice due to the limited nature of the space available on site. Vast areas of space were not required for temporary support/propping during installation as the steel frame was designed to be stable within its own right and installed in a manner to minimise any temporary bracing required. The speed of erection also confirmed steel as the correct material for the structural framing.

Judges’ Comment

:

A prestigious project of great complexity, incorporating two theatres, galleries and support services. The exposed structural steelwork in many areas has been innovatively fire engineered. The combination of steelwork and stainless steel cladding is very effective.
The public already shows great enthusiasm and appreciation for this building, which displays steelwork to good effect.

Footbridge, Plashet Girls School, East Ham

Footbridge, Plashet Girls School, East Ham

Architect

Birds Portsmouth Russum

Structural Engineer

Techniker Ltd

Main Contractor

C Spencer Ltd

Client

London Borough of Newham

This exciting new covered footbridge explores the use of steelwork to deliver a complex brief to a very tight budget and create a bold visual identity for the school which it unites across the road.

Designed to meet a challenging budget of £500,000 for an overall length of 67m, the architectural and structural functions are combined. 914 UB carriage beams were selected to suit both the span and balustrade requirements, with the bridge deck acting as the bottom flange and providing the torsional restraint required to accommodate the curved profile of the bridge.

The bridge connects the two halves of the school across a busy road. Built at different times as two separate schools the buildings are staggered in height and on plan. This is resolved by the S plan form of the bridge which wraps around and saves a mature tree. The bridge rises gently across the road to meet the 5.7m clearance height and enters the building on the far side on the horizontal. The bridge flows seamlessly from one end to the other. This was achieved by firstly minor axis bending the carriage beams to close tolerance on a 17m radius. The beams were then manipulated into shape using heat – a process known as lobster-backing, whereby the underside of the carriage beams are incrementally heated along their length until the right profile is achieved, in this case a spline curve which formed the natural transition from the slope to the horizontal. Once the beam profile has been achieved the plate of the deck box was welded into place following the profile of the beams. A viewing gallery slices through the carriage beams at midspan to form an interlude in the crossing at the centre point. The load path is followed through the projecting seating platform by welded stiffeners forming a cranked beam within their depth. The reduction in stiffness attracts load to the supports leaving a light transition at midspan.

The bridge is supported on sculptural steel piers which emerge as silhouette profiled plates from the ground and clamp the bridge on either side. Longitudinally, the bridge is fixed at one end and free to move along its length. Fabricated from 32mm steel plate welded to semi-circular sections, the piers are suitably flexible in their minor axis to accommodate the longitudinal movement whilst providing sufficient rigidity to resist the twist generated by the S bend. A wedge is driven into the hollowcore tube to clamp the bridge to the piers.

Plate welding is the predominant theme in the steelwork design. Heavy duty butt welds are part of the sculptural repertory of the design allowing the steelwork to flow. In contrast the galvanised lightweight elements bolt on. A simple device of alternating eccentric steel hoops creates an animated pattern and achieves a saddle-backing rigidity for the roof panels. The fabric panels are clamped to the rail on the outside of the hoops, facilitating the tightening of the fabric on site the meet construction tolerances.

The design was conceived to enable the bulk of the bridge to be prefabricated and erected on site during the six week school summer holidays. The bridge came down to London by road in three sections. The central span is 23m long, with the S bend designed to suit the maximum transportable width of 4.5m. All three sections were lifted into place in a single 24-hour road closure and the splices site welded to form a continuous sinuous curve.

Judges’ Comment

:

A simple solution to the school’s 20-year old problem of access to two sites. Radical in plan and elevation and bold in concept, the bridge is something between Miro and Chinese lantern. It is playful and exuberant. The structure is safely enjoyed by staff and children.