Design Awards: 2018

London Bridge Station

© Rick Roxburgh

Architect
Grimshaw

Structural Engineers
Arcadis WSP JV

Steelwork Contractors
Cleveland Bridge UK Ltd and Severfield

Main Contractor
Costain

Client
Network Rail

As part of Network Rail’s London Railway Upgrade Plan, London Bridge Station is undergoing a stunning transformation that will deliver a better experience for users and a reduction in delays. It will also ensure greater connection between London’s home counties and increase passenger capacity by two-thirds.

The station transformation includes an enlarged street level concourse underneath the tracks, new entrances and new platforms for more trains, and three of the nine terminating platforms converted to through platforms. The concourse is set to be one of the largest in Europe.

The rolling redevelopment programme started in 2012 and has been scheduled in such a way as to ensure the station remains open for business at all times. On 2nd January 2018 the final section of the massive new concourse and five platforms opened to the public, with the remaining redevelopment works to be completed in the spring.
Elegant curves are integral to the station’s design and respond to the track geometry and curvature of the site. Steel is the natural material for the project as it allows the necessary design flexibility. It also offers sustainability benefits as it is recyclable and lightweight.

All 15 platforms have been rebuilt to be covered by a striking undulating canopy of steel and aluminium, fabricated and installed by Severfield. The eye-catching canopy roof is modularised using open sections where each module is approximately 9m deep by 3m wide. There are an astonishing 1,200 prefabricated steel cassettes, with each one a bespoke unit due to the changing rooftop geometry. To save time cassettes were prefabricated offsite and then craned into position, allowing the canopy to be built during short night-time construction hours.

The canopy structure comprises Y-shaped columns supporting a longitudinal spine beam formed from fabricated box sections that have extended webs to create service routes. Platforms and canopies sit outboard of the bridge girders, supported on transverse ‘elephant ear’ frames, and as trains pass over the bridges any deflections cause the tips of the ‘elephant ears’ to move longitudinally. The plates that connect the frames to the bridge girders are designed to balance strength and stiffness to resist the applied loads, while remaining flexible enough to avoid fatigue.

The centrepiece of London Bridge Station is the concourse which is nearly 80m wide. There is also an expansive central space at the heart of the concourse which deals with the level changes across the site. The large span of this space was achieved by using a longitudinal V-column to support a 5m deep Vierendeel truss, and this allowed for glazing between the vertical members to form the rooflights above.

Cleveland Bridge supplied steelwork for the rail bridge decks spanning the new concourse. The work has included fabrication, trial erection at the company’s Darlington facility, painting, delivery and installation.

The concourse bridge decks are made up of three to four spans of simply supported decks for each rail line. Each rail bridge deck comprises six main girders braced together and tied at the ends with trimmer beams, delivered and erected as pairs.

Following installation the beams were mass filled with concrete and fitted with platforms, rail lines and canopies.

The main plate girder lengths (spans) were such that no longitudinal splices were required. After fabrication all components were placed in pairs together for a trial assembly to ensure perfect fit and alignment, de-risking the operation on-site. Upon completion of the trial erection, the deck was separated into component pairs ready for dispatch to London.

The main logistical challenges for the project were the severely restricted site access; a requirement to consider scheduling for follow-on trades, and the essential need to keep the station fully functional. The architect Grimshaw designed the station and complex staging process based on the concept of prefabrication and modular offsite construction. This reduced the pressure on the construction programme and again the use of steel was advantageous. For the installation of the decks and canopy the project was split into six phases.

The possessions for working were ‘Rules of the route’ (very short windows when trains are not running) synchronised with restricted short possessions for delivery vehicle road closures. The entire project took place in a busy city centre location with narrow streets through which to move delivery vehicles, large plant and equipment.

The lifting schemes for all steelwork installations included the innovative use of heavy capacity scissor lifts mounted on the top of Self-Propelled Modular Transporters (SPMTs) to solve access problems.

The aim of Cleveland Bridge’s work was to maximise the level of offsite fabrication and preparation to significantly reduce the on-site programme. As the station was operational throughout the project, health and safety was paramount and the overall project was delivered within budget and ahead of schedule, exceeding the client’s expectations.

Judges’ Comment

The project has produced a major upgrade to the existing station, which remained operational throughout. Collaborative offsite manufacture minimised disruption during the project. The use of steel has allowed the design team to create open concourse spaces beneath the tracks and elegant curves to the canopy structures above. The project is a great example of ‘designing for construction’.

Knostrop Weir Foot and Cycle Bridge, Leeds

© Paul White

Architect
Knight Architects

Structural Engineer
Mott MacDonald

Steelwork Contractor
S H Structures Ltd

Main Contractor
BAM Nuttall

Clients
Leeds City Council and Environment Agency

The Leeds Flood Alleviation Scheme (FAS) is led by Leeds City Council in partnership with the Environment Agency. It will provide the city centre and over 3,000 homes and 500 businesses with protection against flood events from the River Aire, whilst enabling key regeneration opportunities in the South Bank area. Another objective of the scheme is the provision of new routes for walkers and cyclists, both along and across the River Aire. Knostrop Weir Foot and Cycle Bridge serves to reconnect the much-used Trans Pennine Trail, following the removal of a section of island between the River Aire and the Aire and Calder Navigation for flood risk reduction purposes.

As part of the FAS improvements a replacement weir would be constructed on the Knostrop site, and the clients wanted to explore the possible synergy between the new weir and the construction of a bridge across the river. The final design uses the new weir walls as pier foundations for the bridge above, providing significant savings in budget, time and resources.

Leeds City Council recognised the wider value for the design to be of high-quality and identifiable with its place. Despite the apparent complexity of the final design’s appearance, it only requires a single curvature in the fabrication of the steel plate elements. This served to simplify fabrication and enabled the bridge to be delivered within budget and programme. In views along the river the appearance is simple and sympathetic to the natural context. A curved soffit combines with the changing deck width to translate the varying plan width into a rippling deck edge detail, producing a dynamic ‘sinuous’ quality to mirror the noise and movement of the falling water beneath. Another unique feature of the design is that in elevation the piers are only 50mm thick and almost invisible in long views, creating the illusion of a floating deck. When viewed on closer approach the appearance of the piers changes, emerging as dramatic projecting cantilevers springing from the weir below. Lookout points have been positioned above each pier enabling people on the bridge to stop and enjoy views over the weir and along the river.

Steel was the obvious material of choice to achieve the required aesthetic and minimise the significant construction challenges of working over water. The 70m long bridge was fabricated in S H Structures’ facility, which is situated just 17 miles from the Knostrop site, and treated at a local facility, minimising the environmental impact of the works.

Construction over a river creates special challenges in order not to harm the waterway and its ecology. Minimising the time and extent of temporary works in the river was an essential aspect of the design. The prefabricated superstructure sections and piers were installed over two weeks using a crane. At the abutments special eel bypasses have been incorporated to allow for migration, whilst a dedicated fish bypass is included in the weir.

Given the accuracy required to successfully realise the complex steelwork geometry and installation, it was decided to embrace Building Information Modelling (BIM) from the outset. The Revit model of the bridge enabled every element to be accurately represented and positioned, including every steel plate in the bridge’s curving geometry and all connection elements. This was particularly valuable when designing the highly complex bolted integral pier connection. During fabrication the BIM model was also utilised to allow every component to be spatially positioned and checked. The model was also used to assist in the design of the workshop temporary works as the complete length was fully assembled, allowing the critical interfaces to be set, checked and maintained during the fabrication process.

In a wet environment over a weir, careful detailing, specification and construction are essential to ensure a long-lasting and durable solution for a bridge. The bridge superstructure is predominantly constructed using weathering steel with a four-coat paint system normally only used for difficult access highway structures. A primary concern was for the durability of the bolted connections between assembled elements of the bridge. This required highly protective details and connections that far exceeded what was needed for structural requirements to minimise water ingress.

One of the key features of this elegant structure is the slim piers. To achieve the required aesthetic and structural performance this area required careful consideration. Once the concrete weir walls had been poured and the holding down bolts installed, a detailed as-built survey was carried out. The recess bolt holes in the curved pier base plates were drilled and machined to match the as- built layout of each bolt group. With this work done, each base plate was trial- fitted to check for fit before the piers were finally installed, surveyed and cast in place. This attention to detail is critical to the successful installation of this type of precision detailing.

Judges’ Comment

This team solved an unusual bridge alignment by producing a thoroughly modern intervention in a post-industrial landscape whose unique qualities are derived from the constraints of the flood relief requirements. Using ingenious geometry and thorough attention to detail, the prefabricated sealed modular deck units appear to float on impossibly slender vertical supports. The result is an economic, robust and graceful solution. The overall rippling effect of the bridge is intriguing, yet it is rooted in logic; a seamless integration of architecture and engineering.

Jaguar Land Rover Engine Manufacturing Centre

© Simon Kennedy

Architect
Arup

Structural Engineer
Arup

Steelwork Contractor
Severfield

Main Contractor
Interserve Construction Ltd

Client
Jaguar Land Rover

The BREEAM ‘Excellent’ Engine Manufacturing Centre comprises 165,000m2 of production space, offices, social support spaces and a community educational centre, and is an exemplar of modern sustainable manufacturing.

Innovation, collaboration and the well-being of people at the facility have shaped the success of the building. A simple layout was derived from optimum operational adjacencies and designed for flexibility, providing both an efficient process flow for manufacturing and giving staff easy access to support facilities. Naturally-lit machine and assembly halls are flanked by supporting office and ancillary buildings. This approach optimised production performance and blurred the boundaries between production and offices through visual transparency, clear movement and social spaces, helping to break down the barriers of communication between staff.

A powerful architectural impression was achieved through the simple, repeating and discretely expressed façade modules, generated by the north lights. The skylights provide generously day-lit spaces throughout the complex, and continuous strips of glass along the ground floor allow the buildings to float, further humanising the scale of the spaces while providing views out to the landscaped surroundings.

With a firm date for starting production, programme was critical. The first phase of this world-class facility was handed over just 24 months after the design team’s appointment. Subsequent phases followed in continuous sequence from 2013 to 2016.

Phase One was one of the first structures in the UK to be designed to the Eurocodes. Arup developed spreadsheets to automate member utilisation checks direct from analysis output, enabling all members to be rapidly optimised. Despite the intensive servicing loads on the roof, this reduced the roof tonnage to only 28kg/m2, which is impressively light for 30m spans.

All the structures comprise braced steel frames, with grids set by the bay sizes of the production areas below. Concept studies explored grid size with the client and compared portal action, but the braced frames were considered the cheapest solution.

The north lights are formed using the primary 30m span trusses to minimise intrusion of the structure into the production spaces and thereby minimise building height. The Machine Hall uses a grid of 30m by 15m, matching the rhythm of the north lights. Assembly Halls have a grid of 30m by 30m, at twice the rhythm of the north lights, so primary support trusses are provided below the north lights on each 30m grid to support the intermediate primary trusses. Secondary trusses are provided at 7.5m centres. These grids provide for future reconfiguring of the assembly lines.

Columns were designed assuming some rotational fixity to minimise second-order effects. This was derived from a study of potential settlement of the pads and considering the need for them to stand without temporary works during erection.

Wind behaviour on saw-tooth roofs is directional relative to the saw-tooth, but large-scale roofs behave differently to small- scale roofs. So, comparing the peak wind effects from the roof geometry with peak wind directions for the site, sheltering benefits and size factors, the uplift loads were reduced by up to 70% for most of the roof.

Mezzanine floors provide support accommodation and plant spaces, using reinforced concrete slabs constructed on profiled metal decking, providing robust fire separation for plant spaces.

Primary services within the spaces distribute at roof level supported from the roof structure. This minimised the need for trenches and steps in the ground slabs, maximising future production flexibility. The roof had to be designed accordingly for intensive servicing and high point loads.

The support and spine buildings are typically two storeys high with accommodation below and plant at first floor level to feed directly into the adjacent halls. The office building uses precast hollowcore slabs to provide an exposed thermal inertia of the soffits to assist with the natural ventilation strategy.

Jaguar Land Rover’s commitment to sustainable, low carbon, manufacturing was supported by Arup’s ability to provide integrated and innovative low-energy design solutions, resulting in one of the largest buildings to achieve BREEAM ‘Excellent’.

Sustainable measures include the UK’s largest PV installation, zero operational waste, extensive grey water recycling, day- lit spaces, naturally-ventilated offices and a pioneering ‘solar cladding’ façade system.

The north lights’ vents open to expel hot air in summer reducing extract energy. Responsive dimming controls for the lighting system help to capitalise on the generous daylighting in the space to save further energy.

The project was a trailblazer for applying level 2 BIM. The one-model approach was extended to embrace Jaguar Land Rover’s own manufacturing designers, who integrated Arup’s BIM model with their Process and Equipment 3D model to create a model of the entire facility, enabling unprecedented levels of coordination to be achieved. The model was also populated with specification and data tagging to enable adoption into Jaguar Land Rover’s facilities management system.

The structural model was produced directly from the analysis model, exported to Tekla, saving the steelwork contractor weeks of modelling.

Judges’ Comment

Drawing on traditional industrial forms, the team has updated these principles to deliver a stunning workplace to train and attract the best talent in the industry. The lightness of the framing, extensive roof-lights and perimeter windows deliver high levels of natural light. The steel is efficiently designed for current operations and adaptation for changes in engine design and technology.

V&A’s Exhibition Road Quarter, London

© Paul Carstairs/Arup

Architect
AL_A

Structural Engineer
Arup

Steelwork Contractor
Bourne Steel Ltd

Main Contractor
Wates Construction

Client
Trustees of the V&A

The most significant intervention undertaken at the V&A’s South Kensington campus for over 100 years, this major development provides a large column-free underground exhibition gallery with an oculus to allow the influx of natural daylight, an open courtyard and significantly improved street level entrance from Exhibition Road into the Museum.

The courtyard also acts as a venue for installations and events and is served by a glass-fronted café.

The Sainsbury Gallery, a new 1,100m2 column-free space, will be one of the largest temporary exhibition spaces in the UK and allow the V&A to significantly improve the way it designs and presents its world-class exhibition programme.

Entry to the new Sackler Courtyard will be through the arches of the 19th Century screen designed by Sir Aston Webb.

From the courtyard, and from key internal locations through the glazed skylights, it is now possible to see previously hidden façades of the museum’s original buildings, including the detailed sgraffito decoration on the Henry Cole Wing which has been revealed to the public for the first time since 1873.

Following an extensive international competition Amanda Levete Architects (AL_A), working with Arup, were appointed as the designers of this scheme. Key to the success of the competition was the use of structural steelwork for the concept design for the ‘folded plate roof’, a system of triangular steel trusses which span 38m across the gallery, support the courtyard, café, and crucially allow the changes of existing ground levels to be fully exploited to fit in a mezzanine floor. As well as the significant vertical loads that this structure supports, it is also resisting significant prop forces as it is the ground level structure of a 15m deep basement.

During the excavation of the basement, 800 tonnes of historic Grade I listed stonework stood on one ‘mega-beam’ formed of four individual steel beams. The ‘mega-beam’ was temporarily supported on steel needles, which were then replaced by four steel columns.

The beams and columns are expressed within the volume of the stairwell, so that as visitors pass from the entrance to the gallery they understand how the façade above is supported, and where they are in relation to the rest of the museum.

The ‘folded plate’ structure comprises 13 ‘Toblerone’ trusses supported on an inclined storey-height mezzanine truss. Through optimising both the overall geometry and the geometry of the members making up the trusses, the design team was able to save 40% of the steel weight of the initial concept. Early engagement by Arup with Bourne, and the steel industry, during the design process meant that the design moved from needing extensive temporary support to erect it to one where the ‘Toblerones’ were self-stable for ease of erection.

Bourne was responsible for the connection design, fabrication and erection of the 13 ‘Toblerone’ trusses, each up to 25m in length and weighing up to 14 tonnes. Transporting and delivering these trusses in London was a logistical minefield requiring careful planning and coordination with Highways England.

The unique geometry of each truss and the difficulty in positioning meant that the fabrication had to be precise in its execution. Due to the geometry and sheer size of the trusses, bespoke jigs needed to be made to aid fabrication, and much of the fabrication needed to be carried out with the use of mobile elevating working platforms (MEWPs).

The form of the structure presented several difficulties for the connection designers, with a combination of heavily loaded and multi-planar joints, nearly all of which were unique, with often a restricted envelope within which to achieve a viable connection. The connection designs had to incorporate allowances for erection and fabrication tolerances. The triangular trusses, which form the principal members of the roof, are an example of the geometric challenges encountered with typically two chord members and four internals intersecting at a point, with none of the members in a common plane, and the remaining members clashing well before they reached the intended connection zone.

Precision checks offsite and on-site showed that exceptional tolerances were achieved, which meant that each of the trusses was dropped into place on time, first time, every time.

The truss geometry and phasing were coordinated in an integrated 3D model between Wates and Bourne to ensure that there were no clashes between the steelwork and the heavy temporary props that laterally restrained the retaining walls before completion of the courtyard structure.

What had been viewed as a high-risk package due to the complex geometry of the steelwork, the critical structural performance requirements and the multiple challenging interfaces between it and follow-on trades, was delivered to an outstanding quality and attention to all details by a committed design, fabrication and site team.

Judges’ Comment

The inverted ‘Toblerone’ shaped trusses form a neat arrangement to support a new public courtyard and entry from Exhibition Road above new basement level galleries. This array of steelwork was hugely refined through the design process to maximise the efficiency of each member. Good use of light and colour for wayfinding in the new extension is exemplified by the striking red steel columns that so appealed to the judges.

Bloomberg London

© Aaron Hargreaves/Foster + Partners

Architect
Foster + Partners

Structural Engineer
AKT II

Steelwork Contractor
William Hare

Main Contractor
Sir Robert McAlpine

Client
Bloomberg

Bloomberg London represents one of the largest, most notable developments to shape the post-Olympic landscape of London. Bloomberg’s new European headquarters is respectful of its location in the heart of the City of London, close to the Bank of England, St Paul’s Cathedral and the church of St Stephen’s Walbrook. It is a true exemplar of sustainable development, with a BREEAM ‘Outstanding’ rating – the highest design-stage score ever achieved by any major office development in the UK.

The architect’s vision consisted of two adjacent 10-storey buildings with a pedestrian access path cutting diagonally through. A steel frame with composite concrete floors is clad with sandstone and metal fins to produce a solid, understated elegance set to last within a hostile city environment.

The structure’s sensitive island location meant that physical limitations were set by the adjacent roads, as well as the remains of London Wall running close by. Constructing close to an existing sewer, the adjacent Waterloo & City line tunnel and the new direct link to Bank Underground station all required third party agreements and considerably affected programming. In two such immensely complex 10-storey structures adding value through design has been key, and AKT II was able to do this from the basement upwards. The location was previously home to Bucklersbury House, a disused 1950s structure demolished prior to start on-site. However, the slab-and-pile foundations were retained following a radar survey which confirmed that the vast majority could remain, with additional piles introduced only in the south-west corner.

On plan, the form and setting out of the north and south buildings respond to the angular nature of the site and the alignment of the new arcade with Watling Street. To achieve this both buildings use a unique structural grid set out on a 13.85m equilateral triangle that maximises open floorplates. The form of construction is similar to that found in orthogonal steel- framed City office buildings. All cores are formed from insitu reinforced concrete but, in contrast to traditional building forms, have been pushed to the perimeter to increase the extent of uninterrupted floor space and improve visual connectivity. To further enhance this, lift shafts have been opened up to animate the façade and act as light wells. The two buildings are also connected at high level with a series of link bridges above the arcade. The scale and precision of the stone and bronze façade is achieved with an independent primary frame which connects to the main columns and eliminates the larger movements in traditional edge beam solutions.

The structural grid is interrupted in several locations with transfer structures to create the unique spaces within the building. The most significant of these occurs above the pantry level which involves a storey deep truss within the level 9 plant floor spanning up to 26m between columns. This allows the suspension of level 8 and the removal of four main internal columns to create a two-storey high vast communal space within the pantry with spectacular views of St Paul’s Cathedral.

Within the centre of the north building is the feature ramp which provides access between floors from level 2 to level 8. The steel ramp structure is 1.5m wide and spans 30m between floors measured along its centreline. The elliptical oculus within the floorplates through which the ramp passes also rotates 120 degrees at each floor level following the plan transcribed by the ramp.

The main reception carves a column-free space under the ramp between ground and level 2, introducing a three-dimensional structural vortex form that spans, displays, announces and integrates architecture and structure for a spectacular experience before revealing the ramp as a structural force majeure.

The benefits of using steel construction for Bloomberg London included providing long-span uninterrupted floorplates and small structural zones relative to the span, with fully integrated services within the structural depth. Complex transfer structures could be incorporated within the building, saving space when compared with other materials. The project showcased skill and workmanship through the creativity of the devised structural solutions that achieved architectural design intent within this modern office environment. Stability was provided to the north and south 10-storey steel-framed buildings by concrete cores which were on the perimeter of the buildings.

The peak site of erection was the north and south buildings running in parallel with each other, which required approximately 600 tonnes of steelwork to be produced per week.

Thanks to 4D BIM planning and offsite manufacture on-site risks were reduced, William Hare worked with the project team to ensure delivery was on time and error free.

Judges’ Comment

The elegant exterior of this major building, a polite addition to the City, conceals a fabulous interior supported by a highly innovative design in steel. The unique triangular column grid and roof transfer system create the large open spaces required by the client, whilst the vortex transfer structure and atrium ramp produce effective yet stimulating circulation routes. The attention to detail throughout the project sets the highest standard for commercial office accommodation.

The Ordsall Chord Viaduct

© Matthew Nichol Photography

Architect
BDP

Structural Engineers
AECOM Mott MacDonald JV

Specialist Designer
Knight Architects

Steelwork Contractor
Severfield

Main Contractors
Skanska BAM JV

Client
Network Rail

The Ordsall Chord Viaduct is the iconic centrepiece at the heart of the Ordsall Chord, a new elevated railway connecting Manchester and Salford. The project reduces railway congestion, allows new passenger services to run, and creates wide economic benefits across the north west of England.

The viaduct carries the new two-track railway across both the River Irwell and the dual carriageway Trinity Way. It sits next to major heritage structures, part of the historic 1830 Liverpool to Manchester Railway, the world’s first inter-city railway.

The context required a design which was of the highest architectural quality, with a structure that would act as a landmark without dominating surrounding buildings.

An 89m span network arch structure was chosen for the main river span, combining great strength and stiffness with a relatively low profile. A 100m long twin girder bridge was selected for the spans over the roadway. All parts of the viaduct are integrated visually to appear like a single ribbon of weathering steel.

This is the first network arch bridge to be built in the UK, and the first asymmetric (tapering) network arch anywhere in the world.

The preliminary design concept illustrated box girder structures throughout the length of the viaduct. The design was modified during the design-and-build phase, adopting box girders for the arch ribs but stiffened plate I-girders for the spans over the highway. This reduced construction costs and simplified future maintenance requirements.

The network arch is visually merged with the girder spans above Trinity Way by the inclusion of steel ‘cascades’ in between. These transition pieces negotiate complex changes in vertical and lateral geometry, and give the impression of a smooth transformation from the hexagonal box to the ribbed I-section.

The river and highway spans of the viaduct both employ steel primary girders, with steel cross girders supporting a composite concrete deck slab. The main span’s hanger network comprises 2 x 46 solid steel hangers each 85mm in diameter.

Steel was the most cost-effective solution to satisfy the client’s structural performance requirements and the desire for an elegant, iconic structure. Steel was ideal for the offsite manufacture of a highly geometrically complex structure and allowed an efficient construction methodology to be developed.

Adoption of weathering steel for the viaduct provides a unifying visual identity and minimises future maintenance requirements.

The network arch was the biggest structural challenge. An existing road bridge had to be demolished before construction could proceed. Steel support trestles were assembled by driving tubular steel piles through its deck, and they were used to prop the structure during demolition. The supports served a dual role; they were then reused as the supports for the network arch span’s during its erection.

The deck girders were installed piecemeal onto the abutments and temporary supports, welded together, and cross girders bolted in place. The arch sections were brought to site in segments and welded together lying on their sides near the river bank. Both arches were then rotated on end pivots to their correct inclination (6 degrees from vertical), overhead bracing installed, and temporary tie cables and struts inserted. The dual-arch assembly weighed nearly 600 tonnes and was erected onto the end nodes of the tie girders with a tandem crane lift using a 750-tonne crawler crane, along with the UK’s largest 1,300-tonne crawler crane.

Hanger stressing was the most complex construction stage, with a total of 136 stages of stressing completed. Two independent load monitoring systems were used in every hanger during construction, with one monitoring system left in place for in-service structural health monitoring. Although the structure behaved generally as predicted, close cooperation was required between the construction and design teams to allow small divergences in hanger load to be corrected.

The box girder elements of the structure were specified as Execution Class 4, one step above normal UK bridgeworks requirements, due to the impossibility of future examination of welds within the highly constrained box sections.

The bridge was fully designed and detailed using BIM, adopting a highly innovative arrangement to reduce programme, increase confidence in the buildability of the design, and allow early ordering of steel plate before the full design was complete. The steelwork contractor’s BIM technicians were ‘loaned’ to the design engineers, embedded in their team, to help produce the BIM model, design drawings, and ensure the design data was simple for the steelwork contractor to re-use in its own processes. This approach is believed to be a first for the UK bridge industry.

Key parts of the design were delivered using a ‘3D-model-only’ approach, minimising the cost and time required to produce conventional 2D structural steelwork design drawings, and improving confidence in the quality of the information shared.

Judges’ Comment

The Ordsall Chord project is a major piece of new railway infrastructure that has a truly civic presence. The project combines a new network arch railway bridge and approach viaducts with integrated public realm. Weathering steel is used as a strong unifying element that flows through from the viaduct and bridge approach upstands into the main arches of the railway bridge, giving the scheme a strong architectural identity within its urban setting.

Two St. Peter’s Square, Manchester

© Daniel Hopkinson

Architect
SimpsonHaugh

Structural Engineer
BuroHappold

Steelwork Contractor
William Hare

Main Contractor
Laing O’Rourke

Client
Mosley Street Ventures Ltd

Two St. Peter’s Square is a new build, Grade A office space in the heart of Manchester city centre. It faces the Grade I listed Town Hall and Grade II listed Central Library. The building is 12 storeys above ground with a two-storey basement.

The key driver for the structural design has been to provide highly flexible column-free accommodation that is attractive to potential tenants. The typical beams are 730mm deep and, over the 18m span, vibration was a key criterion governing many of the section sizes.

At ground level the architectural intent was to provide a colonnade with columns at 12m centres and cantilevers of 6m at either end. Continuing this wide spaced grid on the typical floors above was not economical so a transfer structure at the lower level was utilised.

To maximise the spatial experience of the colonnade at ground floor level the columns are double-height with the first- floor floorplate set-back from the perimeter. Long-span transfer beams at level 2 achieve this with the first floor hung from above. A similar arrangement is adopted at level 10 with transfer beams that support the set-back columns above. This arrangement provides a high value terrace space overlooking the civic heart of Manchester, whilst also responding to the planners’ concerns on massing.

Vertical access for the building, both for people and services, is via the core. Positioned offset on the building floor plan this maximises the available floor area and the length of premium elevations facing the square. Building stability is provided by the reinforced concrete core which acts as a cantilever from the raft foundation at basement level under the lateral loading imposed on it.

Supporting the façade presented several engineering challenges. Each unit was constructed in 6m wide by 4m high mega-panels.

The extent of movement of the frame under the significant façade loading was meticulously calculated during the different phases of the build. This involved pre-setting the steel frame, so it could settle incrementally as the mega-panels were installed.

Long-span beams form the typical floors giving column-free flexible spaces. Economy was achieved by integrating the structural and service zones, utilising composite action between the steel beams and concrete slabs and adopting asymmetric sections.

Two St. Peters Square has regenerated a prime site in central Manchester providing a positive contribution to the city and enhancing the adjacent public realm.

Judges’ Comment

This scheme of new Grade A offices in the heart of Manchester’s civic centre responds to the challenge of this site of prime importance. Not only does the glazed stone tracery respond appropriately to the location, but the elegant steel framed building with 18m clear spans provides flexible accommodation highly attractive to tenants.

The Greenwich Peninsula Low Carbon Energy Centre

© Mark Hadden

Architect
C. F. Møller

Artist
Conrad Shawcross RA

Structural Engineer
Price & Myers

Steelwork Contractor
Billington Structures Ltd

Main Contractor
Kier Group

Client
Knight Dragon

From conception the Energy Centre was developed with innovation and creativity to ensure the structure was a stand-out piece of artwork on the newly-forming Greenwich Peninsula.

Central in the structure is the highly distinctive flue tower, measuring 3m by 18m on plan and 49m tall.

The cladding of the flue tower unites sophisticated engineering and complex optic research to create an impressive sculptural concept on a huge scale. The unique cladding is formed of hundreds of triangular panels, each the height of a London bus, that fold and flow across the surface of the tower. The resulting complex geometric patterns visually break up the elevations to create an uneven sculpted surface that plays with the vanishing points and perspective.

The panels are perforated to exploit the phenomena of the Moiré Effect, and at night an integrated lighting design produces a shifting series of ‘compositions‘ lit from within the structure.

The main building and tower are structurally independent to avoid the effects of cyclic loading and fatigue on the tower affecting the main building.

A series of wind tunnel tests were carried out on the tower structure as the cladding design progressed to assess the detailed loads on the structure and the dynamic sensitivity of the tower. A BRE study was also carried out to provide design data for assessing cyclical fatigue loads.

The tensile strength and ductility of steel made it the obvious choice to cope with the effects of high wind loading on the tall slim structure. The industrial aesthetic of steel lent itself to the historical context of Greenwich Peninsula, whilst the cross bracing of the structure echoes the neighbouring gas holder dating from 1886.

345 tonnes of galvanized steel were erected for the flue tower, which consisted of five main cantilever latticed girders, each formed from three 16m high by 3.15m wide sections spliced at third points on-site and placed 4.5m apart. These were connected with interleaving diagonal secondary members fixed to both chords on the main east and west façades.

Close coordination with the cladding sub- contractor was fundamental to achieving the correct setting out and detailing for the hundreds of fixing brackets; each fabricated as part of the steel frame with sufficient tolerance to allow seamless connection and adjustment of the cladding panels throughout the build.

Judges’ Comment

This project forms the gateway to a new and rapidly developing quarter to the east of London and is a remarkable addition to the heavily urban landscape, both during the day and at night. Steel is used with grace and with flexibility for the future in mind. The collaboration between artist, designers, steelwork contractor and this enlightened client has resulted in a holistically coherent and notable project.

Four Pancras Square, London

© Dirk Lindner/Eric Parry Architects

Architect
Eric Parry Architects

Structural Engineers
AKT II and BAM Design

Steelwork Contractor
Severfield

Main Contractor
BAM Construction

Client
King’s Cross Central Limited Partnership

Four Pancras Square is the last of six new commercial buildings within King’s Cross Central Zone B, located adjacent to St Pancras and King’s Cross stations.

As the square’s prominent ‘keystone’, Four Pancras Square demanded a strong identity that resonates with the site’s industrial heritage. This is encapsulated in Eric Parry Architects’ competition-winning design via an expressive exposed weathering steel frame.

The building was designed as a speculative office, aspiring to exceed the British Council for Offices specification and be the first office to achieve a BREEAM 2014 rating of ‘Outstanding’, succeeding in both.

The building is 57m wide on the north elevation, 27m on the south and 54m on the west, producing a 60 degree angle on the east.

These proportions, combined with the concept, resulted in a regular 4.5m column grid on the upper levels and larger spans around the ground floor retail, typically 13.5m, but up to 27m clear span on the south face. The façade structure continues beyond the set-back 10th floor and the landscaped roof terrace above to crown the building.

The key challenges to the design and detailing of the external steel exoskeleton included:

• forming the full width transfer creating the dramatic southern entrance onto Pancras Square.
• control of thermal movements of the external primary frame relative to the internal structure.
• detailing the structure and finishes to accommodate the movements.
• providing the necessary fire resistance to the unprotected steel exoskeleton.
• ensuring the exposed components of the steel exoskeleton and the junction with the internal structure are designed and detailed to provide the required durability.

A Vierendeel truss wrapping the first floor is a key architectural feature. On the southern elevation to the square it forms the transfer structure creating the column- free open entrance onto Pancras Square. The storey-high truss continues to wrap the remaining elevations of the first floor, resolving the different grids required for the office levels and the public realm. Where the steel exoskeleton interfaces with the façade at the perimeter columns the floor slab sits on steel shelves, ‘hods’, which cantilever off the external columns through the façade. These ‘hods’ are tied into the slab and in turn cantilever out to restrain the columns in both directions.

These ‘hods’ result in structural penetrations through the thermal line of the cladding at 4.5m centres across all floors and were a critical connection detail.

Judges’ Comment

The judges recognised the strong technical collaboration of the entire team to deliver the architect’s vision of an expressed weathering steel exoskeleton without compromise. This was achieved through creative development of key technical details to address thermal bridging, differential thermal movements, fire performance and weathering. The building’s elevations are a celebration of steel.

Belfast Waterfront Conference & Exhibition Centre

© GOC Photography

Architect
Todd Architects

Structural Engineer
Doran Consulting Ltd

Steelwork Contractor
Walter Watson Ltd

Main Contractor
McLaughlin & Harvey Ltd

Client
Belfast City Council

The new steel-framed extension to the Belfast Waterfront stretches from the existing building out to the edge of the River Lagan and provides an additional 7,000m2 of floor space which can facilitate up to 5,000 guests at any one time. There is an 1,800m2 main hall and a 700m2 minor hall, each of which can be sub-divided to allow flexible layouts. These large clear span spaces were most cost-effectively achieved with a steel frame.

The facility has been designed to fit in with its surroundings, wrapping around the existing building and connecting to the existing facilities at multiple levels, though remaining an independent structure. The extension spans over the existing services yard and service building on the riverside. Public access to the river has been maintained. The congested location proved challenging, being extremely restricted in terms of access and by surrounding structures and its proximity to the river.

The use of steel meant the construction works could be accelerated given the opportunity to prefabricate the frame offsite in advance.

The complex primary structure was influenced by several factors. The spatial requirements for the extension involved column-free spaces, a combination of single and double-height spaces and partial intermediate floors, and the need to build over and around retained structure. This led to several framing solutions being employed, using 1,400 tonnes of steel.

Pre-cambered cellular beams were used along with metal deck composite concrete flooring. The degree of pre-cambering was calculated to provide level steelwork after dead load deflection.

Extra levels were squeezed in as the building’s footprint gave very limited floor space. To give this intermediate floor sufficient ceiling height ‘Slimflor’ construction was adopted, using plated UC sections within the floor depth.

‘Cellform’ beams were used to form the main hall roof; this allowed services to pass through the beams and thus maximise ceiling heights. These ‘cellform’ beams had a tapered section to provide integral roof falls (and provide a level soffit for rigging steelwork).

For the accommodation built over the service yard, cantilevered plate girders were used as their supporting columns were offset to maintain clear height for HGV access.

This project was Belfast City’s Council’s first use of BIM on a major project. It was delivered using advanced modelling techniques, which minimised on-site clashes and maximised the efficiency of design and construction.

Judges’ Comment

New conference halls, banqueting and break-out spaces extend the Belfast Waterfront Conference Centre right up to the quay of the River Lagan. The resulting multiple challenges, both physical and financial, were met by a sequence of appropriate and pragmatic structural steel and architectural solutions.