Design Awards: 2005

River Usk Crossing, Newport Southern Distributor Road

River Usk Crossing, Newport Southern Distributor Road

Architect

Yee Associates

Structural Engineer

Faber Maunsell Ltd

Steelwork Contractor

Fairfield-Mabey Ltd

Main Contractor

Morgan-Vinci

Client

Newport City Council

The new Usk River Crossing is a landmark bowstring arch bridge forming the centrepiece of Newport’s Southern Distributor Road (SDR). The 9.5km SDR links M4 Junction 24 to Junction 28 and will provide relief to congested local roads and enhance cross river capacity. It is also intended to act as a key catalyst for local regeneration. Construction of the whole project has lasted two and a half years and at £55m it is the largest local Private Finance Initiative (PFI) scheme in Wales.

At concept stage a number of options were considered, with the arch finally being selected as most appropriate both symbolically and technically for its urban setting and historical context. A single clear span of 187m provided the best environmental solution, avoiding any permanent piers in the river. The arch form adds to the City’s family of notable bridge types and ties in with the city’s desire to develop a riverside walk linking the bridges. Newport’s industrial heritage is reflected by the choice of steel for the bridge’s construction; however, the design is distinctly modern.

Steel is the natural choice for a bridge of this span and type and is used for the primary elements of the superstructure – the arches, the hangers and all the deck beams. The bowstring arch is an efficient structural form that places minimum lateral loads on the foundations. Reinforced concrete is used to provide an economic deck slab, and this acts compositely with the steel beams.

The steel arch members are rectangular in cross section and are parabolic in elevation, tapering in depth towards their apex. They are inclined to convey a sense of enclosure and visual stability. The inclination gives the composition visual interest since the hangers will appear to crisscross when the bridge is viewed from an angle.

The bridge has been delivered by a unified team of designer, main contractor and steelwork contractor, with advice from the architect. This relationship has been a key to the success, and has enabled the design to be carefully tailored to suit not only the preferences of the steelwork contractor and erector, but also respond to the need for the contractor to maintain the bridge for the next 40 years.

Durability was therefore a key issue, which has been addressed in a number of ways. All steelwork above deck level was formed in box sections with no exposed ledges, to promote a clean design. The external surfaces of all the steelwork were treated with a high performance epoxy based paint system, with all box sections being fabricated from weathering steel and left unpainted internally. Weathering steel was utilised for the box members to avoid the significant safety issues associated with applying paint within a confined space, including eliminating the need for future maintenance painting. However, the small additional cost of the steel was more than offset by protective treatment savings.

The steelwork contractor created a fully detailed 3D computer model of the bridge, as input to his automated plate cutting and drilling machines. This model incorporated the significant computed deformations anticipated during erection.

The majority of the deck structure comprises a simple ladder-beam grillage formed from fabricated I sections, to make the most economical use of the steelwork contractor’s automatic ‘T & I’ machine. For the arch, a careful examination of the economics demonstrated that the best solution lay in a rectangular section that was not stiffened longitudinally.

The river has dictated the approach used to erect the bridge. The size and weight of the structure was beyond the capacity of any available cranes to erect in one piece, and so a decision was taken to place two temporary piers in the river, at approximately third points of the span. The River Usk has the second largest tidal range in the world and work time in the river was significantly limited to suit ecological constraints to cater for migratory fish including salmon and the rare chad.

The erection of the superstructure followed a carefully developed sequence. The steel deck structure was assembled in two halves on either side of the river, utilising the pilecaps for the approaches as foundations for the temporary towers. Each half was then launched out over the river, crossing the temporary piers to meet in the middle. Temporary towers were erected on top of the temporary river piers, and a 1200 tonne capacity mobile crane lifted the outer arch sections such that they landed at the abutment and out onto the tower tops.

The central section of the arch was too heavy to lift directly into position, and so it was moved on skates to the centre of the bridge in sections and then welded together to form a single 680 tonne piece which was then raised to its final position using strand jacks. Once all welding was complete, the arch was lowered off the temporary towers to become free standing ready for installation of the hangers.

The initial stressing of the hangers lifted the deck off the temporary piers and was followed by the placing of the precast concrete deck panels. Using precast deck panels enabled most of the weight to be added such that the movements and deformations in the steelwork could take place in a controlled manner. In particular, the tie girder was expected to stretch by about 125mm, which if constrained by a partially constructed insitu concrete deck could produce uncertainty in load paths and cracking of the concrete. Final adjustment of the hangers was carried out before the stitches were concreted.

In conclusion, Newport has gained not only another much needed river crossing, but has gained an elegant steel structure in the process.

Judges’ Comment

s:

The Usk crossing symbolises the best in British bridge engineering. It combines an elegant design, high quality fabrication and innovative construction. The box girder arches, with inclined parabolic form, are fabricated in weathering steel, externally painted and provide long-term maintenance benefits. Its elegance belies the 200 metres span.

The Wellcome Trust, Gibbs Building, London

The Wellcome Trust, Gibbs Building, London

Architect

Hopkins Architects

Structural Engineer

WSP Cantor Seinuk

Steelwork Contractor

William Hare Ltd

Construction Manager

Mace Ltd

Client

The Wellcome Trust

The Gibbs Building at 215 Euston Road is the new home of the Wellcome Trust. Adjacent to the independent research charity’s Greek Revival headquarters (no.183), it provides much needed space for over 500 members of staff. Having won the commission through a design competition held in December 1999, the architects focussed on resolving a number of key issues, responding both to details explicit in the brief and implied throughout the site’s unique urban environment. A headquarters was required that would surpass the efficiency and economic viability of a commercial office building, while offering the prestige that an international organisation such as the Wellcome Trust deserves; distinctive but not flashy, timeless but not extravagant.

The building would also need to respond to the contrasting urban characteristics of Euston Road and Gower Place, to the compositional order of no. 183, and to the need to integrate Euston Square underground station.

Designed to bring the whole administrative team together from disparate office buildings into a single, inspiring, comfortable, ergonomic and socially dynamic workplace, the building comprises two parallel blocks of open plan, flexible, office space. Separated by a 9m wide atria, a ten storey 18m deep block addresses the Euston Road ‘by-pass’, while a 9m wide 5-storey responds more appropriately to the streetscape scale of Gower Place.

Avoiding the banal familiarity of standard office building entrance sequences, where users are traditionally herded through blind lift lobbies to remote and isolated floor plates, in the Gibbs building all users – visitors and staff alike – pass through the lofty atria en-route to the ground floor café and seminar rooms, upper level office spaces or dramatic panoramic roof-scape restaurant. The spatial efficiency of the building is extremely high due to the careful integration of structure and services, with the steel structure being made as slender as possible, braced by plate steel walls, expressed ties and concrete slabs. Through the asymmetrical disposition of the cross section, mini atria, connecting spiral stairs, and differing configurations of atria screens help the building to offer many varied spatial configurations and relationships to the rich urban landscape beyond.

Almost entirely clad in glass, the building incorporates a sophisticated series of triple glazed prefabricated façade cassettes which, while unifying the building through their carefully considered proportion and repeated bay composition, help reduce solar gain and heat build-up during the summer and provide a pre-heated buffer to insulate the building during winter. This component, combined with assisted ventilation through the atria and high day-lighting levels helped achieve an excellent BREEAM Excellent rating. The building is exemplary in its detailed execution, demonstrating the highest order of integration. With no excess, no redundancy and no fuss, the building responds to brief with efficiency and discipline, while producing a working environment that is materially, spatially and functionally rich. Completed in the summer 2004 and occupied shortly afterwards, at a cost of just under £3000 per sq metre, the rigorous attention to detail, careful planning and considered choice of materials sets this building as a benchmark for others to replicate. As a second phase the architects are currently working on the refurbishment of no. 183. Due for completion in 2006, this will be reconfigured as a new public venue incorporating the famous Library and new study rooms with improved access throughout.

Judges’ Comment

s:

This 22,000 sq m building in the heart of London is a most successful outcome of structural and architectural design. Steelwork is at the core of the solution.

It has achieved a simple, clear design that is logical and sensitive in its master-planning, sophisticated in its detailing and uncompromising in its execution. The result is a classic of its type. Congratulations are due for this excellent team effort.

Midland Mainline Bridge Deck A, Kings Cross/St Pancras

Midland Mainline Bridge Deck A, Kings Cross/St Pancras

Architect

Rail Link Engineering

Structural Engineer

Rail Link Engineering

Steelwork Contractor

Watson Steel Structures Ltd

Main Contractors

Kier Nuttall Joint Venture

Client

Union Railways

The Midland Mainline Bridge, links the West Coast Main Line with both the Channel Tunnel Rail Link and the newly refurbished St. Pancras Station. The bridge is a skewed Warren Truss/Arch spanning almost 50m with a centre depth of 9m and a width of 15m. The weight of the bridge is approximately 1000 tonnes. Watson Steel Structures were awarded the contract for the manufacture and installation of the bridge in March 2002 with completion date of June 2003.

Two major design constraints affected the design and choice of materials – how to minimise future maintenance of a structure in place over a major arterial electrified railway corridor and how to place the bridge there in the first place. The first was satisfied by the use of weathering steel to fabricate the lower portions of the deck where future maintenance of a painted structure would be extremely difficult. The second by assembling, welding and painting the deck in an area behind one abutment and then launching it across the railway lines during a 55 hour possession over Christmas 2002.

The two main girders are Warren Trusses with a curved top boom which also benefits from the arch action. The top booms are orientated as an H with 55mm thick webs and 105mm thick flanges and the diagonals are 930mm deep plate girders with 40mm flanges all fabricated from Grade S355 plate.
The bottom boom of the trusses are 2.0m deep plate girders with their 45mm thick bottom flanges in weathering steel, their 60mm thick webs in subgrade J2G3 and their top flanges in Hyzed steel plate. The cross girders, also fabricated from weathering steel plate, are approximately 15m long with webs shaped to create a drainage fall away from the centreline of the deck.

The deck was shop fabricated in large elements weighing up to 45.5 tonnes. The bottom booms were fabricated with a dead load pre-camber and trial assembled together with their cross girders to ensure a correct fit for site welding. The booms were then laid on their sides and the arch sections and diagonals also trial fitted. Both the bottom boom and arch sections were provided with integral run-on, run-off plates on their “trouser legs” and these were match drilled during the trial assembly to allow the arch to be assembled at site with the diagonals bolted using temporary cover plates. To avoid transverse on-site FSBW’s in the arch member webs and flanges, the ends of each member were machined during fabrication and trial fitted to ensure full bearing thus allowing a smaller PPBW’s to be used.
The weight of the arch sections was supported on temporary props during welding.

There was insufficient room behind the abutment to assemble the bridge and so it had to be assembled ‘off-line’ and then rotated into its final position. There were further complications in that part of the launch nose had to be removable during the rotation phase to avoid it clashing with an existing building and the concrete structure behind the abutment was unable to support the weight of the rear of the deck so it had to be supported on the bearing shelf whilst it was rotated into its final position.

The deck was partially concreted prior to the launch and this ensured that any future concreting works could be undertaken without the need for an isolation of the railway. The concrete also contributed to the stability of the deck during the launch although additional concrete kentledge blocks were needed to achieve a satisfactory factor of safety.

The bridge was launched using a combination of 500 and 1000Te hydraulic skid shoes running on tracks on concrete ground beams and fabricated steel beams supported on steel columns founded on piled foundations. The skid shoes were self-powered and allowed the bridge to be driven forward over the railway lines until one corner was directly over its bearing position. This corner then formed the pivot point for the subsequent rotation.

The supports during the rotation phase were additional 1000Te skid shoes that moved along tracks founded on the bearing shelf. These supports not only had to move along the bearing shelf but also allow the bridge to rotate and slide longitudinally above them during final positioning.
Strand jacks attached to the end of the main bridge girders were used to facilitate this longitudinal sliding movement.

When the bridge was above its final position, the load was transferred onto climbing jacks and timber cribbages and then progressively jacked down. As soon as the bridge was sufficiently stable to be supported on four single climbing jacks, the structural bearings were installed and attached to the undersides of the main girders and end trimmers. The bridge was then jacked down to its final level and locked off to allow the bearings to be grouted.

This bridge has provided the client, Union Railways, with an aesthetically pleasing, low maintenance structure installed with minimal disruption to existing infrastructure and services.

Judges’ Comment

s:

In the congested site outside St Pancras and King Cross Stations; the planning, logistics, design and fabrication skills of the team were pushed to the limit in the construction and final positioning of this structure.

The low-maintenance bridge, of 1,000 tonnes, 50 metre span fully welded warren trusses, will link the West Coast mainline to the Channel Tunnel Rail Link. An impressive achievement.

Tower Environs Scheme, Tower of London

Tower Environs Scheme, Tower of London

Architect

Stanton Williams

Structural Engineer

Arup

Steelwork Contractor

Bourne Steel Ltd

Main Contractor

Wallis – Kier Ltd

Client

Historic Royal Palaces

The fundamental purpose of the Tower Environs Scheme is to improve the visitor experience of the Tower of London by enhancing its setting, legibility, accessibility and context.

A major feature of the design is a set of three boldly modern buildings that define and provide scale to a large, open, public space. The quality of the design and materials is of a standard in keeping with the iconic and regal significance of the Tower of London and its status as a World Heritage Site.

The Tower Environs Scheme creates one of the largest public spaces in the City of London and in doing so makes conspicuous use of modern design to reinforce the historic setting.

The use of high quality exposed structural steel for the three buildings was fundamental to that achievement. The buildings are:

  • The Vaults Canopy. Providing a new roof over the Tower of London ticket kiosks, the entrance to the Tower Hill Vaults and a landmark at the top of Tower Hill. Overall dimensions 45m x 12m x 6.5m high.
  • The West Pavilion. Providing a Welcome Centre for the Tower, a Group Ticketing facility and a refreshment kiosk.
  • The Pavilion also defines the west side of Tower Hill and forms a transition from Tower Place to the Tower of London. Overall dimensions 45m x 9m x 6.2m high.
  • The Pumphouse Shop. This replaces a 1930 extension to Salvin’s Pumphouse (a Grade II listed building) and helps to clarify the relationship between Tower Hill
  • and the River Thames. Overall dimensions 22.5m x 5.8m x 6.2m, with a mezzanine of plan dimensions 19.3m x 4.5m.

The apparent ease with which the Tower Environs Scheme presents itself was also the result of much care and effort in founding the buildings. The whole site is underlain by an extensive and rich archaeological resource and a very large number of major modern utility services, critical to the function of the City.

A fundamental architectural objective for the buildings was to achieve elegant simplicity using common detailing themes for all three buildings. The geometric relationship between the envelope and the structure was critical. The purity of the envelope planes and their junctions meant that the rules for locating the steelwork created an arrangement of relatively small but important offset dimensions – requiring great care and virulence by the Designer and Steelwork Contractor.

An important structural engineering aim was to design the steelwork to create the visual precision required without having to resort to workmanship and material standards beyond those of the National Structural Steelwork Specification. To maintain these aspirations through design, fabrication and installation required a collaborative partnership between the Designer and the Steelwork Contractor.

The structural form of all three buildings is relatively simple, essentially arrangements of columns and beams.

In terms of structural exuberance the most challenging and impressive is the Vaults Canopy. It cantilevers over the Tower Hill Vaults and accommodates a large window opening in the granite wall facing Tower Hill. The simplest is the West Pavilion. The smallest and most complex is the Pumphouse Shop; incorporating a mezzanine floor hung from the roof structure.

Stability for all three structures is generally achieved by vertically cantilevering columns in conjunction with cross-braced roofs.

The architectural objective to have the same shallow structural depth for the roofs of all three buildings was a particular challenge in satisfying the requirements of stiffness, strength, dynamic response and economy.

For the Vaults Canopy the main construction challenge related to the positioning and alignment of the cantilevered roof. The dead load deflection was addressed by pre-cambering the beams but the presence of three potentially, interdependent, load paths meant that the pre-camber dimensions were influenced by small dimensional changes (fabrication and erection permitted deviations) and the erection sequencing. The nine-stage erection plan developed in close collaboration between the Designer and Steelwork Contractor incorporated multiple slots at five locations along the horizontal edge beams to facilitate a more exact final positioning. The calculated deflection for each construction stage was measured on site and the temporary conditions were “frozen” by high strength friction bolts in order to achieve the final levelled condition after completion of the roof.

The Heritage Lottery Fund, the Pool of London Partnership and Sir Paul Getty, supported the Tower Environs Scheme.

Judges’ Comment

This trio of neat pavilions form a backdrop to the Tower Environs improvement project. This has greatly improved the experience of visitors to the Tower of London.

There is an elegance about the design and detailing of the buildings, which belies the skills of the designers and the steelwork fabrication, to achieve a mature, precise and classically Miesian simplicity in the project.

Rolling Bridge, Paddington Basin

Rolling Bridge, Paddington Basin

Architect

Thomas Heatherwick Studio

Structural Engineer

SKM Anthony Hunts and Packman Lucas

Steelwork Contractor

Littlehampton Welding Ltd

Main Contractor

Littlehampton Welding Ltd

Client

Chelsfield PLC

Imagine a steel pedestrian bridge rising up over a canal inlet and curling into a ball on one side to allow passing water traffic through. That was the vision that Thomas Heatherwick had when he designed the Rolling Bridge for the new commercial development at Paddington Basin in London.

The 12.9 metre pedestrian bridge spans an 8.5 metre canal inlet at the new commercial development in London’s Paddington Basin. The bridge maintains the continuity of the canal towpath to foot traffic and tackles the issue of access to the inlet in a unique and novel fashion.

With the end bay securely fixed to one side of the dock, the remaining seven bays, powered by hydraulic rams, push the handrails upwards lifting the bridge and then rolling it back to form an enclosed ball. The result is a delicate balance of art, machine and structure.

Designed to open in 180 seconds, the innovative concept was realised by the close cooperation and skills of the design team. The unusual nature of the bridge led to a number of interesting and esoteric engineering challenges as the design has to contend with the ever-changing geometry and load conditions associated with movement. The project required precision bearings and pins with challenging fabrication tolerances. Fabricated with grade S355 hollow section steel tubes, the structural frame has a hardwood timber deck to both faces of the base. The void within the deck is used to route the hydraulic feed and return hoses to power the rams.

The unusual nature of the bridge led to a number of interesting and esoteric engineering challenges.
As well as the usual bending, shear, deflection and dynamics checks common to all structures, the bridge design has also to contend with the ever-changing geometry and load conditions associated with the movement.

In its unrolled ‘bridge’ configuration the handrails act as the top boom of a simple truss. The handrails are pulled below the horizontal to lock the bridge in position, this guarantees that a small component of the compression load is directed downwards ensuring the stability of the bridge under load. The Handrail (compression boom) is afforded lateral restraint by the U frame nature of each segment. As the bridge opens the handrail pushes through the horizontal, this initial movement momentarily extends the top boom causing the bridge to arch. To relieve the large forces that would otherwise be generated by this movement, the ‘fixed’ segment of the bridge is mounted on a rocker allowing the necessary rotation.

At this point the lift begins and the structure changes from a simply supported truss to a cantilevered truss with the obvious load reversal between top and bottom booms. During the lift the hydraulic rams become an integral structural component with a number of the segments once again experiencing complete load reversal as the bridge rolls over centre.
In the closed condition, stops mounted at the top of each hydraulic cylinder carry the static load of the bridge. The hydraulic team achieved the delicate control of the bridge through pure hydraulics. A hydraulic pump drives a master cylinder; which is mechanically linked to 14 slave cylinders. In turn, the slave cylinders drive the bridge cylinders. Ensuring all the cylinders are driven at a constant rate is key to the operation of the bridge. The operation of the bridge is by a remote pendant control, similar to those commonly used on British Waterways installations. The operation is continuous so long as the switch is held in the closed position. Simply releasing the control can facilitate an emergency stop, this presented another engineering challenge, to design for the additional dynamic effects in dissipating the momentum of the moving structure.

The fabrication proved equally challenging. To achieve the geometry in the bridge configuration, and more especially in its closed form, required fabrication tolerances normally found only in the domain of mechanical engineering. When closed, the handrail components converge in the centre of the bridge with a little less than 10mm clearance between them.

PTFE impregnated dry bearings were employed for their dimensional stability, longevity and maintenance free operation. The bearings and (Duplex) stainless steel pins are fitted to a tolerance +/-0.016mm, with a tolerance between pin centres of just +/-0.15mm.

Each bridge segment is fabricated in three sections, two welded side frames and the deck. It was originally intended that the segments would be fully welded frames, but to practically achieve the required machining tolerances a bolted connection was introduced between the side frame and deck.

Extensively modelled in CAD and exported to Robot analysis software, bridge models were used for the static analysis as well as confirmation of the geometry. In addition, using animation tools, a virtual working model was generated to confirm the motion and allow component measurements in any configuration.

Judges’ Comment

s:

This machine-like structure is a wonderful joyful addition to the development around Paddington Basin. Its purpose is to provide a footpath across the entrance of a small dock while still allowing boat passage when rolled up. When in position the elements are configured so as to form a structure without the need for the power hydraulics. When rolled the machine has all the appearance of a Leonardo sketch. The workmanship and detailing of the construction is more reminiscent of the frame of a grand piano than a piece of structural engineering. It is a delight.

Milestones of Flight, RAF Hendon

Milestones of Flight, RAF Hendon

Architects

Feilden Clegg Bradley Architects LLP

Structural Engineer

Buro Happold

Steelwork Contractor

S H Structures Ltd

Main Contractor

Norwest Holst Construction Ltd

Client

The Royal Airforce Museum, Hendon

Feilden Clegg Bradley was appointed in 1999 to consider the phased development of the RAF Museum at Hendon. The Museum needed additional museum space and higher quality accommodation for both permanent and temporary exhibits, and a building that would act as a focus point for the whole site.

The first phase comprises the new “Milestones in Flight” exhibition: a collection of classic aircraft selected from aviation’s 100 year history. This project received a £5.15 million Heritage Lottery award in 1999, went on site in 2002 and was opened to the public on 17 December 2003 on the centenary of the first powered flight by the Wright brothers.

The building bridges the gap between the existing disparate museum buildings. It takes the form of a simple barrel-vaulted structure enclosing the maximum possible volume and providing a structurally efficient frame from which to suspend aircraft.

The barrel vault is clad externally in stainless steel, evoking the sleek fuselages of modern aircraft, and internally in semi-translucent fabric panels which conjure up images of the stick and dope construction of early aircraft. The two ends of the building are entirely glazed in cast glass channels which glow at night and provide diffused light during the day. Internally a series of staggered mezzanine boxes and walkways form a building within a building.
The building form is echoed within the curves of the dramatic steel structure marking the museum entrance. Developed with the Japanese-born sculptor and former architect Kisa Kawakami, ‘Sky Dance’ rises 25 metres into the air, suggesting aspects of aircraft structure, airflow and flight.
Within the building, pollution, temperature and humidity levels are regulated by means of an air-conditioning system. After extensive environmental studies examining the possibility of using passive controls this was seen as the only option given the fragile, and often priceless, nature of the aircraft.

However, unlike all the other museum buildings, which are essentially black box spaces, the building has a strong emphasis on natural light. A continuous roof light at the apex of the barrel vault allows daylight to fall onto the back of the fabric panels, at certain times of day creating huge scalloped shadows. The fabric also acts as an environmental filter preventing harmful UV light from damaging the exhibits.

The Hendon project was severely cash limited but was nevertheless completed both on time and within budget whilst providing a high value for money building of this type and use (in terms of cost/square metre.)

The project value was £7.2 million with a building cost of £5,293,696 (cost per square metre £1,713). Building Area – 3090m2

Judges’ Comment

s:

A crisp solution to provide flexible space to display historic aircraft. The barrel vaulted steel truss structure allows the suspension of aircraft in many different combinations. The incorporation of a membrane inner lining enhances the effectiveness of the space.

The striking entrance canopy/sculpture required skilful fabrication.

Plantation Place South, London

Plantation Place South, London

Architect

Arup Associates

Structural Engineer

Arup Associates

Steelwork Contractor

William Hare Ltd

Main Contractor

Bovis Lend Lease

Client

The British Land Company PLC

Plantation Place South is the second commercial office building designed by Arup Associates for The British Land Company on a 2.5-acre site in the heart of the City of London. It joins the earlier larger building as part of a strategy to knit the new development into the City’s historical context, including the creation of new through pedestrian routes and views of Wren’s St Margaret Pattens church, while establishing a clear identity for itself on the southeast corner of the site.

The objective of the structural design, beyond satisfying the normal functional aspects, was to enhance the delivery and value of the project, these being the key objectives of a speculative commercial development, as well as to incorporate modern innovations where appropriate.

The plan layout was arranged with a central core and basement to mitigate the impact of perimeter site constraints, which were separately addressed in advance of construction. A substructure ring slab was configured to offer open basement construction and give immediate clear access to a slip form core for an early gain on critical path activity.

The structural frame system was optimised for efficiency and buildability. A detailed comparison with a comparable post-tensioned concrete flat slab, with the same overall structure/services depth, showed that the selected steel framed composite slab construction offered a 10% saving in the cost of foundations, a 6% saving in the frame cost, and a 5% saving on the programme time. Also, by taking into account the space between steel beams for services cross-overs and riser entries, additional services flexibility is in fact offered.

A distinction of the building is that it is the first building in the City of London to have been approved by the District Surveyor without applied fire protection to secondary steelwork. This has been achieved by appreciation of real fire behaviour and by state of the art finite element modelling of the mechanical response of the structure so that appropriate robustness can be designed in. The fire engineering approach has developed previous research into a real world practical application that can be applied to future steel framed buildings. A net reduction in total fire proofing costs was achieved, of the order of £5/m2.
An innovative prefabricated modular load-bearing stone façade was developed as a consequence of the urban context, as well as the new Part L building regulations which limit the potential extent of glass. The solution evolved from a pattern established in the first phase of the project, particularly in the use of projecting stone fins to provide self shading and a desire to exploit the high strength properties of the limestone approved by the Planners. The prefab component and infill window approach, incorporating stainless steel interconnections, offered an economically competitive alternative to the more usual and more limited curtain wall cladding market, as well as giving the building its distinctive character and appearance.

Judges’ Comment

s:

The design of this steel framed commercial office building situated in a prominent conservation area in the City has used innovation to optimise the design solution. The adoption of state-of-the-art thermo-mechanical analysis, justifying leaving the majority of the secondary steelwork unprotected, brought significant costs savings resulting in the first approved use of this approach for a building design in the City of London. The load bearing stone façade avoids column obstructions at the office perimeter.

Concast Facility Extension, Port Talbot Steel Works

Concast Facility Extension, Port Talbot Steel Works

Structural Engineer

Rowecord Engineering Ltd

Steelwork Contractor

Rowecord Engineering Ltd

Main Contractor

Rowecord Engineering Ltd

Client

Corus Strip Products UK

Rowecord Engineering Ltd completed this major project for Corus in December 2004. The brief required design, manufacture and erection of a total of 6,000t of structural steel in this 50m high facility covering an area of four football pitches. The project involved some very heavy members – such as structures to support 500t capacity cranes.

The project was entirely commercially driven. It was completed on time and within budget. Functional in the extreme, the project has no aesthetic ambitions. But this is a fine example of innovation, problem solving and construction project management.

The challenge was to design and build a three bay extension to the existing caster building including internal process steelwork, a new water treatment plant and move a 300t per hour conveyor. This will increase the plant’s output by some 1m tpa.

The project presented major design challenges. The nature of the existing plant prohibited conventional erection methods. Despite the large plant size and the volume of steel to be erected, the site was small. Rowecord were set a difficult task of tackling fundamental changes to a major industrial process without interrupting continuous production. As a continuously working plant, focus on safety was directed both at the needs of construction and also continuous production.

The project demonstrates the many benefits of offsite modularisation and on-site assembly of steel structures. Quality is maximised through manufacture in a fully equipped engineering workshop. Time spent on site is also minimised – meeting the needs of continuing production. Most important this makes a vital contribution to best possible health and safety management.

Alterations for new facilities demanded innovative engineering solutions. The most significant change was the removal of a key column weighing some 150t to make way for the new caster turret. Its removal presented a problem of supporting the unit’s two 500t capacity cranes.
The solution was to replace the existing 16m span crane-girders with a single 32m equivalent. This girder needed to be a 4.8m deep plate girder weighing some 120t. This “leviathan” was made in two 60t parts at Rowecord’s site in Newport, transported to site and welded together for installation.

In lieu of nine standard 30m roof trusses, erected singly and subsequently clad, Rowecord designed a solution of pairs of trusses which were fully pre-assembled to create roofing modules with all purlins and cladding fitted. This had a major logistical benefit that a roof which might have taken three weeks to build – and then subsequently clad – took a total of just five days to install.

The project involved relocating and reconfiguring a 45m high water storage tower weighing some 270t. This was lifted to its new location in one piece complete with water tanks using a 1,200t capacity crane.

The concast extension required a 30m diversion of a main materials artery, the “633 Conveyor.” This carries some 300t per hour of vital materials – a process requiring minimal interruption. With a shutdown period of just three days, a new conveyor line was created before a last moment diversion of the materials flow and then dismantling the old conveyor structures.

Judges’ Comment

s:

This extension of the Concast facility, in a continuously working steel plant, displays a highly effective structural design which was subject to frequent design changes, with a “construction-led” philosophy.

The logistical challenge was immense on such a confined working site and with continuously evolving requirements.

Private House, Kingstown St, London NW1

Private House, Kingstown St, London NW1

Architect

Springett Mackay Architecture

Structural Engineer

Techniker Ltd

Steelwork Contractor

Brent Fabrications Ltd

Main Contractor

Harris Calnan Construction Co Ltd

The new house completes a narrow mews in Primrose Hill, North London. Construction on the confined site was complicated by the continuous building frontage and absence of working area around the building. The design of the house makes full use of the available space. A steel framed structural solution was adopted to speed up and simplify the construction process and to allow for the development of ‘lateral space’.

The building is entered from the back of a car parking area sheltered by the first floor overhang. The front door opens into a double height hall with wide steel stair leading up to the main living spaces at first floor level. The stair is carefully detailed with stainless steel handrails and clamp plates to the toughened glass balustrading.

The main structure comprises two storeys of posts and beams set on a foundation of bored concrete piles. The building is approximately 12 metres square on plan and six metres tall. Ground beams and a suspended ground slab support a lower storey of brickwork and lightweight partitions. Subsoil conditions were found to be very sensitive to moisture changes and the pile foundation is taken deep down to the firmer layers of London Clay. Compressible void formers isolate the entire building from the surrounding ground.

The first floor is open plan, column free, with a large window across the entire north elevation. This floor cantilevers out over the rooms below. The wide spans are in-filled with timber stressed skin construction to reduce the overall weight of the building. The floor, wall and roof thicknesses are minimized by the use of universal column sections. Beams and columns are combined to form continuous rings around the upper storey. Axial and bending stresses are allowed to develop in all the structural components so as to reduce overall deflections.

The steel frame was prefabricated and assembled at works then cut into transportable components. Site joints were located away from areas of complicated fabrication and towards points of minimal stress, which could be readily accessed for reassembly. The long cantilevers at first floor level required complicated pre-cambering.
The construction period was slightly less than a year and the frame was erected within the space of four weeks. The dynamic behaviour of the structure was closely studied using a computer model to simulate footfalls. Precise points within the building to be used for study and relaxation were examined to ensure that structural movements would be imperceptible. Completion was in November 2003.

Judges’ Comment

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This cleverly planned London pied-à-terre makes the most of a constrained mews site, and improves the local amenity. The living space is in a clearly expressed “box” on the first floor, thus giving advantages of sunny, elegant living rooms with good views to mews and garden.

Steel framing behind the scenes enables these objectives to be achieved beautifully, relying also on a clear working relationship between architecture, engineering and construction.