Design Awards: 2010

Forthside Pedestrian Bridge, Stirling

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Architect

Wilkinson Eyre Architects

Structural Engineer

Gifford Llp

Steelwork Contractor

Rowecord Engineering Ltd

Main Contractor

Bam Nuttall Ltd

Client

Stirling City Council

M8 Harthill Footbridge Replacement

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Client’s Engineer

Scott Wilson Ltd

Structural Engineer

Buro Happold

Steelwork Contractor

S H Structures Ltd

Main Contractor

Raynesway Construction Ltd

Client

Transport Scotland

Riverside Bridge, Cambridge

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Architect

Ramboll

Structural Engineer

Ramboll

Steelwork Contractor

Watson Steel Structures Ltd (Severfield-Rowen Plc)

Main Contractor

Balfour Beatty

Client

Cambridgeshire County Council

South Courtyard Infill

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Architect

Devereux Architects Ltd

Structural Engineer

Sinclair Knight Merz

Steelwork Contractor

Graham Wood Structural Ltd

Main Contractor

Geoffrey Osborne Ltd

Client

London School Of Hygiene & Tropical Medicine

Monkseaton Community High School

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Architect

Devereux Architects Ltd

Structural Engineer

Parsons Brinckerhoff

Steelwork Contractor

Pocklington Steel Structures Ltd

Main Contractor

Shepherd Construction

Client

North Tyneside Council

North Liverpool Academy

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Architect

Atkins Design & Engineering

Structural Engineer

Atkins Design & Engineering

Steelwork Contractor

Billington Structures Ltd

Main Contractor

Wates Construction Ltd

Client

North Liverpool Academy Ltd

Wind Turbine Enclosure, Strata, London SE1

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Architect

Bfls

Structural Engineer

Wsp

Steelwork Contractor

Bourne Steel Ltd

Main Contractor

Brookfield Construction (UK) Ltd

Client

Brookfield Construction (UK) Ltd

‘Strata SE1’ is the UK’s first building to have integrated wind turbines. The three 9m diameter turbines, which crown the top of the Strata at level 43, generate up to 45kw of electrical power at peak times. The steel enclosure for the turbines is a unique and complex structure.

The Strata’s roof essentially cuts off the building at an angle, resulting in a geometric shape. The sloping roof, formed by a pair of concave surfaces and a pair of convex off-set surfaces, meant that each of the circular openings for the turbines are 3-dimensional with elevated elliptical rings in differing planes to each other.

The turbines’ power was maximised with longer blades achieved by the narrow structural envelope that was used for the 17m high frame. The enclosure for the three turbines consists of 24 individual elliptical CHS sections and six curved CHS sections. Between these components, beams connecting to fin plates form the rib cage for the cladding. Due to the complexity and the scale of the cladding, the elliptical frame design could only be produced using steel, as it allows the curved profiles of the venturis to be accurately followed. Furthermore, steel is both light and flexible, creating considerably more through spaces to ease the design coordination and construction of the wind turbines, mechanical and electrical services, pipes and cladding.

Continuous coordination between all parties including the cladding specialists and turbine manufacturer was vital to ensure a first time fit. To achieve a perfect fit of the turbines and cladding, it was essential that no steel connections breached within each of the circular openings. The elliptical openings for the turbines were formed from a total of 30 curved hollow section segments, all of which were set out in the fabrication shop using electronic survey data to ensure accurate positioning.

Due to the complex geometry of the build, all 400 secondary brackets had to be unique and welded to tight tolerances. Each one is a different size, pitch and angle and had to be welded to the structure in various planes to ensure the cladding could be fixed accurately first time.

The project involved the supply and installation of complex steelwork, at a height of 150m, with only the structural footprint to work on, which is bounded on two sides by busy London artery roads, an existing 21-storey residential tower and a rail viaduct carrying live tracks just 3m from the edge of the site. Consequently, prefabrication and off-site assembly was key to eliminate the risk of work required at height and ensuring accurate geometry.

In order to speed up on-site erection and reduce work at height individual frames were specifically designed to reach the maximum crane capacity of 6.5 tonnes. Although this method reduced the number of site formed connections, there was still a requirement to access some connections over 17m above the steel foundation levels. This access was provided using mobile elevating work platforms (MEWPs), which were positioned on bespoke steel frames built into the permanent structure.

Judges Comment

The Wind Turbine Enclosure makes a crucial contribution to sustainable energy generation, integrated into a building fabric.

Overcoming severe technical challenges of the complex geometry, working at height adjacent to a main rail line and the stringent vibration and deflection criteria, could all be met only by high quality steelwork.

Terminal 2, Dublin Airport

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Architect

Pascall+Watson Architects

Structural Engineer And Project Manager

Arup

Steelwork Contractor

Watson Steel Structures Ltd (Severfield-Rowen Plc)

Construction Manager

Mace

Client

Dublin Airport Authority

Terminal 2 was developed to provide a new terminal, pier and road frontage systems to cater for 10-15 million passengers per annum, which would be a simple, efficient and user-friendly experience for passengers and all other end users. This was achieved by providing a flexible, expandable and contemporary facility, which acknowledged current trends and international industry standards for airport and passenger terminal design

The terminal building consists of arrivals, departures, check-in buildings and link bridges comprising of nearly 12,000 tonnes of structural steelwork, together with 55,000sq m of structural metal decking, stair cores and staircases.

In order to meet the challenging build schedule, Dublin Airport Authority took a package approach to various aspects of the expansion project rather than using prime contractors to build the entire system. This allowed the airport more flexibility with the phasing of the packages and accelerated the process. The packages included steel, structure, fit-out and specialist systems, and MEP (mechanical, electrical and public health), which spans communications infrastructure and alarms.

The client’s brief was to provide a sustainable landmark building that could adapt over time to the ever changing requirements of the airport industry. The building was to be light and airy and make the maximum use of natural light, and provide a calm atmosphere for passengers. The project also had to be delivered at the ‘right cost’ in terms of both construction costs and life cycle costs, safely and in a manner that did not affect the airport capacity during construction. Independent consultants, appointed by the Government, have confirmed that the budgeting process and costs of Terminal 2 were in line with best international practice.

The new terminal was designed to utilise appropriate technology, which remains flexible to ensure future ‘proofing’, and to provide enhanced efficiency for both airlines and the operator. Certain elements of the structure are designed to allow for further expansion and also for the required increase in demand.

The building was designed to be highly architectural and the curved shape of the building combined with the extensive use of glass satisfies that requirement. The shape of the roof and the large designed spans clearly pointed to the use of steel as the most practical and economic way of creating the curved shape of the building. Bespoke fabricated box section roof girders were designed and these were fabricated from curved plates and fully welded in the factory. Prior to despatch the roof girders were fitted and bolted together during the fabrication process to ensure the tolerances and fit-up on site were achieved.

One of the main drivers during the design development period was to reduce the amount of work on site and this was achieved by providing large pre-fabricated units, up to 20 tonnes each. These were bolted together at low level to form the main roof girders. Heavy plate girders and plated columns were also used to create large spans.

In order to achieve a very tight site programme, and to avoid disrupting the existing airport operations, all the works were planned on both a day and night shift basis.

The structure presented a considerable challenge in respect of fabrication workmanship. The roof and the sides of the building are curved in both plan and in elevation. The use of 3D modelling and CNC data transfer to the cutting and drilling machines were essential in achieving the accuracy and tolerances in the individual components. The manual assembly of the components to form the complex shapes required considerable experience and skill. Bespoke fabrication jigs were used extensively combined with 3D laser setting out equipment with the data being transferred from the Tekla model directly onto the shop floor equipment.

The internal superstructure frame of the building is fire engineered using intumescent coatings. The roof structure did not require fire protection and was shop painted with a primer with the final coat applied on site during the fit-out process

Throughout the design process there was a high degree of communication between the design team and the steelwork contractor to overcome the more challenging aspects of the design and erection to produce an efficient cost-effective structure that could be erected safely. This was particularly evident when considering the erection sequence and stability issues.

Judges Comment

A large complex infrastructure scheme designed and constructed in a short time in the midst of the day-to-day life of a busy international airport. The intention is to provide an exceptionally userfriendly experience.

The expression of the steel structure is clear, with consistent detailing.

A well executed project which demonstrates close cooperation between all involved, and a fine example of the capabilities of steelwork.

Helical Stair, 500 Brook Drive, Reading

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Architect Scott

Brownrigg

Structural Engineer

Ramboll

Steelwork Contractor

Littlehampton Welding Ltd

Main Contractor

Miller Construction

Client

Prupim

The helical stair design follows the principle of creating a functional stair for escape purposes in an innovative aesthetic sculptural form.

The delicate structural steel elements of the spring-like form deceive the eye as to how the stair is supported. Steel bracing within the slender landings restrains the spring form to the building providing sufficient stiffness to avoid vibration and movement. The ribbon-like central steel stringer was formed from a steel CHS allowing for a seamless finish and consistent radius.

The steelwork contractor’s fabrication and finishing techniques demonstrate an elevated degree of craftsmanship. This is particularly evident in the hand cut and finished central stringer where all welds were inspected and ground flush to achieve a seamless finish.

Epitomising form follows function, each structural element was sized to be no larger than that required, thus emphasising the architectural concept. The tread goings and risings are set out to Building Regulations and governed the geometry. Provision of the internal hand rail set the structural central stringer height, incorporating the two functions. Trace heating, access call points and lighting cables from the building are routed within the steel hollow sections, concealing the cables from view.

The epoxy paint finish provides 20 years to first maintenance. The building façade is rated for 60 minutes fire resistance allowing the stair to perform its primary function without the need for expensive intumescent treatment.

Each steel member has been designed to be the minimum required size reducing the steel weight. With vertical support provided by the central stringer the traditional central column has been entirely removed.

Fully fabricated off-site in eight pieces including hand rails and finishes, each stair was erected in just two days, reducing demand on the site tower cranes. Site welding and flush finishing the central stringer welded joints gives the stair its continuous ribbon appearance.

Using the four-storey helical central stringer as the stair’s primary support is an innovative solution. The eye is deceived by how the spring-like form can withstand the vertical loading. Torsion in the stringer is braced back to the building by the thin landings and held at the base by the piled foundation. The restraint at these points enables the spring-like form to support the vertical load without deflection or resonant movement. The use of finite element modelling during the design allowed detailed stress analysis to make each structural element more efficient, using less material.

A template jig was constructed in the steelwork contractor’s fabrication facility which was then used to manufacture identical flights without locking in fabrication stresses and ensuring the identical segments matched up on site.

Judges Comment

The dynamic sculptural form of the escape stairs provides a dramatic external feature to the building. The ribbon-like central stringer is formed from a hand-cut and finished CHS.

Designer and steelwork contractor have worked closely to achieve delicacy of the steel elements, and the outstanding results demonstrate craftsmanship of the highest order.

The Riverside Museum, Glasgow

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Architect

Zaha Hadid Architects

Structural Engineer

Buro Happold

Steelwork Contractor

Watson Steel Structures Ltd (Severfield-Rowen Plc)

Main Contractor

BAM-HBG Construction Ltd

Client

Glasgow City Council

The Riverside Museum provides a new exciting environment in which to showcase Glasgow’s rich and varied transport heritage.

The form of the roof structure is roughly z-shaped in plan with structural mullions at each end that not only support the roof, but also allow the glazed end façades to be supported without the need for any secondary members. In section the roof is a series of continuous ridges and valleys that constantly vary in height and width from one gable to the other with no two lines of rafters being geometrically the same. Generally the cross section is a pitched portal frame with a multi pitched rafter spanning between the portal and a perimeter column. There are also curved transition areas where the roof changes direction in plan.

The rafters themselves are not straight in plan but a series of facets that change direction in each valley. To accommodate these changes in line and to facilitate the connection of any incoming bracing and other members, the rafters at the ridges and valleys are joined at the surface of a cylindrical ‘can’. The majority of these ‘cans’ were truly vertical in the preset geometry of the roof, however where the relative slopes either side of the ridge or valley would have generated inordinately long oblique cuts the ‘cans’ were inclined to bisect the angle between adjacent rafters.

The diameter of most of the ‘cans’ was able to be standardised but, in cases of extreme geometry or where the sheer number of incoming members dictated, a larger diameter had to be used to allow all the incoming members to be welded directly to the ‘can’ wall. The most complicated valley connection had 10 incoming members that necessitated the use of a 1.0m diameter ‘can’ over 1.5m tall.

By using vertical ‘cans’ in the valley positions a standard connection between the tops of the tubular support props and the roof structure was designed. This consisted of a thick circular base plate to the ‘can’ with a blind M24 tapped hole in its centre, thus allowing an 80mm diameter tapered shear pin to be bolted directly to the base of the ‘can’.

The accuracy of fabrication was achieved by using a combination of shop jigs and EDM setting out techniques. All the complex rafter members were assembled in shop jigs whilst the geometry of the more simple members was set using EDM’s that were able to set the positions of certain critical splice connection holes. This was made possible by adding virtual “wires” through the centres of some of the holes during the X-Steel modelling. These wires allowed the EDM operator to check its end position in space when a circular prism was placed in the hole. Using this technology it was possible to accurately position the remote end of a steel member to ± 2mm in any direction.

The more complex members were assembled using shop jigs. These jigs were created by extracting a single member (assembly) from the X-Steel model, rotating it in space to create a single reference plane and then modelling in a secondary steelwork “frame” that the individual pieces (fittings) of the assembly could either be supported on or bolted to.

The whole of the building structure is supported on piles with none of the slabs having been designed as ground bearing. The columns are generally founded on individual pile caps with the slab spanning between individual piles so to allow the erection of the roof to be carried out from within the footprint of the building. The ground floor slab was designed to accommodate multiple 10.0 tonne loads at a minimum of 1.8m centres.

Judges Comment

A prominent site by the River Clyde, and an unusual building form, make this project unmissable.

The technical challenges overcome by the steelwork designers and steelwork contractors were formidable, and it is a pity that the large structure will be mainly concealed. Nevertheless the contribution to the building is both crucial and praiseworthy.