Design Awards: 2011: Commendation

River Suir Bridge, N25 Waterford Bypass

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Architect

Yee Associates

Lead Engineer

Ove Arup & Partners Ltd

Structural Engineer

Carlos Fernandez Casado, SL

Steelwork Contractor

Mabey Bridge Ltd

Main Contractor

Bam-Dragados Joint Venture

Client

CRG Waterford Ltd

For over 40 years Waterford City Council had considered providing a second bridge for the City of Waterford over the River Suir. In 1997 it was concluded that, in addition to a river crossing, a new bypass was required which would connect Cork to the port of Rosslare.

A cable stayed bridge was the favoured choice of construction for the crossing as there would be no need for piers. It also provided the option to use reduced thickness decks offering a navigation clearance of 14m – a necessary consideration in a busy shipping area. Time and cost would also be reduced as the decks could be progressively suspended on the cables rather than using temporary supports in the river.

The asymmetrical twin fan of cables used to support the 230m main deck would enhance the 100m centerpiece, an inverted Y-shaped tower planned to stand on the west bank of the river. This 465m long bridge would become the largest span bridge in Ireland and a landmark structure for Waterford City.

Value engineering input assisted with design and build issues faced during the manufacture stage. Changes were recommended, eg all connections of the cross to main girders from welded to bolted joints, which proved to be substantially more cost-effective and reduced the site programme from 12 to eight weeks; erection changes, from using a floating barge craning all the front span decks into position to the decks being erected from behind at deck level reducing installation costs.

The ladder deck structure carrying the dual carriageway road was made up of 80 main girder sections, each approximately 18 tonnes. The fabrication of the main girders for the cable supported section included some elements of complex geometry in the hanger locations. With large welds and complex angles, dimensional control in these areas became critical. Two box sections at the north abutment, each approximately 170 tonnes, were manufactured in the workshop in segments and welded into full lengths at ground level on site. 102 cross girders, each approximately 10 tonnes, were made in full lengths of approximately 20m. Due to the width of the road deck, and to maintain as low a deck weight as possible, the tops of the cross girders were profiled to follow the road camber.

To protect the 2,800 tonnes of steel required for the decks, a Glass Flake Type II Epoxy treatment was recommended and is ideally suited to bridges.

The structure was erected in two main stages. Firstly the back span, erected from ground level with mobile cranes onto trestles up to the central pylon. The deck was subsequently completed with a precast concrete slab up to the pylon which enabled the front span to be erected in cantilever from the pylon using a modular technique. Each module, comprising two main girder sections and cross girders would be delivered piece-small up to the erection crane sited on the cantilevered end of the deck. Over a seven day cycle each module was erected, the cables installed, pre-stressed and the precast concrete deck positioned. In conjunction with the modular build, a supported section of the front span would be erected of which the largest components were the box sections at the north abutment. These were lifted into position using the UK’s largest available floating crane. These sections were supported on an arrangement of trestles and header beams prior to the front span connection being made and subsequently jacked down into the final position and the trestling removed.

The N25 Waterford Bypass was opened 10 months ahead of schedule on 19 October 2009.

Judges’ Comment

A high-profile cable-stayed road bridge, this helps to generate pride in the community.

The complicated arrangements of the multi-national design team presented a real challenge to the experienced steelwork contractor. Perseverance and the pursuit of practicality in the detail design and construction have resulted in a fundamentally elegant bridge which satisfies client and users.

The Hauser Forum, Cambridge

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Architect

Wilkinson Eyre Architects

Structural Engineer

Mott MacDonald

Main Contractor

Willmott Dixon

Client

Turnstone Estates Ltd

The Hauser Forum is a new, mixed-use development at the University of Cambridge’s West Cambridge site. The development comprises the Cambridge Enterprise Building (CEB) and the Broers Building.

The CEB will be the new home for Cambridge Enterprise, a University owned company which assists with the commercialisation of research, and also incorporates a new campus café. The most striking feature is the double height café space which cantilevers 11m from the southern façade of the building.

The Broers Building provides 4,000m2 of high quality commercial, research and development and ancillary space to be let to private organisations. Office space is provided over four storeys, with the steel framed superstructure also boasting a cantilever to the south.

Steel was chosen for both buildings to enable them to meet architectural aspirations and achieve a tight programme. The project retains a large amount of exposed architectural steelwork in canopies and edge detailing. Services and structural zones were combined through the use of cellular beams to limit the floor to floor heights whilst maximizing the available floor to ceiling height in the 18m wide floor plates.

The two buildings are connected visually by a high level steel canopy which covers the new landscaped forum space between the buildings. The canopy also serves a practical purpose in providing solar shading to the buildings.

The principal challenge for the structural design was the double height fully glazed café which cantilevers a total of 11m from the CEB over a reflecting pool under, 3.5m of which forms a terrace extending beyond the building enclosure. Achieving this, while meeting vibration limits for occupant comfort and deflection limitations for the proposed curtain walling system, led to significant analysis and development.

The concept adopted was to use large trusses in the elevations to form the cantilever, which could only be practically achieved in steel. This scheme was developed using Macalloy tension rods as the diagonals in conventional N-trusses. An additional pair of tie bars was added in the southern façade to limit serviceability deflections of the 13.5m single span fabricated box floor beam to the limits required by the curtain walling. The cantilever was erected on temporary props with a precamber of 35mm to counter overall dead load movements and to leave it with an aesthetically pleasing slight upward camber. Once the floor slab had been poured, the Macalloy rods in each elevation were stressed to lift the structure off its temporary seating and the props removed.

The project incorporates numerous design features that enabled both buildings to achieve BREEAM ratings of ‘Very Good’ and EPC ratings of ‘B’. Both buildings are provided with ground source heat pumps installed integrally with the structural piles, which provide up to 117kW of cooling and 188kW of heating. This is approximately 7% of the buildings’ energy demand and delivers a calculated annual carbon saving equivalent to 26,000kg of CO2.

Additional energy savings on heating and cooling were made via the inclusion of innovative thermal labyrinths in the basement of each building. These consist of a series of closely spaced dense concrete block walls arranged in a zig-zag formation through which air is drawn before reaching the building air handling units. This has the effect of lowering the air temperature during the peak summer months by up to 5ºC from ambient, and providing a more stable temperature output throughout the day, reducing the amount of energy expended on conditioning the air. The installed labyrinths were calculated to achieve an equivalent energy output of approximately 91MWh per year, realising a carbon saving equivalent to 10,572kg of CO2.

Judges’ Comment

These two buildings are joined by a covered public space, and the steelwork frames are key to the whole project. Whilst one building is air-conditioned, the other makes effective use of greater mass for natural cooling. The link block has a striking large cantilever over the adjoining lake.

A good example of practical steelwork design integrated into an intelligent solution.

The Rose Bowl, West End, Southampton

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Architects

The Miller Partnership
EPR Architects

Structural Engineer

Ian Black Consulting Ltd

Steelwork Contractor

Rowecord Engineering Ltd

Main Contractor

Andrew Scott Ltd

Client

The Rose Bowl

The addition of two new stands at The Rose Bowl cricket ground in Hampshire has increased capacity from 20,000 to 25,000, making it one of the largest grounds in the country. The number of permanent seats increased to 15,000.

Keen to ensure that the new stands fitted the original visual concept for the ground, a sickle structure was developed visually separating the roof to the permanent seating from the back of house structure, and expressed on the rear elevation by a large visually independent column supporting a timber louvered façade to marry with the surrounding landscape. The stands follow the curve of existing terracing to maintain the bowl concept.

The steel structure which provides the framing for the envelope consists of main frames radially placed at approximately 8.250m centres. Each frame comprises the central accommodation structure, consisting of two floors plus roof. This is 12.2m wide and formed of a regular grid of steel beams acting compositely with a 130mm in-situ slab on a profiled metal deck. A conventional built up system provides the roof to this structure.

Springing from the second floor, the terrace rakers slope down to meet the back of the existing terracing. The rakers are split into two spans by a mid-support which follows the line of the back wall of the new welfare facilities.

Above the two storey structure supported on the front column is the sickle rafter, which forms the main structural member to the canopy roof. This rafter curves round the back corner of the two storey structure forming an independent column which slopes back into the building. This column is discretely connected back to the two storey structure at roof and floor levels. The sickle rafter is formed of standard UB sections with the curved portion formed in plates.

The structure in its final form is a simple braced structure with the floor slabs acting as diaphragms. The main (canopy) roof is braced for the full length to ensure effective transfer of lateral loads. Provision of vertical bracing was only possible longitudinally in the line of columns mid-span of the terrace rakers, and between the sickle columns to the rear of the building. No vertical bracing was possible radially or in the walls of the ‘back of house structure’ due to the numerous openings and glazed areas.

The sickle columns are discretely connected at each floor level and at roof to the accommodation block, taking the form of a radial prop between the columns on each line. At two locations along the length of each stand diagonal members spring from the 914 x 305 UB sickle columns to third points in the adjacent floor edge beams. By this means the sickle columns are discretely connected to the ‘building’ structure, maintaining the required architectural illusion of independence. Thus the vertical bracing between the sickle columns provides the lateral stability to the rear of the building.

The terrace rakers provide a natural brace up to second floor level, the column simply cantilevering from second floor to roof. Again the connectivity to the sickle columns provides a degree of additional stiffness, due to the sheer size of these feature columns.

A cost-effective structural solution was delivered maintaining a ‘simple’ frame, avoiding the need to introduce significant moment connections into the structure, whilst meeting all the architectural requirements in terms of unhindered elevations within the accommodation building, and the main visual impact of an independent roof and rear feature wall.

Judges’ Comment

These two new stands flank the existing pavilion. Simpler than the first building, the design reflects the need for an economic and low-maintenance solution, with clarity of structural steelwork, cladding and the resulting space beneath the stands.

A good example of ‘less is more’.

ExCeL Phase 2, Royal Victoria Dock, London

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Architect

Grimshaw Architects LLP

Structural Engineer

McAlpine Design Group

Steelwork Contractor

Severfield-Reeve Structures Ltd (Severfield-Rowen PLC)

Main Contractor

Sir Robert McAlpine Ltd

Client

Excel London

ExCeL Phase 2 creates new spaces that harmonise with and extend ExCeL’s existing offer in London’s Royal Victoria Docks. Phase 2’s key objective was to provide flexibility to respond to the changing requirements of exhibitors, conference organisers and other users. The Phase 2 developments take ExCeL to a total capacity of 1,000,000 sq ft of flexible space, complemented by the new bespoke conference facility, the 15m high hall, a ‘grand entrance’ and a less crowded, easier-to-navigate arrivals experience for all visitors.

An inhabited spiral accommodates foyer and boulevard facilities and brings the east elevation to life. Elements of the spiral act as the foyer floor, the mezzanine floor accommodating casual dining space, and high-level foyer floor serving the conference hub. It stands independently of walls to dropped exhibition halls so that it can be read autonomously on the east elevation and increase the sense of arrival.

The super structure was fully erected in just over four months and a fully covered working enclosure delivered six weeks later. With the Phase 2 venue pre-booked for the day after practical completion for X Factor auditions, the building was fully constructed in just 22 months.

The clear span halls of 87m are structured through the use of a mast assisted steel truss. The structural masts also pick up the grid of suspended demountable hall partitions. This structural solution was adopted from the existing Phase 1 building which had been proven to be the most cost effective solution, but was distilled and improved upon such that the masts were placed back to back centrally rather than to the perimeter. With this modification it was possible to:

  • Remove the requirement for tie down members and increase structural efficiencies through a balanced structural system.
  • Reveal the structural solution to the visitors occupying the central circulation boulevard.
  • Support the roof lights that line the central boulevard.
  • Avoid any conflict with City Airport take-off and landing zones to the south, along with a clash with the electricity pylon to the north.
  • Construct the building in a logical fashion from east to west by erecting the structurally stable masts, then the trusses.

All environmental solutions were required to be cost neutral in terms of construction costs. Phase 2 includes the provision of a grey water storage tank, waterless urinals and low flow fittings throughout. A significant aspect of energy use for the existing ExCeL venue was through its lighting. Simple effective measures were introduced including PIR occupant sensors and low energy fittings. The main improvement was in the introduction of expansive evenly distributed roof lights to the internalised boulevard and also the upper level breakout space. The Phase 2 building demonstrates a reduction of almost 60% in light energy consumption compared to the equivalent Phase 1 environments.

The use of steel ensured a minimal construction period (just 22 months), a lightweight cost-effective solution, and lent itself to the architectural requirement for numerous cantilevers and large column free spans. Steel really was the only viable structural solution and allowed the design team to express the structural and engineering solutions of the building.

Judges’ Comment

Doubling ExCeL to a million square feet of high column-free space has been admirably achieved by this large steelwork structure. Following the earlier outline, this phase is adapted for the constraints of City Airport and local infrastructure, whilst improving the circulation areas. The cost-effective solution continues the 87m spans, also now with some 15m high bays.

The client is delighted, and exhibitors’ enthusiasm is testament to steelwork’s success.

The St Botolph Building, London EC3

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Architect

Grimshaw Architects LLP

Structural Engineer

Ove Arup & Partners

Steelwork Contractors

Severfield-Reeve Structures Ltd (Severfield-Rowen PLC)
CMF Ltd

Main Contractor

Skanska Construction UK Ltd

Client

Minerva PLC

TThe St Botolph Building is an exceptional new office building offering 560,000 sq ft of lettable space distributed over 13 floors. Planned as a multi-tenanted building, maximum flexibility for letting was crucial.

The design places the cores at the edges of the floorplate which, combined with a stepped internal atrium, creates space suitable for the broadest possible range of occupiers. At the lowest levels, the atrium is offset from the centre of the floor to provide open spaces suitable for small-scale trading. Above this the atrium widens in a series of steps to ultimately occupy the whole centre of the floor. The variety of floorplates created between these two configurations enables a broad range of needs to be met.

The steel frame allowed large structural spans and uninterrupted floorplates. The steel atrium bridges, linking the passenger lifts to each side of the 18m wide atrium, allow the floorplates to be divided into multiple tenancies.

The external form of the building is articulated along each elevation by the expression of perimeter service cores framed in steel with the stairs, lifts and boiler flues on display through steel- framed glazing. The steelwork of these elements is clearly articulated internally and externally. The perimeter stairs were designed as prefabricated steel assemblies, capable of spanning between framing members and bracing the perimeter core structures. This eliminated temporary works and early completion of the stairs provided safe access for trade contractors during construction. Careful coordination greatly reduced the number of site processes required, eg site drilling of steelwork was almost entirely omitted.

A large proportion of the steelwork in the building is visible, clearly displaying its structural function. In the central passenger lift core very tight construction and positional tolerances have been achieved. This was necessary to achieve coordination between the four separate contracts that form the sculptural centrepiece of the building. A comprehensively coordinated floor construction provides the shallow floor/ceiling zone necessary to achieve generous floor to ceiling heights within the maximum permitted building height. Close collaboration within the team resulted in a consistent 690mm deep fabricated beam being used throughout, with flange and web thicknesses tuned to suit loads and spans up to 16.5m.

The team produced a fire engineered solution to minimize the extent of intumescent paint. Fire protection of the perimeter cores was achieved through adjacent slip-formed concrete, omitting the requirement for fire protection to the steelwork of the stair and lift shafts.

A key feature of the building is the innovative passenger lift core. The lifts are situated in a carefully coordinated steel and glass structure visible as a kinetic sculptural centrepiece throughout the building. At higher levels of the structure four atrium bridges brace the steel frame and provide access to the floor plates. The adjacent structures have been designed for future installation of additional bridges, preserving future flexibility.

Temporary steel assemblies built on level 8 transferred the load of four tower cranes directly into the superstructure, allowing the lower crane mast sections to be removed so that completion and fit-out of the floors below could commence early.

Photovoltaic panels contribute electricity directly into the tenants’ small power switchboard. During periods of low demand, the escalators run at a slower, energy saving speed and the lift selection panels in the lobbies switch to an energy saving mode. Car lighting systems switch off automatically when the lifts are not in use.

This impressive building is an excellent example of steel enabling the creation of a dramatic yet functional commercial building.

Judges’ Comment

This large steel framed office is of significant architectural merit.

A major feature is the atrium where banks of twin lifts operate simultaneously in the same open shafts. The steelwork is crisply detailed throughout the floors, glazed atrium bridges, and even to the expressed lift supports.

An exceptionally stylish commercial office building, showing steelwork to great effect.