Design Awards: 2014: Commendation

Gem Bridge, Dartmoor National Park

Gem Bridge, Dartmoor National Park

Architect

Devon County Council

Structural Engineer

Ramboll

Steelwork Contractor

Tema Engineering Ltd

Main Contractor

Dawnus Construction Ltd

Client

Devon County Council

Gem Bridge is part of the 26km long Drakes Trail that connects Plymouth to Tavistock as part of the National Cycleway Network.
The scheme received £600,000 of European funding from the Cross Channel Cycle Project and is also part of wider initiatives to establish better cycling tourism links on both sides of the English Channel.
As the cycleway follows the track bed of a disused GWR Plymouth to Tavistock railway line, Gem Bridge is a replacement of the original Brunel Viaduct that was demolished in the 1960s.
Located on a highly sensitive site in Dartmoor National Park, it was vital that the structure was sympathetic to its surroundings as well as being constructed with minimal environmental impact. The choice of structural steelwork was fundamental to achieving both of these objectives.
The bridge is 200m long and is elevated 24m above a valley floor. It has five spans and comprises of an elegant open steel truss fabricated from hollow sections, with each span having a graceful arched profile. It has a light and open appearance allowing it to easily blend into the wooded area.
The deck is formed from precast panels attached to the top chord of the truss. Viewing galleries are provided at each of the four intermediate piers to give refuge to users.
A steel truss superstructure was chosen as it could be built quickly, with minimal temporary works and fewer on site deliveries than other options.
Buildability was a key factor for this project given its remote location, with access only via the Drakes Trail cycleway for the new structure, the cranes and other plant and equipment.
Comprehensive planning and engagement was required from an early stage to ensure the structure could be constructed. As a result, some of the embankment had to be graded to enable the crane to reach the bottom of the steeply sloping valley.
The structural design of the truss was optimised, not only to minimise material quantities, but also to improve constructability and appearance. Member sizes were also optimised to reduce steel weight and lessen the visual impact. Splice locations were also carefully selected in conjunction with the construction team to minimise the number of lifting operations.
Lifting operations were also constrained by the maximum crane size that could access and operate within the site. The structural design was undertaken with respect to the agreed lifting sequence so all temporary cases and locked in effects were fully accounted for.
Tema fabricated a total of 15 x 15m long steel truss sections in its Cardiff works before being transported to site. Each section had to fit within a 5mm tolerance when assembled into a full span on the valley floor before being lifted into position. The southern 30m span was first to be installed followed by the northern 30m and 40m sections then the central 40m and 60m spans.
Gem Bridge opened in September 2012, providing walkers and cyclists with panoramic views over the steeply sided Walkham Valley and wider Dartmoor countryside.

Judges’ Comment

This is a simple, yet elegant, replacement for a previous historic structure which respects the environment and the heritage of the site. The bridge carries pedestrians and cyclists and spans a deep valley. Site access for construction presented considerable difficulties, which were overcome with careful planning and ingenuity.
The result is a bridge which the public enjoys and of which the client is proud.

Red Bridge House, Crowsborough

Red Bridge House, Crowsborough

Architect

Smerin Architects

Structural Engineer

Lyons O’Neill Structural Engineers

Steelwork Contractor

Southern Fabrications (Sussex) Ltd

Client

Richard and Emma Hannay

Set in an area of ancient woodland in East Sussex, this new build family house is arranged over three levels. The main living spaces occupy the middle floor and lead out on to the veranda hung from and sheltered by the overhanging steel framed roof. The top floor accommodates bedrooms, while the lower level contains a swimming pool.
The structural steelwork frame allows the upper floors to float effortlessly over the hillside, while a series of stainless steel hanging rods define the external veranda wrapping around the house.
A weathering steel plate bridge, that leads to the front door, is set into a steel clad elevation whose oxidised surface echoes the autumnal hue of the trees around.
Internally the steelwork beams, support angles, insitu walls and precast floors are all honestly expressed, while externally glazed areas are set within timber clad elevations on three sides with the fourth overlooking the entrance driveway.
The use of steelwork contributed to the client’s desire to build a house that was architecturally distinguished and environmentally sustainable. The steelwork structure was pared back to the minimum during the design process and this allowed the maximum amount of insulation to be incorporated into the external fabric of the house, while keeping the depth of its exposed edges to the minimum to add elegance to the drama of the suspended upper floors.
As well as being completely recyclable, the steelwork frame has been designed so that each floor is a single structural volume. This will allow the interior of the house to be rearranged to suit future requirements as any number of room configurations are possible.
Similarly, the external cladding and glazing can be removed and replaced or the openings reconfigured without affecting the structural integrity of the overall house.
The use of structural steelwork enabled the 15m clear span to be achieved at the lower ground floor level swimming pool, while providing floor-toceiling openings to the upper floors on the same elevation.
This was achieved by designing part of the steel frame as a two-storey Vierendeel truss. A hanging veranda was also formed using a series of stainless steel tension rods, supported from high level steel beams cantilevering over the truss.
An efficient design was achieved as splices were located at points of contraflexure, and the frame was fabricated in transportable elements to aid erection. This was particularly important as the site is set in ancient woodland with very limited site access and on site welding needed to be minimised.
The use of structural steelwork for this project was crucial in delivering many of the project’s key drivers in a way that no other material could. Steelwork’s advantages in detailed analysis, its ability to transfer load, connection simplicity, versatility, aesthetics, and speed of erection were all fully utilised to help create the client’s unique house.

Judges’ Comment

A striking modern house built on the footprint of its predecessor. This led to a design with a balcony and circulation area thrusting forward of the original building line. The simple, but effective, steel framing incorporates a cantilever steel beam structure, with tension rods carrying the forward perimeter, coping with complex deflections.
Much of the cladding and the access bridge is in weathering steel. So this is an active testament to steel in many forms.

Scale Lane Bridge, Hull

Scale Lane Bridge, Hull

Architect

McDowell+Benedetti

Structural Engineer

Alan Baxter & Associates

Steelwork Contractor

Qualter Hall & Co Ltd

Main Contractor

Qualter Hall & Co Ltd

Client

Hull City Council

This innovative swing bridge over the River Hull is believed to be the first bridge in the world that allows pedestrians the unique experience of riding on it while it opens.
Its black steel appearance and distinct robust form make it a memorable landmark that reflects Hull’s industrial and maritime heritage.
With a 57m span, the 1,000t pedestrian and cycle swing bridge provides a new route that connects the city centre and Old Town Conservation Area to The Deep on the east bank of the River Hull.
The client’s brief was for a bridge that would become an iconic landmark, increase connectivity across the city, unlock regeneration potential and increase the use of the river frontage. The brief also required navigation clearances to be maintained at all times for small boats and the bridge to be able to open for larger vessels.
The bridge’s sweeping form creates a choice of two curving pedestrian routes – one gently sloping, the other stepped. The circular geometry of the bridge’s hub means the walkway is always in contact with the river’s west bank as it swings open, allowing people to walk on and off as it moves.
The structure can carry up to 1,000 people while opening and up to 4,000 people when closed.
The use of steel has allowed the design to incorporate the sweeping curves developed by the architect, while retaining the inherent strength of the steel plate required within the structural design.
Structurally, the bridge consists of a curving steel spine cantilevering from a three-dimensional braced ring that is approximately 15m in diameter. The spine is a hybrid structure with the root section conceived as a diagrid/shell and the tip as a shell. Steel plates clad the surface of the walkways while horizontal bracing provides additional longitudinal stiffness.
The hub structure consists of columns connected to horizontal steel wheel structures forming both levels of the three-dimensional ring. The circular hub section acts as a counterbalance to the cantilever section, with concrete slabs at both levels.
It is supported vertically on a central pintle and six single and four double wheel assemblies running on a flat circular track, secured to a drum supported on 1.6m diameter 30m long piles. Three electric bevel gear units drive the bridge which pivots around a central slew bearing.
The bridge was fabricated in sections at Qualter Hall’s works using temporary support jigs to replicate the finished shape, and trial assembled before transport to site.
On site, the sections were welded together to form the whole bridge structure before being lifted into position in a single operation.

Judges’ Comment

This swing bridge over the River Hull offers the memorable experience of riding on the bridge whilst it opens. The judges appreciated the high quality detail and fabrication of the hybrid spine structure, which forms the sweeping shape. The team successfully integrated a number of complex mechanical, electrical and structural components into this unique rotating structure.
The bridge is greatly enjoyed by the public.

20 Fenchurch Street, London

20 Fenchurch Street, London

Architect

Rafael Viñoly Architects

Structural Engineer

CH2M HILL

Steelwork Contractor

William Hare Ltd

Main Contractor

Canary Wharf Contractors

Client

Land Securities plc and Canary Wharf Group plc

One of the latest prestigious additions of the City of London’s skyline is the 38-storey 20 Fenchurch Street, otherwise known as The Walkie Talkie.
The building has a highly distinctive shape, whereby the floor plates flare outwards to achieve a 50% area increase at the top, compared with the ground level.
The north and south elevations of the structure have a fully glazed profile, while the east and west elevations feature vertical aluminium louvres for solar shading. The louvres line up with the steel members that make up the portal frames over
the Sky Garden, creating the impression that they wrap over the building.
Meanwhile facing the River Thames, the south side of the building is concave and lower in height than the north elevation, which has a triplestorey space over the Sky Garden.
Around 9,000t of steel has been used to form the building’s superstructure, including box section columns, cellular beams and decking.
Double decker lifts reduce the elevator footprint in the building, which means that the services core does not dominate the reduced and tight floor plate at the lower levels.
As the project deviates from the standard office block shape, main contractor Canary Wharf Contractors’ initial challenge was to work with structural engineer CH2M HILL to decide where the core should be located.
The core is usually located in the centre of an orthogonal building, which coincides with its centre of mass. However, at 20 Fenchurch Street the centre of mass and the core are located off-centre, creating spans of varying lengths between the core and perimeter columns. To maintain clear spans between the core and column, and to limit the depth of the beams, prefabricated steel cellular beam I-sections of varying thicknesses were specified and installed by William Hare.
One of the design challenges was how to accommodate the building’s increasing spans higher up the building. At second floor the beams span 11m between the core and the perimeter column, but as the building flares out the perimeter of the building is up to 22m away from the core.
The project team’s solution was to have a maximum 18m span from the core to the perimeter column and make up the remaining distance using a cantilever beam.
All columns are 70mm to 100mm thick plate box sections and inclined to the vertical with the angle of inclination faceting at intervals up the building. For the lower levels of the building faceting straight columns in four-storey units achieved the curved elevation. Near the top, where the building is more curved, faceting takes place every two storeys.
Four-dimensional modelling (3D building information modelling with time added as a fourth dimension) was used to demonstrate the anticipated build and programme, as well as to predict the challenges that needed to be overcome to achieve the highest levels of safety and quality.

Judges’ Comment

The flared shape of this iconic building, in its tight City environment, results in geometric changes at each floor. This presented huge challenges to the design and construction team. By using advanced 4D-BIM modelling, the on site construction problems were minimised.
The steelwork contractor impressed the judges by meeting the challenges of detailing, fabricating and erecting the multiplicity of different floor beams and columns, all culminating in an erection time of just 36 weeks.

Loughor Viaduct Replacement, South Wales

Loughor Viaduct Replacement, South Wales

Structural Engineer

Tony Gee and Partners LLP

Steelwork Contractor

Mabey Bridge Ltd

Main Contractor

Carillion Rail

Client

Network Rail

Forming part of the Gowerton re-doubling scheme, the new replacement steel composite designed Loughor Viaduct has reinstated a double track rail service across the South Wales estuary, improving travel times between Swansea and Llanelli and boosting the local economy.
Originally constructed in 1852, the viaduct was initially a wooden structure and a fine example of Isambard Kingdom Brunel’s once numerous timber viaducts.
Recent detailed site investigations had determined that the old viaduct had reached the end of its life.
In order to improve rail services and restore the line to a double track configuration Network Rail, working with Carillion Rail, opted to replace the entire structure as part of a £48M scheme.
The new bridge has a total of seven spans, five of which are 36m long, and was constructed in structural steelwork.
A primary consideration was how the new viaduct could be constructed within the limited 249-hour blockade provided by Network Rail.
Steelwork contractor Mabey Bridge completed the three-month fabrication of the structural steelwork and walkways at its facility in Chepstow, while temporary works and new bridge piers were being constructed either side of the existing viaduct in the high flow tidal estuary.
Mabey Bridge was also contracted to oversee site assembly, including the supply of temporary pier cross beams to support the launch of the new structure. These beams were installed atop six temporary piers that had been installed on the north side of the existing viaduct.
Steelwork was delivered to site in 24m long lengths and assembled in a laydown area on the west side of the estuary.
Once the first section was assembled, it was launched using strand jacks over the river onto temporary piers. Mabey Bridge then assembled the next section of the deck, bolted it onto the previous section and launched the entire structure further over the river.
This process was repeated a further three times to position the entire new viaduct adjacent to the existing structure. The steelwork was then jacked down onto its permanent bearings. The deck was concreted, waterproofed, ballasted and tracks laid.
The 249-hour rail possession was then initiated and the old structure demolished. Once it had been dismantled and new abutments constructed the new viaduct was slid sideways on its bearings to its permanent location using hydraulic rams.
After the viaduct opened one of Carillion Rail’s final tasks on site was to construct a heritage monument to reflect the old structure. Positioned on the west bank of the estuary, the monument consists of two of the original spans mounted on three of the original trestles.

Judges’ Comment

Replacement of the existing single-track, Brunel inspired viaduct imposed major demands on the team. The practical design of the new twin-track crossing assisted the prefabrication on site of the steel girder deck, which was then launched and slid into place within a 249-hour blockade.
A heroic and successful achievement.