Design Awards: 2015: Commendation

Greenwich Reach Swing Bridge, London

Greenwich Reach 1

Architect
Moxon Architects

Structural Engineer
Flint & Neill Ltd

Steelwork Contractor
S H Structures Ltd

Main Contractor
Raymond Brown Construction Ltd

Client
Galliard Homes Ltd

Long planned as part of the development at Greenwich Reach, the bridge provides a valued link for residents to access public transport links and local attractions.

The bridge has a 44m cable stayed main span supported from a single mast with a central stay plane. A short 8m backspan contains a 120t counterweight to balance the structure. Two pairs of backstays support the tip of the mast laterally and longitudinally.

The structure is supported on a 3.7m diameter slewing ring bearing underneath the mast, with a set of four electric motors to drive the bridge clear of the navigation channel concealed in the machine room within the main concrete pier.

To swing the bridge across the channel, the drive motors rotate the bridge through 110 degrees. As it reaches the end of the swing, two stainless steel nose wheels engage with ramps on the west abutment to lift the nose upwards into its service position. An electrically actuated locking pin then engages to provide a nose restraint against extreme lateral loads.

Faceted planes create an elegant and visually massive backspan and reduce to a more slender main span with a central spine box supporting diagonal struts to the edge of the deck. The plated concept is continued through the main mast, where two vertical flat plates supported by diagonal stiffeners create an innovative open Vierendeel type structure. The inclined web plates create openings to the sky to lighten the appearance for maximum transparency.

Steel is crucial to ensuring that the moving span is as light as possible. By using externally painted weathering steel for closed sections, any requirement for internal inspection and maintenance has been removed.

Rolled ‘T’ section struts are used to support the edge of the deck, creating a thin edge beam and hence a slender appearance. The struts are inclined in plan and elevation to create a lightweight space truss to enhance the torsional stiffness of the deck supported by the central stay plane.

To minimise onsite welding and meet a tight construction programme, sections of the bridge were prefabricated offsite and brought to site by road. The structure was designed to facilitate easy fabrication, and the designers worked closely with the steelwork contractors to ensure an economic construction process.

The sections were craned into place in the open position before the backspan counterweights were installed and site welding completed.

The bridge provides an exciting link for pedestrians while still maintaining a thoroughfare for marine navigation.

Judges’ comment

Through simplicity of form and operation, and structural efficiency, this bridge is exemplary in its use and expression of plated steelwork. It has become a thriving route for cyclists and pedestrians, linking the new communities of Deptford Creek.

At the mouth of the Creek, this forms an effective and attractive feature of the maritime landscape of the Thames.

Heathrow Terminal 2B

Heathrow Terminal 2B 1

Architect
Grimshaw

Structural Engineer
Mott MacDonald Ltd

Steelwork Contractor
Severfield

Main Contractor
Balfour Beatty Plc

Client
Heathrow Airport Ltd

T2B is a satellite pier for the new Heathrow Terminal 2. The structure is rectilinear in form and accommodates 16 stands. A 520m long steel-framed superstructure sits above a two level basement. By elevating arriving passengers over departing, the building offers a sense of space and inverts the familiar ‘undercroft’ experience of the arrivals journey.

The use of structural steel was essential to delivering the satellite pier to the client’s programme. Using steel plunge columns allowed excavation of the basement by top- down construction while the pier’s structural frame was erected above.

Among the first elements fabricated and installed onsite were the 163 plunge columns, assembled from the heaviest UC section and two 40mm thick steel plates, welded together to create a thick-walled box. The efficiency of this section and the novel ‘top hat’ connection – which transfers load from the concrete apron slab into the columns – allows unrestrained column lengths of up to 15m despite loading of 20MN.

Cold-formed steel sections were assembled into lightweight wall and ceiling panels to form the supporting structure for the arrivals corridor cladding.

The design team collaborated across disciplines using a 3D model environment, with the construction team extending this to produce 4D construction phasing and test access routes for mechanical plant modules. The 3D environment allowed virtual testing of exposed steel connection details ahead of fabrication.

To create a large, open space for the central hub, long-span cellular beams were used spanning onto the Vierendeel truss of the arrivals level bridge. This reduced the number of columns needed within the open area to just two, discretely positioned beneath the footbridge.

Architects and engineers worked together to develop a range of connection details and structural concepts that weave the steel frame into the architectural fabric. Suspending the internal glazed screens from roof level keeps the size and visual impact of supporting mullions to a minimum.

Prefabricating elements offsite ensured construction efficiency, minimised wasteful site-based construction activity and eliminated impacts on airport operations. The use of prefabrication, together with time-based 4D BIM, allowed virtual testing of safety issues, which could then be designed out.

By taking a fire engineering approach and limiting the fire load within the passenger concourses, it was possible to omit fire protection to the exposed steelwork.

The design embodies collaboration between architecture, engineering and construction to create an elegant expression of its lean design principles.

T2B is the first UK airport facility to achieve a BREEAM rating of ‘Very Good’.

Judges’ comment

A large and complex project, with severe demands (25% less cost and 10% less time than previously achieved) required the whole team to work exceptionally well and closely in order to satisfy a demanding and knowledgeable client. The varying degrees of complexity of the steelwork, and its architectural exposure, were very well planned, detailed and executed.

A success for steelwork in a challenging flagship project.

Milton Court, Guildhall School of Music & Drama

Milton Court 2

Architect
RHWL Arts Team

Structural Engineer
WSP Cantor Seinuk

Steelwork Contractor
William Hare Ltd

Main Contractor
Sir Robert McAlpine Ltd

Client
Heron Land Developments

Milton Court is a new £89m facility built for the Guildhall School of Music & Drama. Located near the Barbican, it occupies two basement levels and the first six floors of the development. It includes a world-class 609-seat concert hall, two theatres, rehearsal rooms, office space, a TV studio suite, a lobby and bar, as well as an impressive roof garden.

The concert hall and studio theatre were designed to meet very high acoustic performance requirements utilising a ‘box- in-box’ principle. Due to the small footprint of the site, a steel ‘box-in-box’ system gave the benefit of acoustically isolating each internal part of the building from one another. Acoustic isolation was achieved by adopting an internal steel frame encased in concrete with walls constructed out of dense blockwork.

The studio also had a composite slab roof and an internal acoustically separated suspended floor slab. Every element of the structure was seated on isolation bearings.

The acoustically isolated suspended floor slab was constructed utilising Omnia units spanning between upturned steel ‘T’ sections, which in turn were seated on pre-levelled and grouted acoustic bearings. Once all of the units were in place, the whole area had to be completely sealed prior to concreting to prevent any grout leak and consequently a breach of the acoustic isolation.

Due to all columns being seated on bearings this necessitated considerable temporary works to stabilise each structure during construction. To compound the problem the steelwork contractor was not permitted to connect to the adjacent walls due to the high quality finish. Additionally, in the basement studio theatre, temporary connections were not permitted to the floor slab due to the risk of penetrating the waterproofing membrane.

A high quality, high resilience natural rubber was used for all the isolation bearings and they were locked into place during the construction. By isolating the steel structure the construction time increased as bolted connections had to be carefully designed and installed.

The construction of the main tower structure was well in advance of level 6 before the commencement of the steel erection. This meant that the internal steelwork to the studio theatre had to be erected within a closed concrete box.

As a consequence, early coordination was required to ensure timely supply of lifting beams and lifting lugs to be cast into the theatre roof slab to facilitate erection of the structural steel.

The hall now has the largest audience capacity of any London conservatoire which makes it an ideal stage to showcase the talents of the school’s musicians.

Judges’ comment

A highly complex project on a dense urban site, with severe acoustic demands due to traffic noise and underground trains, and isolation between separate performance spaces. The solution is ‘box-in-box’ construction, whereby each performance space is constructed of steelwork built within, and isolated from, the concrete substructure.

Steelwork is key to this world-class music and drama facility.