Design Awards: 2018: Commendation

Two St. Peter’s Square, Manchester

© Daniel Hopkinson

Architect
SimpsonHaugh

Structural Engineer
BuroHappold

Steelwork Contractor
William Hare

Main Contractor
Laing O’Rourke

Client
Mosley Street Ventures Ltd

Two St. Peter’s Square is a new build, Grade A office space in the heart of Manchester city centre. It faces the Grade I listed Town Hall and Grade II listed Central Library. The building is 12 storeys above ground with a two-storey basement.

The key driver for the structural design has been to provide highly flexible column-free accommodation that is attractive to potential tenants. The typical beams are 730mm deep and, over the 18m span, vibration was a key criterion governing many of the section sizes.

At ground level the architectural intent was to provide a colonnade with columns at 12m centres and cantilevers of 6m at either end. Continuing this wide spaced grid on the typical floors above was not economical so a transfer structure at the lower level was utilised.

To maximise the spatial experience of the colonnade at ground floor level the columns are double-height with the first- floor floorplate set-back from the perimeter. Long-span transfer beams at level 2 achieve this with the first floor hung from above. A similar arrangement is adopted at level 10 with transfer beams that support the set-back columns above. This arrangement provides a high value terrace space overlooking the civic heart of Manchester, whilst also responding to the planners’ concerns on massing.

Vertical access for the building, both for people and services, is via the core. Positioned offset on the building floor plan this maximises the available floor area and the length of premium elevations facing the square. Building stability is provided by the reinforced concrete core which acts as a cantilever from the raft foundation at basement level under the lateral loading imposed on it.

Supporting the façade presented several engineering challenges. Each unit was constructed in 6m wide by 4m high mega-panels.

The extent of movement of the frame under the significant façade loading was meticulously calculated during the different phases of the build. This involved pre-setting the steel frame, so it could settle incrementally as the mega-panels were installed.

Long-span beams form the typical floors giving column-free flexible spaces. Economy was achieved by integrating the structural and service zones, utilising composite action between the steel beams and concrete slabs and adopting asymmetric sections.

Two St. Peters Square has regenerated a prime site in central Manchester providing a positive contribution to the city and enhancing the adjacent public realm.

Judges’ Comment

This scheme of new Grade A offices in the heart of Manchester’s civic centre responds to the challenge of this site of prime importance. Not only does the glazed stone tracery respond appropriately to the location, but the elegant steel framed building with 18m clear spans provides flexible accommodation highly attractive to tenants.

The Greenwich Peninsula Low Carbon Energy Centre

© Mark Hadden

Architect
C. F. Møller

Artist
Conrad Shawcross RA

Structural Engineer
Price & Myers

Steelwork Contractor
Billington Structures Ltd

Main Contractor
Kier Group

Client
Knight Dragon

From conception the Energy Centre was developed with innovation and creativity to ensure the structure was a stand-out piece of artwork on the newly-forming Greenwich Peninsula.

Central in the structure is the highly distinctive flue tower, measuring 3m by 18m on plan and 49m tall.

The cladding of the flue tower unites sophisticated engineering and complex optic research to create an impressive sculptural concept on a huge scale. The unique cladding is formed of hundreds of triangular panels, each the height of a London bus, that fold and flow across the surface of the tower. The resulting complex geometric patterns visually break up the elevations to create an uneven sculpted surface that plays with the vanishing points and perspective.

The panels are perforated to exploit the phenomena of the Moiré Effect, and at night an integrated lighting design produces a shifting series of ‘compositions‘ lit from within the structure.

The main building and tower are structurally independent to avoid the effects of cyclic loading and fatigue on the tower affecting the main building.

A series of wind tunnel tests were carried out on the tower structure as the cladding design progressed to assess the detailed loads on the structure and the dynamic sensitivity of the tower. A BRE study was also carried out to provide design data for assessing cyclical fatigue loads.

The tensile strength and ductility of steel made it the obvious choice to cope with the effects of high wind loading on the tall slim structure. The industrial aesthetic of steel lent itself to the historical context of Greenwich Peninsula, whilst the cross bracing of the structure echoes the neighbouring gas holder dating from 1886.

345 tonnes of galvanized steel were erected for the flue tower, which consisted of five main cantilever latticed girders, each formed from three 16m high by 3.15m wide sections spliced at third points on-site and placed 4.5m apart. These were connected with interleaving diagonal secondary members fixed to both chords on the main east and west façades.

Close coordination with the cladding sub- contractor was fundamental to achieving the correct setting out and detailing for the hundreds of fixing brackets; each fabricated as part of the steel frame with sufficient tolerance to allow seamless connection and adjustment of the cladding panels throughout the build.

Judges’ Comment

This project forms the gateway to a new and rapidly developing quarter to the east of London and is a remarkable addition to the heavily urban landscape, both during the day and at night. Steel is used with grace and with flexibility for the future in mind. The collaboration between artist, designers, steelwork contractor and this enlightened client has resulted in a holistically coherent and notable project.

Four Pancras Square, London

© Dirk Lindner/Eric Parry Architects

Architect
Eric Parry Architects

Structural Engineers
AKT II and BAM Design

Steelwork Contractor
Severfield

Main Contractor
BAM Construction

Client
King’s Cross Central Limited Partnership

Four Pancras Square is the last of six new commercial buildings within King’s Cross Central Zone B, located adjacent to St Pancras and King’s Cross stations.

As the square’s prominent ‘keystone’, Four Pancras Square demanded a strong identity that resonates with the site’s industrial heritage. This is encapsulated in Eric Parry Architects’ competition-winning design via an expressive exposed weathering steel frame.

The building was designed as a speculative office, aspiring to exceed the British Council for Offices specification and be the first office to achieve a BREEAM 2014 rating of ‘Outstanding’, succeeding in both.

The building is 57m wide on the north elevation, 27m on the south and 54m on the west, producing a 60 degree angle on the east.

These proportions, combined with the concept, resulted in a regular 4.5m column grid on the upper levels and larger spans around the ground floor retail, typically 13.5m, but up to 27m clear span on the south face. The façade structure continues beyond the set-back 10th floor and the landscaped roof terrace above to crown the building.

The key challenges to the design and detailing of the external steel exoskeleton included:

• forming the full width transfer creating the dramatic southern entrance onto Pancras Square.
• control of thermal movements of the external primary frame relative to the internal structure.
• detailing the structure and finishes to accommodate the movements.
• providing the necessary fire resistance to the unprotected steel exoskeleton.
• ensuring the exposed components of the steel exoskeleton and the junction with the internal structure are designed and detailed to provide the required durability.

A Vierendeel truss wrapping the first floor is a key architectural feature. On the southern elevation to the square it forms the transfer structure creating the column- free open entrance onto Pancras Square. The storey-high truss continues to wrap the remaining elevations of the first floor, resolving the different grids required for the office levels and the public realm. Where the steel exoskeleton interfaces with the façade at the perimeter columns the floor slab sits on steel shelves, ‘hods’, which cantilever off the external columns through the façade. These ‘hods’ are tied into the slab and in turn cantilever out to restrain the columns in both directions.

These ‘hods’ result in structural penetrations through the thermal line of the cladding at 4.5m centres across all floors and were a critical connection detail.

Judges’ Comment

The judges recognised the strong technical collaboration of the entire team to deliver the architect’s vision of an expressed weathering steel exoskeleton without compromise. This was achieved through creative development of key technical details to address thermal bridging, differential thermal movements, fire performance and weathering. The building’s elevations are a celebration of steel.

Brooklands Museum Aircraft Factory and Racetrack Revival

© David Lankester

Architect
Thomas Ford & Partners

Structural Engineer
Alan Baxter Ltd

Steelwork Contractor
Ainscough Industrial

Main Contractor
Brymor Construction Ltd

Client
Brooklands Museum

Brooklands is the birthplace of British motorsport and aviation, and the home of many remarkable engineering and technological achievements throughout the 20th Century. Over the past three years, Brooklands has seen another unique engineering achievement – the successful relocation and refurbishment of the 78-year- old, Grade II listed, Bellman Hangar to reinstate key surviving elements of the original motor racetrack.

The project also included the construction of a new Flight Shed building to house some of the Museum’s expanding aircraft collection, together with workshops and archive facilities. The hangar was re-clad with new profiled steel cladding that matched the original profile externally, but incorporated insulation to provide enhanced environmental conditions inside. As part of the project, a major new exhibition celebrating the history of aircraft manufacture was created within it.

Analysis of the structure showed that there was a weakness in the haunch connection, which could be overstressed in high winds particularly when the hangar doors were open, creating a dominant opening. Low key strengthening works to the haunches were developed, which did not fundamentally affect the nature or appearance of the structure. The repairs are expressed through the use of different section profiles and colours to distinguish new from original elements.

Careful dismantling was undertaken to avoid damaging the existing components of the building. The components were then individually tagged to define their location and orientation to make sure that all the components would fit back together again in the same locations. Once transported to the steelwork contractor’s factory, each element was sand blasted to remove the many layers of old paint and reveal the extent of any damage or corrosion. Where major damage or corrosion was found, elements were repaired to match the original structure. The steelwork was then re-painted and carefully transported back to site for re-erection.

In addition to the re-erection of the hangar, a free-standing mezzanine was designed within the hangar to increase the exhibition space. This mezzanine also included a bridge across to the adjacent Flight Shed, linking the two buildings without the need for extensive alterations to the Bellman Hangar.

The project was successfully completed and opened in November 2017. It is a resounding testament to the flexibility and durability of steel design, both in its original concept and in how it can be sustainably and sympathetically adapted and re-used many years after its original design life has been exceeded.

Judges’ Comment

This project is a testament to the adaptability of steel construction and the care with which the project team managed the task of dismantling the old hangar, refurbishing individual components and re-assembling the structure on a nearby site, providing the ideal accommodation for the museum display.

Belfast Waterfront Conference & Exhibition Centre

© GOC Photography

Architect
Todd Architects

Structural Engineer
Doran Consulting Ltd

Steelwork Contractor
Walter Watson Ltd

Main Contractor
McLaughlin & Harvey Ltd

Client
Belfast City Council

The new steel-framed extension to the Belfast Waterfront stretches from the existing building out to the edge of the River Lagan and provides an additional 7,000m2 of floor space which can facilitate up to 5,000 guests at any one time. There is an 1,800m2 main hall and a 700m2 minor hall, each of which can be sub-divided to allow flexible layouts. These large clear span spaces were most cost-effectively achieved with a steel frame.

The facility has been designed to fit in with its surroundings, wrapping around the existing building and connecting to the existing facilities at multiple levels, though remaining an independent structure. The extension spans over the existing services yard and service building on the riverside. Public access to the river has been maintained. The congested location proved challenging, being extremely restricted in terms of access and by surrounding structures and its proximity to the river.

The use of steel meant the construction works could be accelerated given the opportunity to prefabricate the frame offsite in advance.

The complex primary structure was influenced by several factors. The spatial requirements for the extension involved column-free spaces, a combination of single and double-height spaces and partial intermediate floors, and the need to build over and around retained structure. This led to several framing solutions being employed, using 1,400 tonnes of steel.

Pre-cambered cellular beams were used along with metal deck composite concrete flooring. The degree of pre-cambering was calculated to provide level steelwork after dead load deflection.

Extra levels were squeezed in as the building’s footprint gave very limited floor space. To give this intermediate floor sufficient ceiling height ‘Slimflor’ construction was adopted, using plated UC sections within the floor depth.

‘Cellform’ beams were used to form the main hall roof; this allowed services to pass through the beams and thus maximise ceiling heights. These ‘cellform’ beams had a tapered section to provide integral roof falls (and provide a level soffit for rigging steelwork).

For the accommodation built over the service yard, cantilevered plate girders were used as their supporting columns were offset to maintain clear height for HGV access.

This project was Belfast City’s Council’s first use of BIM on a major project. It was delivered using advanced modelling techniques, which minimised on-site clashes and maximised the efficiency of design and construction.

Judges’ Comment

New conference halls, banqueting and break-out spaces extend the Belfast Waterfront Conference Centre right up to the quay of the River Lagan. The resulting multiple challenges, both physical and financial, were met by a sequence of appropriate and pragmatic structural steel and architectural solutions.

Approach Viaduct South, Queensferry Crossing

© Transport Scotland

Structural Engineer
Ramboll

Steelwork Contractor
Cleveland Bridge UK Ltd

Main Contractor
Forth Crossing Bridge Constructors

Client
Transport Scotland

Opened in August 2017, Transport Scotland’s Queensferry Crossing is one of the most striking engineering icons of the 21st Century.

On the south side of the crossing the approach viaduct (AVS) is 545m long and comprises two composite steel box girders, set 21.75m apart, supported on six V-shaped piers with spans of 64m + 80m + 90m + (3 x 87m). These are directly connected to the main span cable-stayed single box section of the Crossing.

Each approach viaduct is 17.5m wide, accommodating two main carriageways and a hard shoulder. Consideration has been given to future usage, allowing it to be adapted to light rapid transport systems in the future.

The AVS was pre-assembled before being progressively launched into place. Assembly took place in an efficient and controlled environment, keeping work out on the estuary to a minimum. However, this created significant engineering challenges.

The steel twin box girders of the viaduct were fabricated and pre-assembled by Cleveland Bridge in Darlington. The completed girders were transported by road in halves due to the width of the boxes.

Behind the southern approach a 160m long assembly platform work area was prepared. The east and west girders were launched independently and alternately in six stages, proceeding span-by-span. This facilitated a rolling programme of fabrication, segment delivery, site assembly and a staged launch with east and west girders alternating.

The active viaduct launch solution comprised a vertical ‘king post’ and temporary stays. The temporary stay system counteracted girder deflection as the tip reached the next pier, also reducing bending effects during cantilevering. The pulling system consisted of cables anchored to the rear part of the girders. Hydraulic jacks transferred the pulling load to the permanent abutment bearing plinths. The decks were pulled at an average speed of 10m/hr.

Construction of the concrete deck slab and cantilevers was undertaken in phases.

The bridge has low level deck lighting which reduces costs, improves safety and minimises external light pollution. The wind shield provides weather protection for all vehicles for wind speeds up to 115mph, minimising crossing closures.

Maintenance requirements have been kept low. The viaduct box has a dehumidification system, removing any need to repaint the internal steelwork. Externally, a permanent maintenance gantry system has been installed to facilitate access to all faces of the boxes. The use of high-quality paint systems will ensure longevity and will extend the life of maintenance repainting to over 25 years.

Judges’ Comment

In a landscape comprising the Forth Bridge and the Forth Road Bridge, the new Queensferry Crossing, Britain’s tallest bridge, cannot fail to impress. This scheme for the southern approach viaduct embodies the knowledge in design, fabrication and long-term maintenance, in the launching and finishing the twin box viaducts, from some of the world’s most accomplished bridge builders.

The Beacon of Light, Sunderland

Architect
FaulknerBrowns

Structural Engineer
s h e d

Steelwork Contractor
Harry Marsh (Engineers) Ltd

Main Contractor
Tolent Construction

Client
The Foundation of Light

The Beacon of Light is a unique landmark in Sunderland providing educational aspiration through the power of sport. It is a combination of a school, offices, a 12-court sports hall that doubles as a 3,000-seat performance venue and an indoor football pitch on the roof. In total over 10,500m2 of accommodation is provided, built to a very high quality, for only £17M. Architecturally it is a significant feature on the Sunderland skyline and a beacon for the Foundation of Light.

Early in the design concept it was decided that a steel frame would provide a flexible solution that would allow the design to develop right up to the start on site. Without the steel frame the project would not have been affordable, nor would it have been as dramatic and elegant, from the sports and leisure venue right through to the indoor rooftop football pitch under a 60m by 60m clear span fabric roof.

The use of a steel frame was fundamental to:

• keep the amount of piling to a minimum thus reducing environmental impact.
• allow the M&E flexibility by creating clear soffits in the main service run directions keeping coordination simple and fabrication modifications, such as holes in beams, to a minimum.
• create a 60m by 32m clear span sports hall that can be converted into a 3,000-4,000 seat performance venue that has a football pitch over it. It has five different possible uses planned and is designed to be so flexible that the adjacent main accommodation at the upper levels is supported by super trusses to accommodate extra viewing and seating zones with uninterrupted views.
• design a very lightweight and very shallow two-way spanning fabric roof structure and a feature ‘Beacon’ polycarbonate façade that can come alive at night with lighting.
• create a building that fits the superb architecture, within the tight budget, to a very high aesthetic standard.

The project provides a superb community facility for the people of Sunderland. Its amazing column-free spaces and structural forms inside will themselves be an inspiration to those who use the building throughout its lifespan, in particular the two-way spanning 60m by 60m roof which has a design weight of 44kg/m2. It is particularly shallow and required a detailed erection sequence and temporary works to make it possible. The whole roof and polycarbonate frame is in an unheated space and is thermally isolated from the main warm frame underneath.

Judges’ Comment

A new landmark in regenerating Sunderland, this glowing cube of a building, a home for the Foundation of Light, is a community-supported combination of school, sports halls and 3,000-seater performance venue. It even includes a covered football pitch on the roof. The steel frame economically resolves structural challenges from foundations to its 60m by 60m clear span fabric roof.

Somers Town Bridge, London

© John Sturrock

Architect
Moxon Architects

Structural Engineer
Ove Arup & Partners Ltd

Steelwork Contractor
S H Structures Ltd

Client
King’s Cross Central Limited Partnership

Designed for cyclists and pedestrians to cross from Camley Street into King’s Cross Central, a landmark redevelopment project, the bridge spans 38m, weighs 52 tonnes and is only 1,100mm deep at mid- span and 400mm deep at the ends. In keeping with the Victorian heritage of the area, the bridge is unadorned and streamlined, focusing attention on extremely detailed and precise craftsmanship and high-quality materials.

A sweeping ramp leads people up to the bridge and over the water with an elegant parapet transitioning from planed hardwood to stainless steel.

By locating the structural depth above deck level, the design maintains a clear view of the canal south from St Pancras Lock.

One of the planning design drivers was that this should be a ‘green bridge’, taking minimum material use to the extreme that it becomes the defining feature of architectural simplicity. With the use of steel, and its high recycled material content, this has resulted in a low carbon solution.

Power and communications cables run concealed behind the top flanges of the bridge. Whole-life energy-efficient LED strip luminaires light up the footway within the handrails. This arrangement reduces the amount of light required to illuminate the footpath, as well as minimising light pollution.

The use of steel construction facilitated both offsite fabrication and single piece lifting that were required to avoid disruptive construction methods on this heavily trafficked section of canal. This also enabled the offsite and on-site construction activities to run in parallel with associated programme benefits. A lightweight deck also minimised foundation works.

The bridge was optimised to meet the architect’s aspiration for a slender structure that would minimise the shade on the canal. Non-linear analysis of the slender deck ensured that the slenderness would not compromise safety and would provide maximum comfort for users of the bridge. Particular care was placed on satisfying the user comfort criteria, which led to the use of bespoke tuned mass dampers at mid-span to suppress vertical and torsional dynamic modes of the deck.

Every single element of the bridge had a structural meaning and function. For instance, it was designed so no longitudinal stiffeners would be needed, simplifying the structure as well as reducing fabrication complexity and cost.

The bridge was installed using a 750-tonne mobile crane. The lift had to be carefully controlled due to the proximity of the canal and the operational railway lines in and out of St Pancras Station.

Judges’ Comment

A sweeping ramp leads up to this almost impossibly slender steel bridge. Designed for pedestrians and cyclists, the bridge improves access into King’s Cross Central, a landmark redevelopment project. The simplicity of its unadorned and streamlined form focuses attention onto the bridge’s high-quality materials and precise craftsmanship.