Design Awards: 2017: Commendation

The Curve, Slough

© David Butler

Architects
BBLUR architecture and CZWG architects

Structural Engineer
Peter Brett Associates

Steelwork Contractor
Caunton Engineering Ltd

Main Contractor
Morgan Sindall

Client
Slough Borough Council

The Curve initiative is a major development comprising a mixed-use, vibrant community facility with multi-functional spaces and wider cultural offerings, based around the arts with opportunities for performance and exhibitions.

The 90m long x 15m high building’s form, a curved ‘tube,’ features fully glazed entry façades, and opens onto two new public squares created at each end of the building.

A heavily serviced building with a single two-storey enclosed plant area presented particular challenges in incorporating horizontal distribution routes within the building. The composite steel frame allowed floor depths to be kept within a stringent floor zone, whilst allowing for the services’ distribution.

The composite steel solution allowed for full flexibility in the design of an irregular column grid, and provided minimum depth cantilever façade support sections. The aesthetic of the circular hollow section columns has been retained and expressed throughout. The double height performance space required column removal, for which composite universal column sections were able to achieve the spans in the shallowest depth possible. The constrained site utilised a single mobile crane to perform all lifting operations in a carefully planned three phase construction sequence, allowing free site areas open to other trades.

Detailed 3D modelling allowed efficiencies to be gained in specifying a constant bend radius for the façade members, and limiting the supporting tubular transfer beam to three discrete bend radii. This 45m curved CHS beam was then spliced using carefully detailed non-visible connections. Curved edges to the internal atrium required cantilever decking sections to arrive at site with the bend radii pre-cut. Staircases, both front and back-of-house, were formed offsite in steel and installed quickly and prop-free to open up the site to the follow-on trades. Detailed 3D model coordination allowed for accurate placement of pre- applied cladding fixings and secondary support steelwork.

A shop applied painted system provided the corrosion resistance to the members. Fire resistance throughout was provided by intumescent painting of the main structural members up to the 120 minutes’ period required in some areas. The design methodology to use bolted connections reduced the risk of compromising steel coatings that can occur when site welding is required.

Judges’ Comment

Part of the implementation of the masterplan for the regeneration of Slough Town Centre, The Curve provides popular and accessible community facilities. Its striking curved form arose from its proximity to a church and probably could only have been achieved by an integrated team using coordinated BIM design, analysis, fabrication and erection.

Elegant and effective steelwork meets unusual demands.

West Croydon Bus Station

© Alex Upton

Architect
Transport for London

Structural Engineer
Price & Myers

Steelwork Contractor
B&W Engineering Services Ltd

Main Contractor
Quinn London Ltd

Client
Transport for London

West Croydon Bus Station has been transformed from an unsightly, uninviting and poorly functioning 1980s ‘shed’ into a customer-friendly landmark that supports the regeneration of Croydon. The old building has been replaced by an open concourse under an elegant weathering steel canopy. The canopy wraps around and connects two small buildings – a retail unit and a bus operations building.

The choice of materials was carefully considered to reduce whole life costs. The primary material of the project is weathering steel, and is used throughout the canopy structure in combination with translucent Kalwall panels, creating a structure requiring minimal ongoing maintenance.

The weathering steel canopy wraps around the two brick clad buildings, tying the station architecture together on the linear site. The brick and weathering steel were chosen to complement the surroundings. The style and natural flow of the station achieves this while also providing an interesting play of light, shadow and texture. Timber seating and planters are fully integrated into the steel canopy structure, along with customer information and lighting to minimise visual clutter.

The canopy is based around a repeating module where canopy and supporting columns are linked by a curved haunch. This haunch is perforated with variable sized holes to both create interesting visual effects and demonstrate the changing stress intensity across the haunch.

Guttering, downpipes and lighting have all been integrated into the structure to ensure services are not visible nor impact on the final impression of the structure.

The buildings are highly sustainable and environmentally friendly – with solar panels, air source heat pumps, LED lighting and building materials that maximise the buildings’ performance. A building management system ensures energy efficiency and reduces light pollution.

The opaque canopy provides natural lighting and manages glare and heat transfer. Night lighting on the canopy creates an attractive and safe environment.

The whole life value of all aspects of the design was assessed to inform design decisions, such that:

  • The weathering steel of the canopy reduces maintenance and future carbon impact.
  • The design modelled different climate scenarios and was carefully detailed to minimise waste during the build.
  • Prefabricated insulated timber panels reduced on-site labour and the energy required to mechanically condition the buildings throughout their lifetime.

Anti-social behaviour was a significant issue at the old bus station. The new improved open layout, architectural lighting and soft landscaping tackle this issue and create a safer, more socially sustainable, environment.

Judges’ Comment

High quality design and careful selection of materials, with low maintenance a major objective, are evident in this project. The lightweight canopy is framed in weathering steel, carefully prepared and detailed, to provide visual interest.

This is a facility which has transformed passenger experience and provided a significant contribution to the environment.

Central Square, Leeds


Architect
DLA Design

Structural Engineer
WSP

Steelwork Contractor
Elland Steel Structures Ltd

Main Contractor
Wates Construction

Client
M&G Real Estate

Central Square is a 20,400m2 development, providing 18,700m2 of Grade ‘A’ offices with 1,700m2 of retail, leisure and health/fitness.

The scheme provides office accommodation on 10 floor levels and is said to have the largest floorplates available in the city. These are arranged so that they can be subdivided, providing the occupier with both flexible and highly efficient floor space. The development offers an outdoor Sky Garden on the level nine, providing entertainment opportunities and views across the city. In addition, a stunning seven-storey fully glazed atrium houses Central Square’s Winter Garden, where the created contemporary square offers a mixed-use destination for members of the public throughout the day and evening to enjoy the high quality public realm, retail and leisure facilities on offer.

Sitting above a two-level concrete basement, the steel frame forms a U- shaped structure with the central void occupied by the fully glazed Winter Garden created by the glazing sloping down from the underside of level eight within this central void.

In total five 27m long tubular ‘vertical’ bowstring trusses, which were delivered to site in two pieces, form this indoor zone. These trusses, carrying heavy dead load from the attached glazing, are pin connected at the base to architecturally exposed fabricated base assemblies.

The heaviest steel assembly on the project was the 43 tonne, storey-high, Vierendeel truss that supports level eight’s balcony that overlooks the Winter Garden. The Vierendeel truss, comprising heavy UC members, was brought to site in individual sections that were then assembled on the ground before being lifted into place by a 300 tonne capacity mobile crane.

The majority of the steelwork was erected using the site’s tower cranes, with two erection teams being employed that divided the structure in half and erected the frame three levels at time, incorporating placing and subsequently fixing of the metal deck flooring. Each of the U-shaped structure’s tips contains one of the building’s three cores, and this provided each erection team with an ideal and stable starting point. From these outer concrete cores each of the teams worked its way to the centre of the structure, meeting up at the third centrally positioned core.

Above the lower levels of retail and leisure, the offices begin at level two and extend upwards to level 12. Levels two up to seven are identical, with a central portion positioned inside the Winter Garden. The reception for the offices is positioned at level one and accessed via a feature escalator, with the upper levels being accessed by a number of lifts including two glass-clad wall climber lifts.

Judges’ Comment

Central Square is a landmark office and leisure complex within two minutes of Leeds City Station. In this BREEAM ‘Outstanding’ development, the floors are supported on long-span beams enabling 25,000ft2 floorplates, the largest in the city.

The ground and first floors are accessed through a large atrium ‘winter garden’, forming a new and exciting part of the public realm in the area.

STIHL Treetop Walkway, Westonbirt, the National Arboretum

© Paul Box/Forestry Commission

Architect
Glenn Howells Architects

Structural Engineer
BuroHappold Engineering

Steelwork Contractor
S H Structures Ltd

Main Contractor
Speller Metcalfe

Client
Forestry Commission, Westonbirt, the National Arboretum

The STIHL Treetop Walkway is the longest structure of its kind in the UK. Reaching heights of up to 13m, the walkway transports visitors effortlessly on a journey through the park’s Silk Wood.

The structural solution that developed is a hybrid timber and steel structure. The basic structure is a simple arrangement of two perimeter beams supporting the 1.8m wide deck and the balustrades. These beams are formed from curved galvanized steel RHS sections which, with the CHS cross beam, create a laterally stiff structure to transfer loads back to the supports. The use of galvanized steel provided the required stiffness and allowed a shallower deck profile to be created with something that was durable and maintenance-free.

Building the walkway using small assemblies and single elements enabled the size of the construction equipment to be reduced and allowed the use of bolted connections throughout, meaning that future dismantling would be straightforward.

Various support solutions were considered due to the unique constraints of the site. The chosen solution was to use shallow reinforced concrete pads supporting pairs of inclined timber legs at 10.5m centres. The inclined columns provided a more natural feel and allowed the base positions to be easily moved in plan to avoid areas of heavy root coverage.

The client was keen to accentuate the treetop experience by having a degree of movement, and the use of a non-linear dynamic model of the structure enabled an acceptable behaviour to be achieved.

The walkway is punctuated by a number of independent platforms, such as the Crow’s Nest, which serve as educational areas. The ability to curve the hollow steel sections to a very tight radius enabled the architect’s requirements to be achieved. Whilst the main walkway is inherently stable, the cantilevered Crow’s Nest is somewhat more lively, providing visitors with the more dynamic experience requested by the client.

Four different capacity cranes were used during construction, including a mobile tower crane which provided the required reach over the trees. Mobile cranes of up to 350 tonne capacity were used in other locations where prepared bases were constructed in areas that would cause the minimum impact.

The construction followed a repetitive sequence with the pairs of columns being installed first. The columns were temporarily supported with guy lines fixed to concrete kentledge blocks. This methodology enabled the column heads to be positioned correctly whilst causing no damage to the trees and their roots.

Judges’ Comment

Owing much to the romantic tradition of great English landscapes this sinuous walkway carefully winds through the canopy of ancient working woodland, whilst avoiding the precious root zones. A ‘tuneable’ structural system addresses the varying dynamics and geometrical restraints.

The curvilinear route, which heightens the sense of drama and discovery, was facilitated by the use of steel. Apparent simplicity conceals sophistication in this project.

The Hurlingham Club Racquet Centre

© Metsä Wood

Architect
David Morley Architects

Structural Engineer
Price & Myers

Steelwork Contractor
Tubecon

Main Contractor
ISG

Client
The Hurlingham Club

The state-of-the-art Racquet Centre replaces an existing marquee structure and has modern functionality practical to its purpose. Designed to meet high standards of sustainability, it fits sympathetically into its rural surroundings. The Centre is home to four indoor and two outdoor tennis courts, four squash courts, a multi-use games area and changing facilities.

Steelwork was the natural and most cost- effective material, due to the long spans needed by the large 38m x 70m column- free space required by the tennis hall.

A series of tied-arched steel frames, tied with large diameter bespoke tension bars, at 16.5m centres form the primary roof structure. These purpose-engineered welded box sections were paired together to also act as Vierendeel trusses to help distribute horizontal forces back to vertical bracing systems. Further efficiencies of the arch were gained by portalising the structure and providing raking ties at the roof ends, which help minimise the depth and weight of the box sections.

These arches support timber stress-skin panels which span between the arches. The structure is predominantly internal; however, where the structure becomes external, an offsite painted protection system with a life to first maintenance of 20 years has been used and, where necessary, with a decorative top coat. By using steel, the main elements could be fabricated offsite while the groundworks were completed. This prefabrication meant a fast erection process on-site and also assured a high quality finish – imperative as the majority of steelwork is left architecturally exposed.

A key consideration was how the timber panels would bear and tie to the steel frame without visible fixings, and what tolerances would be needed. Creating the primary arches from welded plates allowed the bottom plate to provide a bearing ledge for the timber panels, which were tied to the tops of the steel with steel straps and self-tapping screws to allow them to be completely concealed. Designed to be transportable, the trusses had to be fabricated in three sections with bolted splices connected on-site using a seating jig. Once connected, a tandem lift then raised the 40-45 tonne trusses into place, which cantilevered approximately 2m-3m.

With architecturally exposed steel, all processes required acute accuracy and highly skilled workmanship, from detailing and connection design through to the fabrication and erection process.

Judges’ Comment

A detailed, yet compact, building adds generous new indoor play areas, whilst meeting the requirement for a low profile at the edge of the Club grounds. The stringent dimensional and technical constraints were answered by well-coordinated structure, services, equipment and enclosure.

Steelwork again enables elegance and efficiency in modern sports facilities.

Watermark Westquay Footbridge, Southampton


Architect
ACME

Structural Engineer
David Dexter Associates

Steelwork Contractor
S H Structures Ltd

Main Contractor
Sir Robert McAlpine Ltd

Client
Hammerson plc

The footbridge provides enclosed pedestrian access from an existing car park that serves the old West Quay shopping centre complex in Southampton over Harbour Parade and directly into the new Watermark retail centre.

The bridge is a box truss cross braced on each face which is an efficient structural approach to both giving an enclosure, and achieving the spans of 30m between column supports and a 10m cantilever at the existing car park end.

For the truss sidewall bracing, RHS diagonal bracing elements are used in the idealised compression direction with paired plates lapping these in the idealised tension direction.

The challenge with the detailing was to achieve a uniform appearance throughout the length of the bridge. Thicker RHS bracing elements are used at the support locations with subtle local stiffening. Narrow and thick-walled chords (200 x 200 SHS) were used to give a visually shallow profile. The bottom chord is internally stiffened at the support cross beams to ensure the line of the chords is not visually broken.

The horizontal bracing to the box truss’ roof and floor is in a similar, but less dense, pattern to the sidewalls and is formed with RHS elements of equal size to the RHS wall bracing. A steel deck floor is employed with an anti-slip deck treatment applied.

The vertical supports to the structure are 500 x 250 RHS steel hoop frames, which are independent of the existing car park and new shopping centre structures at each end, and are located to minimise disturbance to the considerable amount of underground service routes in the vicinity.

The footbridge was fabricated and trial assembled within the factory before being separated into two sections for delivery to site. Installation took place during a closure of Harbour Parade enabling a 500 tonne capacity mobile crane to be positioned close to the bridge position.

To facilitate securing the first bridge section in its temporary condition a temporary trestle was installed on the bridge centreline. The top of the trestle was fitted with hydraulic jacks to enable the final lowering of the bridge to be carefully controlled.

With the first section in place the second section was lifted into place. A temporary connection was integrated into the truss members that aligned the two sections, holding them in place until the joint was fully welded.

The use of steel resulted in a lightweight structure that could be quickly erected from prefabricated component parts, minimising the need for temporary works and road closures.

Judges’ Comment

The pedestrian link from parking into the shopping centre was necessarily economical. This latticed box girder bridge does the job without fuss. The diagonal geometry of the faces is composed of both welded flats and tubes, reflecting the forces carried. These support the glass cladding and filter sunlight most elegantly.

A simple and economical concept has been beautifully executed.