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Model answer

building study

Selfridges went in search of the extraordinary and got a Future Systems building that is already a Birmingham landmark

For Britain's second city, Birmingham had a surprisingly small retail core, centred on the 'U' of Corporation Street, New Street and High Street. In 1964, when it opened the Bull Ring Shopping Centre beyond these old streets down a slope to the south, it increased this retail floorspace by 37,500m 2.This incorporated floorspace for displaced market traders beneath a main covered shopping centre, one of Britain's first, said then to be the largest enclosed centre outside the US.

As an interior retail experience, it always felt like a move downmarket compared with the old streets.

Outside it was not a welcoming box, nor connected directly with the rest of the city centre. In the space between, Birmingham built some public open spaces, which would be modestly attractive were it not for the maze of unpleasant underpasses that dealt with the levels of the slope and worked around the impediment of new roads.

These 'urban motorways', or inner ring roads, were another unkindness Birmingham visited on itself, as did other major cities such as Manchester and Sheffield.

These cities were drawn into the spirit of the brave new world found in Colin Buchanan's 1963 government report, Traffic in Towns, which both celebrated the car, the 'go-anywhere self-powered machine for transport and personal locomotion', and, surprisingly, overestimated the rate of growth in car ownership and the potential congestion and paralysis expected to follow.

There was more to Buchanan than these pros and cons, but the headline result was that the city built these relatively free-flowing conduits for car and bus - sometimes elevated, sometimes in cuttings - creating barriers to pedestrians and destroying the local urban grain. Birmingham is not alone in still trying to undo this urban damage - it has cut out a significant amount so far.

The new retail development, now badged 'Bullring', is a major part of the retail-led urban redevelopment by the Birmingham Alliance, a partnership of property interests Hammerson, Henderson Global Investors and Land Securities. Bullring's first phase was a 5,500m 2indoor market opened in 2000 for the market traders. Displacing the traders southward (beyond Edgbaston Street), demolition of the Bull Ring Shopping Centre in 2000/01 and incorporation of the open spaces left a large, potentially coherent site of 11ha. The site runs from the junction of New Street and High Street in the north to St Martin's church in the south, and from New Street station approach in the west to Moor Street station (refurbished by the Alliance) in the east.

Most of Birmingham's successful, more-recent, redevelopment is not here but much further to the west - Centenary Square, Brindleyplace, the Jewellery Quarter, Symphony Hall, the National Indoor Arena. Immediately beyond the Bullring site things fall apart, though with a few strong Victorian buildings as you run into Digbeth to the south-east (site of the Custard Factory). The pivotal exception is St Martin's church, largely taken down and rebuilt in 1873-75 in what Pevsner calls '14thcentury style'. An attractive building, it sits adjacent to the new Selfridges.

The whole Bullring site, with masterplan and most buildings by Benoy, now has an internal coherence and more pedestrian connection with its immediate surroundings than it had before, albeit still somewhat hemmed in by roads - rarely does a shop open onto the site perimeter.

A key planning move has been to start at the pedestrianised junction of New Street and High Street, marked by the circular 25storey Rotunda offices, creating a pedestrian plaza. The road is now buried at this point, allowing the pedestrian realm to flow continuously down from here to St Martin's in a high-quality display of granite landscaping by Gross Max.

Another key move has been to deal with the 19m north-south drop down the site without the old steps and underpasses. The north-south axis slopes continuously, opening out near St Martin's with broad tiers of paving that were working as seating as much as steps on this summer's warm days.

Future Systems won a competitive presentation of ideas requiring just a few days to produce two A1s. Future Systems' presentation also included a small model in plasticine, shaped by Jan Kaplicky, which has changed little in the final realisation. The building flows into the corner of the site, encapsulating more volume than the masterplan outline (25,000m 2, costing £60 million including fit-outs). It confidently addresses St Martin's, reaching out to it with two levels of cantilevered terraces. The masterplan has done St Martin's a favour in providing it with a new more-prominent setting (and the customers for weekday shoppers' services).

Future Systems has gone further in connecting with the church, though not crowding it, and from some angles providing a remarkably effective backdrop to the church's elaborate stonework. At the same time Selfridges is a striking surprise, a focus that this largely nondescript locale could do with, contextual enough.

While the cladding is a simple idea, there is subtlety to it. The size of discs scales the surface and emphasises the curves in three dimensions. (In fact they are set out as horizontal rows of 282 discs, each different-length row with its own equal spacing of discs. ) Their reflective lustre sometimes softens and warms townscape reflections, these reflections shifting a little across neighbouring discs like frames from a movie. A meandering plinth of glass around openings, and mirror-finish stainless steel between these, grounds the building, provides an edge to the field of discs, collects rainwater and protects the lowest discs from vandalism. You even get a rusticated plinth where the mirror finish reflects Park Street block paving.

All this was not without public controversy, as something special usually is, though Amanda Levete says 'Birmingham council was so supportive at every point'.

While the cladding idea came early, the process of realising it was a long one - see 'Evolution of the disc' (page 35). But as the Working Detail illustrates (pages 42-43), this is not the boat-building technological intricacy of Lord's Media Centre (AJ 29.4.99). It is basic concrete construction built to a developer's budget similar to Debenhams'.

Budgetlimitations have made a few marks, such as stopping the discs planned across the roof, though a roof facade is not so much needed in this low city. And the bridge connecting with the car park to the east suffered D&B loss of nerve, or care - the curved bridge deck is capped with faceted, rather than curved, lines and coarser detailing.

Inside, too, budget limits have affected the four architects fitting out the four retail floors - from the bottom up they are Future Systems, Eldridge Smerin, Stanton Williams and Cibic & Partners with Lees Associates. Nearly all the ceiling areas are painted black with exposed services and intumescent-painted structure (fire engineered by Arup). Internal walls are strongly painted, though Eldridge Smerin has left a small area of the envelope exposed for the architectural visitor. Especially in Future Systems' food market, but on other floors too, there has been a concerted attempt to limit the Stansted effect - the distant prospect obscured by too-tall retail franchises and their heterogeneous signage.

Much of the external curvature is lost inside of course - walls feel only two-dimensional and hardly curve in plan at the scale of close attention. The organic focus passes to the atria and their escalators, for Levete a 'theatre of movement'. In the small atrium the escalators are tight within the floor openings, the view upward intestinal. In contrast the large main atrium looks up to a broad plane of glass - rooflight is too narrow a term. Escalators cross at one end of this atrium, letting light flood down through the remainder. The size of floor opening decreases as you go up, changing the perspective.

Looking up, the curved floor edges recede as a tube focused on the glazed roof. From high up, looking down, you see much more of the floor below than in a parallel-sided atrium, increasing visual connection between floors.

This is not a building to be summarised as a best example of its type. It is a one-off, albeit designed within retail imperatives and a developer's budget. Selfridges' Radice dared, and won.

Structure

Ed Clark, Arup

The primary functions of the structural frame are to provide a support skeleton for the free-form building facade and to create large, columnfree retail spaces of maximum height. Columns were positioned around the two internal atria and along the perimeter slab edge, spaced as far apart as economically possible, creating an irregular grid with minimum vertical structure. The curved profile of the building results in different-sized floor plates and hence different framing arrangements at each level. Cantilever beams vary in length by up to 4.5m to create this varying facade and atrium geometry. A systematic rationalisation of beam types was carried out to optimise performance, weight, and component repetition.

The large spans and limited ceiling depth (floor-to-floor heights vary by about 6m) lead to the building services and structure being integrated into the same zone.A solution using notches at the ends of beams for primary ductwork and holes within beam webs for secondary ductwork provides a flexible and fully coordinated design, using flexible plug-in systems for power, air conditioning, data and control.With the aid of CAD/CAM, these members were accurately fabricated and quick to build.

The need to form the curved geometry of the facade without incurring high construction costs presented one of the most complex design challenges of the project. The varying curvature of the facade and large storey heights precluded efficient modularisation of structural components or formwork and prompted us to look at more homogeneous methods of construction.Sprayed concrete was chosen as it allowed a robust substrate to be created by spraying onto a metal mesh held to the correct shape by an adjustable support system.

The structural system divides the surface of the facade into storey-height concrete ribbons running around the perimeter of the building, with each ribbon hung from the slab edge above by a series of connection brackets and separated from the storey below by a joint to allow relative vertical movement. The thickness of the concrete skin was tuned to achieve a substrate of adequate strength and stiffness while minimising the load to be carried by the supporting frame. (See Working Detail, pages 42-43) The design of the footbridge spanning between Selfridges and the Moor Street car park was driven by the architectural aspiration for an elegant form with a clear relationship to the Selfridges building. By using the structure as an exposed sculptural surface we were able to minimise the deck depth and avoided the need for an additional cladding system.

The bridge is constructed as a sculpted steel box girder, curved both on plan and elevation, and is given further support from a cable stay arrangement tied back to the Selfridges frame at roof level. A 3D model was produced to demonstrate that the deck could be fabricated entirely from warped steel plate and segments of bent tubes. This model was also used to produce cutting patterns for the warped surfaces and to extract all other fabrication information.

Evolution of the disc

Matthew Heywood, Future Systems

Selfridges' brief pointed towards a predominantly opaque facade, with most of the glazing at entrance levels. An alternative way to bring depth and interest to the facade was necessary. Our analysis of site and massing led us to design a three-dimensionally curved surface, wrapping around the building and onto the roof, screening plant. From a distance its modulation would reduce the scale, but up close, further articulation of the surface was vital.

We began to design a single repetitive panel, the space between the panels allowing for the curve of the form.Discarding the more obvious triangular solution, we looked to a circular panel, which required less complex alignment. Inspiration came from many sources including the chain-mail dress designs of Paco Rabanne and the shaping of the stonework on Gesù Nuovo church in Naples with its surface pyramids.

By giving the panels a human scale we set up a relationship that would allow an appreciation of the size of the building. The disc was to be between 600-700mm in diameter. There would be approximately 15,000 of them.

The economy of repetition meant that this could be fabricated in many ways and be flat, domed or dished.We explored more than 30 different materials and processes - from lava stone to a vitreous china disc moulded by Armitage Shanks. After creating two 6m-high prototype panels it became clear that the anodised aluminium domed disc was the correct form and material because of the incredible play of light over the surface and the successful way in which we could use the convex form to wrap around the curved surface. The 660mm-diameter discs are pressed and spun to create the form. They are then polished to a very high mirror finish before being anodised.

The construction behind the discs needed to be simple and durable.

Investigating different ways of creating the substrate, we settled upon sprayed concrete as the ideal method of skinning the steel frame.On the outer face there is a liquid applied membrane,75mm of insulation and a skin of render. When first considered, we envisaged the render surface as void or shadow between the floating discs.We now intended that the render should be a strong colour, contrasting with the silver of the disc.

We found inspiration in the work of the artist Yves Klein, particularly the series of monochromatic blue paintings, where he was striving to recreate 'void'on a flat surface. The challenge was now to reproduce this intense blue in a material that would last for 35 years without fading or deteriorating. After extensive lifespan testing we finally arrived at the right product and colour - Monolastex from Liquid Plastics - the sort of coating used on lighthouses and the like.We developed the method of fixing the disc with Arup Façade Engineering, James & Taylor (disc supplier) and Laing O'Rourke (main contractor). The discs must resist the relevant loads (self weight, wind, impact, maintenance and snow), while being quick and easy to install. In addition there needed to be adjustability to allow for tolerances in the setting out. We prototyped several design solutions until we settled on the centrally fixed support disc and dome combination. (See Working Detail, pages 42-43. ) The composition of the facade was completed by areas of glazing designed to make the most of the transition between the disc surface and the areas of flat faceted glass. By pushing the face of the glass outside the envelope and overlapping the disc surface, we were able to provide a tidy way of ending the disc pattern and also increasing the impact of the glazed areas. The junction is obscured by an area of mirror finish on the back surface of the glass.The yellow frit is positioned with a depth of the glass between it and the mirror, recreating on a micro scale the relationship between the discs and the Yves Klein blue surface.

CREDITS

TENDER DATE August 2001

START ON SITE DATE Main frame - June 2000 Laing O'Rourke work - February 2002

BULLRING DEVELOPER Birmingham Alliance

BUILDING CLIENT Selfridges

ARCHITECT Future Systems: Søren Aagaard, Nerida Bergin, Sarah Jayne Bowen, Sheema Chauhan, Lida Caharsouli, Julian Flannery , Harvinder Gabhari, Dominic Harris, Nicola Hawkins, Matthew Heywood, Candas Jennings, Jan Kaplicky, Amanda Levete, Iain MacKay, Glenn Moorley, Andrea Morgante, Thorsten Overberg, Angus Pond, Jessica Salt, Severin Soder

FIT-OUT ARCHITECTS Level 1 - Future Systems Level 2 - Eldridge Smerin Level 3 - Stanton Williams Level 4 - Cibic & Partners with Lees Associates

STRUCTURAL, SERVICE, FACADE ENGINEER Arup QUANTITY SURVEYOR Boyden & Co PROJECT MANAGER Faithful & Gould

MAIN CONTRACTOR Laing O'Rourke

MAIN FRAME CONTRACTOR Sir Robert McAlpine

SUBCONTRACTORS AND SUPPLIERS Glazing Haran Glass; envelope subcontractor 5M: discs James & Taylor; stainless steel panelling Baris, Jordan; sprayed concrete Shotcrete; GRP/GRG subcontractor Diespeker; M&E Haden Young; exterior blue concrete finish Liquid Plastics; fit-out lighting Erco; fire curtains Colt

WEBLINKS

Bullring www. bullring. co. uk

Birmingham Alliance www. birminghamalliance. co. uk

Selfridges www. selfridges. co. uk

Future Systems www. future-systems. com

Eldridge Smerin www. eldridgesmerin. com

Stanton Williams www. stantonwilliams. com

Cibic & Partners www. cibicpartners. com

Lees Associates www. leesassociates. com

Arup www. arup. com

Boyden & Co www. boydengroup. com

Faithful & Gould www. fgould. com

Sir Robert McAlpine www. sir-robert-mcalpine. com

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