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THE STAND HAS TO COPE WITH THE ARDUOUS LOCALCLIMATE

TECHNICAL & PRACTICE

The new 3Ws stand for Barbados'Kensington Oval cricket ground posed several challenges for architect/engineer Arup Associates - not least how to design for the unpredictable Caribbean weather.

During the 2007 Cricket World Cup final, a television commentator likened the curvaceous new main stand at Barbados' Kensington Oval to that of Future Systems' Media Centre at Lords.

But in fact, the differences between the two buildings could not be more marked. While the latter is designed for the relatively temperate UK conditions, Arup Associates' new 3Ws stand in Barbados has to withstand the much more arduous and unpredictable Caribbean climate.

A number of aspects affected the design of the 4,000spectator stand at the home of West Indian cricket, including potential serious seismic activity; torrential downpours; high temperatures; intense humidity; strong trade winds; and extreme light levels and glare.

The 3Ws stand combines a reinforced-concrete base section with a structural steel frame for its upper portions and cantilevered canopy. Designed as a moment frame, the main concrete structure has more uniform stability than a conventional building with cores and walls. In the Caribbean climate, a conventional building structure would have created stiff elements liable to fail in the instance of an earth tremor.

The structural steel frame - including the canopy, which cantilevers up to 20m at the outer edges of the stand and 16m at its centre - was designed to accommodate a wind loading of three times that encountered in the UK. The rear elements of the steel frame were over-sized accordingly, to counteract the potential movement of the huge canopy.

The large cantilever of the canopy provides unobstructed viewing of the entire pitch throughout the stand. Project architect David Parsons says: 'Side supports or columns would have compromised sightlines to the nearside boundaries, but removing side protection altogether would have left spectators at the mercy of the weather - sun or rain.' Arup Associates designed a doublecurved structural beam for the front of the canopy. Created by bisecting the front cone of the canopy with a cylinder, the design produces a cutaway to give the best views while also marrying the canopy structure with the rest of the steel frame.

The double-curved beam was manufactured at low cost from six pieces of hollow steel section. The steel frame was supplied by firms in both Barbados and the UK. All straight steel members came from the Caribbean. However, with no access to a steel bender locals could not complete the order, so the curved sections for the stand's side cheeks were manufactured in Coventry.

Arup was also instrumental in developing a low-cost cladding system. Using a detailed 3D wire-frame model of the stand, the exact size of each of the aluminium panels was plotted to allow the manufacturer to cut them as at shapes. They were then shipped to Barbados and simply pressed over and fixed to the curved structure, with self-tapping surface fixings attached to pre-rolled extruded aluminium carriers, which in turn run along aluminium Z purlins that are bolted to the steel frame.

The canopy roof is clad in profiled polycarbonate sheets.

The roof completely covers all seats within the stand, protecting them from rain and sun. However, shading the spectators also causes potential problems. The contrast in light levels from the shaded rear of the stand to the bright sunlit pitch had the potential to make watching a match uncomfortable on the eyes. But Arup's use of a translucent roof material allows diffuse light to filter through. Parsons says: 'When light shines through, it produces a Japanese lantern effect; you can see the lines of the steel trusses through the tensile fabric inner skin as boxed shadow, and there's a lovely glow to the whole ceiling. It lessens the contrast in light levels between the inside of the stand and the outside, making it a far better environment in which to watch cricket.'

This vast canopy is a boon when, infrequently, the skies open to deluge the ground in torrential rain. A large-capacity gutter system is built into the canopy's front edge, while the side cheeks feature hidden gutters to stop run-off travelling down the curved form and soaking the spectators. Both gutters connect back through downpipes, hidden within the structure, to a central storage tank where water is filtered and reused to flush the WCs.

More common is the prospect of a hot sticky day at the cricket. To promote air movement within the stand, Arup Associates plotted the direction of the prevailing wind before positioning the stand to ensure that it blew into and through the structure. 'The wind blows across the stand at an angle, providing optimum air movement, ' says Parsons. 'Whereas the old stand had pockets of dead air, the new one is ventilated to actively promote the flow of air in all areas.'

Behind the main terrace of seating, the restaurant and bar have an open front and rear allowing air to blow straight through, naturally ventilating the space. This effect is repeated in the twostorey presidential box, where large 1m-wide louvres to the rear allow air to flow while protecting the box from wind-driven rain.

But the smaller corporate boxes don't have this luxury.

Instead, glazed front facades have louvres at low level, which can be opened to encourage airflow into the box and out through high vents at the rear of the space. Even in the open terraced area of the stand the heat can become oppressive. So, to ensure maximum airflow, vents have been installed in the vertical north-facing elements of the saw-tooth design roof. Breezes blow across the rows of spectators, upwards into the stand and out through the vents via perforated sections in the tensile ceiling fabric.

The 3Ws stand is not a particularly high-tech structure, but it is exceptionally well designed. Structural and environmental design and architecture work together here to produce a building that was roundly praised at the opening of the recent World Cup.

Credits Client World Cup Barbados Architect/engineer Arup Associates Quantity surveyor Davis Langdon (London), Cooper Kauffman (Barbados), Tower Bucknall Austin (Barbados) Architect (Barbados) Gillespie & Steel, Tony Brooks Architects Structural engineer (Barbados) Consulting Engineers Partnership, Mahy Chaderton & Ridley M&E engineer (Barbados) Leverage Consulting Engineers, ADeB Consultants, Stantec Consulting International Landscape architect (Barbados) Talma Mill Studios Main contractor (Barbados) Larsen & Toubro

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