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Tuesday29 July 2014

Las Arenas Bullring, Barcelona

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A “floating” domed roof takes centre stage as Rogers Stirk Harbour & Partners’ redevelopment of Barcelona’s 1890s bullring nears completion.

By spring next year Las Arenas, a former bullring in Barcelona, will be playing host to a less bloody spectacle. The original three-storey brick and stone structure, which saw its last bullfight in 1977 and has stood empty since 1990, will have been transformed into a mixed-use five-floor development enclosed under a giant timber domed roof.

Located near the Montjuïc area, home to museums, exhibition halls and the city’s Olympic stadium, the 7,000sq m of mixed-use floor space will provide shops, 12 cinemas, sports and cultural facilities, and an events space at fifth-floor level with restaurants wrapped around its perimeter.

The architect has also created a lower ground level of retail and four floors of underground car parking. These extra levels have been accommodated by excavating under the structure to create five basement levels and by building extra floors within the restored perimeter facade. The top level is capped with an elaborate timber gridshell, which sits on top of a steel-framed dish, appearing to float above the wall.

Alongside the complex, an office block has been built, together with a 27m-tall steel communications tower accessible from the lower ground level of Las Arenas or from a lobby at the base of the tower. Visitors can take a glass lift to a terrace on top of the new development and enjoy panoramic views of the city.

Las Arenas was built around 1898 to the designs of Catalan architect Lluís Domènech i Montaner and is completely circular in plan. The original structure is approximately 94m in diameter and 22m high and the facade features 56 bays of arches on each level. These are large at ground level and become gradually smaller further up the building.

James Leathem, an associate at Rogers Stirk Harbour, says the project is the most complex he has ever worked on in terms of refurbishing an old building. “You don’t know what lies behind,” he says, “and for that reason the project has had to evolve in terms of its engineering, but it has still been an incredible journey.”

Timber Domed Roof structure

A domed roof structure at a diameter of nearly 80m rises about 8.5m from the supporting tubular steel ring beam and encloses the fifth floor level of Las Arenas. Providing weather protection and reducing noise from the development to the surrounding areas, the dome has been made from primary and secondary glulam beams and Kerto roof panels engineered by Finnforest Merk.

Covering a roof area of 5,100sq m, the dome has been constructed from repetitions of glulam beams in a lozenge pattern. This pattern changes at the crown, where the structure terminates in a circular ring beam, defining a 30m diameter oculus, itself built from glulam members. It has been engineered so that the timber members are connected using flitch plates and dowels within the wood, creating the appearance of a continuous timber structure.

Timber was chosen for the roof for several reasons. The design team liked its aesthetic appearance; it is cheaper, lighter and has a lower carbon footprint than steel; and the laminated timber beams have their own integral fire protection which cuts down on costs.

To comply with planning restrictions, the dome is shallow, rising only 10m. This makes it more vulnerable to buckling and large deflections than a dome with a large rise. To ensure it remains structurally stable, Finnforest Merk carried out an analysis that identified the dome’s exact stiffness and any imperfections.

A major challenge the design team faced was how to support a timber roof sitting on a steel dish. Expedition Engineering recommended that the dome’s perimeter beam should spring from a continuous tubular steel ring beam held 3m above the dish by a series of 20 braced boomerang-shaped red steel supports. Where a timber primary member meets the ring beam, three steel plates welded to the tubular steel ring beam will be spliced with flitch plates into the timber and bolted together.

The 3m-tall base has an integrated glass facade around the perimeter, for transparency. Four glazed openings, each 200sq m, at the lower end of the gridshell stretch across two of the boomerang-shaped supports and draw light into the roof space.

The beams have been covered with load-bearing Kerto panels, a layer of insulation at least 50mm thick, and a waterproofing layer before being finished with a beige liquid proofing membrane which lets the roof’s timber structure still be seen.

Supporting the roof

Without doubt it is the new “dish” that really engages the passerby, appearing to hover over Las Arenas’ original facade. The 100m-diameter steel-framed dish creates the top floor of the new development and helps to support the roof above, playing a fundamental part in the overall architectural concept.

Supported beneath on an independent structure of four massive braced, steel legs, the dish is 3m deep at its thickest point forming a fully accessible, services and maintenance zone for air-handling units as well as a plenum for smoke extract from the atrium below.

The dish is comprised of a series of massive, welded, tapered I-section steel beams, with large cut-outs for services and access, radiating from the centre out to the cantilevered beams that support the pre-cast concrete planks with glass lenses which form the 360 degree perimeter terrace. The I-beams are up to 2.7m high but vary according to their specific structural requirements at the node points with the supports below. The soffit on the underside undulates very subtly as it follows the precise line of the structural framework.

The steel legs pass down through the four levels, allowing a large column-free space at level four, together with a more efficient, independent, structural framework for the cinemas, retail and car parking levels below. Within each floor there is a clear legibility of emergency escape routes, toilet pods, public and goods lift access, together with a series of access bridges, platforms and escalators passing in between the structural legs of the dish.

PROJECT TEAM

Architect Rogers Stirk Harbour & Partners, Client Sacresa/Metrovacesa, Co-Architect Alonso Balaguer y Arquitectos Asociados, Structural engineer & facade consultant Expedition Engineering and BOMA, Roofing contractor Finnforest, Acoustics BDSP and Audioscan, Main contractor Dragados, QS TG3 , Services engineer JG and BDSP, Services contractor IMTECH and EMTE, Dish steel contractor Martifer, Bullring facade contractor Joan Obré, Office facade contractor Strunor

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