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Designed by Rogers Stirk Harbour & Partners, the five floor development will provide shops, an events space, sports and cultural facilities, 12 cinemas and restaurants wrapped around its perimeter. The 19th-century structure is located close to Montjuic on the Plaça Espanya, giving the city a new “gateway” from the west. The existing facade will be retained and restored as part of the project, with the base of the facade excavated to create a public domain at ground level. This represents a major engineering exercise, involving the insertion at the base of the existing walls of composite arches which will support new spaces for shops and restaurants. New piazzas are created at ground level and a giant roof terrace will form a “piazza in the sky” with panoramic views over the city. The aim of the project is to provide a high degree of flexibility, accommodating future change and allowing a wide variety of activities to take place in the building.
The roof
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 the project. Timber was chosen for the roof for different 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.
The dome has been made from primary and secondary glulam beams and Kerto roof panels engineered by Finnforest Merk. These beams will provide weather protection and reduce noise from the development to the surrounding areas.
Covering a roof area of 5,100 sq 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.
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 and to make sure 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 façade around the perimeter, for transparency. Four glazed openings, each 200 sq 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.
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Plan Magazine
