Finnforest Merk was selected as the timber engineering partner on the project by the contractor, Dragados, to fulfil the challenging roof design specified by Rogers Stirk Harbour & Partners and engineered firstly by Expedition and then by BOMA of Barcelona.
Transformed from a disused bullring into a mixed-use development, the historic building in the Montjuic area of the city required a dynamic roof structure, to provide protection from the weather, above a flexible floor space below to enable the building to be used for a wide variety of activities. Sports events, fashion shows and exhibitions will take place on the 5th floor ‘Dish’ level which forms part of the 70,000m2 overall building floor area.
The dome structure covers a roof area of 5,100m2 and a diameter of nearly 80m. It rises some 9m from the existing façade of the bullring. This has been retained and restored as part of the project.
There were particular challenges with the roof design, as architect James Leathem explains: “Because of the location of the building the roof had to be fixed in height in order to adhere to local planning restrictions. As a result the dome is quite flat in shape and the structural systems have to work much harder because of the large circumference and tolerances required.”
The structural solution Finnforest Merk produced is based on a timber gridshell and metal ring beam. This has been constructed from repetitions of glulam beams that create a pattern of lozenges. The pattern changes at the crown where the structure terminates in a circular ring beam, defining a 30m diameter oculus, itself constructed of a simplified pattern of glulam members. The wooden superstructure of the dome had to be designed as REI 60 structure based on Eurocode 5 part 2.
Engineered so that the timber members are connected using flitch plates and dowels within the wood, the appearance is one of a continuous timber structure. The beams themselves are then finished with load bearing Kerto Q LVL panels and insulation before the application of a liquid roofing membrane for a weather-proof finish. For the roof glazing Finnforest Merk used a special variation of its KertoConcept system.
The entire roof sits on a 3m high base, overcoming the possibility of unusable low space at the perimeter of the dome. This comprises 20 boomerang shaped columns supporting the dome’s perimeter beam.
“Finnforest Merk worked hard with us and the contractor to keep the original design intent of the scheme,” says James, “The geometry of the structure presented challenges which Finnforest Merk helped to overcome. The team was also very aware of the buildability of the scheme and how easy it would be to construct the dome once onsite. Working with Finnforest Merk on this project has been one of the smoothest parts of the job!”