Rogers Stirk Harbour’s Santa Maria Del Pianto Metro Station, Naples
The practice designed a doubly curved hyperbolic paraboloid canopy roof formed from a lattice of steel plates that tilts back to create the entrance to the metro
Architect Rogers Stirk Harbour & Partners
Structural engineer Expedition Engineering
Location Poggioreale, Naples, Italy
Completion date 2015 for the Metropolitan Line 1 Extension
All Soul’s Day, or the Day of the Dead, proved a decisive factor in Rogers Stirk Harbour’s design for the canopy roof to the new metro station at Santa Maria Del Pianto, north-east of Naples.
The station is near the 90ha Poggioreale cemetery, which is a focal point of the day. Practice director Amarjit Kalsi explains: “The Day of the Dead is a huge festival and a Roman Catholic public holiday that remembers deceased family and friends. It attracts thousands of people that all converge into the cemetery on one day of the year.
“The metro station has to cope with just a few hundred people on a normal day and then tens of thousands on this one day of the year.”
The 2,300sq m roof form the practice designed is a doubly curved hyperbolic paraboloid, ie the shape of a Pringle crisp. The canopy is formed from a lattice of thin steel plates that lands at two points and tilts back to create the entrance to the metro.
It’s perhaps underselling the scheme to describe it as just a metro station. It is also an important transport hub that will include; a bus station for 45 buses, a two-level naturally ventilated parking area set in existing orchards to provide shading in summer for some 1,500 cars and a concourse for arriving and departing passengers with ticket sales, restaurants and shops. When complete, the new underground station will be the last stop before the city’s Capodichino airport where Rogers Stirk Harbour is designing the other metro station, located about 1km north-west of Santa Maria Del Pianto.
Appointed in 2006, Rogers Stirk Harbour along with Future Systems, Dominique Perrault, Massimiliano Fuksas, Mario Botta and others have been commissioned to upgrade the city’s metro system with the aim of relieving the city and roads into Naples from traffic and facilitating better use of public transport. Civil engineering work — the tunnelling — has begun, but work on the metro stations won’t start until regional and government funding is secured.
Evolutionary Algorithm Software
The final design for the Santa Maria Del Pianto’s roof was arrived at with the aid of a bespoke plug in software program developed by Fred Labbe, an associate at Expedition Engineering.
A long-standing collaborative relationship between Expedition and Rogers Stirk Harbour encouraged the architect to experiment with the program, which Labbe developed for use with Rhino using an evolutionary algorithm method.
“Evolutionary algorithms,” explains Labbe, “operate on a population of possible solutions and mimic the process of natural evolution applying the principle of survival of the fittest, to produce better and better approximation to a solution, generation after generation”.
Over the last 10 years the Architectural Association’s Emergent Technologies unit, run by Michael Weinstock, has been experimenting with the method, with the idea that complex patterns emerge out of the repetition of simple interactions.
Before the program could run, the form of the roof had to be determined. By working with Expedition, the architects developed the hyperbolic paraboloid roof formed by a lattice of thin steel plates, vertically aligned, resembling a honeycomb in plan.
The roof’s form was influenced by a number of key factors: maximising sunlight penetration and views to the sky from the bottom of the 40m-deep station shaft; the provision of shading on the lift platform at ground level to prevent overheating in the searing hot Naples summer; preventing rainfall from entering the station; and making the roof structurally efficient using a minimum of materials.
“The geometry of the toroidal surface of the roof was defined to meet the rain cover requirements and for optimum lateral and longitudinal curvatures, thus fixing the main geometry, but leaving the organisation of the 2,700 steel plate elements to be optimised,” says Labbe.
“An evolutionary algorithm was used to optimise the organisation of the honeycomb, as those algorithms are particularly well suited for large search space and multi-objective optimisation problems”.
Over four months, the program identified and located the best arrangement for the roof’s mesh. Labbe says the approach worked very well and for two of the conflicting criteria, daylight and shading, the performance was improved generation after generation.
“The algorithm was effective at identifying an appropriate trade-off solution and gradually improving it,” he says.
“The mesh is loosened above the openings in the slab at ground level to let sunlight into the station, and its density is increased above the lift platform to provide shading.”
Vertically aligned steel plates ranging in thickness from 60mm to 10mm will form an intricate lattice across the 40m x 20m roof canopy. The plates vary in order to be thicker near the main supports where the forces are higher.
The steel lattice, which will be welded together, will act as both a louvre system and primary roof structure, with the mesh being organised to map the daylight requirements and the distribution of forces in the structure. The high strength steel plates had to be vertically oriented to allow for a minimal structure and to maximise daylight into the station.
The steel structure will rest on either side on two concrete cradle supports, reinforced with steel inside, which will form part of the ground’s landscape.
A single-sheet ETFE skin will be rolled out over the honeycomb structure and clamped “like cling film”, says Amarjit Kalsi, allowing for minimal impact on transparency.
The bespoke software program has helped to produce a roof structure that is affordable because it has been mapped to a rational simple build system comprising steel plates and nodes.
Architect Rogers Stirk Harbour & Partners, Structural engineer Expedition Engineering, Client and services Metropolitana di Napoli, Structural engineer carpark/underground Studio Cavuoto, Landscape architect AWP, Traffic engineer Arup Traffic, Fire & AccessArup Fire