Shortlisted #StirlingPrize2014
Design Concept
The architectural concept of the London Aquatic Centre is inspired by the fluid geometries of water in motion, creating spaces and a surrounding environment that reflect the riverside landscapes of the Olympic Park. An undulating roof sweeps up from the ground as a wave - enclosing the pools of the Centre with a unifying gesture of fluidity, while also describing the volume of the swimming and diving pools.
The Aquatics Centre is designed with an inherent flexibility to accommodate 17,500 spectators for the London 2012 Games in ‘Olympic’ mode while also providing the optimum spectator capacity of 2000 for use in ‘Legacy’ mode after the Games.
Site Context
The Aquatics Centre is within the Olympic Park Masterplan. Positioned on the south eastern edge of the Olympic Park with direct proximity to Stratford, a new pedestrian access to the Olympic Park via the east-west bridge (called the Stratford City Bridge) passes directly over the Centre as a primary gateway to the Park. Several smaller pedestrian bridges will also connect the site to the Olympic Park over the existing canal.
The Aquatic Centre addresses the main public spaces implicit within the Olympic Park and Stratford City planning strategies: the east-west connection of the Stratford City Bridge and the continuation of the Olympic Park along the canal.
Layout
The Aquatics Centre is planned on an orthogonal axis that is perpendicular to the Stratford City Bridge. All three pools are aligned on this axis. The training pool is located under the bridge with the competition and diving pools located within the large pool hall enclosed by the roof. The overall strategy is to frame the base of the pool hall as a podium connected to the Stratford City Bridge
This podium element contains of a variety of differentiated and cellular programmes within a single architectural volume which is seen to be completely assimilated with the bridge. The podium emerges from the bridge to cascade around the pool hall to the lower level of the canal.
The pool hall is expressed above the podium by a large roof which arches along the same axis as the pools. Its form is generated by the sightlines of the 17,500 spectators in its Olympic mode. Double-curvature geometry has been used to generate a parabolic arch structure that creates the unique characteristics of the roof. The roof undulates to differentiate between the volumes of competition pool and the diving pool.
Projecting beyond the pool hall envelope, the roof extends to the external areas and to the main entrance on the bridge that will be the primary access in Legacy mode. Structurally, the roof is grounded at 3 primary positions with the opening between the roof and podium used for the additional spectator seating in Olympic mode, then in-filled with a glass façade in Legacy mode.
Legacy Roof
The London Aquatics Centre will mark the gateway to the 2012 Olympic Park. The stunning waveform shape of its complex steel roof sweeps dramatically upwards in a smooth curve from the south end and then down again over the northern cantilever, while the western and eastern tips curve upwards at the edges.
The 11,000m2 structure spans a column free area 160m long and up to 90m wide. It is supported on bearings on two concrete cores 54m apart near its northern end and on a concrete wall at its southern end. The roof contains about 3,200 tonnes of structural steel, of which 2,000 tonnes are fabricated plate girders with the structural connections totalling around 600 tonnes.
The roof structure comprises a series of long span trusses spanning lengthways over the main pool hall from a transverse truss mounted on the southern retaining wall bearings to another transverse truss spanning between the northern concrete cores. The main trusses lie in a fan arrangement to create the plan shape of the roof. The centre fan trusses cantilever northwards beyond the north transverse truss to form an overhanging canopy over the main public entrance plaza of up to 30m.
The centre fan trusses carry load in truss action, spanning between the north and south transverse trusses which carry the load down to the supporting bearings on the concrete structure below. Due to the roof geometry, arches are formed in the wing areas to the west and east of the central area. Under uniform loading the two opposite inclined arches in the wing areas balance each other, forming a compression hoop around the roof perimeter. A tension force arises from the change in geometry of the compression hoop in plan at the kinks which occur at the wing tips, and this is resisted by a tension tie across the centre and a resulting tension force occurs in the central fan trusses.
Lateral stability is provided by a system of horizontal and diagonal cross braces in the roof surface between the top chords of the fan trusses. All of the trusses are formed from fabricated H-sections. The plate thicknesses of the sections vary along the length of the trusses to ensure efficient use of material, with plate thicknesses varying between 8mm and 120mm. At site the members were bolted together to produce erectable truss lengths of around 30-40m. The trusses were lifted onto pre- erected lines of temporary trestles and joined together with bolted splices.
In the permanent condition the roof is designed to be fixed on plan at its northern bearings and free to slide longitudinally at the southern end. However, due to site constraints, it was necessary to construct the roof from south to north, starting with erection of the southern transverse truss which weighed just over 70 tonnes. It was necessary to initially restrain the roof in a longitudinal direction with temporary works at the southern end and then, later in the programme, a controlled transfer of restraint to the northern bearings was carried out whilst simultaneously releasing the southern end.
When 50% of the roof had been erected one of the intermediate lines of trestles had to be removed to allow excavation to start for the deep dive pool. This was achieved by jacking the roof up at the trestle positions to relieve the load from them. The remaining two main lines of trestles were left in position until the main roof structure was complete. On completion of the main erection, the roof was lifted using strand jacks mounted on temporary towers at the south end and allowing it to rotate about the northern bearings. Once the roof was clear the strand jacks were locked off while the trestle heads were dismantled before the roof was lowered to its final position.
All of the bolted connections in the primary structure were designed to be non- slip using tension control bolts. In situations where bolt access was limited by geometric constraints, tension control studs were used. The structure contains about 70,000 bolts.
Due to the highly corrosive environment, rather than leaving faying surfaces unpainted they were coated with zinc silicate paint, slip tests having first been carried out to establish that a suitable slip factor could be achieved. The zinc silicate was used as a primer generally and exposed surfaces were over coated with MIO. In the final condition the steelwork is all concealed by upper and lower surface cladding and so no decorative coat needed to be applied.
A network of 600 linear metres of steel walkways installed throughout the roof space will provide access for regular inspection and maintenance of the structure as well as lighting equipment and other plant.
Temporary stands to the west and east of the structure will provide seating for 14,700 of the full complement of 17,500 spectators for the Olympic mode. These will be removed and recycled on completion of the Olympic and Paralympic Games. The final perimeter façade will then be installed for the legacy mode to provide outstanding community facilities for East London’s future.
