Wind Turbine Enclosure, Strata, London SE1

alt

Architect

Bfls

Structural Engineer

Wsp

Steelwork Contractor

Bourne Steel Ltd

Main Contractor

Brookfield Construction (UK) Ltd

Client

Brookfield Construction (UK) Ltd

‘Strata SE1’ is the UK’s first building to have integrated wind turbines. The three 9m diameter turbines, which crown the top of the Strata at level 43, generate up to 45kw of electrical power at peak times. The steel enclosure for the turbines is a unique and complex structure.

The Strata’s roof essentially cuts off the building at an angle, resulting in a geometric shape. The sloping roof, formed by a pair of concave surfaces and a pair of convex off-set surfaces, meant that each of the circular openings for the turbines are 3-dimensional with elevated elliptical rings in differing planes to each other.

The turbines’ power was maximised with longer blades achieved by the narrow structural envelope that was used for the 17m high frame. The enclosure for the three turbines consists of 24 individual elliptical CHS sections and six curved CHS sections. Between these components, beams connecting to fin plates form the rib cage for the cladding. Due to the complexity and the scale of the cladding, the elliptical frame design could only be produced using steel, as it allows the curved profiles of the venturis to be accurately followed. Furthermore, steel is both light and flexible, creating considerably more through spaces to ease the design coordination and construction of the wind turbines, mechanical and electrical services, pipes and cladding.

Continuous coordination between all parties including the cladding specialists and turbine manufacturer was vital to ensure a first time fit. To achieve a perfect fit of the turbines and cladding, it was essential that no steel connections breached within each of the circular openings. The elliptical openings for the turbines were formed from a total of 30 curved hollow section segments, all of which were set out in the fabrication shop using electronic survey data to ensure accurate positioning.

Due to the complex geometry of the build, all 400 secondary brackets had to be unique and welded to tight tolerances. Each one is a different size, pitch and angle and had to be welded to the structure in various planes to ensure the cladding could be fixed accurately first time.

The project involved the supply and installation of complex steelwork, at a height of 150m, with only the structural footprint to work on, which is bounded on two sides by busy London artery roads, an existing 21-storey residential tower and a rail viaduct carrying live tracks just 3m from the edge of the site. Consequently, prefabrication and off-site assembly was key to eliminate the risk of work required at height and ensuring accurate geometry.

In order to speed up on-site erection and reduce work at height individual frames were specifically designed to reach the maximum crane capacity of 6.5 tonnes. Although this method reduced the number of site formed connections, there was still a requirement to access some connections over 17m above the steel foundation levels. This access was provided using mobile elevating work platforms (MEWPs), which were positioned on bespoke steel frames built into the permanent structure.

Judges Comment

The Wind Turbine Enclosure makes a crucial contribution to sustainable energy generation, integrated into a building fabric.

Overcoming severe technical challenges of the complex geometry, working at height adjacent to a main rail line and the stringent vibration and deflection criteria, could all be met only by high quality steelwork.