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A bridge to the future

Space constraints at the Bridge Academy site in Hackney, London has led to some lateral thinking and inspiring exposed steelwork. Jessica Rowson reports

Bridge Academy in the London Borough of Hackney is being built as part of the City Academies programme, a national initiative to build the next generation of secondary schools in the country's worst performing areas.

Standard guidelines, which recommend space per student, led to trying to fit 15,500m2 of learning and recreational space onto a 6,500m2 site. While in the 1970s, the solution may have to been to simply build up, the integrated BDP team wanted to create an inspirational structure and design out the antisocial behaviour issues inherent in the corridors and staircases of traditional schools.

Costing £33M, Bridge Academy (so called since it is situated between two bridges across the Regents canal) is sure to be something impressive.

Common to most schools, there will be a library, sports halls, play areas and classrooms. But here, the library and a play area will be hung off a huge, central curved truss, creating a large, column free circulation space underneath.

This curved truss or hoop is essentially the heart of the school, inclined towards the Regents Canal and nestled in the centre of the rest of the structure which is made from a composite floor deck and steelwork.

Currently, contractor Maceplus is removing temporary supports from under the library and transferring the loads into the hoop structure. The hoop also supports the façade which is made from ethylene tetrafluoroethylene (ETFE) pillows, the material used on the biomes at Cornwall's Eden Project, keeping the space underneath light and airy.

"We used it [ETFE] because it's sustainable, lightweight and easily replaced" explains Oliver Plunkett, concept designer for BDP. "It's an inclined façade and the school wouldn't want glass for safety reasons." The truss supported façade, creates a heart shape when viewed from across the canal and creates a column free area beneath. So, essentially, even the eaves space is maximised in the design to get the most out of the site.

Other sections of the building are stepped to maximise the amount of flat roof space that can be used for outdoor recreation. One such roof area is used as a football pitch which will take considerable live loading from students. Add to this that the floor below is being used as a sports hall with minimum columns, and hefty 2.2m deep trusses spanning 20m are required to support the structure.

The academy will specialise in music and maths and the structure is being deliberately expressed to show how mathematics and trigonometry can solve real life challenges.

"The initial idea was that the structure would be like a kite with the end of the truss tying the frame into the ground," explains Plunkett. "However, because of the braced nature of the hoop, the forces dissipate into the adjacent wings of the building, so there are only residual horizontal forces left at the point where the trusses meet foundations."

The hoop was developed as a combined support for the two storey inner section of the main building and the cladding to the inner ETFE façade.

The stunning steel structure looks wonderful but needed special care during fabrication to bring it to life. Mike Armstrong, the project manager for contractor Maceplus can't speak highly enough of fabricator Watson Steel. "It used a practical approach and design to get innovative solutions". He explains that the raking columns and hanging structure required substantial forethought as to how they should be safely erected.

Firstly the steelwork of the main surrounding building was completed and the structure of the main library was built off temporary props. Then the massive steel truss hoop structure was built to support the library in the permanent case. Hangers were then installed to support the library and play deck.

Work will continue until September next year when Bridge Academy will accept its first pupils.

HOW THE BUILDING WORKS

LIBRARY
Loads from the library building are transferred to the top of the main block via the truss. The horizontal load at the top is resolved into adjacent truss members, transferring load around the truss into the surrounding frame. Floor loads on raking columns serve to reduce the magnitude of horizontal forces at their highest point and then any residual horizontal forces are resisted by the weight of the lift shafts and where the trusses hit the foundations.

THE SPORTS HALL
has been sunk into the ground to create a softer edge to the site. But this was no easy task since the site is a former gas works crawling with contaminated substances. The dirty soil was removed from the site during the first four months of the 30 month programme.

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