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Selfridges store in Birmingham opened to critical acclaim in September 2003 as part of the redeveloped Bull Ring centre. Its organic form covered in silver discs and its spacious retail area with daylight-filled slanting main atrium has made it an icon for the city. We provided the muti-disciplinary engineering design for all phases of this visionary building.
The structural frame provides a support skeleton for the free-form building façade and creates large, column-free retail spaces of maximum height. The design optimisation process resulted in an irregular structural grid that is framed differently at each level to suit the curved building form.
The large spans and limited ceiling depth lead to the building services and structure being integrated into the same zone. The solution provides a flexible and fully coordinated design that was accurately fabricated and quick to build.
Façade substrate
The need to form the curved geometry of the façade without incurring high construction costs presented one of the most complex design challenges of the project. The varying curvature of the façade and large storey heights precluded efficient modularisation. Sprayed concrete was chosen as the preferred construction method and the free-form façade was constructed for the same cost as a standard façade system.
Services
Selfridges’ retail strategy demands constant change of the shop-fit, and the building services design philosophy is to provide this using flexible, 'plug-in' systems for power, air conditioning, data and controls which minimise cost and disruption to adjacent areas of the floor plates during local refit. This need to accommodate change and the desire to minimise running costs drove the choice of solution. These include variable volume air and chilled water systems, carbon dioxide monitoring for fresh air control and the ability to use free cooling and recirculation where climate conditions allow. The resulting systems use 40% less energy than standard solutions. Co-ordinating and integrating the services with the structural frame and façade geometry required a true multi-disciplinary design approach from the team. 3-D models and contractor’s fabrication data for the steel frame were used to verify co-ordination and eliminate clashes before construction.
Bridge
The elegant curved footbridge spanning between Selfridges and the adjacent car park is constructed as a sculpted steel box girder, curved both on plan and elevation, and is given further support from a cable stay arrangement tied back to the Selfridges frame at roof level. By using the structure as an exposed sculptural surface the deck depth was minimised and no additional cladding system was required.
We used a 3D model to demonstrate that the deck could be fabricated entirely from warped steel plate and segments of bent tubes. This model was also used to produce developed cutting patterns for the warped surfaces and to extract all other fabrication information.
Fire engineering
Our extensive fire engineering services at the early stages of the design process enabled the open retail spaces and canted atrium to be achieved safely and economically, and allowed Selfridges to enjoy use of the main atrium base for retail purposes, a key feature of the design. Modelling of fire growth and escape scenarios allowed a staircase to be removed and reduced the required structural fire rating, allowing intumescent paint to be used and the structure to be expressed.
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