Wilkinson Eyre Architects
Turnstone Estates Ltd
The Hauser Forum is a new, mixed-use development at the University of Cambridge’s West Cambridge site. The development comprises the Cambridge Enterprise Building (CEB) and the Broers Building.
The CEB will be the new home for Cambridge Enterprise, a University owned company which assists with the commercialisation of research, and also incorporates a new campus café. The most striking feature is the double height café space which cantilevers 11m from the southern façade of the building.
The Broers Building provides 4,000m2 of high quality commercial, research and development and ancillary space to be let to private organisations. Office space is provided over four storeys, with the steel framed superstructure also boasting a cantilever to the south.
Steel was chosen for both buildings to enable them to meet architectural aspirations and achieve a tight programme. The project retains a large amount of exposed architectural steelwork in canopies and edge detailing. Services and structural zones were combined through the use of cellular beams to limit the floor to floor heights whilst maximizing the available floor to ceiling height in the 18m wide floor plates.
The two buildings are connected visually by a high level steel canopy which covers the new landscaped forum space between the buildings. The canopy also serves a practical purpose in providing solar shading to the buildings.
The principal challenge for the structural design was the double height fully glazed café which cantilevers a total of 11m from the CEB over a reflecting pool under, 3.5m of which forms a terrace extending beyond the building enclosure. Achieving this, while meeting vibration limits for occupant comfort and deflection limitations for the proposed curtain walling system, led to significant analysis and development.
The concept adopted was to use large trusses in the elevations to form the cantilever, which could only be practically achieved in steel. This scheme was developed using Macalloy tension rods as the diagonals in conventional N-trusses. An additional pair of tie bars was added in the southern façade to limit serviceability deflections of the 13.5m single span fabricated box floor beam to the limits required by the curtain walling. The cantilever was erected on temporary props with a precamber of 35mm to counter overall dead load movements and to leave it with an aesthetically pleasing slight upward camber. Once the floor slab had been poured, the Macalloy rods in each elevation were stressed to lift the structure off its temporary seating and the props removed.
The project incorporates numerous design features that enabled both buildings to achieve BREEAM ratings of ‘Very Good’ and EPC ratings of ‘B’. Both buildings are provided with ground source heat pumps installed integrally with the structural piles, which provide up to 117kW of cooling and 188kW of heating. This is approximately 7% of the buildings’ energy demand and delivers a calculated annual carbon saving equivalent to 26,000kg of CO2.
Additional energy savings on heating and cooling were made via the inclusion of innovative thermal labyrinths in the basement of each building. These consist of a series of closely spaced dense concrete block walls arranged in a zig-zag formation through which air is drawn before reaching the building air handling units. This has the effect of lowering the air temperature during the peak summer months by up to 5ºC from ambient, and providing a more stable temperature output throughout the day, reducing the amount of energy expended on conditioning the air. The installed labyrinths were calculated to achieve an equivalent energy output of approximately 91MWh per year, realising a carbon saving equivalent to 10,572kg of CO2.
These two buildings are joined by a covered public space, and the steelwork frames are key to the whole project. Whilst one building is air-conditioned, the other makes effective use of greater mass for natural cooling. The link block has a striking large cantilever over the adjoining lake.
A good example of practical steelwork design integrated into an intelligent solution.