Structural Engineer:AKT II
Main Contractor:Willmott Dixon
The new Town House at London’s Kingston University is a mixed-use building that has in recent years become increasingly popular with academic institutions. Its six storeys house lecture theatres, study rooms, dance studios, an auditorium, a library and a cafe.
One of the key factors for the design team was the long spans required to create some of the interior spaces: For example, the large double-height lecture theatre and a courtyard/auditorium which is triple height and requires spans of more than 15m.
The solution for the interior frame involves 550mm2 precast concrete columns arranged on a 6.4m grid running along the front of the building. A similar arrangement supports the rear of the structure and these shorter spans are bridged mainly by pre-stressed, hollowcore slabs 225mm deep. But in between, and where longer spans are required, these are achieved using 229 precast, pre-stressed “double T” beams cast in C60 concrete and weighing up to 18 tonnes each.
The double T system is more usually to be found in multistorey car parks but they were found to be very efficient and several advantages result from using them. Firstly the depth of the downstand part of the T can be varied depending on the span and loading involved – so there were three variations: 610mm, 810mm and 1,010mm-deep including the ‘tabletop’ formed by the TT. The depth of the tabletop is 60mm and above this is a 115mm-deep reinforced structural screed.
This effectively creates a hybrid precast/in-situ slab of 175mm above integral downstands which vary between 550mm and 950mm depending on the space they are spanning.
In all, the interior frame of Town House comprises 229 double-T units, a further 318 beams, 275 columns, 50 solid wall units and 52 core sections. The exterior frame required a further 300 beams and columns, together with 175 mullion and spandrel panels. Despite these daunting numbers, an impressive time-lapse video on PCE’s website shows the building’s structure being constructed in a little over 12 months.
Town House’s colonnade comprises some substantial elements – many of the columns are 12m high. However, it remains structurally independent from the interior frame, being simply tied back to it. The resulting absence of cantilevered slabs meant there were no issues with inserting insulation at the slab edges to prevent cold bridging.
The precast terrace slabs supported by the colonnade provide useable outdoor space for students and contain planters from which climbing plants are already growing. The plan is that vines will eventually entwine around most of the exterior columns, softening the architecture with greenery.
Town House, Kingston University was awarded the RIBA Stirling Prize 2021.