The new roof structure of the Wellington Academy in Tidworth is nearing completion. The cross-laminated timber panels and glulam beams/columns are carefully organised over the entrance foyer exploiting the structural potential of the material and the welcoming phenomenology of the exposed timber grain.

Techniker’s role

Techniker are appointed as structural engineers by B&K Structures the specialist timber contractor, to develop the design and detailing the timber frame for the new £32m building in Wiltshire. The building has been designed by BDP and awarded to B&K Structures on the base of a Design and Build contract through the main contractor Kier Moss.

Technical features

The main feature of the project is a semi-circular timber roof, measuring approximately 75m wide x 43m with a four degree monopitch slope. The roof structural system consists of 198mm thick cross-laminated timber panels spanning up to 8.32m across 915 x 215mm deep glulam beams typically parallel to each other. The depth and prominence of the beam elements within the space has been minimized by engaging the roof panels structurally in a screwed partial shear connection. An articulated plate steel capital connects the beam elements to the slender vertical glulam columns.

Key achievements

The roof is also characterized by large circular glazed openings with diameters of 3.5m bringing beams of natural light into the building. This dramatic three storey high internal space was achieved thanks to the two-way spanning properties of the timber and a carefully rationalized panel layout to maximize the cross-laminated timber potential.

Coordination challenges

Significant attention has been paid to the interfaces with structural elements designed and by other specialist contractors (i.e. concrete frame and main steel frame). Secondary steel elements such as cross bracing and steel stubs directly connected to the timber members were also included in the design. The major challenge on the project has arisen out of the fast track construction programme and the inevitable design iterations required to fully coordinate these interfaces.

Other design features

Techniker are also appointed for the design of the boarding house, a two-storey student residential building formed by two wings linked by a central hub. The irregular geometry of the central portion of the complex, characterized by floor spans of approximately 8m and a full height entrance hall have brought with them significant structural challenges. Some floors are hung from the roof structure with slender steels incorporated to provide the necessary robustness.

The sensitivity of the floor to footfall induced vibrations has also been investigated for the floors with longer spans in the hub.

The two wings comprise 146mm thick cross laminated timber floor and roof panels bearing on 98mm cross laminated timber walls and. All the timber panels have an inherent 30 minutes fire resistance on one side. Only in few locations glulam beams and columns were implemented to create more open space.

Connection details between horizontal and vertical partitions were developed in close collaboration with BDP’s acoustic engineers in order to achieve the required sound insulation in accordance with Approved Document E.

Visuals and aerial plan by BDP.

See for yourself!

Time-lapse video of construction: www.wellingtonacademy.org.uk