Structural engineer's account
Harris & Sutherland
The structure of the Ruskin Library is a product of its unique shape - two chorded bows set side by side. The need for secure storage space in a stable internal environment led to the idea of a heavy external wall surrounding, but not touching, a separate structure containing the archive. This structural separation became a powerful symbol from which the strength of the building is derived.
The outer envelope relies on a stiff spine comprising a pair of reinforced concrete portals which span lengthwise along the two chords. These two frames, linked by a slab, provide all the necessary stiffness to resist the exceptional wind loading - the inescapable penalty of a west-facing site at the top of a hill close to the sea. To transfer this wind force, the curved form offered two advantages: a streamlined shape to reduce the wind pressures, and the potential for arch action for walls spanning horizontally between abutments. In practice it proved to be cheaper to reinforce the walls vertically, and so abandon the idea of a 30m-long slender arch.
The archive itself is a free-standing stack built of concrete - blockwork for the walls, in-situ reinforced concrete for the floors, and precast concrete for the staircases. This heavy, independent structure bears on a raft foundation built directly off the stiff boulder clay beneath the basement.
The suspended floors are simple flat slabs spanning between loadbearing blockwork walls. The visual separation of the archive is enhanced by using glass for the entrance foyer and link-bridge floors, all supported by minimal structural steelwork.
One hidden detail is the use of bed-joint reinforcement to avoid the need for movement joints in the external skin of blockwork. As a precaution against corrosion in the salty air, this reinforcement is stainless-steel.