Michael Hadi Associates, formerly of Techniker
Structural design began at competition stage in conversation with the architect about Enric Miralles' cable-supported roof for the Huesca Sports Hall. However, cable trusses were ruled out following analyses which confirmed that it would be too flexible for pedestrian occupation of the glass roof, and that the structure at the abutments would be unacceptably cumbersome.
The roof quickly evolved into a hierarchical system of deep primary and secondary beams, arranged on a 10m orthogonal grid, supporting shallow secondary and tertiary beams and the glass skin. This grillage design allowed flexibility in the layout of the supporting structures; indeed, the arrangement of columns and walls is substantially independent from the orthogonal roof grid.
Primary roof beams are fabricated steel-plate girders, evoking Wearside's ship-building history. At their northern end, the girders are supported on an 8m-high fair-faced reinforced concrete counterforted retaining wall. The depth of the girders reduces from the retaining wall to their southern extremities, where they cantilever up to 12m beyond the river facade. The varying depth responds to structural requirements and to the architectural intent to anchor the building to the hillside.
On the line of the glazed river facade the girders are supported by vierendeel trussed columns. Rigid steel frames cantilever from the columns to support lattice-trussed transomes, incorporating maintenance walkways and solar shading frameworks.
At the western end of the river facade the free-standing seminar room straddles the glazing line, supported on four concrete-filled steel legs. The floor and enclosure comprise a hybrid concrete, steel and timber structure to achieve the complex three-dimensional geometry.
Technologies such as Prova-lite and Therma-vit (variable opacity and heating glasses produced by Saint Gobain) and the use of glass - both boulons and ground - to produce semi-opaque thin panels of structural concrete using ferrocimento techniques, were investigated but ruled out.
The glass roof remains. Arup Facade Engineering carried out the detailed design for the roof cladding system, which, like all structural applications of glass, is an agglomeration of smaller elements to create a whole. There are strong parallels between the structural and drainage designs for the glass cladding; with some redundancy in both such that the failure of one component will not lead to a catastrophic failure of the whole.
The reclamation, involving the removal of reinforced concrete slipways and peaty material arising from wooden shipbuilding, was phased over two years and involved the import, exchange and compaction of some 200,000m3 of crushed concrete and colliery spoil from the nearby Monkwearmouth coal mine. Reinforced concrete strip and pad footings for the Glass Centre are founded on these imported materials.