uilt using the ‘thin shell’ technique, which leverages the inherent action of arches to enable huge unsupported spans of very thin concrete, the building also has architectural and engineering significance.
Uline Arena’s latest incarnation preserves this heritage while transforming the single-storey hangar to four levels of office and retail space. The building’s ribbed, barrel-arched roof sits on concrete columns. This has been retained, but sections of the original thin concrete shell panels have been demolished to form roof-level terraces.
The challenge was that the panels and arched ribs were designed to act together structurally. Consequently, if roof panels were removed without any support, the loads in the arched beams would deflect and push outwards on the columns, which would then have been at risk of buckling under self-weight.
New intermediate post-tensioned floors by CCL prevent the columns from buckling and resist thrust forces in the completed project, but a temporary solution was also required to prevent the roof from collapsing during construction.
A temporary steel support structure was cost-prohibitive and involved buildability challenges. Instead, the CCL team helped to devise a post-tensioned (PT) solution that would put an equivalent counteracting force through internal ties within the structure.
The PT cables were fixed onto an anchor block on the column using a specially-designed bracket, then slung across the full 48m span of the arena. They were then fixed to an equivalent anchor block on the other side. This allowed the PT cables to be used as thrust restraints. Groups of cables were installed at each column-beam location and stressed in a carefully-controlled sequence.
The contractor was then able to start taking out sections of the roof slab to update the building while preserving the original roof structure and, though it plays no permanent structural role, the temporary solution was incorporated into the building.