The East West Atrium consists of a curved roof, made up of diagonally spanning primary bow trusses supporting the secondary diagrid. The primary bow trusses form ‘three pinned arches’ are tied by a stainless steel high yield tension rod system.
The bow trusses are pinned to specially fabricated castings which are welded onto large CHS columns. The lateral movement north south is resisted by the columns cantilevering from their bases, whereas east west the bases are effectively pinned to allow the structure to move under thermal expansion, the stability being provided by the Central Atrium core of four fixed columns.
The secondary steelwork typically comprises a diamond shaped grid of circular hollow sections spanning between pinned supports. The supports are either taken directly off the main building via bolted tee brackets, or off primary edge members/trusses.
The secondary diagrid steelwork was prefabricated using fully welded joints, brought to site in manageable sections and connected up using concealed bolted splices with cover plates matching the profile of the circular sections. The intention was to provide a network of tubular members which appeared to be unjointed and continuous.
The west entrance canopy also in tubular steel cantilevers out over its two support columns, it copes with the differential movement between the two buildings using specially designed support brackets that allow horizontal movement on a system of glacier stainless steel/PTFE pad bearings.