A delicate steel screen spans 23.25m in a gentle curve between the staircase towers of two four-storey buildings - the Genetics Institute and the Bioscience Centre. Its purpose is to visually complete the enclosure of the central square and provide continuity to the roofline.
The screen is designed as an open grid without using cross-bracing; it is formed from a series of 'ladderframes' - vertical hangers of paired 150 x 18mm steel plates set 1.8m apart and welded to horizontal 114.3mm diameter CHSs.
At the top of the screen an open braced canopy and a lattice box girder span between the two stair towers.
The ladder-frames are suspended from one side of the girder; to avoid rotation caused by the eccentric loading it is braced diagonally with 60.3mm SHSs.
The ladder-frames are connected to three horizontal bow girders which prevent out-of-plane distortion and carry wind forces back to the stair towers. The 114.3mm diameter tubes act as the inner string of each girder; the outer 139.7mm diameter CHS string is welded to a cruciform outrigger which spans across to the hangers and is bolted between the spacer blocks. The bow girders have no diagonal bracing and act as vierendeels.
The four plates of each outrigger taper horizontally and vertically in opposing directions to reflect the forces - the vertical plates are deepest at the face of the screen to provide maximum cantilever moment resistance.
The interaction of moments, axial forces and their effect on stability were examined using a fully elastic second order analysis, a 3D model and structural analysis software.