Simplicity is Deceiving

The case study presented is a 195 meters tall office tower with a raised podium made of 16 meters full height glass panels (and smaller). The panels are only restrained by prestressed high-strength stainless-steel rods, lying entirely in the glass panel build up, composed by four 12 mm thick plies, laminated with 1.52 mm thick sheets of ionoplast interlayer, with an overall thickness of approx. 52 mm. Due to the facade geometry and the high wind expected, movement joints between rods are introduced, allowing for differential movement to avoid peak stresses in the glass panels. Also, smooth transition between a rod rectangular section at the interface with glass panels to circular section at anchor points needs to be ensured by CNC machining to avoid failure of the rod anchors due to fatigue. Sophisticated non-linear 3D FEM models had to be analyzed to predict glass stresses, differential movement to be accommodated by the joints and geometrical transition between rod sections.

The main innovation of this facade was the use of prestressed rods in conjunction with jumbo size glass panels. As tension structures experience large movement, it was crucial to understand the effect of these deformations imposed by the rods onto the full height glass panels, analyzing steel and glass members together as a single facade entity. Furthermore, in contrast to typical cable wall facade where the prestressed elements (cables) are offset form the glass line, here the rods are located in the plane of the glass panels and completely flush with them, ensuring the thinnest possible build-up in relation to the large facade span. A rocking portal frame, moving together with the rods to avoid excessive warping in the glass panels, has been used as a solution to deal with the required opening in the facade. An additional complication was given by the high wind load (typhoon) applied on the facade which required rods’ prestress in the order of 1000 Kilonewton in order to limit glass stresses and deflection.