The engineering of free form envelopes: the case of the Hadid Tower twisting shape façade

The use of glass in architecture has shown a significant increase in the last decades. Thanks to its characteristics of transparency, durability and flexibility, glass is today largely used in the production of free forms building envelopes. From this point of view there are many manufacturing technologies that can reproduce almost perfectly the complex form of the designed envelope, while others can only approximate it, while still providing a satisfactory aesthetic result. The paper, after analysing the different technologies used for the production of transparent envelopes with complex shapes, presents the case of the Hadid Tower, located in the new Citylife business centre in Milan (Italy). The features and the characteristics of this innovative twisting shape double skin envelope, as well as the particularities related to its complex geometry, are discussed. Moreover, the critical issues of the project engineering, in particular the cold bending of the outer skin façade cells, are analysed and described in detail. The study results and the numerical simulations run for the case study are proposed as an example for innovative façade systems design in buildings where cold bent glass solutions will be used.