Wind effects on permeable tall building envelopes: Issues and potentialities

To achieve even higher aesthetic value, energy efficiency and fire safety, the envelope is becoming a crucial element for certain tall buildings. The request to meet increasingly restrictive requirements is a challenging task, and the use of Permeable Building Envelopes (PBE) seems one of the best ways to design safe, sustainable and beautiful tall buildings of the future. One of the main loads acting on such envelopes is the wind action. Nevertheless, due to the complexity of this multi-scale problem, a complete comprehension of the wind effects on PBEs is still an open issue. From a wind-engineering point of view, a PBE can be considered as an additional layer fixed to the main building structure, which creates internal cavities connected to the exterior. The external layer permeability, the gap width and the internal compartmentations are only few of the many potential influencing parameters that make the study of the resulting fluid-dynamic system quite complicated. The current work aims at shedding some light on the aerodynamic behavior of permeable envelopes of tall buildings, especially focusing on the possible external/internal flow interaction that may strongly influence the overall system. Results from experimental tests show that a remarkable aerodynamic interaction can occur. This stresses the importance of an iterative dialogue between the experts involved in the design process of such permeable façades and, at the same time, it offers new possibilities related to the control of the complex aerodynamic effects that a PBE can create.