Experimental evaluation of permeable cable-supported façades subjected to wind and earthquake loads

Abstract

In building engineering, non-structural components represent a significant cost of the overall budget of a construction project. However, in many cases their design is essentially based on architectural criteria rather than on structural performance mainly because the structure stability does not necessary rely on them. Among nonstructural elements, façades are one of the most visible and expensive components where innovation is very popular. Permeable cable-supported façades are a recent frontage proposal designed to allow not only flexible exterior finishes, but also the flow of natural light and the apparent building transformation according to the daytime and light; however, their structural performance for wind and earthquake loads is still a subject of research. This paper, for the first time, experimentally evaluates the wind and seismic behavior of these type of façades. A five-step comprehensive approach is proposed for the evaluation of cable-supported masonry facades including field and laboratory tests. In the first step, the individual capacity of the connections and materials of the system is evaluated under standardized and non-standardized procedures. The next step consisted in quantifying the fundamental vibration periods and the modal shapes of the façade system including the effect of the border and hanging conditions. The following phase is to estimate the wind load using computational fluid dynamics (CFD). In order to understand the effect of the wind at the different scales of the structure, simulations are performed starting with few bricks and progressively increasing the size of the computational model until assessing the entire building. These analyses allow understanding how the micro and macro components distribution and geometry can affect the wind in-and-out-flow and the possibility of vortexes. Then, a full-scale experimental sub-assembly specimen of a representative module of the façade is subjected to uniformly distributed pressures; the setup considered the border conditions, tension loads, and actual materials. Finally, the seismic assessment phase includes a simplified non-linear procedure to calculate critical accelerations at the building roof, and shaking-table tests of full-scale specimens subjected to these demands. The proposed methodology is apply to a case study consisting on a 40-m height permeable façade of the 12-story Santafe Foundation Hospital located in Bogota (Colombia). The main conclusions of this study are: (1) the dynamic properties of the system mainly rely on the cable tensioning and mass of the system; (2) fundamental vibration frequencies of the façade are much higher than wind demands, so no wind-related amplifications are expected; (3) the façade porosity avoids that high wind pressures may be developed; and (4) for design level earthquakes no major damage is expected. Overall, results show an appropriate performance of this type of façades.