Nonlinear dynamic analyses of a cable-net glass façade under earthquake excitation

Cable-net glass facades are the unique trait of an increasing number of modern iconic architectures (e.g., Market Hall, Rotterdam; Sony Centre, Berlin). This facade system, composed of glazing units supported by a net of orthogonal pre-tensioned steel cables, meets several architectural demands such as a minimal supporting system and a remarkable transparency of the building envelope, an efficient use of natural lighting, a peculiar aesthetic value. Issues may arise, however, due to the high flexibility of the cables and the deflections, possibly very large, of the facade under horizontal loadings (wind, earthquake). Therefore, a cable-net facade could be a major contributor to non-structural earthquake damage and losses, in terms of building downtime, costly repairs and even injuries to the occupants. Nevertheless, research and literature on the seismic performance of cable-net facades are still very limited. In this study, the seismic response of a cable-net glass facade under earthquake excitation is investigated. A case study concerning a facade originally designed without considering the seismic loading is presented. A finite element model of the facade is developed, fully accounting for the geometric nonlinearity in the mechanical behaviour of pre-tensioned cables under large displacements. Nonlinear response history analyses under earthquake excitation are carried out by direct numerical integration of the equations of motion. Seismic input is modelled by way of artificial accelerograms matching the pseudo-acceleration elastic design spectra given by Eurocode 8. Increasing levels of the design peak ground acceleration and five different ground types are considered to derive the elastic design spectra and to generate the artificial accelerograms. Numerical simulations aim at exploring the influence of the intensity and frequency content of seismic input on the facade response. According to Eurocode 8 provisions, response parameters of the facade are evaluated in terms of statistical averages across a set of seven records per each analysis. Out-of-plane displacements and absolute accelerations of the facade, variations of the tension force in the cables, and incremental loads in the connection joints are examined.