Seismic Assessment and Design of Glass Curtain Wall

Abstract

GCW is widely used as an exterior as the trend in modern commercial, residential, and public buildings. GCW primarily resists wind pressure bluntly acting on the building in addition to its self-weight. The design of GCW is restricted to checking for DL and WL cases and their combination. However, mostly followed standards like ASCE 7, EN 1998, and IS 16700:2017 suggested that GCW shall accommodate the design drift. GCW is considered a displacement sensitive NC for loads in its plane in which it is most vulnerable. Past earthquakes like the Loma Prieta earthquake in 1989 and the Fukuoka earthquake 2010 GCW failure were observed. Hence, considering potential life and economic losses occurring due to failure of GCW, many researchers across the world conducted experiment-based seismic assessments, which mainly involved in-plane racking crescendo test as per guidelines given by AAMA, shake table test and development of FEM model calibrated based on experimental results. These experiments did not involve the connection of GCW with primary structures (mainly RCC); hence the behavior of the connections and correlation of damage of RC frame and GCW for in-plane loading was missing. To simulate the behavior of GCW with its connection to RCC structure experiment was carried out in collaboration with Hilti India Pvt. Ltd. in which a test specimen consisting of stick-built GCW mounted on a two-story RCC frame using a standard post-installed anchor bracket connection. The experiment was carried out in a quasi-static test facility using the loading protocol suggested by ACI 374.1-05. Glass panel number 7 failure occurred at 3.5% drift attributable to damage of structural silicone. Falling out of GP7 was delayed because of temporary clips attached to fix the glass panels. Prior to glass panel failure damage in structural silicone, severe cracking in the RC frame was observed. After performance of the quasistatic test, pullout testing caried out for the associated crack width resulted in significant decrease in its capacity due cracking the concrete surrounding the anchor location. FEA on the single panel of the same GCW, like the crescendo test, was carried out to determine the failure of its various components based on stress criteria. The mullion section is the most vulnerable component, failing at 1.1% drift, and structural silicone was the 2nd most susceptible component, failing at nearly 2.5% drift. In the case of GP, fracture stress was considered, which is achieved at 2.5 % drift. The Transom section remained undamaged during the analysis. Considering max story drift criteria suggested by IS 1893:2016, i.e., 0.4%, GCW was found safe for DBE earthquakes and unsafe for MCE earthquakes for 2%. Hence, to design GCW for seismic forces, the mullion & transom section shall be checked for induced flexural and combined stresses, structural silicone shall be designed for distortion and adhesion capacity, and the glass panel for fracture induced due to glass-frame interaction.