The glass flooring of a bridge in Indonesia shattered this past week, killing one tourist and injuring three others.
The glass-bottomed-bridge at the Geong tourist site within the Limpakuwus Pine Forest, located in the Banyumas Regency of Central Java, shattered around 10 a.m. on Wednesday, Oct. 25, 2023, sending two people plummeting to the ground 32-feet below. Two other tourists clung to the damaged bridge before onlookers rescued them.
Reports indicate the glass flooring was extremely thin, measuring only 1.2 centimeters. According to Julia Schimmelpenningh, architectural industry technical manager for the Advanced Material Interlayers business of Eastman Chemical Company, glass floors should be designed with a minimum of three layers of glass, two layers being able to support the load with the third to be redundant in case of breakage.
“Glass floors are beautiful and have been around since before the 1970s,” says Schimmelpenningh. “Their incorporation in buildings has grown over the years from being a small portal or an elevated platform with water or artwork and lighting under it to full bridges and slides.”
For glass-bottomed-bridges to function properly, Schimmelpenningh says engineers “must consider all aspects of the products such as loads, temperatures (both hot and cold), wear and redundancy, which are appropriate for the application and use when designing.”
That wasn’t the case at the Geong tourist site. The Jakarta Post reports Banyumas City Police officials discovered the bridge had been improperly maintained and there had been no safety testing. Furthermore, there were no safety nets around the bridge, no warning signs and no safety instructions. Reports indicate the ticket attendants also lacked knowledge of visitor safety procedures.
Schimmelpenningh explains that an ASTM International standard exists to guide the calculation of walkways that would be a minimum reference for most designs. ASTM E2751/E2751M, Standard Practice for Design and Performance of Supported Laminated Glass Walkways, addresses “elements related to load-bearing glass walkways, glass treads and glass landings constructed with laminated glass. This standard includes performance, design and safe behavior considerations.”
Glass Floors are beautiful and have been around in abundance since 1930’s. Many Carnegie Libraries possess glass floors. The first glass flooring project I could find was made in the late 19th century. 90% of the projects that are holding pedestrian loads should be at least 1-1/4″, 3 ply, and tempered. SGP can be added for additional strength. 1.2cm thick is criminal!
The glass thickness may not be the sole problem. In the video views of the fragments, I see no evidence of any interlayers. There should be at least two of SGP, separated by at least 12mm of glass, as a minimum. Even then, the edges of the laminate should be adhesive bonded to the framing so that if loads (or, more likely, vandals) break all three glass plates, the interlayers form a diaphragm. The material I see in the videos of this accident would not even suffice for a balustrade.