The strength of modern structural glass is somewhat astonishing, and the progress from the first glass staircases in the 1920s to the gleaming curtain walls commonly framing city skylines is a testament to manufacturing excellence and innovation.
All of this serves to prove false the common misconception that glass is inherently brittle and fragile, and perhaps the grandest display of the capabilities of structural glass was showcased in 2016 with a glass-bottomed bridge across a great canyon.
Zhangjiajie Glass Bridge
The Zhangjiajie Grand Canyon features the highest and second-longest glass bridge in the world, spanning between two of the peaks of the canyon and allowing for some utterly spectacular panoramic views, as well as the sight of walking on air 1300 feet above the ground.
Designed by Haim Dotan, the bridge is made up of 120 glass panels that feature triple-layered, two-inch thick tempered glass that is so thick that a tank can allegedly drive over them without causing any damage.
Of course, such a bold claim is unlikely to be believed without evidence, and engineers in Hunan Province were more than happy to oblige, putting the bridge not only through the typical stress testing required of any structural engineering project but a few more unusual tests besides that.
The first was to invite a journalist to try and break one of the glass panels using a sledgehammer, failing to break it despite his best efforts although other reports claim he did manage to cause superficial damage to the top layer.
The other, more dramatic test was to allow a Volvo XC90 car to drive across the full length of the bridge. The two-tonne car made it across at a remarkable speed without causing more than superficial damage to the glass, which was easily and quickly replaced.
The strength of the glass was such that it was claimed they could easily endure wind speeds of over 100 miles per hour.
Rather infamously, the bridge was a victim of its own success, as it was famously closed 13 days after it was opened because it was too popular.
The bridge was designed to hold 800 people at any one time, with a total visitor cap of 8000 visitors each day, similar to other tourist attractions of its type.
However, it managed to attract over ten times this amount, with an alleged 80,000 visitors trying and failing to visit in the first couple of weeks it was open.
This led to the bridge being closed for safety, whilst the authority in charge of maintaining the bridge urgently improved the infrastructure surrounding it
This included a monitoring system at the entrance and exit, a more robust booking system to manage visitors to the National Park, as well as setting up a shuttle bus to take visitors to and from the area.
Whilst the bridge was not the first monument with a glass floor; many skyscrapers have glass floors and balustrades and the first floor of the Eiffel Tower added such structural glass in 2014, its sheer audacity and robustness has proven that glass is so much stronger than you might expect.
