Death Fall: A Review on the Issues of Skyscrapers

Have you ever wondered why many buildings in city areas have dull and unappealing scaffolding in front of them? Well, it’s much more interesting than you think. Many cities have these semi-permanent scaffolding to do frequent inspections on skyscraper buildings. But why do these skyscrapers need such frequent checkups?

In the world of modern architecture, skyscrapers stand as a testament to human ingenuity and engineering prowess, dominating city skylines and symbolizing progress and innovation. However, beneath their gleaming surfaces lies a complex interplay of forces and materials that can sometimes lead to unexpected failures.

The term skyscraper was first used during the 1880s and applied to buildings that had around 10 to 20 stories. However, later in the 20th century, when advances in architecture and construction prospered, the term was used to describe buildings that were generally greater than 40 stories. Two major influences in the demand for skyscrapers included the rise of the Bessemer process and the increase in population density. The Bessemer process is a process of making steel from the Industrial Age that involves clearing impurities from metal with blasts of air. This was advantageous for the construction of skyscrapers because steel is stronger and lighter than iron, making it a better material for tall building frames. Not only this, but the Bessemer process allowed steel to be mass produced without fuel and more cost-effective. Even the tallest of the tallest buildings today use steel framing to maintain their structure: The Burj Khalifa, Shanghai Tower, World Trade Center.

Recently, in September 2023, over 30 high rise windows from San Francisco skyscrapers were reported to have fallen or broken. The broken glass and debris plummeted onto the streets, injuring nearby pedestrians, even almost killing them. However, this is not the first time it's happened. In fact, being hit by fallen debris is pretty common in urban cities. According to the Occupational Safety and Health Administration, more than 50,000 people in New York City are hit by fallen debris annually. In particular, the CNA Center in Chicago has had repeated issues with its high rise windows.

When it was first constructed back in June 1975, there were already issues with the infrastructure and materials used. The windows used were never heat treated which made them weak and easier to break. This was evident because many of the high rise windows ended up breaking and falling. The simple solution was to just replace all the windows with

heat treated ones to lessen the possibility of breakage. But… of course CNA Center chose the cheaper way out. Instead of using a more quality solution, CNA Center hired a group of engineers to figure out ways to prevent their windows from breaking without a costly consequence. The engineers advised them to lift all the blinds up to a certain level to lessen the heat stress within the windows.

While this worked as a temporary solution, their windows did end up failing again and injured many people walking near the building. Avoiding the costly price of replacing all their windows again, CNA Center decided to just put a protective film to make sure that even if the glass breaks, it will be held together by the film to make sure there is no falling debris. Most unfortunately, during the process of laying the film on each window, one of the windows with the protective film shattered and a piece of the window ended up killing a mother walking with her child on the street. This incident occurred in 1999. The CNA Center then proceeded to replace all of their windows. Absurd right? But the question is: why and how do high rise windows shatter?

Three key factors contribute to the risk of skyscraper window breakage: heat, wind, and the type of glass used.

Heat: When glass is heated, it expands, creating tensile stress at the edges of the panels. Over time, this accumulation of stress can lead to breakage. Additionally, the process of heat soaking, which involves reheating the glass, can reduce its surface compression, further lowering its durability and performance.

Wind: Wind can pose catastrophic dangers to high-rise windows. When wind strikes a building, it creates a high-pressure zone on the windward side and a strong suction on the leeward side. This suction and pressure can be more than three times the strength of the original wind gusts, significantly increasing the risk of window breakage, especially when combined with heat stress.

Type of Glass: The type of glass used in skyscraper windows is crucial to their safety. Different glass types have varying levels of strength and shatter resistance, which can impact the severity and frequency of accidents. Tempered glass is made by heating pre-cut panels and then rapidly cooling them through quenching. The repeated cycle of heating and cooling creates a state of compression on the surfaces and edges while leaving the core in tension, resulting in a glass that is approximately four times stronger than regular glass. However, when tempered glass breaks, it shatters into countless tiny pieces. This fragmentation, while reducing the risk of large, dangerous shards, poses a significant hazard for high-rise windows, as the small glass pieces can fall from great heights and injure pedestrians below. Unsurprisingly, most incidents of window debris causing fatalities involve tempered glass.

To reduce the frequency of these dangerous incidents, engineers and architects advocate for the use of heat-strengthened glass. This glass undergoes a specialized process where it is reheated after forming and then rapidly cooled. This technique increases the compressive forces on the outer layers while maintaining tensile strength in the core, significantly enhancing the glass's overall durability. As a result, heat-strengthened glass is much more resistant to shattering, making it a safer and more reliable choice for high-rise windows.

The presence of scaffolding on city buildings may seem unsightly, but it serves a vital purpose in the world of modern architecture. Frequent inspections and maintenance of skyscrapers are essential to ensure the safety and integrity of these towering structures. Despite their impressive engineering, skyscrapers are subject to a complex interplay of forces and materials that can lead to unexpected failures, as evidenced by incidents in cities like San Francisco and Chicago. As we continue to push the boundaries of architectural design and construction, it is crucial to balance innovation with vigilance, always prioritizing safety and durability in our quest to reach new heights. I hope you learned something new! Keep a lookout for the next post!

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References

Britannica, T. Editors of Encyclopaedia. (2024 July 2). skyscraper. Encyclopedia Britannica. Retrieved July 12, 2024, from https://www.britannica.com/technology/skyscraper

Corboy & Demetrio. (n.d.). $18 MILLION SETTLEMENT IN DEATH OF PEDESTRIAN FROM FALLING GLASS FROM CNA WINDOW. Corboy & Demetrio. Retrieved July 12, 2024, from https://www.corboydemetrio.com/newsroom-news-Death-from-Fall-of-Window

Morelli Law Firm. (n.d.). Who’s Liable for Falling Debris in New York City?. Morelli Law Firm. Retrieved July 12, 2024, from https://www.morellilaw.com/faq/whos-liable-for-falling-debris-in-new-york-city/

News Editor. (2023 Sep. 28). SAN FRANCISCO HIGH-RISE WINDOWS FAILED BEFORE WINDSTORMS. US Glass Metal & Glazing. Retrieved July 12, 2024, from https://www.usglassmag.com/san-francisco-high-rise-windows-failed-before-windstorms

Rupert, M. L. (2013 Dec. 17). Spontaneous Glass Breakage: Why it happens and what to do about it. The Construction Specifier. Retrieved July 12, 2024, from https://www.constructionspecifier.com/spontaneous-glass-breakage-why-it-happens-and-what-to-do-about-it/

Stewart Hicks. (2024 Apr. 4). The Weird Flaw Plaguing Skyscraper Windows. [Video]. YouTube. Retrieved July 12, 2024, from https://www.youtube.com/watch?v=zFk1FM6I4Jk