John Hancock Tower Structural Failure

John Hancock Tower, Boston

By FELIX JAGGI

START

Introduction

The John Hancock Tower was a 60-story skyscraper located in the Back Bay neighborhood in Boston, Massachusetts. It was 790 feet high, and the tallest building in Boston. Its best known structural failure is when the windows had failed and caused the whole building to overturn through the strong winds. The windows were the most dangerous aspect of the entire building, and it is proven why it was the cause of the structural failure. Right now, I will present about the history of the John Hancock Tower and how it failed. Without further ado.......it.............starts........NOW!

History of the John Hancock Tower

Construction of the skyscraper started in 1968, after Robert Slater, CEO of the Boston-based John Hancock Mutual Insurance Company was an agressive businessman whose expectations of the company were taken to a new level. In expression to the success of his company, Slater wanted to create a tall building as their headquarters after their rival, the Prudential Insurance Company, another Boston-based insurance company, built the Prudential Tower earlier in the 1960s. The original design for the tower was a masonry cylinder sliced to create a courtyard on Clarendon Street. It was one of three proposed buildings for this complex. Due to internal changes with the Hancock company, the design process was delayed for a whole year. When they finally restarted, they brought new requirements for the proposed headquarters. The original creator for this project, I.E. Pei, dropped this project and handed it to his partner, Henry Cobb. He started designing from scratch on September 15th, 1967. Due to the significant buildings on Copley Square, he wanted to make one with the least presence on Copley Square. His design was to be a 790' high tower with 60 stories. One of the face was slim and faced toward Copley Square. To make the face more slender, Cobb removed triangular notches that run from the bottom to the top of the facade. He also chose a reflective double-layered mirror glass skin for the facade's material.

Destruction

A year later, construction of the tower began. There were many issues, including the digging of the foundation which affected the other buildings surrounding it. It damaged the foundations of those buildings, and in worse case of the older buildings, the wood pilings they sit on shifted, and the building may even fall. Trinity Church was one of the badly damaged ones. Another failure, perhaps the most notorious failure, is the glass facade's windows. In 1971, sporadic breakage occurred in the windows. Two years later in 1973, a terrible windstorm struck Boston. During the storm, over a hundred sheets of glass fell from the entire building. They temporarily fixed the problem by installing black plywood sheets as openings. This eventually, caused the whole building to fall.

Cause of Failure

As I stated earlier, the main cause of the tower's failure is the design of the windows. The windows were soldered right into the building's columns really tightly, making it unable to flex. The construction of the windows alone were a big problem. They were made of three columns. Two of them were made of glass, and the third one was made of chromium. Seperating these columns, were air gaps. Surrounding all of these columns was a metal frame, which was soldered to the chromium. This bond was the main cause of the tower's failure. It made the windows too strong, and disallowed the windows to expand or vibrate, which most windows naturally do. When the windows tried to flex, they cracked at their connections to the rest of their building, and therefore plunging to the ground. Eventually, all the old panels were replaced by single pain tempered glass, which was paid with just as much money as the original windows.

Prevention of Failure

What could have been done to prevent this is that they could have done a better job at attaching the windows to the building without the whole metal frame surrounding the chromium layer. That would have made the windows easier to flex through their frames, and even expand properly without cracking. The windows struggled to sway, and therefore they cracked when attempting to move. One of the biggest problems with the windows is that they were soldered on extremely tightly to the metal frame. For another improvement, they could have made a foundation on another street bordering Copley Square, so the other buildings would not have been damaged. It would have flexed more easily even through wind, and would have been made harder to break if the windows were made of a stronger glass, and no metal frame.

Redesign/Rebuilding

Two years after its failure, they started redesigning the building in 1973. The engineers who pointed out the failures of the original design, they temporarily fixed this problem by installing plywood sheets, which gave the building the nickname "Plywood Palace". Roughly 85% of the glass was replaced during May of 1975. Another problem with the original design was the building's tendancy to sway. Because of that, they braced the inner core of the tower. Afterwards, the tower opened in 1976, roughly 4 years behind schedule. It costed $160 million, exactly twice as much as what it was estimated to cost. Several criticisms encountered the new project during construction, but many others took pictures to put in magazine covers and postcards. Today, the John Hancock Tower is recognized as an amazing modern skyscraper that shapes the Boston skyline. It gives the Boston skyline a reminder that buildings can have hidden problems.

Resources

https://explorebostonhistory.org/items/show/2#:~:text=The%20next%20and%20most%20notorious,glass%20fell%20from%20the%20facades. https://civildigital.com/failure-john-hancock-tower-boston-mass/ https://www.theguardian.com/news/2014/nov/12/weatherwatch-skyscraper-gusts-glass-panes-boston