Group 8 Façade failure of the John Hancock Building

“The Hancock” Construction completed in m high. Tallest building in Boston and the135 th tallest in the world. It’s fully glazed façade was comprised of 10,344 windows. American Institute of Architecture Award (1977)

Problems with the Building Budget overrun, $75m to $175m Collapse of temporary retaining walls during excavation….This caused damage to nearby buildings, including the famous Trinity Church. Motion Sickness experienced by people in the upper floors. A tuned mass damper costing $3m was installed on the 58 th floor to combat the problem.

Façade Failure!!! January 20, 1973, building still under construction. Winter Storm, gusts reaching 75mph at the upper floors. The huge panels of glass, each weighing 500 pounds, fell off. Holes were covered with sheets of painted black plywood. Over the next few months, more windows kept falling off, nobody knew why!

Incorrect theories These theories erupted due a legal pact signed by all parties involved in it’s construction, not to disclose what really happened. The tower was swaying too much. The glass was sucked out by excessive wind forces at “hotspots” caused the sharp angles of the tower’s rhomboid shape. The windows stressed when the tower’s foundations settled.

What really happened Each layer was a “sandwich”, two panes of glass with an air space in between held together with a metal frame. To cut the glare and heat of the sun, the inside surface of the outside pane of glass was coated with a reflective coating of chromium. The window frame was bonded to the chromium with a lead solder. The lead solder was bonding too well with the glass!!!

Now the joint couldn’t absorb any movement! But glass always moves as it expands and contracts with temperature and vibrates with the wind. So the solder fatigued and cracked, and the crack continued through the glass.

Solution All 10,344 double-pane windows were replaced with single sheets of tempered glass. The window maker covered the cost of $7m. The 5,000 undamaged windows that were removed went on sale in bargain outlets in Boston at $100 each!

Further Problems The architect needed further assurance the building was safe, hired Thurlimann, the world’s leading authority on high-rise steel frame buildings. He announced under entirely possible wind conditions, the building might fall over on it’s thin side, despite it being built to every structural code. Solution: The tower was stiffened from its base to the top with 1,500 tonnes of diagonal steel braces costing $5m.

Lessons learned The problem with the glass façade was rectified and not used again in future design. More research into structural behaviour. Greater understanding of high rise structures due to the extensive testing the Hancock building underwent.

The paradox After all the testing the Hancock underwent, it must be one of the safest high rises in the world!