Authorities do not yet know what caused the shocking collapse of a condo tower in Florida, but the tragedy unfolding there has many people questioning the safety of our buildings. And there’s a glittering reminder on the Boston skyline that even the most impressive can have hidden problems.
The iconic John Hancock Tower, a 62-story rhomboid sheathed in mirrored glass that reflects the sky and the buildings around it, was once deemed to be at risk of literally falling down.
The most visible sign of trouble at the tower, Boston’s tallest building (now officially known as 200 Clarendon St.), was the windows, which began falling out of the ambitious structure even before it was finished, earning a place in the city’s folklore — and in the minds of many a person walking through Copley Square for years.
During a winter storm on the night of Jan. 20, 1973, while the tower was still being built, dozens of huge panels of glass, each weighing 500 pounds, dropped off the building, smashing into others as they fell, the Globe’s architecture critic at the time, Robert Campbell, wrote in 1995.
The 10,344 windows on the 790-foot-tall building had begun to fail almost from the start, Campbell wrote in a column that was part of the body of work that won him a 1996 Pulitzer Prize.
The fallen panes were replaced by sheets of plywood painted black, and people began calling it the “Plywood Palace,” the “Woodpecker Palace,” or the “US Plywood Building.”
A number of culprits were considered for the window problems, but eventually it turned out to be the design of the windows themselves. Every one of the windows was replaced.
“What hardly anyone understands — and this is the real story of the Hancock — is that problems with the windows weren’t even the biggest disaster to strike this haunted high-rise mirror, which always seems to be reflecting clouds as if it were brooding on its own grim beginning,” Campbell wrote.
There were other problems that weren’t visible to the eye. During the excavation for the building’s basement, the sides of the hole in the ground were braced with steel that was inadequate and the sides caved in, causing earth around the site to shift and settle. Cracks appeared in nearby buildings, utility lines ruptured, and part of Trinity Church came near collapse, Campbell wrote.
Experts studying the building also found that it was swaying too much. “The tower, in ordinary wind conditions, was accelerating too fast for comfort. It was doing a sort of cobra’s dance, swaying a few inches forward and back and, at the same time, twisting,” Campbell wrote. How bad was it? In high winds, it would sway as much as 3 feet off center, the Globe reported in 2006.
The problem was not affecting the building’s structural integrity, but it was “making life very uneasy for people on the upper floors,” he wrote. The solution was to stabilize the building by installing a device called a tuned mass damper on the 58th floor of the building, involving two giant 300-ton weights, springs and shock absorbers.
Mehrdad Sasani, a professor of civil and environmental engineering at Northeastern University, said Friday in a telephone interview that the “heavy masses” in the device “bring the building back” to its rightful place when it sways in the wind. He said the dampers are “not something that many buildings use.” Another “very effective” method, he said, is the use of “shear walls” made of reinforced concrete.
But that wasn’t even the worst of the Hancock’s hidden problems. Looking for reassurance that his building was safe, the architect of the tower, Harry Cobb, hired Swiss engineer Bruno Thurlimann to review its structural integrity. Thurlimann was the world’s leading authority on high-rise steel-frame buildings.
“He said, ‘We’re in trouble, Bruno. Can you come over?’” Thurlimann recalled in a Globe interview in 2006.
Thurlimann came back to Cobb with bad news. “He announced that, according to his calculations, under certain rare but entirely possible wind conditions, the Hancock might fall over,” Campbell wrote. “The danger was that it might collapse on a narrow edge. It would be as if a book standing upright on a table were to fall on its spine.”
The solution this time: “The tower was stiffened from its base to its top with 1,500 tons of diagonal steel braces. These were placed along the walls of the service core, the central blob of elevators and toilets. In that location — purely by chance — there was just enough room for them. It was the Hancock’s only stroke of luck,” Campbell wrote.
The New York Times architectural critic Paul Goldberger wrote in 1988 that the building was “just a bit ahead of its time. ... [Cobb] proposed a design of great esthetic power, and eventually engineers made it happen. This was a time when the art of architecture lurched forward rather than leaped gracefully — but it did move ahead, and we remain the better for it.”
Campbell wrote that nobody was to blame for the problems. The building met every structural building code, and codes were changed after that because of it.
“Is it safe today?” Campbell wrote. “After all the testing it went through, the Hancock today has got to be one of the safest high-rises in the world. It possesses the strength of a survivor.”
James Lambrechts, a civil engineering professor at the Wentworth Institute of Technology, said Friday in a telephone interview that “certainly the Hancock was notable for several problems” back in the 1970s.
“Occasionally, you find things that slipped by during the design” phase of a project, though it doesn’t happen frequently, he said.
Asked if he felt the tower was safe today, Lambrechts said, “Oh, yeah, ... I wouldn’t have any problem being on the upper floor in a hurricane.”
Jeremiah Manion of the Globe staff contributed to this report.