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THE John Hancock Tower, officially named Hancock Place and colloquially known as The Hancock, is a 60-story, 790-foot (241m) skyscraper in Boston.

The tower, the tallest in the city, was designed by Henry N. Cobb of the firm now known as Pei Cobb Freed & Partners and was completed in 1976 In 1977, the American Institute of Architects presented the firm with a National Honour Award for the building. It has been the tallest building in Boston for more than 30 years, and is the tallest building in New England, as well as, the 198th tallest building in the world.

Its street address is 200 Clarendon Street. The company uses both 'Hancock Place' and '200 Clarendon Street' as mailing addresses for offices in the building. John Hancock Insurance was originally the main tenant of the building, but the insurance company announced in 2004 that some offices would relocate to a new building at 601 Congress Street, in Boston's Back Bay.

Tall, skinny glass structures were a goal of modernist architecture since Mies Van Der Rohe proposed a glass skyscraper for Berlin. Such buildings as Gordon Bunshaft's Lever House and Mies' Seagram Building in New York City, and Frank Lloyd Wright's Johnson Wax Headquarters attempted this goal, but many of these designs retained structural artifacts that prevented a consistent, monolithic look.

In 1972, Cobb's design of the Hancock Tower took the glass monolith skyscraper concept to new heights. The tower is an achievement in minimalist, modernist skyscraper design.

Minimalism was the design principle behind the tower. The largest panes of glass possible were used. There are no spandrel panels, and the mullions are minimal. Cobb added a geometric modernist twist by using a parallelogram shape for the tower floor plan. From the most common views, this design makes the corners of the tower appear very sharp. The highly reflective window glass is tinted slightly blue, which results in the tower having only a slight contrast with the sky on a clear day.

As a final modernist touch, the short sides of the parallelogram are marked with a deep vertical notch, breaking up the tower's mass and emphasising its verticality. In late evening, the vertical notch to the northwest catches the last light of the sky, while the larger portions of glass reflect the darkening.

A major concern of the architects while designing the tower was its proximity to Boston's Trinity Church, a prominent National Historic Landmark. Their concern led them to redesign the tower's plans, as there was a public outcry when it was revealed that the Hancock Tower would cast its shadow on the church.

The building was a much-anticipated landmark from the country's most respected design firm, but at one time, the tower was more notorious for its engineering flaws than for its architectural achievement. Its opening was delayed from 1971 to 1976, and the total cost is rumored to have rocketed from $75M to $175M. It was an embarrassment for the firm, modernist architects, and the architecture industry.

Hancock Tower was plagued with problems before construction started. During the excavation of the tower's foundation, temporary steel retaining walls were erected to create a void on which to build. The walls warped, giving way to the clay and mud fill of the Back Bay, which they were supposed to hold back.

The inward bend of the retaining walls damaged utility lines, the sidewalk pavement, and nearby buildings—including the historic Trinity Church across the street. Hancock ultimately paid for all the repairs.

Soon after the building was completed, windowpanes began detaching from the building and falling to the street below. These were temporarily replaced with plywood.

Inventing a way to use the blue mirror glass in a steel tower came at a high price. The building's most dangerous and conspicuous flaw was faulty glass windows. Entire 4' x 11', 500-lb (1.2 x 3.4 m, 227 kg) windowpanes detached from the building and crashed to the sidewalk hundreds of feet below.

Police had to close off surrounding streets whenever winds reached 45 mph (72 km/h). According to the Boston Globe, a scale model of the entire Back Bay was built in MIT's Wright Brothers Wind Tunnel to identify the problem. The research raised questions about the structural integrity of the entire building (due to unanticipated twisting of the structure), but it did not account for the loss of the glass panels.

An independent laboratory eventually confirmed that the failure of the glass was due to oscillations and repeated thermal stresses caused by the expansion and contraction of the air between the inner and outer glass panels which formed each window, the bonding between the inner glass, reflective material, and outer glass was so stiff that it transmitted (instead of absorbing) the force to the outer glass and caused it to fail.

In October 1973, I.M. Pei & Partners announced that all 10,344 window panes would be replaced by a single pane, heat-treated variety, costing between $5 million and $7 million. During the repairs, sheets of plywood replaced empty windows of the building, earning it the nicknames 'Plywood Palace' and 'Plywood Ranch' (the same name as a suburban lumber-yard chain at the time). The joke was that the Hancock Tower was 'the world's tallest plywood building.'

The building's upper-floor occupants suffered from motion sickness when the building swayed in the wind. To stabilise the movement, contractors installed a device called a tuned mass damper on the 58th floor. As described by Robert Campbell, architecture critic for the Boston Globe.

'Two 300-ton weights sit at opposite ends of the 58th floor of the Hancock. Each weight is a box of steel, filled with lead, 17 feet (5.2 m) square by 3 feet (0.9 m) high. Each weight rests on a steel plate. The plate is covered with lubricant so the weight is free to slide. But the weight is attached to the steel frame of the building by means of springs and shock absorbers.

'When the Hancock sways, the weight tends to remain still… allowing the floor to slide underneath it. Then, as the springs and shocks take hold, they begin to tug the building back. The effect is like that of a gyroscope, stabilising the tower. The reason there are two weights, instead of one, is so they can tug in opposite directions when the building twists. The cost of the damper was $3 million. The dampers are free to move a few feet relative to the floor.'

The John Hancock Tower seen from the Prudential Tower, on the left is Copley Square (and Trinity Church), to the upper left is the Boston Common, on the right is the Massachusetts Turnpike (I-90) and to the top right is Logan International Airport.

According to Robert Campbell, it was discovered that—despite the mass damper—the building could have fallen over under a certain kind of wind loading. It was assessed as more unstable on its narrow sides than on the big flat sides. Some 1,500 tons of diagonal steel bracing, costing $5 million, were added to prevent such an event.

An observation deck with spectacular views of Boston was a popular attraction. It was closed after the September 11, 2001, terrorist attacks. As of fall 2009, the observation deck remains closed (as is that of the Transamerica Pyramid in San Francisco). Because of the closure of the John Hancock Tower's observation deck, the highest observation deck open to the public in Boston is in the Prudential Tower.

The building's owners cite security as the reason for the continued closure. They have rented the deck for private functions and have expressed intent to replace it with more office space. Boston city officials contend that security concerns are moot, since most similar attractions have long since reopened.

In addition, they note that a public observation deck was a requirement for the original building permits to gain public benefit from the high tower. However, they have not been able to locate the documentation of this requirement.

In 2006, Broadway Partners acquired Hancock Place for $1.3 billion. By 2009, they had defaulted on the loans they used to buy the building, and it fell into foreclosure. On March 30, 2009, Hancock Place was sold at auction for $660 million ($20 million was new equity and the $640 million of in-place debt was assumed by the buyer) to a consortium of 'Normandy Real Estate Partners' and 'Five Mile Capital Partners.'

The companies had been slowly increasing their investment over the previous months. In October 2010, Boston Properties acquired the John Hancock Tower for $930 million.