Group 8 John Hancock Tower Facade Failure
The John Hancock Tower is a 60 storey skyscraper located in Copley Square, Boston,
Massachusetts. The building stands 241metres and has been the tallest building in Boston for
over thirty years and is currently the 112th tallest building in the world. It is owned and built
by the John Hancock Mutual Life Insurance Company. Construction of the tower began in
1968 and was completed in 1976, the completion date was delayed by four years due to a
series of structural failures and deficiencies. The architects involved in the construction were
I.M Pei & Partners, one of the most prestigious architectural firms in the U.S, and developed
by Beacon Capital Partners.
View of the tower with Copley Square in the foreground, Trinity Church can be seen in the centre foreground.
Pei’s goal was to create an architectural first with a tall skinny glass box in the Boston
skyline. To achieve this Pei decided to create a floor plan that was in the shape of
parallelogram so that the tower edges appear sharper and more defined, this gave the illusion
that the tower was standing on point shoes, the main feature of the tower is its extensive glass
facade. Each bay of each floor is a single pane of glass, the reflective glass is tinted blue. The
narrow sides of the building are finished with a pinstriped geometrical design that emphasises
the. All of these features combine to enable the tower to unobtrusively blend into the Boston
skyline.
While from an aesthetical point the tower proved a huge success, from an engineering
standpoint the tower turned into a nightmare, form foundation to facade structural
deficiencies. The first problem encountered was during excavation the retaining walls warped
and gave way the clay and mud fill, causing damage to nearby historical buildings including
the Trinity Church, nearby utility lines and the sidewalk pavement. On completion of the
building it was discovered that in certain wind conditions the sway of the building was above
acceptable standards. To counteract this 300 ton weights were added on the 58th floor which
acted as dampers to prevent the swaying of the upper floors. However, the most famous and
embarrassing failure of the structure was the failure of the glass panels of the curtain wall
facade.
The facade was originally covered with 10,344 double-paned insulating reflective
glass, the panes were separated by a 13mm air space. Shortly after the completion of
construction in 1972, the glass panes began to crack and by October 1973 3500 panes had
cracked some of which had fallen onto the streets below. This resulted in major disruption to
the city centre as police had to close off surrounding streets when winds reached 72km/hr.
The cracked panels were temporarily replaced with plywood panels while testing was carried
out to try and remedy the problem. The double panes were replaced with single tempered
safety glass panes of the same dimensions as the original double panes. The reglazing began
in May 1974 and was completed in August 1975, at a reported contract cost of 8.5$ million.
This picture shows the facade complete with plywood panels
From the moment the panes began to fail in late 1972, myths with varying degrees of
truth began to emerge as possible explanations to the failure. The first of which, attributed the
failure to the swaying of the building induced by the wind which caused a stress and pressure
build up in the panes causing them to crack and ultimately fail. Another theory which
emerged was that the rhombus shape of the structure in combination with the wind resulted in
the formation of hot spots causing thermal stress to lead the panes to failure. Both of these
theories were proven inaccurate as a result of wind tunnel tests carried out in the University
of Western Ontario, Canada. Another myth circulated that settlement in the foundations led to
increased stress in the panes causing failure.
The most widely accepted theory put forward held the unique double glazed bond
technique responsible. The glass units were made up of two panes connected by a lead tape
spacer which was soldered to each of the panes. The inside surface of the outer pane was
coated with a highly reflective chromium film which was in turn soldered to the lead spacer.
The chromium film was included to reduce glare. It was this bond that led to the ultimate
failure of the panes. This bond between the film and lead spacer was too strong and rigid and
didn’t accommodate any vibrations induced by the wind or any thermal movement. Due to
repeated thermal movement and wind vibrations, the soldered connection fatigued and
cracked leading to increased stresses in the outer pane. This in turn caused cracks to form in
the outer pane and in many cases led to ultimate failure.
This image shows a cross section of the original windows. The lead spacer can be seen in the middle, bonded to
the two panes.
Unfortunately, it has been nearly impossible, even to this day, to access reliable
information about the John Hancock case. In a court hearing in 1981 a settlement was
reached that included provision for an oath of secrecy regarding the exact details of failure.
As a result of the facade failure, the dangers involved in using new design in large
scale buildings, such as the original pane design, without sufficient testing became evident.
The consequences of this led to major financial losses, public embarrassment, time delays
and danger to public safety. There are lessons in the John Hancock case for geotechnical and
foundation consultants, curtain wall designers, wind researchers, structural engineers,
architects and building owners. As a direct result, building regulations in the U.S now
recognize non-uniform, fluctuating wind pressures. The facade failures experienced by the
John Hancock Building led to greater use and redesign of wind tunnel testing and to other
advances in the field of wind engineering.