Hartford Civic Arena Roof Collapse
Group 16:
Group 16 consists of four students: Antoine Gaudin, Andrew Lochaden, Brendan
McCabe and Eoghan MacTighearnáin.
Introduction:
The Hartford Civic Centre Arena is a sports arena with a seating capacity of ten
thousand. It is situated in the city of Hartford, Connecticut in the north east of the USA. Early in
the morning of the 18th of January 1978, just 3 years after its completion, its space truss roof
collapsed under loading resulting from a heavy snowfall. Fortunately, there were no injuries or
fatalities.
Space Frame Roof Design:
In 1970, Vincent Kling was commissioned to be the architect for the Hartford Civic
Centre. He hired Fraoli, Blum, and Yesselman, Engineers shortly afterwards. An innovative space
frame roof design was proposed.
The 91m x 110m roof consisted of two grids composed of horizontal steel bars (9m for
the top bars, 6.4m for the intermediate) separated by 9m diagonal members connecting the
nodes of the upper and lower grids. The members in the top grid were also braced diagonally at
Figure 1: Elevation of space frame roof
their midpoints. The resulting space frame looked like a series of linked pyramidal trusses as
below. Refer to figures one and two.
Figure 2: pyramid module
This innovative space roof design had three particularly unusual features: 1) the truss
members had a “cross” cross-sectional configuration, which did not give good resistance to
buckling. The cross shaped section provided a much smaller radius of gyration than either a
Universal Beam or Tube Shaped Beam. 2) The top horizontal members and the diagonal
members intersected at different points instead of at the same point making the roof particularly
vulnerable to buckling. 3) Instead of the roof being supported by boundary columns or walls, it sat
on four pylon legs. Refer to figures one and two.
Because of these changes from normal practice, computer analysis was used to check
the safety of the building design.
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Indications of failure:
In order to save money, the structure was assembled on the ground. While it was still on
the ground, the engineers were notified that excessive deflections had been found at some of the
nodes. Once the roof was put into position the deflections were measured and found to be twice
that which was predicted by the computer analysis. Again, the engineers were notified but they
claimed that such derivations from the theoretical deflections were to be expected. When a
subcontractor was attempting to fit the steel frame supports for fascia panels on the outside of the
truss, difficulties were encountered due to excessive deflections. Approximately a year after the
building was constructed, a citizen contacted the engineers to express concern about the large
deflection he’d noticed. He was assured that the building was safe.
Reasons for roof failure:
After the building had collapsed it was determined that the load due to the self weight of
the roof had been underestimated by 20%. However, the sum of the dead and live loads was less
than the total assumed in the design.
The midpoint braces for the rods in the top layer had not been installed. The exterior rods
were only braced every 30-feet, rather than the 15-feet intervals specified, and the interior rods
were insufficiently braced at their midpoints. Along the frame edges, the diagonals and top bars
were in the same inclined plane; hence buckling out of this plane wasn’t prevented. The top bars
were free to bend outward in a direction perpendicular to that plane.
Figure 3: Buckling of top horizontal chord
The diagram to the left illustrates some
of the differences between the original
design and the design as was
implemented on site, for the east-west
edges of the roof.
As can be seen, the difference caused
a huge reduction in the allowable
forces for the structure.
The diagonal members were attached
some distance below the horizontal
members. The flexibility of the
connection reduced the effectiveness
of the bracing by introducing a spring
brace instead of the hard brace that
had been assumed.
Figure 4: Designed versus as-built connections
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The most overstressed members in the top layer buckled under the snow load, leading to the
bucking of other members and the collapse. There were some other faults with the design,
including:
 The slenderness ratio of some members violated American Institute of Steel Construction
(AISC) guidelines, as did members with bolt holes greater than 85% of cross-sectional
area.
 Some of the diagonal members were misplaced
Analysis of the failure:
A study was made of the progressive failure of the roof. A computer model of the roof
structure, with correct buckling lengths and stiffnesses of all bars, was “loaded” in steps,
searching for the value of the load at which the first bar would buckle. This load was
conservatively evaluated to be 13% below the total load actually on the roof on the day of failure.
Loading of the model was increased further to examine what happened after the first bar
buckled. When a member of a frame buckles, it transfers its load to adjacent bars. Most of the
time, the adjacent bars cannot carry the extra load and then also buckle. The failure of additional
bars transfers their load progressively to new bars until the roof cannot carry any greater load and
begins to collapse. Progressive collapse can start as the result of even a minor deficiency unless
redundancy is introduced as structural insurance. The addition of less than fifty bars to brace the
top outer horizontal bars to a frame consisting of almost five thousand bars would have made the
Hartford roof safe by preventing bar buckling.
Conclusion:
The engineers for the Hartford Arena depended on computer analysis to assess the safety of
their cost cutting design. The roof design was extremely susceptible to buckling which was a
mode of failure not considered by that particular computer analysis and, therefore, left
undiscovered. Construction costs were reduced but the analysis of the innovative design was not
meticulous enough.
The Hartford Arena contract was divided into five subcontracts coordinated by a
construction manager. Not only did this fragmentation allow mistakes to slip through the cracks, it
also left confusion over who was responsible for the project as a whole. Even though the architect
recommended that a qualified structural engineer be hired to oversee the construction, the
construction manager refused saying that it was a waste of money and that he would inspect the
project himself. After the collapse he disclaimed all responsibility on the grounds that a design
error had caused the collapse. As a result of the construction manager's refusal to hire a
structural engineer for the purpose of inspection, no one realized the structural implications of the
bowing structures. This collapse illustrates the importance of having a structural engineer,
especially the designer, perform the field inspection.
The excessive deflections apparent during construction were brought to the engineer's
attention multiple times. The engineer, confident in his design and the computer analysis that
confirmed it, ignored these warnings and did not take the time to recheck his work.
For projects of this scale, a peer review of the design is usually required. However, the
authorities did not require it for this particular project. In all likeliness, a peer review would have
revealed the design flaws responsible for the collapse of the roof.
If all or some of the lessons learned from such engineering disasters are understood and
taken on board by all engineers, then such failures may be avoided. Most importantly, the risk of
injury or death to members of the public who use these structures may be dramatically reduced.
References:
Levy, Matthys and Salvadori, Mario (1992), Why Buildings Fall Down: How Structures Fail. W. W.
Norton, New York, NY
Martin, Hartford Civic Center Arena Roof Collapse,
http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Hartford%20Civic%20Center/h
artford.htm
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