4A6(1) Case Study Hartford Arena Roof Collapse Group 11. 4A6(1) Case Study. Group 11: Hartford Arena Roof Collapse

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1 4A6(1) Case Study Group 11: Hartford Arena Roof Collapse Date: Authors: 21/10/2011 Seán Keane Eoin Norton Stephen Dent- Neville Figure 1: Image of the collapsed roof

2 Introduction The Hartford Arena was constructed in 1973 and housed a basketball court and seating for 5,000 spectators. On January 18, 1978, during a heavy snowfall, the 2.4 acre roof of the arena suddenly collapsed, only 5 hours after a fully attended game. The collapse was traced to an oversimplified computer analysis. The arena is known as the first computer aided failure. Design and construction Vincent Kling was commissioned to be the architect for the Hartford Civic Centre with Fraoli, Blum, and Yesselman as the structural design engineers. The design of the Hartford Civic Centre they chose incorporated the use of an original space frame roof design that required using a complicated, expensive, and innovative computer program. The estimated savings from the refined state- of- the- art analysis, compared to a more conventional design, was half a million dollars. The innovative design consisted of a 91.4 x 110m space frame roof, 25.3m in height over the arena. The proposed roof consisted of horizontal steel bars spaced 6.4m apart. Diagonal members, 9.14m long, connected the joints of the upper and lower layers and, in turn, were braced by an intermediate layer of horizontal members. The 9.14 m members in the top layer were also braced at their midpoint by intermediate diagonal members as shown in Figure 2. Figure 2: Detailing of Hartford Civic Centers roof

3 Design Flaws There were multiple design flaws found to be associated with design of the space frame itself, including: The cross- sectional area of the truss members didn t give sufficient resistance to buckling. The cross shaped sections used in this project provided a smaller radius of gyration than both a UB and tube shaped beam (see Figure 3 below). The slenderness ratio of the built up diagonals violated the AISC code (The US equivalent to Eurocodes) which prohibits the slenderness ratio of each component of a member to be larger than the slenderness ratio of the entire built- up member. 4 Another violation was that bolt holes punching through some members exceeded 85% of the gross area. Dead loads were underestimated by more than 20%. Under design led to the East and West face exterior top layer compression members to be 852% overloaded (Figure 3); the North and South face exterior compression members to be 213% overloaded, and the interior East- West compression members to be 72% overloaded. 6 The computer model assumed that all of the top chords were laterally braced, but in fact only the interior frame met the criteria because of the diagonal bracing. The exterior edges of the frame s diagonal bracing only offered in plane restraints, which allowed the top bars to buckle outward from the bracing. Once in position, the deflection was noted as being twice that as predicted by the computer analysis.

4 Collapse Figure 3: Assumed fixed versus spring like connection of diagonal bracing The roof of the Hartford Civic Centre collapsed in less than ten seconds. Three different observations have been given to the exact cause of this collapse. 1) It was believed that the initial cause of the collapse was a design deficiency related directly to the inadequate bracing of all top chord compression members of the truss. 2) Loomis and Loomis Inc 3 also investigated the cause of the failure and found it to be under- designed but believed it was due to torsional buckling of the diagonal compression members. They also noted that members close to the middle of the truss were critically loaded even before live loads were added. Torsional buckling at the time was not studied as it was found to be an uncommon mode of failure. 8 3) Hannsrarl Bandal believed that a faulty weld connecting the scoreboard to the roof was the main cause of failure. The explosive weld release could have triggered a huge energy release, and hence caused the entire structure to collapse. 3 The three accounts above give differing explanations as to what was the initial cause of the collapse. However, all cases can be attributed to a lack of redundancy. 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. Redundancy is needed in a design as a matter of structural insurance. Note that it was reported that the addition of fifty bars to brace the outer horizontals to a frame of almost five thousand bars would have made the Hartford roof safe by preventing bar buckling. Conclusions and Recommendations In conclusion, looking back over the story of the Hartford Civic Centres roof collapse, three aspects of its overall construction could have clearly helped prevent its failure. These are the technical, project management and ethical aspects. 1) Technical Aspects The Hartford Arena collapse is known as the first computer aided failure. 5 This can be attributed to the use of an untested, non- conventional design and computer analysis. Computer programs are only ever as good as the programmers themselves. Hence Engineers are responsible for verifying that any results obtained from computer programs are reliable and valid. Professional engineers should: examine and understand the methodologies and input parameters, as well as the limitations of the results obtained; and should compare with other programs where possible that have already been tried and tested for general use. In the

5 absence of such comparison work, the engineer should establish and conduct suitable tests to determine whether the software performs what is required to do. 2) Project Management Five different sub- contractors worked on the construction of the roof of the arena, all coordinated by the one construction manager who was not a structural engineer. After his refusal to appoint an engineer on site the roof was according to him, built exactly to the design specification. After failure, the manager argued that he was not responsible for the design error. This story highlights the importance of having a qualified structural engineer to perform field inspection while knowing the original design. 3) Ethical Aspects Workers and the public had informed the designers of the obvious deflections that became apparent during and after construction but the engineer shrugged off these warning confident in the computer analysis. These unexpected deflection offer a clear warning signal to the engineer that something is not right in the structure and that the behaviour of the structure is different from anticipated. Overall this case offers a startling insight into difficulties that may occur during the construction of highly complex structures. One clear lesson that can be learned, is that there should never be an over dependence on computer software and should be considered a tool only to aid the designer.

6 References: 1. Figure 1 : 2. Figure 2 : Original Lev Zetlin Associates 3. Figure 3: Beyond failure: forensic case studies for civil engineers, by Norbert J. Delatte 4. Lev Zetlin Associates: Structural Engineering Services 5. Canadian Professional Engineering and Geoscience: Practice and Ethics By G. C. Andrews 6. Martin, Rachel, and Delatte, Norbert J., 1999, Another Look at Hartford Civic Center Coliseum Collapse 7. Levy, Matthys and Salvadori, Mario (1992), Why Buildings Fall Down: How Structures Fail. W. W. Norton, New York, NY 8. Feld and Carper, Salvadori, Mario, Why Buildings Stand up