10 ACCIDENT ANALYSIS IN CONSTRUCTION
The collapse of the Hyatt Regency Hotel: what lessons must be learnt?
In 1981, at the opening of the magnificent Hyatt Regency Hotel in Kansas City, a tragic accident occurred in which many people were killed and maimed. Several investigations into the devastating accident were carried out and it appears to be the case that an elementary error in structural engineering design was to blame. However, much of the data also suggested that ‘a more fundamental cause was a series of communication failures between the structural engineer and the steel fabricator’ (Banset & Parsons, 1989: p.273).
The background to the incident is as follows. The hotel and restaurant were crowded and there was a dancing competition in the atrium. Above the atrium, on the second and fourth floors, were walkways (Fig. 2). As people crossed the walkways, they stopped to watch the dancing, and began tapping their feet in time to the music. Suddenly the two walkways began to fall. They crashed one on top of the other and then into the atrium below: 114 people were killed and more than 200 others were injured.
Several studies seem to agree that the people who were tapping to the music created resonance in the walkway structure. Once resonance starts, it continues to increase in intensity until the cause is removed or the structure breaks up. The central hanger rod in the fourth floor walkway (see Fig. 2) tore through its box beam. The remaining rods could not support the extra load, so they tore through the beams one by one, leaving the rods hanging from the roof trusses while the walkway fell loose. Because the second-floor walkway was suspended from the fourth-floor walkway, the two fell together.
However, resonance aside, there was probably a much simpler explanation of why the structure failed. An investigation found that the builders had changed the design specifications during construction. In order to hang the walkways, they had used two shorter rods instead of one continuous threaded rod through both walkways – from the roof to the fourth floor, and from the fourth floor to the second floor (Fig. 4). This decision was due to the cost of producing a continuous threaded rod of this length, which then meant that the top box beam-rod connection had to carry the weight of both walkways, rather than just the top walkway as it was originally designed to. In hindsight, it would seem obvious that this design change was bound to lead to failure, yet no one detected it. As Taylor and Moncarz observed, the collapse was the result of ‘an ill-considered change of an ill-defined structural detail’ (2000: p.46).
Several studies have pointed out that there was a problem with the concrete used in the walkways. The walkways were designed with a corrugated steel deck carrying a layer of 82 mm of concrete. On investigation, it was found that the concrete had been topped with cement and consequently the dead load on the walkways was 8% higher than specified. As a result, any unexpected stress on the structure would lead to collapse (Fig. 5).
Other studies have claimed that the original design of a continuous threaded rod was contrary to the city building code. Nonetheless, the evidence does not support the claim that this would have caused an accident. The actual live load of the people on the walkways was only 420 kN, which was a fraction of the live load of 3,200 kN specified by the city engineers.
Investigations into the accident concluded that a structural design flaw was the immediate cause. However, in parallel with other studies, Conn et al., 1982, considered that the collapse ‘ultimately resulted from poor communication between the designers and the fabricators.’
In agreement, Carper stated that many of these types of failures are ‘the results of flawed management and project delivery systems rather than technical considerations’ (2001: p.1). It seems the most important lesson to be learnt from this accident is that responsibility for checking and approving all modifications made to structural design during the construction process must be made absolutely clear.
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