Vanities of the Bonfire - Pushing the Limits: New Adventures in Engineering - page 121

Those efforts included the development of a composite design of “the historical Bonfire” and its
examination by means of the general-purpose finite-element-analysis computer program ABAQUS.
The computer-based model enabled an engineering team to simulate hypothesized conditions in the
ill-fated log stack and to confirm its posited behavior. In the final analysis, the commission found
the collapse to be driven by a combination of factors rather than any single factor, and each of those
factors pointed to a mind-set among the university's students and administration characterized by
complacency, hubris, and a disrespect for the forces of nature:
The bonfire was built on slightly sloping ground. Although the ground was solid, it was not
level, dropping about one foot from the northwest to the southeast side of the structure, which
was on the order of fifty feet across. This meant that the first tier of logs leaned to the south-
east. The upper tiers of logs and the tall center pole they were built around were aligned with
the true vertical, however, creating a bent structure not unlike the Tower of Pisa. For a two-
million-pound tower of logs to be built in this manner is to invite instability, and the structure
did in fact collapse downhill to the southeast.
The logs used were more crooked than usual. In previous bonfires, the logs used were very
straight and so fit closely together, like uncooked spaghetti held tightly in the fist. The logs
used in the fatal stack, by being more crooked than usual, allowed numerous gaps to exist
among the logs in the lower tiers. This feature might actually have been seen as a plus by the
bonfire erectors, since upper-tier logs could be inserted into the gaps, thus providing an inter-
connection between tiers. In fact, rather than providing a beneficial interconnection, the logs
so used proved to be a major contributor to the collapse.
Upper-tier logs were wedged between lower-tier logs. The advantage of interconnection be-
came a disadvantage when the second-tier logs were wedged so tightly and so deeply into
the tier below that additional outward pressure was created in the foundation stack. Because
wedging was used more aggressively in 1999 than in previous bonfires, the lower stack was
like an already full pencil holder being stuffed with more and more pencils. In effect, the stack
was filled to bursting.
The upper tiers of logs were built out farther than in past years. After Bonfire reached 109
feet high, in 1969, there were restrictions imposed on the height and width of the stack of logs.
However, the width restriction of forty-five feet was interpreted to apply only to the base of
the stack and to place no restrictions on higher levels. In order that Bonfire contain as many
logs as possible, the 1999 structure was being constructed with wider upper stacks. Like a
skyscraper built without regard for setback restrictions, the bonfire had a larger than anticip-
ated volume and therefore bore down with a greater weight on its lower levels. This additional
weight caused the wedged logs to be driven even deeper into the tiers below and created still
further outward pressure on the ground-level logs in the bonfire.
Steel cables were not wrapped around the lowest logs. In previous bonfires, the lowest tier
of logs was held together by steel cables wrapped around the outside of the entire bundle.
However, there had been some disappointment in recent years that bonfires were burning too
quickly, and this was attributed by some students to the use of the cables. For this and other
reasons, steel cables were not used in the fatal stack, perhaps in part because it was thought,