If the rubble always contained the secret of why a building collapsed, the work of investigating engineers would be greatly facilitated.
As it is, digging through and photographing the rubble is only a part of the work entailed. Thorough examination must be made of the building’s history from the time it was conceived by an architect.
This means locating and studying the architect’s and engineer’s drawings, the engineering calculations, the shop drawings of contractors and subcontractors for each part, and the quality control records kept during the building’s construction. An investigating committee would search for any documentation of a problem that was never corrected, although if an engineer or contractor were aware of such an error, he might not have kept the document around.
As is apparent, determining the cause of a building’s collapse is a task for an intuitive Sherlock Holmes with a comprehensive education in engineering. When lawsuits are involved (and they generally are when millions of dollars are at stake), you can be sure the investigators won’t leave a single beam, rock, or page unturned.
Buildings fail because of one or a combination of the following: design errors, construction errors, material deficiencies, or a natural disaster that exceeds the safety risk determined by a code, which usually is based on what might happen once in a hundred years.
The first three factors are what concern an investigator, and they generally derive from ignorance, carelessness, or greed.
For example, if an engineer misconstrued the architect’s intention and used beams that are too thin to support the roof load or an expected snow load, the building suffers from a design error. If the contractor failed to use enough guys, or supporting wires, while building, the collapse is the result of faulty construction.
Another possibility is that someone along the way tried to cut costs by using concrete that doesn’t meet the strength requirements necessary for the building. A sample of concrete is taken at the outset of construction and tested for twenty eight days; as the building is begun during this time, “shores” are used to support it until the concrete is fully dry and has been proved adequate. Early removal of these shores by hasty contractors is a prevalent cause of collapse.
Not all collapses are as spectacular as that of the Hartford Civic Center Coliseum, which fell on January 18, 1978. Nor are investigations always so extensive as that done by Lev Zetlin Associates, Inc., an engineering firm that did an exhaustive study of the entire project. But a glimpse at some of their proceedings gives an idea of what is involved in determining the cause of a building’s collapse.
From the start there were investigators in the field, examining and photographing the roof structure, a space truss specifically designed for the Coliseum. The space truss consisted of 120 inverted pyramid modules, each 30 feet square, with intermediate bracing members.
Initially, 15 feet of rubble from the roof lay in the middle of the Coliseum and obscured what later aerial photographs revealed to be a line of buckling right down the middle of the building. Findings in the field were constantly compared and contrasted with independent studies of architectural, structural, and mechanical drawings; electrical, plumbing, and space truss architectural drawings; and steel shop drawings for the space truss.
Especially useful were computer analyses of the roof, which simulated its structural behavior in various sequences of failure. For example, a series of pictures was drawn simulating how the space truss would react under different roof loads. Although many Hartford residents thought that snow caused the roof collapse, the committee found that the snow load on January 18 was only 17 pounds per square foot, and the design allowed for 30 pounds per square foot.
On the other hand, the roof load (excluding outside factors such as snow) was designed for 40 pounds per square foot, but the actual load was found to be 53 pounds per square foot. On a total load basis, the roof structure was supporting (or trying to support) 1.5 million pounds more than it was designed to sustain. In addition to all this, a metallurgical report was drawn up evaluating materials used and their conformity to safety codes.
By studying the computer drawings and photographs of the Coliseum that indicated the direction of collapse, the committee realized that failure was progressive, that individual members had given way, causing others to fail, a domino like process that began at the time the space truss was erected. A highly technical, mathematical analysis of the pyramid modules showed the bracing to be inadequate.
Collapse was primarily caused by miscalculation of the buckling capacity of certain members of the space frame.