Structures and Snow

As I type this, a blizzard of massive proportions is bearing down on me and my home. This snowstorm is forecast to sweep across New England, leaving over two feet of snow in its wake. From New York to Boston, public buildings have been shut and people have been told that the only buildings they should go to instead of homes are police-designated shelters. Is this really necessary?

 

The answer is yes- snowfall is perhaps the leading cause of major structural failures. A study by the Bechtel company reports that from 1989 to 2009 there were well over a thousand snow-related collapses in the United States alone, mostly in New York, New Hampshire, and Massachusetts. These incidents most commonly involve wide-spanning roofs that are not strong enough to support the extra load created by snow. The following collapses are three of the most high-profile collapses in the US and abroad.

 

The Hubert H. Humphrey Metrodome was possibly the most hated building in Minneapolis. It was notorious for its brutal utilitarian design- one official said its only purpose was to “get fans in, let ’em see a game, and let ’em go home.” Its most distinctive feature was its ten-acre roof, one layer of teflon fiberglass and one layer of acoustic fabric, supported by air pressure from twenty giant fans. It was only the second stadium ever to have such a roof, and was thus a sort of design experiment. Unfortunately, wintery Minnesota was not the best place to hold this experiment. In the years following the Metrodome’s opening, snowfall caused tearing and deflation in three instances, for it created pressure on the outside of the dome and increased pressure on the inside that the thin materials were unable to withstand. Though measures were taken like pumping hot air through the roof to melt snow, the dome’s tearing and deflation in 2010 was the last straw for municipal authorities, who had the building demolished.

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While few Minnesotans were surprised by the final collapse and demolition of the Metrodome, the 1978 collapse of the Hartford Civic Arena came as a shock. Once again, it was a wide unsupported roof that failed after a blizzard. However, the Civic Arena’s roof was based on a truss and should have been stable even with the added load. The full causes of collapse are worthy of their own article, but the main issue was a truss design that sacrificed structural soundness for economy. There were sections of the truss where diagonal girders were supposed to connect to horizontal ones, but rather than build complicated and expensive truss nodes connecting all four diagonal and all four horizontal girders, two four-way joints were joined by short “posts”. It was these posts that took a large amount of stress due to the snow load, causing them to buckle and snap, which eventually led to the final collapse.

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Both these instances fortunately occurred at night when the buildings were not in use, so there were no casualties. This was sadly not the case in several European snow-related collapses, the worst of which was the failure of the roof of Poland’s Katowice Trade Hall in 2006, which killed 65 and injured 170 people. The trade hall was by no means a daring design- the trussed battens supporting the roof were held up by regularly spaced columns. The collapse was due to a major design oversight. The building had been engineered to handle a heavy snowfall, but only if that snowfall was evenly spread across the roof. On the day of the collapse high winds had caused massive snowdrifts, larger than the structure’s load-bearing capacity, to build up in a certain small area of the roof, distorting and eventually snapping the structural members and joints there.

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As with all accidents, all these incidents were tragic and damaging. However, they had the benefit of teaching lessons to future engineers. As building codes become more advanced, failure due to snow will certainly lessen. Codes have already become strict in developed areas of the US, so New England residents have no need to worry about the current blizzard.

First picture from AP, by Ann Heisenfelt

Second picture from Hartford Courier, by Arman G. Hatsian

Third Picture from public domain

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