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Statistics of snowfall plus small-scale simulations help engineers design buildings that can withstand the loads of roof top drifts
The snow-covered scenes depicted on holiday cards suggest that people like a little snow during the wintertime. Nevertheless, a lot of snow can cause serious problems. The blizzard of March 1993, for instance, left much of the eastern United States covered in snow: 15 inches in Birmingham, Alabama, more than 2 feet around Albany, New York, and 8-foot drifts in eastern Kentucky. That snowfall resulted in more than 200 deaths, 3 million people without power because of downed power lines and the closure of six major airports between Atlanta and Boston. Blizzards can be even worse. The biggest U.S. snowstorm on record-the blizzard of March 1888-blanketed Albany, New York, in about 4 feet of snow and caused around 400 deaths.
Such large snowstorms can also cause structural damage to buildings. After the blizzard in March 1993, one large insurer of industrial facilities reported more than 100 losses with a total damage of about $200 million to buildings and their contents. The same insurer reported that in an average year-during the period from 1977 through 1989-it paid for 78 snowand ice-related losses with a total value (property damage and business disruption) of about $23 million.
Consequently, rooftop snow is an important consideration for the design of buildings in many parts of the United States. This article describes the various types of snow hazards for building structures, the methods currently used by engineers to quantify these hazards and emerging laboratorybased techniques for evaluating snow loading on buildings.
Estimating Snow Loads
Structural engineers design buildings for two types of loads: vertical loads, which are downward-directed loads caused by the weight supported by a structure, and lateral loads, which are horizontally directed loads caused by wind or earthquakes. Perhaps surprisingly, snow loads on a roof influence both vertical- and lateral-load design. For vertical loads, the design constraints seem fairly obvious: Structural members must be capable of supporting the weight of snow on a roof. But the magnitude of lateral loads--specifically earthquake loads-can also be influenced by roof snow loads, because a lateral load generated during an earthquake is proportional to the total weight of the structure, which includes the...