FOR RELEASE: Jan. 19, 1999
Contact: Blaine P. Friedlander, Jr.
Office: (607) 255-3290
E-Mail: [email protected]
Compuserve: Bill Steele, 72650,565
http://www.news.cornell.edu
ITHACA, N.Y. -- Melting snow and ice might not have had sufficient "critical weight" to cause several roof collapses in the Northeast, according to a Cornell University climatologist.
"The amount of rain and snow we have had in the Northeast -- even adding all the snow we've had since last year -- should not approach critical weight needed for a roof collapse. In other words, the roofs should bear this weight," says Arthur T. DeGaetano, a senior climatologist at the Northeast Regional Climate Center at Cornell University.
In recent days, there have been several roof collapses following heavy snow and ice storms, including the Museum of Science and Technology and a domed road-salt storage facility, both in Syracuse, N.Y., and Olympic Stadium in Montreal. DeGaetano emphasizes, however, that he has no specific knowledge of the circumstances under which these roofs collapsed.
But he notes, "In older buildings or buildings like barns, you might expect to see some collapses. But, engineered buildings comply with codes. These recent snow events are not all that spectacular, the snow-load weight is not out of the ordinary."
In snowbelt cities like Syracuse, DeGaetano says, roofs can withstand 10 inches of water, or about 52 pounds per square foot of pressure. "That's a winter-full of snow all at once. So far in January, Syracuse has seen 3.89 inches of water, in addition to 2 inches in December. All that water didn't add up to the weight needed to collapse a roof." One inch of water equals between 10 and 15 inches of snow, depending on the outside temperature.
DeGaetano recalls the Blizzard of '96, the heaviest snow of the century in the Northeast. This was the 125-year storm that have engineers and scientists a way to assess snowloads on roofs.
"In places where roofs should have collapsed (in 1996), they didn't collapse," says DeGaetano. "This showed that most buildings exceeded the minimum building code requirements."
The Blizzard of '96 (Jan. 8-10, 1996) was a whopper, but with snow resting on rooftops, another smaller storm followed and contributed to even greater snow weight on roofs. News reports of roof failures throughout the Northeast corridor -- Boston to Washington -- prompted DeGaetano; Thomas W. Schmidlin, associate professor of geography, Kent State University; and Daniel S. Wilks, Cornell associate professor of meteorology, to author a peer-reviewed paper, "Evaluation of East Coast Snow Loads Following the January 1996 Storms," in the Journal of Performance of Constructed Facilities (May 1997), a publication of the American Society of Civil Engineers, New York City. The study was funded by the National Oceanic and Atmospheric Administration.
DeGaetano and the other scientists examined the weight of snow during the period Jan. 6-15, 1996. Once the snow weights were determined based on water content within the snow, they corroborated the climatological information with minimum building codes for given areas. Some of the hardest hit areas were northern and central New Jersey, even though local building-code minimums generally require roofs to withstand snow weights of 21 pounds per square foot -- the equivalent of a storm that occurs once every 50 years. More infrequent storms bring snow weights of 26 pounds-per-square-foot in 100-year events, and 31 pounds-per-square-foot for 200-year values. The Blizzard of '96 and the subsequent storm amounted to the equivalent snow weight of a 125-year snowstorm.
News reports during the Blizzard of '96 and the subsequent snow storms provided the scientists with anecdotal information as well, lending insight to the type of structures and geographic locations to pay attention to. For example, a barn collapsed in Woodsboro, Md., killing 150 cows inside; a supermarket roof collapsed in Massapequa, N.Y., injuring 10 people; a 2,500-square-foot section of shopping mall collapsed in Tewksbury, Mass.; a building that housed a printing company in Bethesda, Md., collapsed; and a lawn and garden shop in Berks County, Pa., collapsed under the snow weight, killing one person.
"Climatology affects a lot of different fields, someone has to show how much snow can fall and what an engineered-structure can handle," DeGaetano says. "You have to ask what's the maximum snow weight that a roof can hold, what's the frost depth for underground utility lines, what's the max winds in an area so that roofs can withstand the winds, what's the maximum rainfall for an area, so that sewers can handle rainfall. That's what climatology is all about."
Seasonal Snowfall Summary for the Northeast
(all values in inches)
City Seasonal Departure from Percent of
Snowfall Normal Normal
Thru 1/19/99
Erie, Pa. 82.4 34.1 171%
Buffalo, NY 74.4 24.6 150%
Cleveland 34.4 8.5 133%
Rochester, NY 53.8 10.3 124%
Caribou, Maine 69.6 12.9 123%
Syracuse, NY 59.9 3.9 107%
Pittsburgh 18.6 -0.6 97%
Ithaca, NY 26.5 -5.2 84%
Portland, Maine 25.3 -6.5 79%
Baltimore 6.9 -1.8 79%
New York City 6.5 -1.9 78%
Philadelphia 6.9 -2.0 78%
Boston 12.9 -3.8 77%
Binghamton, N.Y. 29.7 -9.0 77%
Williamsport, Pa. 14.6 -4.5 76%
Burlington, Vt. 30.8 -9.8 76%
Providence, R.I. 11.0 -3.7 75%
Bridgeport, Conn. 7.3 -3.3 69%
Charleston, W.V. 10.1 -5.3 66%
Albany, N.Y. 20.1 -11.9 63%
Newark, N.J. 5.2 -4.7 53%
Concord, N.H. 14.4 -15.6 48%
Washington, D.C. 2.7 -5.2 34%
(National Airport)
Data compiled by the Northeast Regional Climate Center at Cornell University.
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