by Joseph W. Ward, P.E.
The winter of 2010-2011 was especially snowy in upstate New York, with near-record total snowfall in Syracuse. At Colgate University's Huntington Gymnasium, in Hamilton, New York, the snow slides off the pitched roof, sometimes in icy sheets. This has been happening at Huntington Gymnasium since it was built in 1924.
After an addition to Huntington Gymnasium was constructed a few
| Huntington Hall snow retention structure |
years ago, falling snow and ice from Huntington's high roof were piling up dangerously close to windows and exits of the addition. Klepper, Hahn & Hyatt reviewed the structure to determine whether rigid snow guards could be mounted on the roof to hold the snow until the spring thaw.
Our analysis showed that snow guards mounted on the roof would overload the structure. Reinforcing the existing riveted structure to support a revised snow load would not only be expensive but very intrusive to the use of the interior gymnasium space, since the truss peak is roughly 50 feet above the gymnasium floor.
That's when we started looking outside the box. We developed an external tower that acted as a snow shield, and was mounted to a new foundation and braced to the second floor framing. The structure includes two W18 columns and a lattice of tubes and pipes at the top to break up the sliding snow and ice, and redirect their trajectory downward. Two end shields keep the snow and ice from spreading out the ends onto another adjacent roof.
Structural engineers are well aware of the load effect sliding snow can have on lower roof structures, and account for this effect using the requirements of ASCE 7 - Minimum Design Loads on Buildings and Other Structures. However, this standard does not provide guidance on design loads for snow sliding into vertical surfaces. For this, we referred to a European Commission research report titled The Design of Avalanche Protection Dams. While Huntington Gymnasium's sliding snow is far from being considered an avalanche, we believed the structural dynamic principles involved were applicable. From this we estimated the horizontal impact force that sliding snow could impart on the snow shield and designed the columns to resist this force.
Because the structure is adjacent to the roof eave, it is constantly exposed to roof run-off. The structure was hot-dipped galvanized and has an additional powder-coat protection. All exterior field joints are bolted. Originally, the columns were to be wrapped with ashlar stone to match the gymnasium exterior walls, but because construction occurred in late fall at the onset of cold weather, the stone wrap was not included.
Following two warmer winter seasons, the snow retention structure functioned as intended during the cold and snowy winter of 2013-2014.
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