An icing study for a future suspended bridge at Montmorency Falls

TitleAn icing study for a future suspended bridge at Montmorency Falls
Publication TypeConference Proceedings
Year of Conference1993
AuthorsMcComber, P., and Paradis A.
Conference Name61st Annual Western Snow Conference
Series TitleProceedings of the 61st Annual Western Snow Conference
Date PublishedJune 1993
PublisherWestern Snow Conference
Conference LocationQuebec City, Quebec
KeywordsGlaze, Ice loads, Icing, Rime, Snow loads

The site chosen by SÉPAQ (Société des établisenments de plein air du Québec) for a pedestrian bridge over Montmorency falls is particularly exposed to icing from droplet spray. ROCHE Ltd, responsible for the design of the bridge, has required a study to estimate the probable ice loads prior to the design of the suspended bridge.A 12.5 mm diameter steel cable was installed on existing towers at the location site of the future bridge. A load sell measured the end tension in the cable. Measurements of icing rate temperature, wind velocity and direction were also collected on site during the 1992-1993 winter, and compared with AES (Atmospheric Environment Service) meteorological data to establish an estimation valid over a longer period of time.Results have shown that a maximum 5 kg of ice collected can be attributed to droplet spray from the falls. In fact, two freezing events 4 and 22 January 1993, have resulted in glaze icing loads from atmospheric sources 3 to 4 times that amount. These results appear to be related to two factors. Firstly, most of the time the spray droplets do not appear to be in the supercooled state essential for their adhesion to the structure. Secondly, the random direction of the droplet cloud results in a low water content impinging locally on the cable. A numerical simulation has shown that in such a case the icing rate on a structure would be small and only very soft rime would form. This type of atmospheric icing would not constitute a hazard for the planned bridge.In conclusion, the additional icing due to the presence of the fall is small and therefore the design has been based on other estimated loads such as wind and glaze icing loads.