OCR Text |
Show 9 environment, it could be serious in areas of heavy wet snows and less frequent strong winds. ( 5) Jet roofs should be erected where sufficient wind is available to keep them operable; otherwise, they may become filled or covered with drifted snow. The weight of the snow thus accumulated could distort or break the jet roof. ( 6) The most efficient inclination for the jet roof is that which approximates the angle of the lee slope. This confirms similar conclusions by Hopf and Bernard, ( 1963), but further discussion of this aspect is given below. Note that throughout this paper the angle of inclination referred to is measured with respect to the horizontal plane. Jet Roof Inclinations. For experimental purposes on Bridger Ridge, a jet roof was inclined at 40°, an angle deemed too steep for efficient operation over the 30° slope. A sharp cup- shaped hollow developed in the snow to the lee of the structure, but a secondary cornice accumulated beyond the hollow. By comparison, an adjacent jet roof inclined 25 was distinctly superior. The roof at 25° produced a long furrow completely eliminating the cornice on the lee slope. Steeply inclined jet roofs can be used, however, in conjunction with very steep or vertical lee slopes, for above these slopes there is insufficient support for extensive horizontal cornice development to occur even if jet roofs were not used. Dangerous cornices can develop over such steep slopes if not controlled, for considerable vertical accumulation without horizontal extension is common. Model Experiments. In order to better understand the dynamics of jet roof action, a full- sized jet roof was erected on a level field |