Windward Snow Drift Loads

摘要

AbstractWindward snow drifts are an important consideration for many roof geometrics, including roof steps, parapet walls, and various roof projections. Current code provisions for windward roof snow drifts are based upon a database wherein the larger windward drifts were difficult to distinguish from leeward drifts. This was due to the fact that windward drifts can change shape as they grow. Initially windward drifts are generally smaller in size and have a general (nonright) triangular shape with a gap between the peak drift depth and the wall. As they grow they morph into the same right triangular shape as leeward drifts with the peak drift nominally adjacent to the wall. However, recent Norwegian full scale measurements of windward drifts over time allow improved qualitative and quantitative understanding of the actual windward drift formation process. These measurements confirm that the windward drifts initially have a general (nonright) triangular shape and given enough upwind snow transport will morph into a right triangular shape. Based upon those new Norwegian measurements, actual windward drifts are substantially larger than windward drifts currently prescribed by ASCE 7. Proposed code provisions are provided which result in windward drifts generally consistent with the new Norwegian measurements. The height of the roof step or parapet wall with respect to the expected amount of driftable snow is shown to be the key parameter as windward drifts morph from an initial general triangle shape to possibly a final right triangular shape.