Drift Snow Load refers to the additional load imposed on structures due to the formation of snow drifts. Snow drifts occur when wind blows across an obstruction, such as a building or a change in terrain, causing the snow to accumulate in specific areas. Drift Snow Load calculations are important for designing structures in regions prone to drifting snow, as these loads can significantly affect the structural integrity of roofs, walls, and other components.
Different types of Drift Snow Load can be categorized based on the factors that influence their formation. Here are three common types:
- Roof Snow Drift Load: This type of drift snow load occurs on the roofs of buildings. When wind encounters a building, it creates areas of high pressure on the windward side and low pressure on the leeward side. As a result, snow is pushed against the windward side and accumulates in the form of a drift. Roof Snow Drift Load calculations take into account factors such as the building height, shape, and orientation, as well as the wind speed and direction. Engineers use wind tunnel testing, computational fluid dynamics (CFD), or simplified mathematical models to estimate the snow drift loads on roofs.
Example: Consider a tall, rectangular building situated in an area prone to strong winds and drifting snow. The prevailing wind direction is from the west. As the wind encounters the building, it creates a snow drift on the east side (windward side) of the roof. The height and shape of the building contribute to the formation of the drift. To design the roof appropriately, engineers would calculate the Roof Snow Drift Load based on the wind speed, the building dimensions, and other relevant parameters. The design would ensure that the roof can safely support the additional load imposed by the snow drift.
- Wall Snow Drift Load: Wall Snow Drift Load refers to the snow accumulation and pressure on the walls of a building caused by wind-driven snow. Wind can cause snow to accumulate against the walls, especially on the windward side. The height and shape of the building, as well as the surrounding terrain, influence the formation of wall snow drifts. Calculations for Wall Snow Drift Load consider factors such as the wind speed, the building height, the distance between the wall and adjacent obstructions, and the surface roughness of the terrain. Structural engineers use analytical methods or computer simulations to estimate the additional load on the walls due to snow drifts.
- Obstruction Snow Drift Load: Obstruction Snow Drift Load occurs when snow drifts form around obstructions such as fences, trees, or equipment. These obstructions disrupt the natural movement of wind, causing snow to accumulate on the leeward side. Obstruction Snow Drift Load calculations depend on factors such as the height, shape, and orientation of the obstruction, as well as the wind speed and direction. Engineers consider the dimensions of the obstruction and its distance from nearby structures to estimate the additional load imposed by the snow drift.
Example: Imagine a warehouse located near a row of tall trees in a region with significant snowfall and strong winds. The trees act as obstructions, causing snow to accumulate on the leeward side of the warehouse. To design the warehouse’s walls properly, engineers would calculate the Obstruction Snow Drift Load based on the wind speed, the height and distance of the trees, and other relevant parameters. This calculation would ensure that the walls can withstand the additional load caused by the snow drift.
Drift Snow Load calculations require a thorough understanding of wind patterns, site conditions, and the interaction between wind and snow. Consulting with experienced structural engineers and utilizing appropriate design standards and codes specific to the region are crucial when accounting for Drift Snow Load in structural designs.
