Civil Engineering Reference
In-Depth Information
Figure 14.1
Mean and maximum pressure
difference coefficients for free-standing walls
(normal wind).
of wall. About a 20% reduction in peak net load occurs as the wall length increases from
1 to 4 wall heights.
For a wind direction at 45° to the plane of the walls, the average net pressure
coefficients are shown in Figure 14.2. In this case, the net mean pressure coefficient
reaches a maximum for a
b/h
ratio of about 3 with lower values for longer walls. For this
wind direction, there is a strong separation on the leeward face of the walls of this length
ratio. For longer walls, re-attachment occurs and generates lower magnitude pressures on
the leeward face.
For mean wind directions normal to the wall, the net pressures do not vary much along
the length of the wall. However, this is not the case for the oblique wind direction. Figure
14.3 shows how the mean net pressure coefficient varies along the wall length. The flow
separation behind the windward edge generates very high pressures for the first 1 to 2
wall heights from the windward edge. This also occurs for elevated hoardings (Figure 4.8
and Section 14.2.4) and is usually the critical design case for wind loads.
14.2.2
Walls with corners
The effect of a right-angled corner at a free end of a wall for various wind directions on
mean pressure coefficients averaged over a vertical line, at a distance
y
from the corner,
is shown in Figures 14.4 and 14.5.
