Civil Engineering Reference
In-Depth Information
Figure 8.19
Largest minimum pressure
coefficients for hipped roofs of 15°, 20° and
30° pitch, for any wind direction (Xu and
Reardon, 1998). Reprinted with permission
from Elsevier.
contours of worst minimum (negative) peak pressure coefficients, referenced to mean
dynamic pressure at eaves height, and can be compared with the equivalent gable roof
values in Figures 8.11 and 8.12. Note that, at 30° pitch, the worst negative pressure
coefficients of about −5.0 are similar for the two roof types.
8.4.4
Effect of surrounding buildings—shelter and interference
Most low-rise buildings are in an urban situation and are often surrounded by buildings of
similar size. The shelter and aerodynamic interference effect of upstream buildings can
be very significant on the wind loads. This aspect was the motivation for the studies by
Lee and Soliman (1977) and Hussain and Lee (1980) on grouped buildings, as discussed
in Section 8.2.1. Three flow regimes were identified based on the building spacing. The
study on tropical houses, described by Holmes (1994), included a large number of
grouped building situations for buildings with roofs of 10° pitch. This study showed that
upstream buildings of the same height reduced the wall pressures and the pressures at the
leading edge of the roof significantly, but had less effect on pressures on other parts of
the roof. The building height/spacing ratio was the major parameter, with the number of
shielding rows being of lesser importance.
A series of wind-tunnel pressure measurements, for both structural loads and local
cladding loads, on a flat-roofed building, situated in a variety of 'random city'
environments was carried out by Ho
et al.
(1990, 1991). It was found that the mean
component of the wind loads decreased and the fluctuating component increased,
resulting in a less distinct variation in peak wind load with direction. The expected peak
loads in the urban environment were much lower than those on the isolated building. It
was also found that a high coefficient of variation (60-80%) of wind loads occurred on
the building in the urban environment due to the variation in the
location
of the building.
