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The response in AS1170.2-1975 was the specification of a single cyclonic strip within
50 kilometres of the ‘smoothed’ coastline north of Latitude 27 o S, with a value of V 50
of 55m/s. This value reduced by 5m/s over each of another two 10 kilometre strips
(Figure 2.2).
Figure 2.2. Regional basic wind speeds V 50 (m/s) – AS1170.2-1975 to AS1170.2-
1983
The map shown in Figure 2.2 was retained in the 1981 and 1983 editions of the
Standard. The ‘Cyclone Factor’ of 1.15 was also retained in the 1975, 1981 and
1983 editions. Tabulated values at return periods of 5, 25, 50 and 100 years were
also given for all the stations shown in Table 2.2. For all the stations except Onslow
and Willis Island the value of V 100 was specified as 60 m/s. These locations retained
the same values given in AS1170.2-1973; thus for Onslow the value of V 100 was given
as 67 m/s, and for Willis Island 63 m/s was specified.
Table 2.3 shows the values of V 100 specified between 1975 and 1983 compared to the
present values. The ratios are now much closer to 1, with the exceptions being
Carnarvon and Port Hedland which are now rated much higher than previously
(together with Onslow they are now zoned in the higher Region D).
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