Wind loading codes and standards - Wind Loading of Structures - page 349

speeds averaged in four different ways and the 10-min velocity pressure, q ref , used as a
basis for calculation of wind loads (see Equation (15.1)).
Table 15.1 Definitions of basic wind speeds

Code Averaging time Basic return period (years)

ISO 4354 10 min 50 years

prEN 1991-1-4.6 10 min 50 years

ASCE-7 3 s 50 years

AIJ 10 min 100 years

AS/NZS 11 70.2 3 s 500 years

BS6399: Part 2 1 h 50 years

The European pre-Standard prEN 1991 of 2004 also does not give basic wind speeds,
although the previous (1994) draft gave 'reference wind velocities', for 18 countries in
Europe in an informative Annex. National Annexes will provide basic wind speed
information for individual countries in Europe.
The American Standard (ASCE-7) contains maps with two zones in the majority of the
country and closely specified contours for Alaska and the coastal regions adjacent to the
Gulf of Mexico and the Atlantic Ocean. In the latter case, the effects of hurricanes are of
particular concern. The values of basic wind speed given on these maps are peak gust
wind speed, with an annual probability of exceedence of 0.02. The methodology for the
derivation of the basic wind speed maps for the United States has been described by
Peterka and Shahid (1998).
The recommendations of the AIJ gives a detailed map showing contours of the basic
wind speed (10-min mean with 100-year return period). Single values are given for
outlying territories such as Okinawa. A map of 500-year return period values is also
given to enable users to interpolate for intermediate return periods.
In the Australian/New Zealand Standard, basic wind speeds are given in the form of
maps with five regions, denoted by A, B, C, D and W. Two of these regions (C and D)
comprise a coastal strip exposed to the effects of tropical cyclones (Section 1.3.2).
Regional wind speeds are specified for each Region as a function of annual probability of
exceedence. The 500-year return period in Table 15.1 applies to the majority of buildings
in Australia (Importance Level 2 in the Building Code of Australia). The analysis of
extreme wind speeds for Region A, covering most of Australia, in the 2002 Australian
Standard was described by Holmes (2002). The analysis of wind speeds for Regions C
and D was discussed by Dorman (1984).
In the British Standard, BS6399.2:1997, the basic wind speed, V b (1-h mean), is given
in a map, which covers Ireland as well as the United Kingdom. This has an annual risk of
exceedence of 0.02, i.e. a 50-year return period.