Wind speeds and pressures

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Wind speeds have a dramatic effect on the requirements of windows. It is necessary to know the wind speed at the local position of the window to estimate the local pressure applied to the window and to verify if the window will withstand the requirements for air and water resistance.

Beaufort Scale

The Beaufort scale was introduced in 1806 by Admiral Sir Francis Beaufort of the British Navy to describe the wind effects on a fully rigged man-of-war at sea. It has now been extended to cover the effects of various wind speeds on land objects. The Beaufort scale is useful because it gives us a physical picture of the various wind speeds. As a scale each Beaufort number covers a range of wind speeds because it is designed for estimates only.

Beaufort number

Beaufort description

Wind speed (knots)

Physical effects

0

Calm

0-1 knots

Smoke rises vertically.

1

Light Air

1-3 knots

Smoke shows the direction of the wind.

2

Light Breeze

4-6 knots

Wind is felt on the face and leaves rustle in the trees.

3

-

7-10 knots

-

4

Moderate Breeze

11-16 knots

Loose paper blows around and whitecaps seen on water.

5

-

17-21 knots

-

6

Strong Breeze

22-27 knots

Wind whistling in telephone wires and spray on water.

7

Moderate Gale

28-33 knots

Large trees sway.

8

Fresh Gale

34-40 knots

Twigs break from trees.

9

Strong Gale

41-47 knots

Branches break from trees.

10

Whole Gale

48-55 knots

Trees uprooted.

11

Storm

56-63 knots

Widespread damage

12

Hurricane

64 knots and higher

Structural damage on land and storm waves at sea.

1 knot = 1 nautical mile/hour = 1.85 km/hour = 1.15 mile/hour

  Conversion

Conversion from any given wind speed to another wind speeds is relatively easy. This is not the case when attempting to convert from a wind speed to a wind pressure. Wind pressure is affected by many local features and whilst a rough conversion is possible it is not published here because of the uncertainty.

Last edited: 11/03/10

Tangram Technology Ltd. 1998

Our standard disclaimer regarding Internet data applies.