Wind Conditions and Crane Safety

Wind speed for crane anemometers, construction forecast, offshore cranes, crawlers, luffing & tower cranes and outdoor events

Operating tower cranes and any other heavy lifting equipment like crawler cranes bring clear financial and personal responsibility.

Cranes are exposed to a vast amount of hazards that make them prone to accidents and wind speed is a critical risk factor for cranes and lifting equipment, even when they are idle.

Between 2000 and 2010 there were 1,125 accidents and 780 fatalities worldwide in tower crane accidents⁽¹⁾:

• 23% of these accidents were caused by high winds

Forecasting is essential when working at height, and a safety requirement for operating cranes and heavy lifting equipment.

Major contractors, crane manufacturers, the CPA Tower Crane Interest Group and the UK Heath and Safety Executive conclude that -  The maximum recommended wind speed for tower cranes in the UK should be:

• 38mph (16.5m/s or 60kph) and
• completely prohibited over 45mph (20m/s or 72kph)

Ultimately the crane may be taken out of operation at lower wind speeds due to the type of load being lifted or difficulty in controlling it under wind pressure. The crane operator has the primary responsibility in conjunction with the crane supervisor to make that decision.

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Anemometers and Accurate Wind Monitoring

While weather forecasts give an idea of the expected wind conditions at project sites, accurate decisions with respect to crane operation are only possible with live measurements from a wind monitoring system on-site. To determine if crane operation is safe, an anemometer (wind speed sensor) should be installed on the crane to keep track of dangerous conditions.

Some countries make this mandatory: both recording wind speed and having the means to alert site operators on the ground when dangerous conditions are detected.

A typical 'cups' anemometer has a rotational body with 3 cups that capture the wind and rotates at the same speed as the wind speed, therefore measuring the speed of the wind. There are also ultrasonic and propeller-type anemometers. You can find out more on this blog about: how to measure wind speed.

Wind Monitoring at height

Correct positioning of anemometers is vitally important:

• Most weather forecasts assume a height of 10m, which does not reflect the working conditions for vertical construction and tower cranes.
• Since wind speeds tend to increase with altitude, the conditions for a tower crane can be quite different from those at ground level.

In our experience, the increase of wind speed within cities and chances of turbulent winds are higher than they may feel at ground level.

In city centre locations, the wind speed and in particular the wind gusts can be easily more than double of the ones measured at a ground level. Also nearby buildings can have a strong impact on the wind turbulence and therefore increasing the wind loading and variance pressure on the tower and mobile cranes.

Anemometers should be installed directly on cranes at the highest possible point to get accurate measurements. The unit should also be positioned so it can measure wind speed without obstruction from the tower crane or adjacent structures.

There are also some applications that require simultaneous wind speed measurement at two different heights (luffing cranes are one example).
However, the main concern when operating a tower crane is not wind speed, but the force exerted by wind pressure. Wind turbulence intensity (how much the wind changes above and below its average value) is also an important factor.

Wind exerts pressure on surfaces and objects, and faster winds exert stronger forces. In cranes and other structures, this is known as the wind load. Put simply, every time the wind speed doubles, the wind load pressure increases by a factor of four.

For example, if the average wind speed is 5m/s, a wind gust over 10m/s means that the wind load on the crane would have increased by a factor of 4 in just a few seconds. Now imagine this force pushing and pulling the crane as the gusts of wind reach the structure. If you want to know more see this blog about how wind turbulence affects cranes: Wind speed turbulence intensity in cranes

While there are rules of thumb for wind gusts and height effects, they are not a reliable alternative for direct wind measurement at the required location and height. To ensure accuracy, speed of collection and analysis of wind data, a specifically built crane anemometer with advanced data processing is required.

Smart Wind Forecasts for
Tower Cranes and Construction Sites

WINDCRANE uses both historic measurements and live data science to analyse site specific volumes of information - providing micro-forecasts for specific sites.

WINDCRANE provides an early warning for crane operators, project managers and other key personnel involved in construction on site - delivering comprehensive analysis of wind data, within minutes.

The accuracy of WINDCRANE is better than 20ppm (parts per million) - that is an accuracy better than 0.007% for wind speed measurement.

WINDCRANE analyses the deviation of each consecutive measurement with respect to the average wind speed. The system samples the anemometer faster than 1Hz (once per second) and is compliant with EN 13000 and IEC-61400.

WINDCRANE is a live, reliable, fully wireless wind speed system, with a global reach using the GSM network.

 

Here you can read more about improving site safety with the benefits of wind data:

                                                                              ⁽¹⁾ The American National Standards Institute (ANSI)

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