When should you stop a crane due to strong wind speed?

Harsh weather adds risk to lifting operations, and quick action may be needed to prevent accidents. To manage risk, the first step is knowing the exact wind conditions at all times. Based on crane specifications, operators and project managers can decide if a lift can proceed safely.

• Crane manufacturers must provide loading tables, derating factors and maximum wind speeds. Note that these specifications change depending on the type of load.
• When this data is lacking, contractors can follow general safety protocols from construction associations.
• Wind direction is also important, since it determines how the crane will be loaded. For example, lateral winds have different effects than wind blowing from behind the crane.
• Turbulence intensity must also be considered, since it creates additional loads even when the average wind speed hasn’t changed. 

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Safe wind speed to stop operating cranes:

In general crane manufacturers, contractors and the Heath and Safety Executive recommend a maximum wind speed for tower cranes at 38mph (16.5m/s or 60kph) and completely prohibited over 20m/s (45mph or 72kph)

Wind speed from the crane anemometer can be divided as guideline:

     Very calm or still - wind speeds below 1.99 m/s (4.47mph)
     Calm - wind speeds between 2 and 4.99 m/s (4.48 to 11.16mph)
     Low - wind speeds between 5 and 9.99 m/s (11.17mph to 22.35mph)
     Medium / Caution - wind speeds between 10 and 14.99 m/s (22.36mph to 33.53mph)
     High / Risk - wind speeds between 15 m/s and 20 m/s (over 34mph)

Does wind speed affect crane capacity?

Cranes have a loading limit, like any structure. The wind exerts a larger force when its speed increases, and the crane uses some of its loading capacity to withstand this force. As a result, the crane’s effective capacity is reduced. Crane manufacturers should be contacted if the loading data is missing. This information should be available for everyone involved in the lift, especially the operator.

When a project involves different types of cranes, having specific information for each one is important, since loading characteristics may change. Also consider that wind conditions may change across small distances and heights, and they should be measured for every crane involved. A single weather station in a site with multiple cranes does not offer enough certain-ability.

There may be cases where a lift is already programmed, and some data from the crane manufacturer is still missing. If the lift cannot be postponed and specific crane load information is not available, contractors can follow general safety guidelines:

• A common “rule of thumb” is considering stopping the crane if the wind speed reaches 20 mph.
• Project managers and Appointed persons should reconsider lifts if the wind speed increases dangerously, even before it reaches 20 mph.

Ultimately the crane operator may decide to take the crane out of operation at lower wind speeds due to the type of load being lifted or difficult to control it under wind pressure. The forces exerted on a crane can change due to external factors, even if the load itself has not changed. For example, wind blowing from behind a crane can push the load away. This increases the swing radius and the bending force.

Since wind speed tends to increase with height, it should be measured at the highest possible point of each crane. A ground-level measurement is of little use, since it does not reflect the wind conditions to which the crane is exposed.

Summary

Crane operations become safer when manufacturers provide accurate loading data which is updated with wind speed data when the weather is monitored on-site. Activities can be scheduled based on weather forecasts and historical data, while weather and wind speed  monitoring allows quick decisions during a lift.

Crane derating data from the manufacturer is useful to prevent overloading, and accurate instruments can warn construction managers when dangerous winds are imminent.

If you would like to learn more about wind monitoring for construction sites, you can give us a call or send an email. We will be glad to answer your questions on how to track the weather effectively in construction sites.