RR1172 - Mechanical assessment of tower crane slewing brakes

Tower cranes are used extensively on construction projects. All lifting operations must be carried out in a safe manner. Collapse of a crane is a principal hazard: crane collapse incidents present significant potential for multiple fatal injuries, both on and off-site.

Slewing motors are used on tower cranes to control their rotation. They feature a slewing brake which prevents the crane from rotating unintentionally during a lifting operation. When the crane is left out of service, the slewing brake must be released so that the crane can weather vane, or rotate and “free slew” in the direction of the wind such that the jib is aligned with the prevailing wind direction. This prevents the crane jib from being subjected to wind forces larger than it is designed to withstand.

The Health and Safety Executive has investigated a number of incidents in recent years where the slewing brake had either not been released or was only partially released when leaving the crane out of service, leading to catastrophic damage of the crane structure.

This report examines the main causal factors of these incidents, the different types of slew brakes, their operation, ease of use and maintenance. The report aims to inform users and standards makers of the issues identified in order to reduce the likelihood of future incidents associated with the slew brake during extreme wind conditions acting on out of service tower cranes.

This report and the work it describes were funded by the Health and Safety Executive. Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

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Updated 2022-07-11