As Hurricane Irma approached, Zurich customers turned to us for risk engineering advice for their business sites. One customer reached out seeking guidance for hammerhead tower cranes on a site along Irma’s predicted path. With not a moment to spare, we offered these general suggestions for securing the cranes to the extent possible, in anticipation that a significant storm surge could inundate the site:
- Before any action is taken on the cranes, the manufacturer’s instructions (usually found in the operator’s manual) should be consulted. This should provide information on static wind resistance and any precautions for expected storms that may be unique for your equipment.
- Hammerhead tower cranes must be left to weathervane at all times when unattended, not just during storms. This requires each crane’s swing radius to be unencumbered, including positioning the jibs at different elevations so the cranes will not strike each other. Winds will naturally point the counter jib (short section with the counterweights) into the wind, and the longer jib (with the trolley attached) pointing downwind. This naturally configures the crane to resist the greatest wind load. The trolley (hook) should be raised as close to the jib as possible. The machine deck should be checked for loose materials. There should be nothing hanging from the crane’s hook.
- If you have luffing jib cranes (using a jib that can be raised and lowered to change the radius), the jib should be lowered as close to the horizontal as possible, hook raised as high as possible, and the crane left to weathervane as above. Caution: This type of tower crane is usually selected due to obstructions that may prevent safe operation of hammerhead cranes, so the full swing radius should be verified to be free of obstructions, including the other crane.
- The taller the mast on your cranes, the greater the wind exposure. Tower cranes can be erected without horizontal bracing to a height specified by the crane manufacturer. There is also a height limit above the highest mast collar (bracing point.) The closer the crane is set to the manufacturer’s limit, the greater the exposure.
- If there are any banners or signs that were not applied by the manufacturer, these should be removed from the jibs and mast.
- Crane removal eliminates the wind exposure on site, but this comes with a cost. If the crane is low enough, and a suitable mobile crane is available, the counterweights, counter jib and lifting jib can be removed in advance of the storm, leaving the mast and cab. This reduces the cost and time required for protection.
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