Over the past year there have been several news stories about tower crane accidents. I thought this would be a good point to touch on in this week’s blog post.
Tower cranes are only supported by a small structural mass below it and they tend to be susceptible to the elements. Due to their extreme height, tower cranes are not aerodynamic by any stretch of the imagination. They will blow as the wind desires and there is nothing anyone can really do about it. However there are some precautionary steps you can take to ensure that your crane survives even the worst of storms.
One of the major reasons for the destruction of a tower crane during a storm is wind. Cranes are prone to being in the direct path of strong wind currents and thus precautions must be taken. The first step to ensure safety is when an operator leaves a crane at the end of their shift or on break. They must make sure that the crane is left with the jib luffed up in parking position if they are using a luffing jib. If they are using a hammerhead or flat top crane they need to make sure the hook block is brought back to the jib and left slightly away from the cabin. This will ensure that the hook block will not blow in the wind freely and hit the cabin or swing around and injure workers below.
Secondly, the crane parking break should be released and left in free slew when high winds are expected. In order for this to be done safely you must ensure that there is nothing that can make contact with the jib within a 360 degree radius around the crane. By leaving the crane in free slew this allows the slew ring to move freely with the wind and not fight against it. If the parking break is left on and the slew ring is parked in a fixed position then you are risking having the wind blow against the jib and impose loads on the crane that it’s not engineered to sustain.
For example we have seen high winds blow the jib of a luffing crane backwards and the jib ended up hanging off of the back jib only being held on by the hoisting ropes. This is a direct result of severe winds and a crane being left in a fixed parking position and not allowed to move with the wind.
It’s also very important to ensure that there are no tools, bolts, nuts or any debris that can blow off the top of a crane during severe weather. This can result in a major incident or fatality for not only the workers on the job site, but also innocent pedestrians which are passing by the construction site.
From an engineering stand point you must take into consideration not only the horizontal and vertical loads which a tower crane imposes on the building and foundation but also the potential wind loadings. This is particularly the case when a tower crane must be climbed past free standing height and must be tied to the building to ensure its stability.
Once the storm has subsided it’s recommended to conduct a thorough examination of the tower crane to ensure that everything is in working order. It’s also important to perform a max load test to make sure there hasn’t been significant damage to the crane during the storm. The site structural engineer should inspect the tie in points of the tower crane to the building to ensure that the structural stability of the crane has not been compromised due to additional wind loadings on the crane and building. If everything checks out fine then the crane can continue to work as per normal.
These are just a handful of tips to ensure that a tower crane is operated safely. Taking the necessary steps to secure a crane during high winds is a top priority on any project. I hope that you found these insights helpful. Please feel free to contact me directly if you have any specific questions as we pride ourselves on our safety record and can help you do the same.