What You Need To Know About ‘Boom Deflection’
We are all familiar with those news clips of large suspension bridges and high-rise buildings swaying during high winds or earth tremors. But did you know this same type of flexibility is also inbuilt in crane booms?
The next time you observe a crane lifting a heavy load watch the boom, and you will notice a distinct bend appearing, as it takes up the weight of the load. This is known as boom deflection and is an inbuilt safety feature of both lattice and hydraulic booms. It is designed to absorb the weight being lifted as the crane takes up the load, and reduces the risk of metal fatigue or fracturing of the crane’s boom. It can also be affected by changes in barometric pressure and wind speed.
Watching a crane’s boom beginning to bend as it starts to lift its load can be an unnerving experience to the uninitiated and is a phenomenon covered in greater detail during our Emerson Crane operator courses. It is one of the three main sectors that need to be considered to ensure a safe, problem-free lift is undertaken.
Load swing can be a major safety hazard and can be instigated if the additional radius from the boom’s deflection hasn’t been taken into account. As the deflection takes the strain, the operator will recentralise the boom, to ensure the lift remains totally vertical.
To be sure of a safe lift, the boom and hook should be 100% directly above the lifting points, ensuring the load is lifted straight up, and doesn’t begin to slide horizontally as the weight is lifted. If this happens, you now often have tons of machinery swinging uncontrollably a few inches off the ground, where it could hit buildings, vehicles, or personnel; as well as affecting the stability of the lifting vehicle.
Quickly dropping the load back on the ground to stop the swinging can also cause problems. As the weight is suddenly removed, the crane boom deflection springs back to normal, which can send damaging shockwaves through the boom.
In situations where the lift has to be delivered to an area tight for space, the crane boom deflection has to be taken into account. The greater the deflection, the shorter the straight-line length of the boom. As the load is placed in position, and the weight removed, the deflection is released and the boom returns to normal length, with the possible jamming on close walls or buildings. On hydraulic cranes, this is usually avoided by the extended boom being drawn in as the deflection is reduced.
Even our smaller city cranes are subject to boom deflection, and care has to be taken when moving heavy machinery into workshops with low roofs. As the heavy lathe or press is lowered onto its concrete plinth, deflection is removed and the boom could jam into the ceiling. Gently lowering or retracting the arm as the weight is transferred usually avoids such accidents.
The allowable amount of deflection is designed and built into all mobile cranes depending on their maximum lifting capacity, and the distance the load is from the crane. The further the load is from the crane, the further the boom has to be extended and the greater the deflection, meaning less weight can be safely lifted.
Here at Emerson Crane Hire, safety-first has always been our number one priority. Our operator and lift assistant courses cover all aspects of crane operation. From the best types of crane for specific jobs, to site preparation, safe slinging and signalling, daily checks, site supervision of operations, competent persons, documents, reports, and a crane’s deflection limits.
If you have any queries regarding the safe operation of heavy lift cranes or would like to register for one of our courses, please contact us today and speak to one of our operations or course managers.