Crane toppled on lorry injuring two at Jurong Port

Straits Times reported a crane toppled onto a lorry at Jurong Port in 2016, injuring two people. What role does moments play in causing a crane to topple? Where is the pivot? What weights are responsible for the clockwise and anti-clockwise moments? Is it the weight of the load or the perpendicular distance that the crane operator needs to be mindful of when operating the crane?

The principle of moments states that the total sum of the anti-clockwise moment is equal to the total sum of the clockwise moment when in equilibrium. “In equilibrium” here means when all the forces acting on the system cancel each other out when a system is stable or balance. In this video, you can see that the anti-clockwise moment due to the load about the pivot is greater than the clockwise moment due to the weight of the crane. Therefore, the crane topples. For the safety of all workers, it is important to ensure that load is not too heavy and the horizontal distance between the load and the pivot is not too large. You can see from the video that the crane did not topple when the crane’s boom is almost vertical. When the crane’s boom is almost vertical, the horizontal distance between the load and the pivot is short. Thus, the moment due to the load is lower. But when the crane’s boom is tilted forward, the horizontal distance between the load and the pivot increases. This causes the moment due to the load to increase. This is when the crane topples.