Analysis of Common Accidents of Tower Cranes

The year 2004 was an extraordinary one. All kinds of construction undertakings in our country were thriving and flourishing. It was also a year marked by frequent safety accidents. From the Daping mine accident to the Tongchuan mine accident, safety incidents occurred one after another. Tower crane safety accidents at construction sites are also a frequently occurring area. Tower crane accidents can be said to frequently appear in the news media, whether in Jinan, Shandong or even across the country. Since I started working, I have been engaged in the production, manufacturing, design and development of tower cranes. I have also participated in the investigation and analysis of many accidents involving our factory's products and tower cranes in the same industry, and have gained a lot of insights. According to the investigation and analysis, some accidents are caused by design and manufacturing defects, but most of them are directly related to improper use and maintenance. If we were a little more careful and attentive during use, perhaps the accidents would not have occurred at all.

"Preparation leads to success; lack of it leads to failure." Recalling the recent Indian Ocean tsunami, it also offers us many inspirations. The death toll has exceeded 150,000. Objectively speaking, it is a natural disaster, but it is also directly related to the lack of a corresponding early warning mechanism. From the report that "no carcasses of animals died from the tsunami were found in Sri Lanka after the tsunami" to the incident where an Indian working in Singapore "saved a 500-person fishing village with a transoceanic phone call", the inspiration behind it is thought-provoking: Human beings, the most advanced animals in nature, can land on the moon, explore the ocean floor and send robots to Mars. However, they lost to animals that excel in senses in this tsunami. Just one phone call could save a fishing village with over 500 people. In today's highly developed communication and network technology era, such a huge disaster cannot but be regarded as a human tragedy. While we marvel at the brilliant achievements of human technological progress, we have also gained a clear understanding of the boundless power of nature. In the future, while we are taking advantage of the rapid development brought by science and technology and enjoying a happy life, should we not remain as vigilant and alert as animals?

Looking back on the usage status of tower cranes, a sense of mission spontaneously arises. I am delighted to take up my pen and write down my feelings from over a decade of engaging in the design, manufacture, and development of tower cranes, as well as my participation in the investigation and analysis of tower crane accidents in the industry. I will also summarize the common accidents in the tower crane industry and share them with all user friends for mutual encouragement, with the aim of reminding myself and all user friends to remain vigilant.

Accidents caused by violation of operating procedures (classified into the following categories)

1.1 Overloading caused tower crane accidents

A. Lifting exceeds the rated lifting moment, and the moment limiter is damaged, removed, not adjusted or not regularly checked, causing the moment limit to malfunction and leading to an accident. Such accidents are frequent and the damage caused after they occur is also considerable. It is well known that the quality of tower crane drivers varies greatly. Many drivers believe that tower cranes all have a certain safety factor and it doesn't matter if they exceed the load limit. Little do people know that the safety factor of tower cranes is set up to adapt to different working conditions. One overloading was not a big deal, but two overloads did not cause any accidents. Not only did they not sense the potential for an accident emerging, but they also took it as an experience and even as a capital to show off: "The arm end is supposed to lift 1 ton, but I lifted 2 tons and there was no problem." And they didn't know that disaster was quietly approaching.

Comment: The moment limiter is the most crucial safety device for tower cranes and should be regularly maintained, adjusted and checked.

B. The moment limiter malfunctions, causing lifting at night, lifting heavy objects, or the lifting wire rope getting caught on buildings or unknown objects, resulting in sudden overload of the tower crane or sudden unloading of the tower crane, leading to an accident.

Comment: Blurred vision at night makes it easy to make wrong judgments. At this time, drivers are working while fatigued and often have a complacent and lucky mentality of "finishing the work early and taking a break early".

1.2 Accidents caused by improper installation and disassembly

The installation, disassembly, jacking up and setting down of tower cranes are crucial steps. Operators should undergo strict training and hold relevant certificates before taking up their posts. Before commencing construction work, relevant operators should carefully read the product user manual, formulate a construction plan, and conduct thorough safety and technical briefings. Such as the installation and disassembly sequence, the connection and fastening of each component, the installation and disassembly sequence of counterweights, the adjustment of the balance at the upper part of the cylinder during jacking and lowering, the adjustment of the gap between the guide wheel of the frame and the tower body, the placement position of the jacking plate beam and the tower body step, the connection and disassembly of the lower support and the tower body, and the positioning of the rotation during jacking and lowering. The lifting, placing and supervision of the two climbing claws on the frame must all be carried out with high vigilance.

Comment: The installation, dismantling, jacking up and lowering of tower cranes are the links where accidents occur frequently. Special attention should be paid and they should be assigned to specific personnel.

1.3 Accidents are caused by the foundation not meeting the requirements

A. The ground bearing capacity test was not conducted as required by the manual, and the tower crane overturned due to insufficient bearing capacity of the foundation.

B. Construction was not carried out in accordance with the requirements of the manual, and the foundation was too small to meet the stability requirements of various working conditions of the tower crane.

C. The self-made anchor bolts failed to meet the requirements specified in the manual, and the anchor bolts broke, causing the tower crane to overturn.

D. Weld the anchor bolts to the foundation reinforcing bars. As the materials of the anchor bolts are mostly 45# or 40Cr, the welded parts are prone to brittleness and breakage.

1.4 Improper attachment of tower cranes causes accidents

A. The independent lifting height of the tower crane above the attachment point exceeds the requirements of the manual.

B. The attachment rods and the attachment spacing are increased at will without calculation or design.

The accident was caused by fatigue of the tower crane and improper use and maintenance

2.1 Fatigue of steel structures causes cracks in the base metal of key parts or cracks in key welds

The occurrence of fatigue cracks is influenced by multiple factors and is related to design, manufacturing, and materials. However, the majority of fatigue cracks are closely associated with long-term overloading and are the result of gradual accumulation. With the technological revolution in China's construction industry, the speed of engineering construction has advanced by leaps and turns. It is no longer a myth that a floor can be built in three days. Projects that were completed in the past few years can now be finished in just a few months. With such a fast pace, more attention should be paid to the standardized operation and maintenance of equipment. On the contrary, the original specialized management institutions - the Equipment Department and the Machinery Department - have mostly been optimized and streamlined, with their functions greatly weakened. In some companies, there is even no equipment management department at all. Not only that, it is common for some leaders to adopt the tactic of "resting people but not horses" in order to increase the construction speed. Little do people know that even horses can get tired and fall ill. If they are not carefully fed and cared for, they can also stumble. Steel structure fatigue initially starts as very small cracks. Only when they gradually extend to a certain extent will accidents occur. If we frequently inspect, detect problems in time and handle them promptly, such accidents can be completely avoided. The main parts prone to fatigue are: the connection between the foundation section and the bottom beam, the welds of the main limbs or connecting sleeves of the reinforcing sections or standard sections above the diagonal braces, the sections of the tower body with variable cross-sections, the upper and lower supports, the rotating tower body, the main limbs or ear plates at the lower part of the tower top, etc.

Comment: Accidents caused by fatigue in steel structures and welds are also relatively common. Equipment that has been in use for many years is prone to accidents due to fatigue. Many of these accidents are caused by a combination of fatigue and improper operation.

2.2 Accidents are caused by fatigue and loosening of connecting bolts

According to the JG/T5057.40-1995 standard for high-strength fasteners in construction machinery and equipment: High-strength bolts and nuts, after being disassembled and reused, generally should not exceed two times. Moreover, the removed bolts and nuts must be free from any damage, deformation, stripped threads, missing threads, rust, or significant changes in thread roughness. In actual use, there are few things that users can do, but it is necessary to pay attention to strengthening the inspection, tightening, maintenance and regular replacement of high-strength fasteners to avoid their mixed use.

2.3 The pin shaft fell off, causing an accident

A. The movement of the pin shaft cuts through the split pin, causing the pin shaft to fall off.

B. During installation, cotter pins were not installed or pliers were used instead.

C. Without installing pressure plates or cotter pins, weld the pin shafts to the structure. Due to the poor weldability of the pin shaft, it is very easy to come apart under vibration and impact, causing the pin shaft to fall off.

D. The fastening bolts of the shaft end baffle were not fastened with spring washers or were not securely fastened and fell off due to long-term vibration. The pressure plate did not function properly, causing the pin shaft to fall off.

E. The triangular baffle at the boom joint has deformed or come apart due to multiple disassemblies, causing the boom pin shaft to fall off.

2.4 The breakage of the steel wire rope caused an accident

A. Broken wires and strands of the steel wire rope were not detected and replaced in time.

B. When the hook suddenly drops to the ground, the anti-rope disengagement pulleys at the hook, trolley and other parts are either absent or damaged, causing the steel wire rope to come out of the groove and thus break the steel wire rope.

C. The height limit is ineffective, and the hook hits the crossbeam of the trolley, breaking the steel wire rope.

2.5 Accidents are caused by damage, removal or malfunction of other safety devices

Such as brakes, weight limiters, height limiters, slewing limiters, luffing limiters, large vehicle travel limiters, etc.

3. Design and manufacturing defects cause accidents

1. Design flaws such as insufficient stability of tower cranes, one-sided pursuit of boom length performance, and inadequate rigidity or strength of the tower body;

2. Defects in manufacturing, such as the arbitrary use of substitute materials or main materials not meeting standards;

3. Failure to comply with welding process standards, with defects such as slag inclusion, cracks, key welds not meeting the required dimensions or having false welds;

4. Unqualified safety devices, incomplete protective devices, etc.

The above are some of my personal insights and summaries. If there are any shortcomings, please offer more valuable suggestions. I would be very glad if I could provide you with any hints or inspirations while you are reading.