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Key points and precautions for the safe use of tower cranes. Safety comes first. Tower cranes are essential equipment for lifting and transporting operations in construction projects. Without effective safety management and preventive measures, tower crane overturning accidents can easily occur, resulting in significant losses. Therefore, proper safety management of tower cranes at construction sites is of utmost importance. Next, let’s take a look at the key points and precautions for the safe use of tower cranes. http://img.civilcn.com/d/file/zhishi/gcgl/2020-04-15/10daf4cd66bbfb5ff34734f4ab00892c.jpg01 Key points to note for the safe use of tower cranes 1. The dismantling of tower cranes must be carried out by a professional team possessing a dismantling qualification certificate issued by the construction administrative authority; technical and safety personnel must also be present to supervise the process. 2. Before dismantling a tower crane, it is necessary to formulate the disassembly and assembly procedures, quality requirements, and safety technical measures in accordance with relevant factory regulations. After being approved by the enterprise’s technical supervisor, these shall serve as the technical plan for the dismantling operation, and must be communicated to all personnel involved in the work. 3. When raising or lowering the tower body of a tower crane, the following requirements shall be met. (1) During lifting operations, there must be a dedicated person to give instructions, another dedicated person to monitor the power supply, another dedicated person to operate the hydraulic system, and another dedicated person to tighten or loosen bolts. Personnel who are not authorized to perform tasks shall not ascend to the control panel of the jacking frame. Only one person is allowed to operate from the control room, and they must follow the command signals. (2) Lifting and lowering operations should be carried out during the day; in special circumstances where night-time operations are necessary, there must be adequate lighting. (3) When the wind speed is at level 4 or higher, lifting and lowering operations shall not be carried out. When the wind speed suddenly increases to level 4 during operations, operations must be immediately halted, and all connecting bolts of the upper and lower tower sections should be tightened. (4) Before lifting, the cable should be loosened in advance; its length should be greater than the total lifting height. The cable drum must also be secured properly. During descent, the cable should be tightened at appropriate times. (5) During lifting and lowering, it is necessary to adjust the gap between the rollers of the jacking frame and the standard sections of the tower. The boom and counterweight arm must be kept in a balanced state as specified, and the rotation mechanism must be braked. When it is difficult to remove the last connecting bolt (pin) between the rotation platform and the standard sections of the tower, the bolts at diagonal positions should be reinserted first, followed by other corrective measures. Do not use the rotation of the boom to loosen bolts (pins). (6) When lifting or lowering, after the lifting feet (claws) are in place, a safety pin should be inserted before proceeding to the next step. (7) After the lifting is complete, all connection bolts should be tightened to the specified torque, the hydraulic control lever should be returned to the middle position, and the power supply to the hydraulic lifting mechanism should be cut off. 4. All safety devices on the tower crane must be kept sensitive and functional; any defective safety devices should be repaired or replaced promptly. After all safety devices have been adjusted, they should be sealed (with seal wax or lead seals) to keep them in place; unauthorized adjustments are strictly prohibited. 5. The key inspection items before lifting shall meet the following requirements. (1) The appearance of the metal structure and operating mechanism is normal. (2) All safety devices and indicating instruments are complete and in good condition. (3) Each gearbox and hydraulic oil tank meet the specified requirements. (4) The connection bolts in the main areas are not loose. (5) The wear condition of the steel wire rope and the threading of it through each pulley comply with regulations. (6) The power supply cable is undamaged. 6. Before power is supplied, the handles of all controllers should be in the zero position. When powering on, a test pen should be used to check the metal structural parts; only after ensuring there is no electrical leakage can the machine be operated. 7. Before starting work, perform a no-load test to check whether all working mechanisms are operating properly, whether there is any noise or abnormal sounds, and whether the brakes and safety devices of each mechanism are functional. Work can only begin after confirming that everything is normal. 8. When lifting heavy objects, the total weight of the object and the lifting equipment shall not exceed the lifting capacity specified for that radius of the tower crane. 9. The appropriate operating speed should be selected based on the weight being lifted and the conditions at the site. Operating the various controllers should start from the stop position (zero point), with the speed being increased gradually step by step; it is strictly prohibited to shift gears directly. To change the direction of operation, turn the controller handle to the zero position and wait until the motor has stopped before switching to the other direction; it is not allowed to change the direction of operation directly, or to adjust the speed or apply braking suddenly. 10. Before the hook is lifted, or before the crane trolley or traveling mechanism reaches the limit device, it should slow down and come to a stop at an appropriate distance from the limit device (at least 1 m for the hook, and at least 2 m for the traveling wheels). It is strictly prohibited to use limit devices as control switches to stop operation. 11. When lifting heavy objects, free falling is strictly prohibited. When the heavy object is to be placed in position, a positioning mechanism can be used or brakes can be employed to lower it slowly. 12. When lifting a heavy object for horizontal movement, it should be at least 0.5 m above the obstacles it crosses. During operation, in the event of a power outage or voltage drop, the controller should be immediately switched to position 0 and the power supply disconnected. If there is a heavy object hanging from the hook, the brake should be used repeatedly with slight adjustments to allow the object to descend slowly to a safe location. 13. After the work is completed, the boom of the tower crane should be turned in the direction of the wind; the swing brake should be released, the trolley and counterweight should be set to a non-operational state, and the hook should be raised to a height of 2–3 meters above the top of the boom. 14. When shutting down, set each controller back to position 0, turn off the switches one by one, close the doors and windows of the control room. After leaving the machine, turn off the power switch and activate the high-altitude indicator light. 15. When maintenance personnel climb to high areas such as the tower body, boom, and counterweight arm for inspection or repair, they must wear safety belts. http://img.civilcn.com/d/file/zhishi/gcgl/2020-04-15/7150947b42ec8cf76df26f630d7e061d.jpg02 Precautions for installing the attachment device on tower cranes 1. Preparation and inspection before anchoring the attachment device (1) Inspect the attachment frame, attachment rods, and attachment supports to ensure there is no deformation, welding defects, or cracks; the length of the attachment rods should meet the requirements, and fasteners such as bolts, pins, and shims should be present in sufficient quantity. (2) Test the strength of the concrete at the attachment points on the building (the concrete poured for the frame beams with embedded anchorages must reach the specified strength before they can be used). Check whether the structural dimensions of the attachment points meet the installation requirements. The design drawings of the concrete structures at the attachment points shall be kept for future reference. 2. Key operation points: (1) Use a theodolite to adjust the axis of the tower body, so that the crane is in a balanced state with the axis of the tower body as the center, and ensure that the boom is in a position perpendicular to the direction of attachment. (2) The steel sections such as angle steel or channel steel at the four corners of the truss on the outside of the adjustment screw shall be welded securely. (3) Remove all residual concrete from the surface of the embedded steel plate and bolts, and weld them firmly to the attached members. (4) After the attachment members have been anchored, lift the standard section to the predetermined lifting height, tighten the bolts, and secure the standard section in place. 3. Key inspections after the attachment anchoring is completed: (1) Whether the installation position of the attachment frame in the standard section complies with the original manufacturer’s technical specifications. (2) Check whether the attachment frame and standard sections are firmly fixed relative to each other; there should be no looseness between the frame and the standard sections. The bolts at each fixing point must be securely tightened, the pins must not be loose, and fasteners such as shims and wedges must be complete and reliable, in compliance with the technical specifications. (3) The arrangement pattern, horizontal angle, and vertical angle of the attachment rod shall meet the original manufacturer’s technical requirements. (4) The connections between various sections of the attachment rod, as well as between the attachment rod and the attachment supports via the attachment frame, are firm and reliable, in compliance with technical specifications. (5) The wall structure at the attachment point of the building should be firmly connected to the attachment support, with fasteners such as bolts and pins being securely tightened. (6) After anchoring is completed and the structure is lifted to the predetermined lifting height, it should be checked that the free height from the anchoring point to the lifting hinge meets the original manufacturer’s technical specifications. The combination of standard sections complies with technical specifications. (7) For the inspection of the tower shaft axis below the highest anchoring point, the verticality deviation shall be 4‰ at the free height, and 2‰ after installation against the wall. 4. Technical requirements and precautions: (1) Since the wall-attached rod can only withstand tension and compression, but not bending, its length should be adjustable; generally, 200 mm is a suitable value. (2) The attachment frame is installed at the horizontal web in the middle of the tower body, with an upward or downward offset of no more than 200~300 mm; an internal support rod is installed inside the topmost attachment frame. (3) When installing and removing the attachment rods, the tower crane must be in a balanced state with its tower axis as the center. After installation, a theodolite should be used to measure the verticality of the tower; below the highest anchoring point, the allowable deviation in verticality is 2‰. (4) When installing each attachment rod, the tower body must not be arbitrarily raised. It is necessary to ensure that, prior to attachment, the free height of the crane complies with the specifications stated in the operating manual. When removing the tower body, the anchoring devices should be removed simultaneously as the tower body is lowered; removal must take place as the tower body descends. When removing the attachment rods, the tower body must first be lowered so that the free height of the tower crane after the removal of those attachment rods meets the specifications outlined in the user manual. (5) The connections between the attachment struts and the attachment frame as well as the connection supports, as well as the connection between the attachment frame and the top rod of the tower, must be reliable. For tower cranes in the attached state, one section out of every three intermediate sections should be relaxed from the tower body to reduce the additional load on it. After operation, it is necessary to regularly check for any looseness and make adjustments promptly. 5. Safety measures: (1) Installation work must be carried out in accordance with specified procedures, with wind speeds not exceeding 60 km/h. (2) During installation, the staff must wear safety belts and helmets. (3) All kinds of limit protection and safety devices must be properly installed and tested. (4) All operations are prohibited until the attachment anchoring work is completed. 03 Key points for safety inspections at construction sites 1. Foundation inspection: The foundation of a tower crane is an important factor related to the safety of such cranes. During the inspection, the first thing to check is whether the bearing capacity of the tower crane foundation meets the design requirements specified by the manufacturer. Currently, the required bearing capacity of the foundation for most tower cranes on the ground is generally 200–300 kPa; it is necessary to check the geological survey report to determine whether this requirement is met. For those whose actual load-bearing capacity does not meet the design requirements, check whether corresponding measures such as piling or reinforcement of the tower crane foundation have been taken. For the following foundation treatment methods for tower cranes, special attention should be paid to the following inspection points during inspections. (1) Foundation settlement pattern. The foundation settlement type refers to the situation where the bottom surface of the tower crane foundation is below ±0.000, located at the elevation of the bottom of the basement excavation. For this type of tower crane foundation treatment, attention should be paid to drainage at the foundation area to prevent water accumulation. (2) When the foundation is placed on a slope, pile driving is required for such a foundation. In addition to the requirements mentioned above, the lateral pressure generated by the slope must also be taken into full consideration. During inspections, it should be required that the construction party take measures to counteract this lateral pressure when excavating the slope, such as using soil nailing or anchor rods for protection. (3) For embedded components, it is recommended to use embedded bases or fixing legs. When high-strength bolts are used, the materials must be supplied by the manufacturer, who shall provide a test report. The construction party must submit this report to the supervision party for approval before the components can be embedded, and relevant records of hidden work inspection must be kept. (4) No soil layer should be placed over the foundation of the tower crane; this not only increases the bearing capacity of the foundation, but also makes it difficult to inspect the welds on the base. 2. Metal structure connections (1) Tower body bolt connections. Regarding the connection of metal structures, the **Regulations on Inspection and Supervision of Lifting Machinery issued by the General Administration of Quality Supervision, Inspection and Quarantine stipulate that: bolt connections must not be loose, and there should be no defects such as missing parts or damage; high-strength bolts must have an adequate pre-tightening torque.** The inspection method specified is to use a torque wrench to check the condition of the high-strength bolt connections. The preload torque is very important in the high-strength bolt connections of towers. Due to the torque generated when the tower rotates, if the pre-tightening torque of the high-strength bolt pairs in the tower fails to meet the design requirements, the bolts will be subjected to shear forces. This results in the bolts being subjected to both shear and tensile forces unevenly, making their stress conditions even more complex and hazardous. During the inspection of the bolt preload torque in the standard sections of the tower, an initial inspection using a visual method can be employed; that is, the inspector stands in the middle of the standard section and observes the connection at the main tension members of the tower. If slight gaps are visible at these connections, it indicates that the bolt preload is insufficient ； At the same time, when rotating the tower crane from side to side, if a screeching sound of metal is heard, it indicates that the bolt connections are not tight enough ； Subsequently, carefully inspect using a torque wrench or other methods to improve the inspection efficiency. (2) Boom pin connection. When checking the connection condition of the boom pin, attention should be paid to the fixing condition of the shaft end shims and the split pins of the pin. 3. Safe distance between tower cranes and power transmission lines sowie multi-tower operations (1) In urban construction, there are many construction sites where tower cranes come into contact with overhead power transmission lines; **standards and inspection regulations require that the safe distance between any part of the crane and the power lines must meet certain specified requirements. During inspections, if it is found that the load being lifted by the tower crane or the steel cables might enter the dangerous area surrounding the power transmission lines, appropriate action shall be taken. Protective requirements should be stipulated, demanding that the contractor erect protective barriers and establish safety protection measures and systems. During normal operation, a protective barrier ensures that the load lifted by the tower crane and its steel cables do not enter the dangerous area around the power lines. In non-operational conditions where wind speed exceeds 20 m/s, operations must be halted, and the hook should be placed at the base of the boom to prevent the hook and steel wire rope from entering hazardous areas near power transmission lines when subjected to wind-induced rotation. (2) For multi-tower operations, during inspection it should be required that the construction unit prepare a plan for such operations; this plan must be approved by the technical supervisor of the construction unit and the chief supervision engineer before work can proceed. It is absolutely not allowed for the safety distance between the boom of a lower tower and the standard sections of a higher tower to be insufficient ； When such a situation occurs, the testing unit should immediately report it to the higher-level administrative authorities for handling. 4. In the case of an electromagnetic clutch in the lifting mechanism reducer of a tower crane, special attention should be paid to the contact condition between the electromagnetic clutch and the brushes. At the same time, it is also necessary to check the operation of the electromagnetic clutch undercurrent relay to ensure its reliable functioning. In the past, accidents have occurred due to excessive wear of the electromagnetic clutch brushes and the failure of the undercurrent relay, which resulted in the loss of power to the clutch and consequently the drop of the lifted load; this should be taken into consideration during inspections. 5. Inspection of safety protection devices: (1) The lifting torque limiter is a crucial safety device for tower cranes. Lifting torque is an essential parameter, and operating beyond the allowable torque level is extremely dangerous; it can lead to machine damage and loss of life. After passing the inspection, it is worth considering whether a sealing method similar to those used by power supply companies for electricity meters should be employed, along with photographic evidence as proof – this is a topic worthy of discussion among professionals ； It is absolutely not allowed for anyone to adjust the torque limit after the tower crane has passed the inspection. (2) The lifting capacity limiter is also a very important safety device. Its function is, first, to protect the motor from excessive overload, and second, to send a signal to promptly change the number of poles of the motor, thereby preventing lifting heavy loads at high speeds and avoiding accidents such as reverse rotation of the lifting mechanism. 6. Safety issues for inspectors when checking the boom of a tower crane: When inspectors examine the boom of a tower crane, the crane is in operation mode and its zero-position protection is active. Moreover, communication between the inspectors and the crane operator usually takes place verbally, over a considerable distance; as a result, the operator may not hear clearly, and instinctive movements could cause the inspector’s body to touch the control levers, leading to unintended operations of the crane. 7. Regular inspection of tower cranes attached to walls: (1) The installation height of the wall-attachment device shall not exceed the range specified in the manual. (2) There are records of the verticality test. A re-inspection should be conducted before acceptance. Currently, there are issues with the proper installation of the wall-attachment frames, wall-attachment members, and embedded components in tower cranes; some leasing companies even use bolts from standard sections as pivot shafts for these components. In many cases, the distance between the tower crane and the building exceeds the values specified in the manual. In such situations, it is essential that the installation company include detailed calculation data regarding these wall-attachment members and embedded components in their installation plan. During inspections, special attention should be paid to the stiffness of these wall-attachment members and their angle of attachment. Under the rated load of the tower crane and under the most adverse operating conditions, these members should show no signs of twisting or deformation, with the angle not exceeding ±8°.