1 Introduction
On the one hand, the extensive use of hoisting machinery improves labor productivity and reduces labor intensity; On the other hand, due to the carelessness of relevant personnel during the installation and use of hoisting machinery, the problem of nonstandard installation of hoisting machinery often occurs, which leads to various safety hazards and even directly leads to safety accidents of construction hoisting machinery, seriously threatening people's lives and property. In this paper, the relevant standards of tower crane are quoted, and the correct treatment methods are put forward in combination with the safety hazards found in daily inspection, so as to better eliminate the safety hazards and ensure safe and efficient production. 2 Analysis and treatment of existing problems of tower crane (due to the limited space of the article, only some key parts are extracted for analysis)
2. 1 Main load-bearing structural members
(1) There are some phenomena: the transverse web of the boom is missing and the web of the boom is cracked; (2) Setting requirements: ① There should be no visible cracks in the main load-bearing structural parts of the tower crane and their welds, and there should be no overall or local plastic deformation in the structural parts; (2) The parent metal of the structural member should not be seriously corroded or worn; (3) Treatment measures: ① Conduct a comprehensive inspection and maintenance of the equipment before installation; (2) Replace defective structural parts. If it is inconvenient to replace, the manufacturer needs to arrange technicians to repair them before using them.
2.2 Climbing system
(1) There are some phenomena: the pin shaft of the jacking guide wheel is unreliable, and the jacking step is deformed and cracked;
(2) Setting requirements: ① There should be no deformation, visible cracks and other defects in the jacking support beam, climbing claw and climbing support seat; (2) The guide rollers of jack-up jacket shall be complete and the safe position shall be correct and reliable; (3) Treatment measures: ① Conduct a comprehensive inspection and maintain the equipment before installation; (2) For the existing problems, arrange technicians to make rectification before use, and those that cannot be rectified need to be replaced before use.
2.3 Working environment
(1) There are some phenomena: the crane arm covers the transformer and high-voltage line, and the protection is not perfect; The safe distance between adjacent tower cranes does not meet the requirements; (2) Setting requirements: ① The distance between any part of the tower crane and the overhead transmission line should comply with the provisions in the table, otherwise effective safety protection measures must be taken; (2) the distance between the tail of tower crane and surrounding buildings and peripheral construction facilities is ≥0. 6m； In the non-working state, the rotating part of the tower crane should be able to rotate freely 360; (3) The horizontal distance between the boom end of the low-level tower crane and the tower body of the high-level tower crane and another tower crane is ≥2m, and the vertical distance between the lowest position of the high-level tower crane and the highest position component of the low-level tower crane is ≥ 2m; (3) Treatment measures: ① Protective measures for covering transformers and high-voltage lines within the projection range of the boom: a. Increase the power standby power supply to prevent the power tower crane from unloading and completing the hook-up action in case of sudden power failure. B. Increase the standby power supply of the rotary brake to prevent the rotary brake from locking quickly in case of sudden power failure. C. Set the rotary limit and amplitude limit according to the actual situation, and try to avoid the lifting trolley from crossing the high-voltage line and transformer. D according to the on-site protection, formulate a perfect special protection scheme for transformers and high-voltage lines. (2) When the safe distance between the tower crane and obstacles does not meet the requirements, the following measures can be taken according to the actual situation of the construction site: a. First, we can consider making a tower crane with a wall, so that the tower crane can be higher than the surrounding buildings and its construction equipment, so that it can rotate freely. B. If the tower crane has reached the specified maximum suspension height, consider lowering the boom.
2.4 Foundation
(1) There are some problems: the foundation is fixed by transition joint, the tower crane foundation is irregular, the anchor bolt connection is unreliable, and the excavation around the foundation pile cap is not backfilled; (2) Setting requirements: ① The user should design and manufacture the concrete foundation according to the load parameters provided by the original tower crane manufacturer, and the concrete foundation should be designed by professional engineers and form a complete scheme; ② If the concrete foundation recommended by the original manufacturer of tower crane is adopted, the fixed legs, embedded joints and anchor bolts shall be used in the manner specified by the original manufacturer; (3) The actual production of concrete foundation shall comply with the provisions of the scheme or instruction manual. Tower crane foundation should be smooth, and drainage measures; (3) Treatment measures: ① Remove the accumulated water in the foundation, remove the silt, tighten the anchor bolt with a wrench, and check and maintain it regularly; (2) The tower crane foundation shall be flat, and the foundation shall not be leveled with steel bars, but filled with steel bars; (3) The anchor bolt shall be tightened with a wrench and accurately embedded according to the manufacturer's instruction manual. It is forbidden to knock the anchor bolt with a sledgehammer; ④ The anchor bolts shall be used according to the method specified by the original manufacturer. When the installed model is inconsistent with the corresponding model of the embedded anchor bolt, the opinions of the tower crane installation manufacturer shall be sought; ⑤ Make the corresponding basic conversion section, and the conversion section should have the corresponding calculation scheme and manufacturer's qualification certificate; ⑥ Try to avoid excavation around the cap of tower crane foundation, so as to prevent potential safety hazards caused by insufficient strength of cap after excavation. After excavation, the pile caps should be backfilled as soon as possible, and the tower crane can be used only after reinforcement.
2.5 Installation and connection of structural members
2.5. 1 Bolted connection of main structural members
(1) There are some phenomena: the lock nut of standard section bolt is not tightened, and the connecting bolt of standard section is replaced by pin shaft; (2) Setting requirements: ① High-strength bolts should be used in the bolt connection parts of the main stressed structural parts, and the high-strength bolts should have performance grade marks, and their models, specifications and quantities should meet the requirements of the operating instructions of the tower crane, and there should be no defects such as parts and cracks; ② When connecting high-strength bolts, tighten them with a torque wrench or a special wrench according to the assembly technical requirements, and the exposed part of the thread should be 2 ~ 3 buttons; (3) Treatment measures: ① Before installation, check whether the standard section high-strength bolts have performance grade marks, and the model, specification and quantity should meet the requirements of the tower crane operation manual. For bolts without performance grade marks, bolts with serious corrosion should be replaced in time; (2) When connecting high-strength bolts, tighten them as required. The exposed part of the thread should be 2 ~ 3 threads, and anti-loosening measures should be taken. Bolts with insufficient length should be replaced in time.
2.5.2 Pin connection
(1) Setting requirements: ① When the structural members are connected by pins, their specifications and quantity shall meet the requirements of the instruction manual or design scheme; (2) the pin shaft should be free of defects such as parts, visible cracks and serious wear, and its axial positioning device should be standardized and reliable; (2) Treatment measures: ① When structural members are connected by pins, the axial positioning pressure plate should be standardized and reliable, and the pressure plate bolts should be complete; (2) When the structural members are connected by pins, the specifications and quantity shall comply with the specifications; (3) The pin shaft and its axial positioning vertical pin should be installed in place, and the cotter pin should be standardized and reliable.
2.5.3 Component replacement
(1) Installation requirements: ① Only with the formal written permission of the manufacturer can the structural components of different types of tower cranes be replaced; (2) It is forbidden to replace tower crane structural members from different manufacturers; (2) Treatment measures: ① The manufacturer shall issue relevant certification documents for the replacement of standard sections of different types of tower cranes; ② The replacement of standard sections of tower cranes from different manufacturers needs to be dismantled and replaced with the original standard sections.
2.6 connecting device
(1) There are some problems: the length of the connecting bolt of the attachment frame is insufficient, the attachment device does not conform to the specification, and the height of the cantilever end exceeds the specification: ① When the tower crane needs to be attached for use, a scheme must be made according to the actual situation on site and the requirements of the reference specification, and the attachment shall be carried out according to the scheme. The attachment scheme shall include the following contents: a. Attachment distance; B. the attachment distance of each track; C. arrangement of connecting rod system; D. the connection form with the building; E the height of the tower is higher than the cantilever height of the highest attachment point; F. Check the bearing capacity of ancillary structures and accessories; G. Details of accessories, fittings and embedded parts; Other special requirements. (2) The attachment frame and attachment rod installed on the tower crane shall have the manufacturing certificate of the original manufacturer. Under special circumstances, if it is necessary to manufacture separately, there shall be a manufacturing certificate issued by a professional manufacturer, and its qualification level shall not be lower than that of the original manufacturer. (3) The installation and connection between the attachment device and the tower section and accessories must be safe and reliable. All connectors such as bolts and pins must be complete, and there must be no missing parts or looseness. The accessories connected with the attachment rod must not be cracked or damaged. Expansion bolts should not be used to connect connecting rods and accessories. (4) The attachment rod and the attachment are not suitable for welding connection. When welding connection is adopted, the following information must be provided: a. welder qualification certificate; B. welding process requirements; C. weld size requirements; D. weld appearance quality and nondestructive testing results.
(2) Treatment measures: ① Make a plan according to the actual situation on site and the requirements of the reference manual, and attach it according to the plan; (2) If the length and layout of the attachment rod system are inconsistent with the specifications, the manufacturer's calculation sheet and factory certificate shall be provided; ③ The attachment frame and attachment rod installed on the tower crane shall be manufactured by the original manufacturer. Under special circumstances, if it is necessary to manufacture separately, there shall be a manufacturing certificate issued by a professional manufacturer, and its qualification level shall not be lower than that of the original manufacturer; (4) The installation and connection between the attachment device and the tower section and accessories must be safe and reliable, and all connectors such as bolts and pin shafts must be complete, without missing parts or looseness, and the attachment rod and accessories shall not be connected with expansion bolts; ⑤ The attachment rod and the attachment are not suitable for welding connection. When welding connection is adopted, relevant technical data shall be provided.
3 Conclusion
As a major hazard source of safety accidents, tower crane can not be ignored in the process of installation and use. Installation units, leasing units, users and other parties should work together, pay enough attention to it, strictly formulate on-site management systems and conscientiously implement them, so as to minimize and avoid the occurrence of safety accidents of construction hoisting machinery, thus ensuring the safety of people's lives and property and ensuring safe production.
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