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With the gradual development of construction projects towards tall and short construction period, the demolition of tower cranes in construction is becoming more and more frequent, and the assembly and disassembly has become a very important work link. Based on ten years of work experience, the author discusses several issues that should be paid attention to in tower crane demolition with colleagues in order to improve.

1 Selection of installation site

On the premise that the tower crane type has been selected, the following items should be taken into account in the selection of the installation site: ① one installation can complete the overall project construction and avoid secondary displacement; ② avoid dead corners on the construction plane; ③ convenient selection and installation of fixed attachment points; ④ convenient disassembly and transportation of tower crane after construction; ⑤ avoid its sub-buildings and high-voltage power grid in the construction space; ⑥ Help to install other equipment and lift building components according to construction needs.

2 Organization of personnel

Tower crane assembly and disassembly is an important, dangerous and tense three-dimensional operation project, which must be attached great importance to ideologically and fully guaranteed from the organization. In addition to the necessary construction management and professional and technical personnel, all construction workers shall receive professional education, have the corresponding type of work safety knowledge, operation skills, and work with certificates. The tower crane assembly and disassembly construction shall be carried out by professional construction team.

3 Demolition of construction equipment and equipment preparation

3.1 should pay attention to the problem

Tower crane migration generally involves disassembly, transportation, installation and other links, the equipment and tools must be carefully organized, not only to ensure safety, but also to improve efficiency and economic benefits. Attention should be paid to: ① All lifting and installation equipment should avoid overuse and overload capacity; ② The transportation equipment should be arranged according to the quality and external dimensions of each component of the tower crane, and try to avoid over-length, over-height, over-width and over-weight transportation. ③ Try to adopt the construction method of disassembly, loading and transportation and installation to avoid secondary transportation or occupation of unwanted construction sites; ④ The site shall be equipped with workers or ambulances, and the high-altitude operation shall also be equipped with necessary communication tools to facilitate safe operation and normal construction.

Selection of 3.2 lifting and sling

Tower crane assembly and disassembly construction should generally be equipped with white hemp rope or nylon rope, various specifications of wire rope sleeve, steel cable, a certain number of 8# wire and special tools. These appliances have sufficient allowable tensile force and safety factor, and different performance slings and rigging must be used and discarded according to corresponding standards.

Inventory and preparation of 3.3 equipment parts

In order to ensure the construction progress, the management, inspection and maintenance of the above components should be strengthened. Special small parts and spare parts for equipment; Special and universal bolts, mother and pad; Connection pins and shafts of various specifications and quantities; Special tools for equipment assembly and disassembly; Finishing tools for damage and deformation of some structural parts; Wire rope clamp, rope ring, etc.

4 Tower crane foundation

Tower crane installation must ensure that there is a correct, intact foundation, tower crane foundation for the fixed base type and track walking type two, should pay attention to the following issues.

1) The ground bearing capacity of the foundation is the foundation of the foundation, and necessary measures should be taken to ensure that the ground bearing capacity is 10-20t/m2. Can be used 3:7 lime soil compaction or compaction and other methods of construction. Do not directly use backfill soil and garbage as a base or track without treatment.

2) The fixed base shall be constructed according to the design requirements, and the dimensions of each part, especially the embedded bolts, must be guaranteed to meet the requirements of the dimensions between the foundation center and the building, so as to facilitate the construction and attachment installation.

3) The rail-type foundation shall be constructed according to the design requirements to ensure the technical requirements such as gravel thickness, roadbed width, sleeper spacing, rail type, rail joint, connecting rod, vehicle stop, grounding, etc.

4) There shall be no hidden ditch, air-raid shelter, etc. under the tower crane foundation, and necessary drainage facilities shall be provided.

5) The tower crane shall be installed on the ground, and the distance from the tower crane to the edge of the foundation pit shall be guaranteed during the construction of underground works.

5 Installation and disassembly of tower crane

Preparation before 5.1 assembly and disassembly

The assembly and disassembly of tower crane is the central link of construction, which is very dangerous. Full preparation must be made before construction: ① Technicians should make construction plan or construction organization design according to the installation and operation instructions and the specific characteristics of construction, and have the contents of safety technical disclosure. The construction plan must reach all construction personnel before the operation, and avoid going through the motions; ② The construction plan should make detailed calculations and discussions on the assembly and disassembly methods of key and difficult parts, have clear construction methods, and select correct equipment, slings, lifting points, binding methods, etc.

5.2 assembly and disassembly operation

The flag worker process must be unified thinking, unified command, according to the relevant safe use of operating procedures for construction. Attention should be paid to: ① The legs of lifting equipment for construction should be laid on a solid ground with necessary boards or square wood; ② Oblique hanging, side hanging and lifting shall select appropriate lifting point positions and auxiliary traction measures; ③ Safety protection shall be provided for aerial work above 2m. The operation shall be stopped in rainy days and when the wind force is greater than level 5. The tower crane must be installed in a safe state in case of wind and rain during construction; ④ During lifting operation, the crane boom shall never be turned and shall be protected by special personnel. ⑤ Assembly and disassembly must be carried out in strict accordance with the sequence required by the construction plan. No counterweight shall be added at the front of the crane boom installation, and no heavy objects shall be lifted without counterweight. When disassembling, the counterweight should be removed first and then the boom should be removed. ⑥ Check whether the connecting parts of the tower crane are complete, reliable and effective, and whether the lifting and rigging are safe.

Selection of 5.3 lifting point

The selection of lifting points and the method of assembly and disassembly in the construction of tower crane are important links to ensure the safety of construction, and several problems should be paid attention.

① The lifting point of each component should use fixed position or special lifting point as far as possible, and can be designed and configured by oneself if necessary. Reasonable inclination angle shall be ensured during side and oblique hoisting. When there is an inner jacket structure, the lifting point shall be selected on the inner jacket structure to avoid internal and external separation, such as the tower tip of TQ60/80 tower crane. ② lifting arm and balance arm and other components should be as far as possible to ensure that the level and direction, the longer lifting arm installation as far as possible the length of the non-horizontal lifting method, that is, the arrangement of the arm of the articulated end is higher than the end of the arm, articulated and then the lifting arm is installed to the horizontal position, such as FO/23B tower crane 50m boom. ③ Tower crane boom for the front and rear parts of the hinged into a whole, the lifting point should be selected as far as possible to make the arm level, temporary connection rope stress smaller position. ④ Disassembly is the reverse operation of installation, which is more dangerous. It should be operated in strict accordance with the respective order in the assembly and disassembly instructions of the construction plan, and the order must not be reversed. ⑤ Try not to use hooks and ropes to lift heavy objects.

6 Inspection and commissioning of tower crane

Inspection and debugging is the last process of tower crane installation and construction, and it is also the last pass before the tower surface is used. Therefore, inspection and debugging are also a very important work. Attention should be paid to: ① the inspection of all parts of the whole machine must be complete and detailed, and problems found should be solved in time; ② maintenance of all parts should be done at the same time during inspection and debugging; ③ all working institutions of the tower crane should operate normally, and all safety protection devices should be complete and effective; ④ the inspection and debugging of the whole machine should be recorded for the acceptance of the tower crane.

7 Development of management system

The installation and disassembly of tower crane is a systematic and strong management construction project. According to years of experience and lessons learned, our unit has formulated a set of relatively systematic and fast management measures, which are fully guaranteed in terms of organization and system. More detailed regulations are formulated for each link of management construction, such as tower crane foundation acceptance regulations and technical files, installation and disassembly task book, installation and disassembly safety technical disclosure, track acceptance records, assembly and disassembly construction records, assembly and disassembly inspection records, parts inventory records, use safety technical disclosure, etc. Practice has proved effective.