Tower crane torque limiter, insurance, ladder, wall attachment, electrical, installation acceptance supervision and control points

(I) Moment Limiter 1. Analysis of many tower crane collapse accidents shows that the main reason is overloading. Overloading is caused by either the weight of the heavy object exceeding the specified limit or the horizontal distance of the heavy object exceeding the operating radius. After installing the moment limiter, when the moment exceeds the technical performance of the tower crane due to overweight or excessive operating radius, the power source for lifting or luffing is automatically cut off and an alarm signal is issued to prevent accidents. 2. Currently, there are two types of moment limiters: one is electronic and the other is mechanical. The electronic type can display moment, operating radius, and weight data simultaneously. When approaching the allowable moment of the tower crane, there is an early warning signal. It is easy to use but greatly affected by operating conditions, has poor reliability, is easy to damage, and is inconvenient to repair. The mechanical type has no display device or early warning signal but is reliable in work and more suitable for on-site construction conditions. It has a simple structure and a low damage rate. 3. When a tower crane is reassembled in a different location, changes the lifting ratio, or changes the length of the boom, the moment limiter must be adjusted. The overload alarm point of the electronic type must also be recalibrated by actual test lifting with actual operating radius and actual weight. For tower cranes with trolley luffing, when choosing a mechanical moment limiter, it must be compatible with the tower crane (the same factory model should be selected). 4. For tower cranes with a mechanical moment limiter and a luffing boom, after each luffing operation, the tonnage of the overload limit must be adjusted in time according to the allowable load of the operating radius. 5. During safety inspections, if there is no condition to test the reliability of the moment limiter, the test run records after the installation of the machine can be checked to confirm that the test results of the moment limiter at that time meet the requirements and the comprehensive accuracy of the moment limiter system meets the ±5% requirement. 6. Overload limiter (lifting load limiter). According to regulations, some tower crane models are also equipped with overload limiters. When the load reaches 90% of the rated lifting weight, an alarm signal is issued; when the lifting weight exceeds the rated lifting weight, the power supply in the upward direction should be cut off, and the mechanism can move in the downward direction. During safety inspections, tests should be carried out simultaneously for confirmation. (II) Limiters 1. Upper limit limiter. Also known as the upper lifting limit position limiter. When the tower crane hook rises to the limit position, the power supply for the lifting mechanism is automatically cut off, and the mechanism can move downward. During safety inspections, action tests should be performed for verification. 2. Luffing limiters. Including trolley luffing and boom luffing. Tests should be performed for verification during safety inspections. (1) Trolley luffing. Tower cranes use horizontal booms. The lifting load is suspended on the lifting trolley and luffing is achieved by the trolley moving horizontally on the boom. The trolley luffing limiter uses two travel switches and buffer devices installed at the head and root of the boom to limit the running position of the trolley. (2) Boom luffing. Tower cranes change the working radius (amplitude) by changing the elevation angle of the boom. Through the change of device contacts, the light signal is transmitted to the indicator panel in the driver's cab and indicates the elevation angle. When the elevation angle of the boom reaches the upper and lower limits respectively, the limit switches are pressed to cut off the power supply to prevent instability of the tower crane due to excessive elevation angle. During on-site action verification, experienced personnel should act as guardians and commanders to prevent accidents. 3. Travel limiters. For rail-mounted tower cranes, they prevent derailment accidents during operation. During safety inspections, tower crane travel action tests should be performed to verify the reliability of the limiters by colliding with them. (III) Safety Devices 1. Hook safety device. Mainly prevents rope detachment accidents caused by the hook continuing to descend when the descent of heavy objects is blocked while the tower crane is working. This device is a spring pressure cover installed at the opening of the hook. The pressure cover can only be opened downward and cannot be opened upward to prevent ropes from coming out of the opening. 2. Drum safety device. Mainly prevents accidents such as rope biting when the transmission mechanism fails and the steel wire rope cannot be arranged smoothly on the drum and exceeds the end flange of the drum. 3. Ladder guard ring (1) When the passage height of the ladder is greater than 5m, a guard ring should be set starting from 2m above the platform. The guard ring should be kept intact and there should be no excessive deformation, missing rings, open welding, etc. (2) When the ladder is located inside the structure and the distance between the ladder and the structure is less than 1.2m, a guard ring is not required. (IV) Attached Devices and Rail Clamps 1. The free height of self-climbing towers should be in accordance with the requirements of the manual. When it exceeds the specified limit, it should be attached to the building to ensure the stability of the tower crane. 2. Attached devices (1) When attached to a building, its stress strength must meet the design requirements. (2) When attaching, use a theodolite to check the verticality of the tower body and adjust it. The layout of the struts of each attached device, the mutual spacing, and the vertical distance of the attached device should be in accordance with the manual. (3) When the length and angle of the attached rod need to be changed due to the particularity of the project, the strength, stiffness, and stability of the attached device should be checked and calculated to ensure that it is not lower than the original design safety level. (4) When rail-mounted cranes are used in attached mode, the bearing capacity of the rail foundation must be improved and the power supply of the traveling mechanism must be cut off. 3. Rail clamps. When rail-mounted cranes are used outdoors, windproof rail clamps should be installed. 4. The rail clamp device must ensure the braking effect after being clamped. When the driver leaves for lunch, gets off work, or temporarily stops in the middle and needs to leave the tower crane, the rail clamps of the tower crane must be fully clamped before leaving as required. (V) Installation and Disassembly 1. The installation and disassembly of tower cranes is a complex and dangerous work. Coupled with the many types of tower cranes and different operating environments, and the varying familiarity of installation teams, it is required that before work, a detailed construction plan must be formulated based on the characteristics of the tower crane type, the requirements of the manual, and the operating conditions. This includes: operating procedures, the number and working positions of personnel, the types and working positions of cooperative lifting machinery, the embedding of anchors, the preparation of rigging, and the protection of the on-site operating environment. For the jacking work of self-climbing towers, there must be specific requirements for maintaining the balance of the boom and counterweight boom, as well as the jacking steps and reliable measures to prohibit slewing operations during the jacking process. 2. The installation and disassembly work of tower cranes must be carried out by professional teams with qualification certificates issued by relevant municipal departments. And a special person should be appointed to command. (VI) Tower Crane Command 1. Tower crane drivers are special operation personnel and should undergo formal training and assessment and obtain a qualification certificate. The content of the certificate or training assessment must match the type of crane driven by the driver. 2. The signal commander of tower cranes should undergo formal training and assessment and obtain a qualification certificate. Its signals should comply with the provisions of the national standard GB5052-85 "Lifting and Handling Command Signals". 3. When multiple tower cranes on site interfere with each other, or when the driver of a high tower crane cannot clearly hear the whistle and see the gestures of the signal commander, flag language or walkie-talkies should be used for command in combination with the actual site conditions. (VII) Subgrade and Track 1. The laying of the subgrade and track of tower cranes must be carried out strictly in accordance with the provisions of their manuals. Generally, the bearing capacity of subgrade soil: medium tower (3-15t) is 0.12-0.16MPa; heavy tower (more than 15t) is >0.2MPa. It should be trimmed, leveled, and compacted. Sand and ballast should be laid on it, and there should be drainage measures. 2. The sleeper material can be wood, reinforced concrete, or steel sleepers. Its cross-sectional dimensions are specified according to the manual (such as 16×240, 180×260, etc.). The length of the sleepers should be at least 1200mm longer than the gauge size. When using a combination of one long and two short sleepers, a channel steel tie rod should be added every about 6m to ensure the gauge. The sleeper spacing is 600mm. When using standardized subgrade boxes, they should be inspected and accepted before use to confirm that they meet the requirements. 3. The two sides of the track should be firmly nailed down on each sleeper with track nails (or pressed firmly with pressure plates). There should be no missing or loose nails. The joints of the track should be staggered. The joints should be placed on sleepers. The height difference at both ends should not be greater than 2mm. The joint splints should be matched with the track and all bolts should be fully installed and tightened. 4. The horizontal deviation of the track should not be greater than 1/1000 in the longitudinal and transverse directions. (A level should be used. On two tracks, within a range of 10m, no less than three points should be measured respectively, and the average value should be taken). 5. At 1m from the end of the track, a limit position stopper (stop device) should be set. Its height should be greater than the radius of the traveling wheel to prevent the tower crane from derailing after power failure and sliding. 6. The foundation construction of a fixed tower crane should be carried out according to the design drawings. Its design calculation and construction details should be included in one of the special construction organization design contents of the tower crane. After construction, it should be inspected and accepted and there should be records. (VIII) Electrical Safety 1. The cable of the tower crane is not allowed to walk on the ground. A cable reel with a tensioning device should be installed. As the tower crane moves, the cable reel will automatically wind the cable to prevent the cable from rubbing against sleepers or being entangled by debris on the track and causing accidents. 2. The safety distance between overhead lines on the construction site and tower cranes should comply with the provisions of the temporary power usage code: "For rotary boom cranes, the minimum horizontal distance between any part (including the lifted object) and the edge of the overhead line below 10kV should not be less than 2m." When it is less than this distance, protective frames should be erected as required. For night construction, there should be 36V colored bubbles (or red bulbs). When the crane operation radius passes above the overhead line, there should also be protective measures above the line. 3. When the TT system is adopted on site, the tower crane should be grounded, and its resistance value should not be greater than 4Ω; when the TN system is adopted, in addition to being used for protective zero connection, it should also be grounded repeatedly in accordance with the provisions of the temporary power usage code, and its resistance value should not be greater than 10Ω. 4. The repeated grounding of tower cranes should be set up in two groups at both ends of the track. For longer tracks, a set of grounding devices should be added every 30m. Reinforcing bars or flat irons should be used to make annular electrical connections between the two tracks. The joints of the tracks should be electrically connected by conductors. 5. The protective zero connection and grounding wire of the tower crane must be separated. The power supply line can be sent to the distribution box at the end of the track of the tower crane. The PE line is led out from this box and connected to the repeated grounding wire of the track, that is, the PE line is connected to the equipment casing through the track wheel. (IX) Multi-Tower Operation 1. When two or more tower cranes operate on adjacent tracks or on the same track, the minimum distance between the two machines should be maintained. (1) For mobile tower cranes, the distance between any parts (including lifted objects) should not be less than 5m. The vertical distance between the hook of the tower crane and the low-position tower should not be less than 2m. 2. When construction is restricted by site operating conditions and cannot meet the requirements, two measures should be taken simultaneously. (1) Organizational measures. Specify the operation and walking routes of tower cranes and supervise and implement them by specially appointed guardians. (2) Technical measures. Limit devices should be set up to shorten the boom, raise (lower) the tower body and other measures to prevent tower cranes from exceeding the specified operating range due to misoperation and causing collision accidents. (X) Installation and Acceptance 1. The test run and acceptance of tower cranes are divided into three situations: before leaving the factory, after major overhauls, and after repeated use and installation. Here, it mainly refers to the test run and acceptance after repeated use and installation. It should include the following parts: (1) Technical inspection. Inspect the firmness of the tower crane, the contact condition between the pulley and the steel wire rope, the electrical circuit, safety devices, and the installation accuracy of the tower crane. Under no load conditions, the vertical deviation of the tower body from the ground should not exceed three thousandths. (2) No-load test. Perform action tests on the lifting, slewing, luffing, and traveling mechanisms respectively, and perform combined action tests of lifting, traveling, and slewing. During the test, collide with each limit switch to test its sensitivity. (3) Rated load test. The boom is at the minimum working amplitude, lifts the rated maximum lifting weight, and the heavy object is 20cm off the ground and maintained for ten minutes. The ground distance remains unchanged (at this time, the moment limiter should send out an alarm signal). After the test is qualified, perform lifting, traveling, and slewing action tests and combined action tests at the maximum, minimum, and intermediate working amplitudes. During the above tests, a theodolite should be used to observe the deformation and recovery deformation of the tower crane in two directions, observe whether there are abnormal phenomena such as heating, oil leakage, and paint peeling during the test process, record and measure, and finally confirm that it is qualified and can be put into operation. For the participants and test results of the test run and acceptance, there should be detailed and truthful records, and relevant personnel should sign to confirm that they meet the requirements.