L48A1 Mast Section Common Problems, Hazards and Corresponding Solutions of Tower Suspension
In construction, the common problems, hazards and corresponding solutions of Tower hoisting. I tower crane manufacturers, in the construction of the use of Tower hanging safety problems and may cause problems, put forward solutions to the construction of safety management can start a positive role.
1, tower hanging foundation
Common disease: the foundation water is serious.
Caused problems: due to the strong corrosiveness of wastewater on the construction site, the foundation of the tower crane, the foot bolt, the material of the base section or the cross beam and the weld erosion are strong, long-term water accumulation, is bound to affect the safety of the tower crane. At the same time, the water is not conducive to the daily monitoring of the pre-tightening force of the bolt, base joint and cross beam connecting bolts.
Solution: the foundation of the tower crane should be equipped with drains and water wells, while ensuring smooth drainage or timely extraction.
2, the pre-tightening force of the standard joint connection bolt
Common disease: standard joint bolt loosening or pretightening force does not meet the requirements.
Causes problems: The transmission of Tower lifting force is mainly transmitted by the main string rod. The transfer of the main strut force depends on the pre-tightening force of the high-strength connecting bolt. The pretightening force can not meet the requirements and can only be borne by the connection bolts. The result is that the tower crane not only bears the pull force but also bears the shear force during the use process. The shear resistance of high-strength connecting bolts is poor, which may cause the connection bolts to break and cause an inverted tower accident.
Solution: Use a dedicated torque wrench to tighten the bolt so that the pretightening force meets the requirements(such as 368kN for the bolt of the M30, 1800N • M for the pretightening moment). Daily check work, found loose timely tighten. Here's a reminder: high strength connection bolt pairs are disassembled and re-used, usually not more than twice. And the bolt should be maintained and inspected, and if necessary to carry out inspection, after passing the test can be used.
3, the opening pin setting of the pin
Common disease: the setting of the opening pin is not standardized mainly:(1) the opening pin is small,(2) the opening pin is not open or the opening degree is not enough,(3) the opening pin is replaced by wire or electric welding rod, and(4) the opening pin rust is serious.
The problem arises: Since the strength of the opening pin or the strength of the substitute does not meet the requirements, the opening pin will often be cut under the axial force of the pin shaft. The opening pin without opening or not enough opening is easy to fall during use, and the pin without opening pin will detach itself during use, which will cause a major accident of folding arm. For example, the QTZ80 tower boom used at a Jiayuan site.
Solution: The opening pin should be set up strictly in accordance with the requirements of the manual to be equipped and installed, can not be replaced with a smaller size of the opening pin, wire or welding rod, and before installation, also check the unopened opening pin corrosion degree and opening degree, So as not to increase the difficulty and safety risk of replacement after installation. After installation, the opening pin requires that both sides should open and reach 90 °.
4, safety limit device
General disease:(1) safety limiting device does not work,(2) safety limiting device is not sensitive,(3) artificial short connection or removal.
The question arises: Although there was no problem at the time, the safety limit device did not work and buried a major safety hazard. The long-term overloading operation causes the fatigue of the metal structure and shortens the life of the tower crane.
Solution: the qualified tower crane has been tested, and its safety limit device has been basically tested and qualified, and the project department and the operator can not arbitrarily dismantle and adjust. At the same time, daily check the integrity of the limiting device.
Quality of operators
General:(1) The quality of the operator is not high(certified incompetence), and(2) operating without a license.
Lead to question: Because operator quality is not high, sense of responsibility is not strong. The frequent accidents caused by tower lifting operations, several recent inverted towers and broken arms accidents in a city are related to the operator's illegal operations and skills.
Solution: special operators should strictly conduct training in theory and practice, after a special assessment, after the assessment of qualified post. At the same time, we should strengthen the supervision and control of workers. Strictly follow the operating rules and regulations to prevent undocumented employment.
