L46A1 Mast SectionSpecial attention should be paid to the key points in the safety inspection of tower crane
For the foundation treatment form of tower crane, special attention shall be paid to the following inspection points during the inspection: the foundation sinking form refers to the form that the bottom surface of tower crane foundation is lower than ± 0.00 elevation and placed at the bottom elevation of basement foundation pit. For this type of tower crane foundation treatment, attention should be paid to the drainage of the tower crane foundation to avoid water accumulation. Last year, there was a tower crane collapse accident in Xiamen due to the accumulated water in the foundation joint of the tower crane, which affected the inspection of drivers and inspectors, but failed to find the cracks in the base weld of the foundation joint in time, coupled with the serious fatigue damage of the steel at the weld joint. The foundation is placed on the side slope, which must be pile driven. In addition to the above requirements, the side pressure generated by the side slope shall be fully considered. During the inspection, the construction company shall be required to take anti side pressure measures when excavating the side slope, such as soil nail protection or anchor bolt treatment. During the inspection return visit of our door, the construction company has not considered the side pressure of the side slope for too many reasons Pressure, earth excavation, tower crane foundation caused by serious cases of displacement, to the construction unit brings not small economic losses;
For the embedded parts, it is recommended to use the embedded base or fixed leg. For the embedded high-strength bolt, the material shall be provided by the original factory, the manufacturer shall provide the test report, and the construction unit shall report to the supervision unit for approval before embedding, and make the relevant concealed acceptance records. A tower crane collapse accident happened in Xiamen at the beginning of this year, which was caused by the high-strength bolts embedded in the rental unit not meeting the requirements, the nuts and bolts were confused with metric system and English system. When the tower crane was installed to the first section of the crane, the tower crane toppled over; the foundation of the tower crane could not be covered with soil layer, which increased the bearing capacity of the foundation and was not conducive to the observation of the base Welds: last year, there was a tower crane with foundation covered with soil in Xiamen. Fortunately, the driver was quite experienced. When he felt that the tower crane made a strange noise, he immediately checked all the bolts of the standard section. No problem was found, and then the soil was removed. As a result, it was found that the welds of the substructure steel structure were cracked. After timely treatment, no major consequences were caused. For the connection of metal structure, it is clearly required in the supervision and inspection regulations for cranes that the bolt connection shall not be loose, and there shall be no defects such as missing parts and damage. The high-strength bolt shall have enough pre tightening torque. The inspection method is to check the connection condition of high-strength bolt with torque wrench. The pre tightening moment is very important in height strength bolt connection of tower. Due to the torque generated during the rotation of the tower body, if the pre tightening torque of the height strength bolt pair of the tower fails to meet the design requirements, the bolt will be subject to shear force, resulting in the bolt being sheared, tensioned at the same time and uneven stress, making the stress condition of the bolt more complex and dangerous.
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In the inspection, the pre tightening torque of the standard section bolt of the tower crane can be inspected by the visual method first, that is, the inspector is in the middle of the standard section of the tower body to observe the connection of the standard section at the main chord of the tower body under tension. If there is a small gap at the connection of the standard section, it indicates that the pre tightening force of the bolt is not enough; at the same time, let the tower crane rotate left and right, if you can hear the metal squeaking, it also indicates that the bolt connection After that, use torque wrench or other methods to check carefully, so as to improve the inspection efficiency. During the inspection of pin shaft connection of boom, attention shall be paid to the fixation of shaft end stop and pin shaft cotter pin. When the tower crane has been used for many years, the pin block is easy to wear or fall off, which may cause the pin to move and fall off, resulting in the accident of arm folding. In Xiamen last year, there was a broken arm accident caused by the inward falling of the boom pin. Special attention should be paid to the condition of the pin block during the inspection.
The safe distance between tower crane and transmission line and the construction site where tower crane and overhead transmission line negotiate in urban construction are many. Because of the collision between tower crane and steel wire rope entering the dangerous area of overhead transmission line and transmission line, the accidents of short circuit of transmission line, broken steel wire rope and falling of crane have occurred in many other areas. The national standards and inspection regulations have the requirements that the safety distance between any part of the crane and the transmission line must meet a certain safety distance. During the inspection, it is found that tower crane and steel wire rope may enter the dangerous area of the transmission line. It is required to put forward protection requirements, require the construction party to set up protective barriers, and establish safety protection measures and systems. During the normal operation of the tower crane, the protective barrier shall ensure that the crane and steel wire rope cannot enter the dangerous area of the transmission line. When the wind force is greater than 20 m / s, the crane shall stop working, and the hook shall be placed at the root end of the boom to avoid the hook and steel wire rope entering the dangerous area of the transmission line when rotating with the wind
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