Tower crane safety is very important. With the resumption of construction site, what problems should be paid attention to in tower crane safety inspection? The following on the tower crane safety inspection to say some experience, to explore the key points of the tower crane safety inspection, tower crane safety inspection should pay attention to those problems?
1、 Foundation inspection:
Tower crane foundation is an important part of tower crane safety. In the inspection, attention should be paid to whether the foundation endurance of tower crane meets the design requirements of the manufacturer. At present, the ground endurance requirement of most tower crane foundations is generally 200 ~ 300kPa. Check the geological survey report to see if it meets the requirements. If the actual bearing capacity does not meet the design requirements, check whether the tower crane foundation has been piling, foundation enlargement and other corresponding treatment.
For the following types of tower crane foundation treatment forms, special attention should be paid to the following inspection points:
The form of foundation subsidence refers to 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 form of tower crane foundation treatment, attention should be paid to the drainage of tower crane foundation to avoid ponding. A tower collapse accident occurred in Xiamen last year due to the water accumulation in the foundation section of the tower crane, which affected the inspection of drivers and inspectors, and failed to find the cracks in the base weld seam in time.
If the foundation is placed on the slope, the pile driving treatment must be carried out for this foundation. In addition to the above requirements, the side pressure generated by the slope should be fully considered. During the inspection, the construction unit should be required to take anti lateral pressure measures when excavating the slope, such as taking soil nailing protection or anchor rod treatment. In our inspection and return visit, there are too many reasons for the construction unit not considering the side slope Pressure, earth excavation, causing serious deviation of tower crane foundation, which brings great economic loss to the construction unit;
For the embedded parts, the author thinks that the use of embedded base or fixed legs should be advocated. For the use of embedded high-strength bolts, the materials should be provided by the original factory, the manufacturer should provide the test report, and the construction unit should report to the supervision unit for approval before embedding, and make relevant concealed acceptance records. A tower crane collapse accident occurred in Xiamen at the beginning of this year. It was because the high-strength bolts embedded by the leasing unit did not meet the requirements, and the metric system and English system of nuts and bolts were confused. When the tower crane was installed to the first section of the crane, the tower crane collapsed;
The foundation of the tower crane shall not be covered with soil. On the one hand, it increases the bearing capacity of the foundation; on the other hand, it is not conducive to the observation of the weld joint of the base. Last year, there was a tower crane with the foundation covered with soil in Xiamen. Fortunately, when the driver was more experienced and felt that the tower crane had abnormal noise, he immediately checked all the standard bolts. After that, the soil was removed. As a result, cracks were found in the weld of the steel structure of the base After being dealt with in time, it did not cause serious consequences.
2、 Metal structure connection:
Bolt connection of tower body
For the connection of metal structure, the State Administration of quality supervision and inspection of crane equipment clearly requires: "the bolt connection shall not be loose, there shall be no defects such as missing parts and damage, and the high-strength bolt shall have sufficient pre tightening torque". The inspection method is specified as "check the connection condition of high-strength bolt with torque wrench". The pre tightening torque is very important in the bolt connection of tower height and strength. If the pre tightening torque of the tower height strength bolt pair fails to meet the design requirements, the bolt will be subject to shear force, which will cause the bolt to be sheared and tensioned at the same time, and the force is uneven, which makes the bolt stress state more complex and dangerous. During the inspection, the bolt pre tightening torque of standard section of tower body can be checked by visual method first, that is, the inspector is located in the middle of the standard section of tower body to observe the connection of standard section at the tension main chord of tower body. If there is a small gap at the connection of standard section, it indicates that the bolt pre tightening force is not enough; at the same time, let the tower crane left and right When rotating, if you can hear the metal squeak, it also indicates that the bolt connection is not tight; after that, use the torque wrench or other methods to check carefully to improve the inspection efficiency. The author once encountered a case of bolt cracking in the upper part of tower crane base reinforcement joint due to bolt loosening. Fortunately, no major accident occurred due to the discovery and timely treatment;
When checking the connection condition of boom pin shaft, attention should be paid to the fixing condition of shaft end shield and pin shaft cotter pin. Special attention should be paid to the connection form of the pin shaft of the crane boom. The pin shaft is of equal diameter, and the internal displacement movement of the pin axis is stopped by the pin shaft stop plate. 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 shaft to move off and cause arm folding accident. There was an accident in Xiamen City last year, which was caused by the pin shaft of this kind of crane boom falling inward. Special attention should be paid to the condition of the pin block during the inspection.
3、 Safe distance between tower crane and transmission line:
In urban construction, there are many construction sites where tower crane and overhead transmission line negotiate. As tower crane and steel wire rope enter the dangerous area of overhead transmission line and collide with transmission line, the accidents of short circuit of transmission line, fracture of steel wire rope and falling of lifting objects have occurred in other areas. According to national standards and inspection regulations, the safety distance between any part of crane and transmission line shall meet the requirements of certain safety distance. During the inspection, if it is found that the tower crane objects and wire ropes may enter the dangerous area of the transmission line. Protection requirements should be put forward, requiring the construction party to set up protective barriers and establish safety protection measures and systems. During the normal operation of tower crane, the protective barrier ensures that the lifting objects and steel wire ropes of tower crane can not enter the dangerous area of transmission line. When the wind force is greater than 20m / s, it should stop working and put the hook at the root of the boom to avoid the hook and wire rope from entering the dangerous area of the transmission line when the wind rotates;
4、 Tower group operation:
For multi tower operation, the construction unit shall be reminded to prepare multi tower operation scheme during detection, which shall be submitted to the technical director of the construction unit and the chief supervision engineer for approval before operation. It is not allowed that the safety distance between the large arm of the low tower and the standard section of the high tower is insufficient; in case of such a situation, the detection unit shall immediately report to the higher administrative department for treatment;
5、 In case of electromagnetic clutch in reducer of hoisting mechanism:
When there is an electromagnetic clutch in the reducer of tower crane lifting mechanism, special attention should be paid to the contact condition between the electromagnetic clutch and the brush. At the same time, the working condition of the electromagnetic clutch under current relay should be checked to ensure the reliable operation of the electromagnetic clutch. In the past, due to excessive wear of electromagnetic clutch brush, failure of under current relay and clutch power loss, the lifting objects fall down, which should be paid attention to during inspection.
6、 Detection of safety protection device:
The lifting moment limiter is a vital safety device for tower crane. The lifting torque is a crucial parameter. Over torque lifting is the most dangerous thing. If it is not properly handled, it will lead to machine damage and death. After passing the test, whether the lead sealing form adopted by the power supply bureau for electricity meters can be used, together with photos for evidence collection, is worth discussing. No one is allowed to adjust the torque limit after the tower crane is qualified Bit.
The lifting weight limiter is also a very important safety device. Its function is to protect the motor from overload. On the other hand, it sends a signal to switch the number of poles of the motor in time, so as to avoid heavy load of high-speed gear crane and prevent the reverse sliding accident of the lifting mechanism;
7、 The safety problems of the inspection personnel during the inspection of the boom of the tower crane are as follows:
When the Inspector checks on the boom of the tower crane, the tower crane is in operation and its zero position protection has been turned on. At the same time, the contact between the inspection personnel and the tower crane driver mostly uses oral communication, and the distance is often relatively far Sometimes I can't hear clearly, subconsciously bending action, it's easy for the body to touch the operating lever, causing the car to malfunction. I have had such an example when I detected it. Fortunately, I reacted quickly and did not cause a major accident;
8、 Wire rope inspection:
The wire rope shall not be twisted, flattened, bent, broken strand, broken wire, broken core, cage distortion and other deformation, and the wire rope shall be well lubricated and kept clean.
Finally, the safety of tower crane is very important. The safety inspection of tower crane must be thorough. When the construction is carried out on the construction site, you must be familiar with the environment of the construction site. If the surrounding works are not shut down when the project is shut down, the construction site may change, and the ground lifting objects may encounter freezing and adhesion phenomenon. All of these need to be confirmed to ensure safe production.