L68A1 Mast Section the main problems of tower crane safety inspection
1. Basic inspection
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Tower crane foundation is an important link of tower crane safety. In the inspection, first of all, pay attention to whether the tower crane foundation endurance meets the design requirements of the manufacturer. At present, the requirements for ground endurance of most tower crane foundations are generally 200-300kpa. Check the geological survey report to see if they meet the requirements. If the actual endurance does not meet the design requirements, check whether the tower crane foundation has been pile driving, foundation expansion and other corresponding treatment.
For the following forms of tower crane foundation treatment, special attention shall be paid to the following inspection points:
(1) Foundation sinking form
The form of foundation sinking 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 collapse accident in Xiamen due to the water accumulation in the foundation joint of the tower crane, which affected the inspection of drivers and inspectors and failed to find the cracks in the foundation joint base in time, coupled with the serious fatigue damage of the steel at the weld joint.
(2) Foundation on slope
This foundation must be pile driven. In addition to the above requirements, the side pressure generated by the slope shall be fully considered. During the inspection, the construction unit shall be required to take anti side pressure measures when excavating the slope, such as soil nailing protection or anchor bolt treatment. During the inspection and return visit of our door, too many reasons have occurred that the construction unit did not consider the side pressure of the slope, and during the earthwork excavation The case of serious deviation of tower crane foundation will bring considerable economic loss to the construction unit.
(3) Problems of 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. The collapse of a tower crane in Xiamen at the beginning of this year was caused by the failure of the high-strength bolts embedded in the rental unit, the confusion between the metric system and the English system of nuts and bolts, and the collapse of the tower crane when the first section of the crane was installed.
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(4) The foundation of tower crane shall not be covered with soil layer
The foundation of the tower crane shall not be covered with soil layer, one is to increase the bearing capacity of the foundation, the other is not conducive to the observation of the welding seam 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 bolts of the standard section, found no problem, and then removed the soil. As a result, it was found that the welding seam of the steel structure of the base had cracks After timely handling, no major consequences have been caused.
2. Metal structure connection
(1) Bolt connection of tower body
For the connection of metal structure, the State Administration of quality supervision, inspection and Quarantine of the people's Republic of China (AQSIQ) "rules for supervision and inspection of crane machinery" clearly requires: "bolt connection shall not be loose, there shall be no defects such as missing parts, damage, etc., high-strength bolts shall have enough pre tightening torque", and the inspection method is specified as "using torque wrench to check the connection condition of high-strength bolts". The pre tightening moment is very important in height strength bolt connection of tower. Due to the torque produced 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 shear, tension and uneven stress at the same time, making the bolt stress situation more complex and dangerous. During the inspection, the pre tightening moment of standard section bolt of tower body can be inspected by visual method first, that is, the inspector is in the middle of standard section of tower body to observe the connection of standard section at the main chord of tower body under tension. If there is a small gap at the connection of standard section, it indicates that the pre tightening force of bolt is not enough; at the same time, let the tower crane to the left and right Rotate, if you can hear the metal creak, it also indicates that the bolt connection is not tight; then use torque wrench or other methods to carefully check, so as to improve the inspection efficiency. The author once encountered a case that the bolt on the upper part of the reinforced section of the tower crane base was pulled and cracked due to the loose bolt. Fortunately, no major accident occurred due to the discovery and timely treatment.
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