To return to work after the festival, let’s talk about some experience on the safety inspection of tower crane, discuss the key points in the safety inspection of lower tower crane, and what problems should be paid attention to in the safety inspection of tower crane? 1
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Inspection of foundation: the foundation of tower crane is an important link related to the safety of tower crane
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In the inspection, we should first pay attention to whether the endurance of the tower crane foundation meets the design requirements of the manufacturer
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At present, the requirements of most tower crane foundations for ground endurance are generally 200 ~ 300kPa
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Check the geological survey report to see if it meets the requirements
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If the actual ground endurance does not meet the design requirements, check whether the tower crane foundation has been piling, foundation enlargement and other corresponding treatment
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For the following forms of tower crane foundation treatment, special attention should be paid to the following inspection points in 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 is placed at the bottom elevation of basement foundation pit
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For this type of tower crane foundation treatment, attention should be paid to the drainage of the tower crane foundation to avoid ponding
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There was a tower collapse accident 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 weld cracks in the base of the foundation section in time
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In addition, the steel fatigue damage at the weld was serious
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1.2 when the foundation is placed on the slope, piling treatment must be carried out for this foundation
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In addition to the above requirements, the lateral pressure generated by the slope should also be fully considered
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During the detection, the construction unit should be required to take anti lateral pressure measures when excavating the slope, such as taking soil nailing protection or anchor treatment
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In our inspection visit, too many causes occurred, and the construction unit did not consider the slope Side pressure, earthwork excavation, cause serious deviation of tower crane foundation, bring not small economic losses to the construction unit; 1.3 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 review It can be embedded, and relevant concealed acceptance records shall be made
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The collapse of a tower crane in Xiamen at the beginning of this year is due to the fact that the high-strength bolts embedded in the rental unit do not meet the requirements, and the nuts and bolts are confused in metric and English systems
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When the tower crane is installed to the first section of the counterweight of the crane, the tower crane collapses
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1.4 the foundation of the tower crane shall not be covered with soil layer, which increases the bearing capacity of the foundation and is not conducive to observing the weld condition of the base Last year, there was a tower crane in Xiamen whose foundation was covered with soil
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Fortunately, the driver was more experienced
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When he felt that the tower crane made an abnormal noise, he immediately checked all the bolts of the standard section
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No problem was found, and then the soil was removed
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As a result, it was found that the weld of the steel structure of the base cracked
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After timely treatment, no major consequences were caused
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2
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Metal structure connection: 2.1 tower body bolt connection: for the connection of metal structure, the General Administration of quality supervision, inspection and Quarantine of the people’s Republic of China “crane supervision and inspection regulations” clearly requires: “bolt connection shall not be loose, there shall be no missing parts, damage and other defects, high strength bolts shall have enough pre tightening torque”, the inspection method is “use torque wrench to check the high strength bolt connection”
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The pre tightening moment is very important in the tower height strength bolt connection
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Due to the torque generated when the tower body rotates, if the pre tightening torque of the tower height strength bolt pair can not meet the design requirements, the bolt will be subject to shear, resulting in the bolt being sheared and pulled at the same time, and the force is uneven, which makes the bolt stress more complex and dangerous
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During the inspection, the pre tightening torque of the standard section bolts of the tower body can be checked by the visual method, that is, the inspectors are located 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
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If they can see a small gap at the connection of the standard section, it indicates that the pre tightening force of the bolts is not enough; at the same time, if the tower crane rotates left and right, if they can hear the metal squeaking, it also indicates that the bolts are connected After that, use torque wrench or other methods to check carefully, so as to improve the inspection efficiency
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The author once encountered a case of bolt cracking on the upper part of tower crane base reinforcement joint due to bolt loosening
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Fortunately, no major accident occurred due to discovery and timely treatment
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When checking the connection condition of boom pin shaft, attention should be paid to the fixing condition of shaft end baffle and pin shaft opening pin
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Special attention should be paid to the connection form of boom pin shaft as shown in Figure 2
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This pin shaft is an equal diameter pin shaft, and the inner displacement of the pin shaft is stopped by the pin shaft baffle
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After the tower crane has been used for many years, the pin shaft baffle is easy to wear or fall off, which may cause the pin shaft to move off and cause the arm folding accident
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Last year, there was a boom folding accident caused by the inward falling off of the boom pin in Xiamen city
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Special attention should be paid to the condition of the pin baffle during the inspection
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3
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Safe distance between tower crane and transmission line in urban construction, there are many construction sites where tower crane negotiates with overhead transmission line
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There are many accidents in other areas, such as short circuit of transmission line, broken wire rope and falling of suspended object, caused by collision between tower crane and overhead transmission line in dangerous area
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National standards and inspection procedures all have the requirements that the safe distance between any part of the crane and the transmission line should reach a certain safety distance
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During the inspection, if it is found that the objects and wire ropes of tower crane may enter the dangerous area of transmission line
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It is necessary to put forward protection requirements, require the construction party to set up protective barriers, and establish safety protection measures and systems
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During the normal operation of the tower crane, the protective barrier ensures that the lifting objects and wire ropes of the tower crane cannot enter the dangerous area of the transmission line
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When the wind force is greater than 20m / s, the work should be stopped, and the hook should be placed at the root end of the crane arm to avoid the hook and wire rope entering the dangerous area of the transmission line when it rotates with the wind; 4
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Group tower operation: for multi tower operation, the construction unit should be reminded to prepare the multi tower operation scheme during the detection, and the construction unit’s technical director and chief supervision engineer should be submitted for approval If the safety distance between the big arm of the low tower and the standard section of the high tower is insufficient, the inspection unit shall report to the superior administrative department immediately for treatment; 5
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If there is an electromagnetic clutch in the reducer of the lifting mechanism, special attention shall be paid to the connection between the electromagnetic clutch and the electric brush At the same time, check the working condition of the electromagnetic clutch under current relay to ensure the reliability of the electromagnetic clutch
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In the past, due to excessive wear of the brush of the electromagnetic clutch, failure of the under current relay and loss of power of the clutch, the hanging objects fell down, which should be paid attention to in the inspection
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6
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Detection of safety protection device: lifting moment limiter is the most important safety device of tower crane, and lifting moment is the most important parameter
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Over torque lifting is the most dangerous thing
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If not, it will lead to machine damage and human death
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After passing the detection, it is worth discussing whether the lead seal form adopted by power supply bureau for electricity meter can be adopted, together with photographic evidence collection
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It is absolutely not allowed to be used Who can adjust the torque limit after the tower crane passes the test.
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