290HC Mast Section Treatment of tower crane incline due to uneven settlement of foundation
Due to the uneven settlement of the foundation, tower crane inclines from time to time, which does not meet the safety use requirements of tower crane verticality of 4 ‰. For example, qtz60 tower crane in a construction site of our company has a lifting height of 40 m, a concrete foundation of 5 m × 5 m × 1.3 m and a mass of 81.3 t. In the non working state, M = 218.3tm; FH = 7.8T; FNU = 108t. There is part of backfill in the south of the foundation, and uneven settlement of the foundation occurs due to heavy rain. At the measurable height of 35m, it inclines to the south by 315mm. In this paper, the treatment measures of tower crane inclination caused by uneven settlement of foundation are summarized.
290HC Mast Section：
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Safety measures for the initial stage of tower crane tilting
When the tower crane inclines and its perpendicularity exceeds 4 ‰, it shall be stopped immediately. When the tower crane is in the most unfavorable condition (non working state), the critical maximum inclination L, which can ensure that the tower crane does not overturn at the measurable height, is calculated. Pay attention to regularly observe the tilt speed and amount of the tower crane, and make records. Once the tilt reaches 0.5L and continues to tilt, it is necessary to take decisive measures such as tower removal. The following safety measures can be taken if the tower crane cannot be stopped immediately and the deflection is not more than 0.25L.
1) increase the weight block on the concrete foundation (place more in the opposite direction where the inclination occurs), increase the foundation quality, reduce the height of the tower crane center of gravity and reduce the E value.
2) add wall attachment device at appropriate height of tower crane.
3) the cable wind rope shall be set at the appropriate height of the tower crane to prevent the tower crane from continuing to tilt.
2 tower crane inclination correction
After the tower crane stops tilting, in order to restore the verticality of the tower crane to within 4 ‰ and meet the requirements of safe use, it is necessary to rectify the deviation of the tower crane.
2.1 correction steps
290HC Mast Section：
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1) based on the principle of similar triangle, the thickness of pad on the leg of tower crane is calculated.
2) according to the cross-section shape of the leg, prepare 6 pieces of gasket with the outline size slightly larger than the cross-section shape for the 2 legs to be lifted, including 4 pieces with the thickness of 6mm and 2 pieces with the thickness of 1.5mm. In order to easily insert the gasket between the standard section and the outrigger, each gasket can be divided into 4 parts, as shown in Figure 1.
3) refer to Fig. 2 for the production of lifting iron shoes. The iron shoe shall be able to bear the negative jacking load without deformation, be able to be conveniently installed on the main limb of the standard joint and be able to provide enough friction with the standard joint.
4) adjust the position of luffing trolley or lift a certain amount of load to make the tower crane balanced and ensure that the four legs are under pressure.
5) install the iron shoe on the main limb of a standard section to be padded, and loosen the connection bolt of the standard section by a gap of 6mm. At the same time, loosen the bolt on the other leg to be padded, so that the bolt has neither prestress nor clearance.
6) after the jack is padded with the skid, slowly jack up until there is a gap of 6mm between the standard section and the outrigger, insert a piece of gasket (4 parts in 1, 2, 3 and 4 in Figure 1). At this time, the bolt shall be free of prestress and allowance.
7) install the iron shoe on the main leg of the standard section which needs to be padded on the other side, pad the jack with a pad wood, loosen the bolt to a clearance of 13.5mm, and slowly jack up the jack until there is a clearance of 13.5mm in the standard section, insert three pieces of gasket (6mm, 6mm, 1.5mm). At this time, the bolts shall be free of prestress and allowance.
8) install the iron shoe on the main leg of the first jacking standard section, and add the remaining 2 pieces of gasket (6mm, 1.5mm).
9) after fastening the connecting bolts of the two legs which have been padded to the specified pre tightening force, loosen the bolts of the two legs on the other side one by one. If there is a gap between the legs and the standard section, the bolts shall be tightened after the amount of gap is padded.
10) use a theodolite to check the verticality of the tower body. After meeting the requirements, use electric welding to connect the pad with the leg by spot welding.
2.2 safety precautions for deviation correction
1) formulate rectification scheme and safety technical measures, and introduce rectification process, methods, steps and safety technical problems to drivers and operators in detail.
2) set cable and wind rope on the tower.
3) during the rectification operation, the weather shall be free of rain and snow, and the wind force shall not exceed level 4.
4) after the tower crane is kept in balance, no further action is allowed, and it is ensured that all four legs are under pressure. It is forbidden to rectify the deviation under the unbalanced state of tower crane.
5) the clearance for loosening the connecting bolts of each leg shall be the same, and it is not allowed to loosen all the bolts or pull out the bolts.
6) special personnel shall be assigned to observe the change of verticality of tower body with theodolite.
7) the jack must be well padded with skids to prevent slipping.
8) the thickness of each pad is not easy to be too large to prevent the deformation of standard section structure. It is better to prepare a certain number of pads with a thickness of 1mm, and plug them in at any time after there is a gap in jacking, so as to keep the gap between the leg and the standard section at about 1mm.
290HC Mast Section：
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