256HC Mast Section the inspection requirements and causes of deformation of tower crane steel structure
The deformation of tower crane steel structure includes local bending deformation, distortion and eccentricity. According to the deformation inspection requirements of tower crane steel structure, if it exceeds the following range, it is regarded as deformation:
1. The straightness tolerance of members along the longitudinal axis of the whole length is 1 / 750.
2. The deformation of the main chord in use shall not be more than 3 ‰ - 5 ‰.
3. The deformation of web member shall not be more than 2-4mm.
4. The error of bolt hole distance of rod connection shall not exceed 1 / 2 of assembly clearance, and the roundness error of screw hole shall not exceed 1 / 2 of assembly clearance.
The causes of tower crane steel structure deformation are as follows:
① Local bending deformation of steel structure is caused by collision and knocking;
② Due to the looseness of the connecting bolt, the screw hole is worn into an ellipse, resulting in additional bending moment caused by the eccentricity between the arms and members;
③ If the operating mechanism is out of control and the boom is tilted backward, the collision with the tower body will cause serious deformation;
④ The steel structure will produce yield deformation (permanent deformation) due to long-term overload.
If the balance of the upper structure is not adjusted during jacking, the center of gravity of the jacking part is not placed on the jacking oil cylinder, so that the top structure is out of balance or even the center of gravity deviates greatly. The guide wheel of the climbing frame has too much pressure on the main chord of the standard section, which causes bending deformation of the main chord of the tower body and instability of the tower crane steel structure, resulting in accidents.
