Figure 1: Crack at tower mast segment no. 10

The mast sections of a topless tower crane in Johore Bahru were found to be defective and cracked. The cracks were located at segments no. 2, 3, and 10. They were found during routine monthly inspection. All the cracks were located at around similar locations (refer Figure 1)on the three mast sections.

The tower crane was erected in 2010 with safe lifting capacity of 1.8 tonne and capable of freestanding height of about 66 meters. The crane with 60m boom was made in 1995.

The cracks may have been initiated by some defects in the weldments. Then by repeated loadings, the crack propagated along the loading axis. This type of defect may not be detected visually during the early stages until the defect deteriorated further and propagated onto the surface.

Suggestions for improvement:-

1. Tower crane erectors must ensure that the structures and components are properly and thoroughly inspected by the competent person on the ground and free of any defects before erection work for the crane can commence.
2. Routine and periodic inspections must be done regularly to pick up any irregularity on the crane and its components. Report shall be made to the employer on any defect that is found on the tower crane. All findings must be recorded for easy reference and further analysis. Such written records shall be forwarded for the Inspector’s attention when requested.
3. Operation of the tower crane with such defect must be stopped immediately and cannot be operated again until it has been certified safe for continual operation by the department.
4. Approval from the authority has to be obtained for repair works by welding involving any structural parts of the crane.
5. Any welding work that need to be carried out on the structural parts of the crane shall be undertaken by an approved welder. All such work shall conform to the crane’s manufacturer requirements or specifications.
6. Wall ties for the tower crane that need to be installed have to conform with the manufacturer’s specifications and requirements to prevent overstressing on the crane mast sections.

References:-

1. Guidelines For Public Safety And Health At Construction Sites (1st Revision)
   http://www.dosh.gov.my/doshV2/phocadownload/guidelines/gl_construction_site_bi.pdf
2. Code Of Practice For Safe Use Of Tower Cranes (Occupational Safety and Health Branch-UK)
   http://www.labour.gov.hk/eng/public/os/B/crane.pdf
3. MS 1544 : Part 1 : 2002 : Cranes - Safe use : Part 1 : General
4. MS 1580 : 2003 : Cranes – Test codes and procedures
5. EN 14439:2006+A2:2009 : Cranes - Safety - Tower cranes
6. CEN/TS 13001-3-1:2004 : Cranes - General design - Part 3-1: Limit states and proof of competence of steel structures