Forensic Failure Analysis of Damaged Mining Lift Hook

We performed a forensic failure analysis on a damaged mining lift hook. As a worker was lifting and moving a cylindrical metal basket loaded with parts, the lift hook bracket assembly that secured the basket to the crane hook had failed. Consequently, the (approximately 1,600 pound) basket loaded with parts had fallen and struck the employee.

An attorney asked O’Donnell Consulting to investigate to evaluate the safety, design and structural integrity of the lift hook bracket assembly and determine the root cause of the accident. A three dimensional finite element model of the lift hook assembly was performed, consisting of over 75,000 elements and 120,00 nodes to evaluate the failure mode.

The model included the base plate, the lift hook bracket and the nuts connecting the lift hook bracket to the plate. Several studies were performed on the location of the 1500 lb load.

Several conclusions were made:

• The failure was due to fatigue
• Even if the load was centered, the stresses in the bracket assembly still would have failed in fatigue
• The original design of the lift hook had a very limited safe life of 5,000 cycles
• The sudden failure was due to improper design of the lift hook bracket

In addition to design, analysis and troubleshooting services – we also perform forensic engineering investigations.