Failure Investigation of an Aluminium Ladder on board a vessel

Introduction

An aluminium ladder, used during salvage operations aboard a barge vessel, failed catastrophically. It consisted of two aluminium ladders fixed together with duct tape and polypropylene lashings to extend the length.

1 (Custom)

Side member failures located at and near the joint.

Investigation

The fracture surfaces of the side members were inspected. The material composition was analysed to determine which aluminium alloy the material most closely resembled.  The stress in the ladder was analysed at various orientations to determine the root cause for failure.

What We Found

Results

The ladder material was found to be appropriate for the application, both in terms of composition and mechanical strength.  Analysis of the failure surface shows that the side members failed by plastic yielding. This is shown by the plastic deformation and final failure regions on the fracture surfaces. The nature of operation of the ladder suggests that this failure is a result of an abnormal bending moment.

Table 1: Assessment of Possible Ladder Orientations

The ladder material was found to be appropriate for the application, both in terms of composition and mechanical strength.  Analysis of the failure surface shows that the side members failed by plastic yielding. This is shown by the plastic deformation and final failure regions on the fracture surfaces. The nature of operation of the ladder suggests that this failure is a result of an abnormal bending moment.

Conclusion

The ladder overlap, overall length and angle to the horizon resulted in an abnormal bending stress. This caused a yielding failure in one side member, followed by fast fracture failure of the remaining side member.  In short the ladder was used more as a bridge than as a ladder and as such the load orientation caused it to fail catastrophically.  No fault could be found in the ladder material.

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