Failure analysis of the bolted connection in a shipboard crane tower: A case study of catastrophic bolt fracture

Abstract

This paper presents a comprehensive forensic engineering analysis of the catastrophic failure of a shipboard crane's tower-base connection. The incident involved the separation of the crane tower from its base due to the failure of high-strength bolts. The investigation employed visual inspection, dimensional analysis, spectroscopic chemical analysis, metallographic examination, and fractography on the failed components. Quantitative results verified that the bolt material strictly complied with ISO 898-1 Property Class 10.9 specifications, definitively ruling out material defects or corrosion as primary causes. Instead, the investigation identified a progressive failure mechanism initiated by bolt loosening. This loss of preload led to uneven load distribution, causing accelerated fatigue failure in the remaining tight bolts and thread stripping or ductile overload fracture in the loosened ones. The root cause is attributed to inadequate maintenance and inspection protocols, which failed to detect pre-existing looseness and incipient fatigue cracks. The study underscores the criticality of proper bolt preload maintenance in dynamically loaded maritime structures and recommends enhanced non-destructive testing protocols.