POLA STS Crane Portal Frame Fatigue Study

Fatigue cracks were found in the portal beams of Noell cranes at Pier 400, Los Angeles. Cracking had occurred most frequently at the end of an internal stiffener where the portal beam tapered, and at seafastening lugs that remain on the cranes at the portal-to-leg connections. Other cracking had occurred in the main equalizer brackets.

Liftech performed a study that included measuring strains, accelerations, and displacements. The measurements were made to understand the effects of trolley movement, hanging load movement, damping, load control, skewing, and crane transfer around curved rails on the strains in the portal structure.

The study confirmed that the trolley accelerations and load sway caused significant fatigue damage in the portal frame, and that the tapered portal beam geometry resulted in a significant local stress concentration.

Liftech provided recommendations for operational and structural modifications, and periodic structural inspections.