This case study on a 23-year-old grab ship unloader was performed to assess its structural health by field tests and numerical analyses. Using the strain gages mounted to the adequate points, the real strain responses were obtained during the static test and long-term monitoring. The static test was performed under different operating conditions including boom up and down, trolley stopped on critical locations with grab full and empty. The measured data were used to evaluate the current safety level according to the national design standard for crane. Then, the strains were recording over one year to obtain the real stress range histograms for fatigue assessment by using the rainflow counting method.
The results show that the front tie members were subjected to unpredictable moments that induce large stresses enough to damage the safety. This problem arises from end pins that are not free to rotate. Some members having lower safety levels should be monitored until repairs, and some spots need to be inspected for the fatigue crack at a shorter interval due to their high probability of fatigue damage. Besides, the recommendations for the design details of new crane are also presented.