The safety performance of bridge type grab ship unloaders are the main factors in the normal operation of a bulk cargo wharf. This article made a research of the stress test technology on the use of safety assessment on the structure of the bridge type grab ship unloader, through the dynamic stress test of ship unloader key parts of the structure under the use of the condition, analysis bridge type grab ship unloader safety performance is at ordinary times and maintenance and inspection needs to focus on the dangerous site.Stress test shows that the Maximum compressive stress is Point 7, its maximum dynamic compressive stress is 82.5MPa; while the maximum tensile stress occurs at point 11, its maximum dynamic tensile stress of 72.5MPa. After 17 years used, The force main parts (except former trolleys) of the ship unloader are basically the same as its design value.

Old giant cranes in corrosive environment are in serious hidden danger of structural instability and failure, the modal analysis is an important part of dynamics analysis in the Crane Safety Evaluation to guarantee the safety of cranes. A Modal Analysis of a 28-year old 100t giant shipbuilding tower crane was done using ANSYS. Comparing with the vibration frequencies and modal shapes, Modal analysis shows that the Natural Frequency of the crane reduces from 1.0024Hz to 1.0003Hz, beside all the Modal vibration frequencies (first 10 Order) of the crane are lower than the designed value, means the strength of the tower crane has decreased; the Modal Vibration Frequencies (first 10 Order) of the tower crane are between 1 Hz and 2 Hz. The Mmodal analysis provided theoretical basis for safe use, design and transformation of this crane.

In order to get the displacement response curve of the Gantry Crane Girder under three stage of lifting process, the vibration differential equation and displacement response expression were deduced, combining with the actual case, the displacement response expression and displacement response curve were deduced in the load duration time 0.8 s and 0.2 s. The results show that: the lifting process is an important factor affecting the structural vibration; Displacement peak and load duration time are inversely proportional; Increase the load duration time can reduce the vibration of the structure.

In order to get the displacement response curve of the Portal Crane under four phase of unloading process, the vibration system was built, the vibration differential equation and displacement response expression were deduced, combining with the actual case, the displacement response expression and displacement response curve were deduced in the open grab time 1.5 s and 4 s. The results show that: the unloading process is an important factor affecting the structural vibration; Displacement peak and open grab time are inversely proportional; Increase the open grab time can reduce the vibration of the structure.