# Safety Assessment for Upper Part of Floating Crane Considering Minimum Luffing Angle
## 4 Consideration and Discussion of Structure Analysis Result
### Discussion and Limitations  
In this study, a design to minimize the luffing angle was conducted as a way to increase the utilization rate of floating cranes. Section 2.2 summarizes additional considerations. In addition, the structural safety was evaluated in terms of deformation, stress, and buckling using finite element analysis based on the classification society's rule (from Section 4.1 to Section 4.3). These safety assessments by using finite element analysis results can be said to be a universal procedure for the ship structure [36; 37; 38; 39]. However, the question of how far the safety assessment procedure of floating cranes conducted in this study can be applied may be concerning. When applying the methodology of this study, the key to be considered is the formal identity of floating cranes. In other words, the crane should be installed on the barge or monohull, and the crane type should be applied with the boom (or truss) and back tower method. It is considered that the methodology of this study can be applied to floating cranes of less than about 4000 tons that are used for offshore work adjacent to land from this point of view, as mentioned in Section 2.2. On the other hand, higher profits can be expected by increasing the utilization rate from the perspective of crane managers, so it is expected that the solution proposed in this study will be actively employed. However, there remains a problem to consider both the expectation of profits from lowering the luffing angle and the increase in cost of installing extra equipment (hydraulic cylinders, etc.). The safety of the upper structure of the floating crane, which was developed mainly based on the relevant regulations of the Korean Register of Shipping, was evaluated in this study. In addition, evaluation criteria of DNVGL and ABS were also applied to check out the appropriateness of this safety assessment. As a result, both the stress and buckling strength evaluation were found to be safe. However, it was investigated that there is no explicit deformation allowance standard regarding the deformation within the regulations related to the cranes of the two classification societies. Nevertheless, the deformation \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Pos.no** & **B-1** & **B-2** & **B-3** & **B-4** & **B-5** & **B-6** \\ \hline \(\sigma_{xmax}\) & 45.4 & \(-63.0\) & 75.0 & \(-1.9\) & \(-58.9\) & \(-43.9\) \\ \(\sigma_{ymax}\) & 1.1 & 1.8 & 6.1 & \(-64.2\) & \(-1.1\) & \(-1.1\) \\ \(\tau\) & 3.2 & 5.9 & 3.2 & \(-0.6\) & \(-7.3\) & 0.6 \\ \(\sigma_{Cx}\) & 164.4 & 2778.8 & 922.0 & 77.2 & 619.6 & 1317.1 \\ \(\sigma_{Cy}\) & 4 & \(-79.4\) & 75.0 & 2608.8 & 11.6 & 33.0 \\ \(\tau_{C}\) & 165.89 & 165.02 & 175.93 & 172.72 & 174.09 & 171.96 \\ Equation (5) & 0.423 & 0.0064 & 0.0377 & 0.0034 & 0.055 & 0.0062 \\ check & OK & OK & OK & OK & OK & OK \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Results for buckling calculation by ABS rule (stress unit: MPa). tolerance standard (span/800 or less) applied in this study seems to be appropriate because it is considered to be a general deformation tolerance range. The lower hull (barge) is not covered in this study. Considering the effect of the luffing angle minimization design on the barge, it is considered that the possibility of capsizing due to the movement of the center of gravity in very lower luffing operation should be reviewed. When navigating under the marine bridge while maintaining the minimum luffing angle, a relatively large incline in the forward or backward direction of the crane may occur due to changes in the forward speed and center of gravity. This problem can be accurately predicted and solved by analyzing the movement characteristics of the barge due to external force [40]. A relatively simple solution would also be useful to increase the reserve buoyancy in the direction of the barge where the boom moves. In addition, one of the issues not addressed in the safety aspect of the developed barge could be a safety review by fatigue load.