Crane Foundation

5. ANALYSIS RESULTS

5.1. General Solution Checks

The following post-run checks were performed:

• Equilibrium between the applied loads and the reactions;
• Inspection of the displacement shape of the structure to ensure that were no discontinuities in the model;
• Inspection of the stress contours to ensure the adequacy of the mesh used. All error and warning meshes output by ANSYS were investigated.

5.2. Post Processing Method

The ANSYS graphical post-processor was extensively used to review stress and displacement results. In all stress contours, plot element solution un-averaged was used. The displacements and rotation are calculated at each node but stress and strain are evaluated at the element integration points, then these results are extrapolated to the nodes. Each node can be common to different elements so the nodes can have multiple values of stress from each element. Thus, the average of those values is considered as a nodal solution and they are continuous across the elements. On the other hand, the element solution has un-averaged stress values.

5.3. Structural Response

5.3.1.Displacement and VonMises Stress

The finite element analysis was run for the load cases listed in Section 3.5. Table 5.1 lists the maximum values of stress and displacement obtained.

It can be observed that all the maximum values occurred in the top of the crane pedestal, namely in the boundary with the rigid links. These maximum values can be seen as singularities 7 due to the proximity with the imposed load. Moreover, remember that the crane pedestal is out of the scope of this study, the assessment is to be made for the supporting structure, not for the pedestal (Section 3.2).

Load Case	Stress [MPa]*	Description	Displacement [mm]	Description
0 deg	394.59	Pedestal top	8.93	Pedestal top
45 deg	406.96	Pedestal top	7.93	Pedestal top
90 deg	378.26	Pedestal top	6.70	Pedestal top
135 deg	401.86	Pedestal top	8.03	Pedestal top
180 deg	402.94	Pedestal top	8.92	Pedestal top
225 deg	399.63	Pedestal top	7.51	Pedestal top
270 deg	382.86	Pedestal top	6.00	Pedestal top
315 deg	391.58	Pedestal top	7.61	Pedestal top

Table 5.1: Maximum Stress and displacement values

*VonMises Stress

• 0 deg Load Case:

The deflected shape of the structure is shown in Figure 5.1 and Figure 5.2. The displacement at the deckhouse top is approximately 3 mm.

The VonMises stress plot is shown in Figure 5.3. For this load case, the longitudinal at 7140 mm FCL is under the higher stresses (Figure 5.4). The stress range acting in this area is between 30 and 100 MPa. Except for the two corners near the opening where a local maximum is reached above 150 MPa. On the forward bulkhead, near the boundary conditions, the stress reaches values around 80 MPa.

• 45 deg Load Case:

The deflected shape of the structure is shown in Figure 5.5 and Figure 5.6. The displacement at the deckhouse top is approximately 2.5 mm.

The VonMises stress plot is shown in Figure 5.7. In this case, the load is no longer aligned with the longitudinal 7140 mm FCL, this causes that the longitudinal is not so requested (comparatively to the last case). The higher stresses are now concentrated in the “ring” structure that connects the pedestal to the internal structure (3980 mm above the main deck) reaching values of 130/150 MPa. This can be seen in Figure 5.8.

• 90 deg Load Case:

The deflected shape of the structure is shown in Figure 5.9 and Figure 5.10. The displacement at the deckhouse top is approximately 2.3 mm.

The VonMises stress plot is shown in Figure 5.11. The structural response behaviour follows the same nature seen in the previous two cases, i.e., the requested zones are the ones aligned with the load direction (as expected). In this case, the load is aligned with frame #11. The stress range in frame #11 is between 30 and 80 MPa. The connection between this frame, the deckhouse top and the crane pedestal has a maximum near to 150 MPa (Figure 5.12). The connection with this frame and the shell plates has a maximum value of 70 MPa.

• 135 deg Load Case:

The deflected shape of the structure is shown in Figure 5.13 and Figure 5.14.

The VonMises stress plot is shown in Figure 5.15. In this case, like in the load case for 45 degrees, the higher stress zone is concentrated in the “ring” structure that connects the 8 pedestals to the internal structure reaching values of 130/150 MPa.

This can be seen in Figure 5.16. On the aft bulkhead, near the boundary conditions, the stress reaches values around 100 MPa.

• 180 deg Load Case:

The deflected shape of the structure is shown in Figure 5.17 and Figure 5.18.

The VonMises stress plot is shown in Figure 5.19. The internal structure, namely the longitudinal 7140 FCL, reaches values up to 100. Once again near the boundary condition in the aft bulkhead, stress reaches values of 60 MPa (max 100 MPa). The longitudinal bellow main deck (5850mm FCL) is slightly under stress (Figure 5.20).

• 225 deg Load Case:

The deflected shape of the structure is shown in Figure 5.21 and Figure 5.22.

The VonMises stress plot is shown in Figure 5.23. The higher stresses are concentrated in the “ring” structure that connects the pedestal to the internal structure (3980 mm above the main deck) and in the girder at 2000mm above the main deck, reaching values of 130/150 MPa. This can be seen in Figure 5.24.

• 270 deg Load Case:

The deflected shape of the structure is shown in Figure 5.25 and Figure 5.26.

The VonMises stress plot is shown in Figure 5.27. The structural response behaviour follows the same nature seen in the Load case for 90 degrees. The load is aligned with frame #11. The stress range in frame #11 is between 30 and 100 MPa. The higher stresses are concentrated in the “ring” structure that connects the pedestal to the internal structure (3980 mm above the main deck, in the girder at 2000mm above the main deck and in the connection between frame #11 and the deckhouse top, with values up to 100/150 MPa. This can be seen in Figure 5.28.

• 315 deg Load Case:

The deflected shape of the structure is shown in Figure 5.29 and Figure 5.30.

The VonMises stress plot is shown in Figure 5.31. Like in the previous case the “ring” structure that connects the pedestal to the internal structure is under higher stresses (Figure 5.32).

5.3.2.Buckling Check

The buckling check was made based on DNV-RP-201 (Ref.5). For this check, two types of panels were selected: girder panel (plate and girder) and simple panel (plate only).

Based on the analysis made on the previous subsection the 180deg load case was selected for this code check. From all the considered load cases this is the one who causes more stress in the internal structure.

Two girder panels and one simple panel were selected for this check, which is located at the longitudinal 7140 FCL. Figure 5.33 shows the three panels. The plate associated with the girder panel has the following dimensions: 2588x1850mm for Girder Panel 1 and 2035x1850mm for Girder Panel 2. The simple panel is a 2615x2033mm plate. All thicknesses are according to Ref.3.

The three panels were checked with the Ref.5 to see the maximum stresses (Sigxx and Sigyy) that would cause buckling (see Annex A). Table 5.2 lists the stresses obtained.

Panel	Sigxx [MPa]	Sigyy [MPa]
Panel Girder 1	100	80
Panel Girder 2	90	90
Simple Panel	50	45

Table 5.2: Buckling Stresses according to Ref.5

Figures 5.34, 5.35, 5.36, 5.37, 5.38 and 5.39 show the stresses for the same three panels obtained by the finite element model. The stresses magnitudes are well below the stresses listed in Table 5.2, meaning that these panels will not suffer buckling effects.