Study on the effects of lifting loads on the longitudinal strength of a crane barge during heavy lifting operations due to various angle of crane rotation

The different positions of lifting loads on a crane barge during Heavy Lifting operations have a significant impact on longitudinal strength. This study focuses on the analysis of longitudinal strength on a crane barge with a configuration of Topside structure loading direction during the installation. The variations used the crane rotation angle from starboard to bow at 15° increments. The results showed that the load distribution for all variations followed similar trendlines, using analytical and numerical methods. Significant changes occurred at frame 3–19 as the location of the superstructure, frame 13–40 as the ballast tank loads, and frame 45–55 as the lifting loads. Regarding the maximum shear force and bending moment, occurred when the net load changes from positive to negative and the position of the crane. The maximum shear force occurred at frame 40, while the maximum bending moment occurred at frame 47, 48, and 49. The comparison between analytical and numerical methods for shear force and bending moment showed that the error values are below 5% of the allowable value according to the DNV standards.


Introduction
In the construction of offshore platforms, there is a phase called installation, a series of activities to place structures at predetermined locations offshore; a commonly used method for this installation is the lift method [1].This lifting method is referred to as a conventional method that uses a crane barge to lift and position the structures installed onto the jacket, and one of the operational categories is Heavy Lifting [2].This crane barge provides flexible and efficient maritime transportation in Heavy Lifting operations, including installation and decommissioning activities [3].Heavy Lifting operations on a crane barge typically handle the structure with weights ranging from 60 to 60,000 tons, with any Structure lighter or heavier falling outside the scope of Heavy Lifting [4].As infrastructure supports activities, the use of crane barges for Heavy Lifting operations is steadily increasing within the maritime business sector.Therefore, ensuring the safe operation of crane barges in the open sea is essential [5].
A crane barge is a type of barge equipped with a crane and accommodation facilities.It is a support vessel for offshore platform activities, particularly for lifting operations, where structures are lifted and moved from one place to another [6].During Heavy Lifting operations, the loads the ship receives affect the crane barge, such as the load of the lifted structure.It can affect the longitudinal strength of the crane barge because of the load distribution that occurs during Heavy Lifting operations [7].Analyzing the longitudinal strength of the crane barge during Heavy Lifting operations is necessary to find out how  The longitudinal strength calculation is performed using analytical and numerical methods for each loading angle, where the weight data of the lifted load is shown in Table 1, categorizing the load as a Heavy Lifting operation.The utilized operational configuration involves ballasting conditions and variations in the lifting angle of the Topside structure from the ship's starboard side to the ship's bow in 15° crane rotations, as shown in Figure 1.The load distribution data is determined from the Stability Booklet, and the ballasting configuration for this operation is determined through trim and heel degree parameters at equilibrium conditions.Thus, the ballasting configuration used involves tank No.

Data of the Crane Barge
The XYZ crane barge data was designed based on the X barge with the operating location area in the Meliwis Gas Field.It showed the following data used in this research in

Modelling of Crane Barge
The numerical modeling of the XYZ crane barge consisted of the barge hull, crane, and superstructure, using MAXSURF Modeller regarding the data in Table 1-2 and the general arrangement (GA) in the Stability Booklet.Meanwhile, the numerical modeling of the tanks referred to the data in the Stability Booklet using MAXSURF Stability-the numerical modeling of the XYZ crane barge, as shown in Figure 2.Then, the numerical modeling was validated based on the data hydrostatic and volume tanks from the existing ship regarding the validation tolerance limits according to American Bureau of Shipping (ABS) regulations [8].The result of the numerical modeling shows that the numerical modeling has satisfied the tolerance limits of the ABS regulations.Thus, the model can be used for numerical longitudinal strength calculations using MAXSURF Stability.

Calculate the Longitudinal Strength
The analysis is conducted first by analyzing the buoyancy distribution, considering the effect of trim (x) using the equation ( 1)-( 3): • Fore draft (dF) > Aft draft (dA) • Fore draft (dF) < Aft draft (dA) • For station/frame 0 with:  = distance of station/frame After obtaining the draft values at each station/frame, the buoyancy values can be determined using interpolation.Then, for the calculation of load distribution in the form of LWT and DWT, the equation ( 4) is used [9]: with:  0 = first mass distribution at each station/frame  = distance of distribution The shear force and bending moment can be determined from the obtained load distribution and buoyancy distribution, where shear force is the integration of the difference between the load distribution and buoyancy distribution (net load), and bending moment is the integration of the shear force.The equations for shear force and bending moment used shown in equation ( 5)-( 6) [10]: (5) The steps for conducting a numerical analysis of longitudinal strength are: • Modeling the barge hull, crane, and superstructure.
• Modeling the tanks.
• Modeling the operational conditions.The rules or standards in this case are DNV RU-SHIP Pt. 3 Ch.5 [11] for the allowable shear force and bending moment.The equations used for the still water conditions are shown in equation ( 7)-( 10): • Shear Force For the comparison of shear force and bending moment results based on the analytical method against the numerical method with an error percentage below 5%, where the numerical method results are used as a reference due to the lack of existing ship data, the equation ( 11) is used [12]: • 100 (11) with: = numerical method data  ′   = analytical method data   = allowable value

Result and Discussion
The analysis of longitudinal strength on XYZ crane barge is reviewed based on 55 frames, under ballast conditions (condition 0), and with lifting load directions ranging from the starboard side to the bow of the ship at every 15 degrees (conditions 1-7), as shown in Figure 3.The results from the conducted analysis using analytical and numerical methods include the load distribution, shear force, bending moment that occurs in response to the load distribution, and the comparison between the analytical and numerical results for shear force and bending moment.For the load distribution on XYZ crane barge under each lifting load direction condition shown in Figure 4, the shear force and bending moment values occurring on XYZ crane barge under each lifting load direction condition indicated in Figure 5 and Figure 6, as well as the comparison of longitudinal strength results on XYZ crane barge during operations, are presented in Table 4.It can be observed that the trendline of the load distribution occurring on the XYZ crane barge, using both the analytical and numerical methods, exhibits similarities.The positioning of each load along the vessel's length caused significant changes in the spreading pattern along the XYZ crane barge.The increases are noted in the position from frame 3 to frame 19, which corresponds to the location of the superstructure, from frame 13 to frame 40, where the water ballast tanks are located, and from frame 45 to frame 55, which corresponds to the lifting load area with variations in the crane rotation angle.The shear force and bending moment results on the XYZ crane barge, using both the analytical and numerical methods, show similar trendline shapes.The maximum shear force occurs at frames with significant net load values transitioning from positive to negative, and the maximum bending moment occurs at frames where the crane is positioned.Specifically, the shear force occurs at frame 40, while the bending moment occurs at frame 47, frame 48, and frame 49, as tabulated in Table 4.

Conclusions
It can be concluded that the trendline of the load distribution on the crane barge shows changes in the shape of the load distribution for each rotation angle of the lifting load.These changes occur in the lifting load region, specifically between frame 45 and frame 55.The maximum shear force occurs at frame 40 for each rotation angle of the lifting load.It corresponds to a significant change in the net load value from positive to negative, where the analytically and numerically calculated shear force values are 775 tons and 736 tons, respectively.The maximum bending moment occurs at frame 47, corresponding to the crane's position, where the analytically and numerically calculated bending moment values are 2107 ton.m and 2126 ton.m, respectively.With these results, the percentage error for both shear force and bending moment, compared between analytical and numerical calculations, remains below 5% of the allowable limits based on DNV Rules, where the maximum percentage errors are 1.52% and 4.82%.Based on the results in Table 4, the analytical and numerical methods exhibit increased shear force and bending moment values with each change in the lifting load rotation angle.The highest shear force and bending moment values occur at condition 7 using analytical and numerical methods.Specifically, for condition 7, the shear force values are 755 tons and 736 tons, while the bending moment values are 2107 tons and 2126 tons.m.Table 5 shows that comparing shear force and bending moment results between the analytical and numerical methods on the XYZ crane barge complies with the tolerance limits.The percentage errors obtained are below 5% when using the standard DNV RU-SHIP Pt. 3 Ch.5 as allowable.The maximum percentage errors occur at frame 12, frame 40, and frame 51.The most significant percentage errors for shear force and bending moment among all conditions are observed in condition 7, where the percentage errors are 1.52% and 4.82%.

Note: fr. = frame
1298 (2024) 012021 IOP Publishing doi:10.1088/1755-1315/1298/1/012021 2 much the loading effects occur and determine the minimum required strength for safe operation.The longitudinal strength analysis is carried out in free-floating conditions without considering environmental factors.The structure lifted in this Heavy Lifting operation is the Topside of the Meliwis Wellhead Platform, where various angle variations of the lifting load conditions are used in this Heavy Lifting operation scenario, as shown in Figure 1.The resulting longitudinal strength of the crane barge is checked against the safe limits according to Det Norske Veritas (DNV) Rules (DNV RU-SHIP Pt. 3 Ch.5).

Figure 3 .
Figure 3. Division of XYZ crane barge based on 55 frames in operational condition (side view).

Figure 4 .
Figure 4. Load distribution graphics in each condition of lifting load direction using analytical and numerical methods.

Figure 5 .
Figure 5. Shear force graph in each condition of lifting load direction using analytical and numerical methods.

Figure 6 .
Figure 6.Bending moment graph in each condition of lifting load direction using analytical and numerical methods.

Table 1 .
Summary weight data of the Topside structure.

Table 2 .
Principal dimension of XYZ crane barge.

Table 5 .
Percentage of maximum longitudinal strength error.

Table 4 .
Maximum shear force and bending moment values.