The increasing global container trade has intensified demands on container handling technology. Automation has addressed many challenges, but limitations persist, particularly in spreader design. These attachments, equipped with rotating twist locks, rely on remote-controlled actuators and sensors. However, current designs exhibit frequent maintenance, multiple failure points, and limited sensing capabilities. Additionally, dependence on external power restricts mobility, limiting their use in smaller terminals and remote operations. This research employs an iterative design approach to develop a novel spreader that reduces maintenance frequency by 75 percent, minimizes failure points by 50 percent, and integrates an advanced control algorithm with built-in error detection. This reduces reliance on remote operators, enhancing safety by mitigating operator fatigue-induced errors. An internal power source enables 20 hours of continuous operation, while the independent control system reduces downtime by 1 hour, minimizing delays from operator breaks.

In heavy lifting a paradoxical problem has arisen: A gantry is brought to life to omit the use of a large crane, because of spatial, durational, and monetary reasons. But, in order to assemble and disassemble the gantry, a large crane is needed. This thesis presents a solution to this paradoxical problem. The solution is a novel design that is able to (dis)assemble a gantry without a large crane.

The design is established via a set of requirements based on a case study, crane capacities, and ways of working in Mammoet. Best practice solutions were developed for the five stages from assembly to disassembly of a gantry. A selection of best practice solutions, based on the requirements, was put in a morphological chart. This chart generated seven concepts that were evaluated using a qualitative multi criteria analysis. The top three concepts had similar scores, therefore a second round of assessment was performed to decide on a final concept.

The final concept is a climbing frame. This frame consists of two climbing cages that are connected via two gantry beams. Each climbing frame is equipped with a hoisting system that is used to lift and roll the new MLS mast sections in place. The two towers that form the gantry will be erected simultaneously, with the total upper structure on top. Climbing will happen via the vertical moving frame. This frame is equipped with retractable pins that grab on to jack-up blocks that are present on the mast sections. The vertical moving frame can translate in vertical direction by means of winches that are connected to the climbing frame. It was required that the disassembly procedure happened using the same system as the assembly procedure. Disassembly would be impossible if the upper structure is still over the vessel. Therefore, after the gantry lifted the vessel, the gantry beams must split. To split the gantry beams, two cantilevering guidance beams are present. The climbing frame is designed such, that when the gantry is in its final position, the case study gantry design is established. The only difference is that the self-weight of the climbing frame is acting on the gantry. Meaning that solely the original top frame beams and the added self-weight are decisive in the validity of the gantry’s main purpose; lifting the vessel. This also means that the climbing frames are solely meant for climbing.

The validation of the final design follows from hand calculations and a finite element model made in SCIA Engineer. Fundamental design features, such as the climbing system, the MLS hoisting system, and skidding of the upper structure are designed and validated too.

Debatable elements of this research are the scope limitations like other duties of the assist crane or being a tailored solution for a Mammoet gantry. However, this design offers freedom in projects and the route to arrive at the design can be applied more broadly. The subjective nature of the qualitative multi criteria analysis, the assumptions made, and the preliminary design stage are debatable too. Therefore, it is recommended to investigate other solutions to the problem. Promising solutions according to this thesis are; a climbing crane, a climbing frame that climbs from the bottom, and a skidding system that translates the whole gantry. Also, all assumptions need to be investigated to be able to fabricate and use this design.

Nevertheless, a proof of concept can be concluded from this research. This self-erecting gantry system is able to (dis)assemble a gantry. Compared to the crawler crane that was needed to perform the critical lift for the case study gantry, this design saves roughly 2100 m2 of space. That is a reduction of 65%. Approximately €6,000,000.- is needed for the realization of this design. Meaning that during the ninth project the costs for the crawler crane are earned back. It is estimated that the erection of the gantry and the assembly of the climbing frame is comparable to the assembly of the crawler crane and the erection of the gantry. All in all, the design is a future proof solution that can conquer the never-ending need for cheaper and faster heavy lifting projects on dense locations.

Crane hardstands serve as crucial platforms for supporting heavy lifting equipment and ensuring operational efficiency. However, crane hardstands are not infinitely stiff and will deform upon loading. Uneven loading during wind turbine installation will result in differential deformation of the crane hardstand, causing the crane to tilt. A small tilt of 0.3°, which is equivalent to around 30-60mm differential settlement depending on the crane, will create safety hazards, causing construction to be discontinued. As a result accurate deformation predictions are required to design a sufficient crane hardstand.

This research is conducted to investigate the influence factors of the deformation of a crane hardstand, evaluate the current prediction method and to improve the accuracy of future deformation predictions, so the hardstands can be designed more efficiently.

The research begins with a literature study on the above surface influences on the magnitude of the load and the corresponding soil behaviour of the soil profile beneath the hardstand. Furthermore the current prediction method is analyzed to dictate shortcomings. The expected influences found in the literature study are examined with full scale monitoring and testing cases. Finally, a sensitivity analysis is performed on the current prediction model to specify the parameters with the biggest influence on deformation for different variants. These parameters are then assessed on how a more accurate determination might influence the predicted deformations.

The numerical simulations are carried out using advanced finite element analysis software Plaxis, specifically the HS(small strain) model. This model enables the investigation of various factors affecting hardstand deformation, such as varying soil stiffness, load distribution, and foundation characteristics.

The biggest shortcoming of the current prediction method is found to be the exclusion of time dependent behavior. And the most influential soil parameters of the HS(small strain) model after the addition of a consolidation phase to the model are found to be the stiffness and permeability parameters. The deformation prediction is done for the entire range of uncertainty of these parameters (5-, 25-, 50-, 75-, 95- percentiles) to quantify prediction accuracy improvements were these parameters determined witch precise. For both peat and clean clay the permeability coefficient is found to, when determined more accurately, have a 50% chance to result in a predicted deformation reduction of between 40 to 60 %, while a more accurate prediction of the stiffness parameters E_oed E₅₀ E_ur has a 50% chance to result in a predicted deformation reduction of between 65 to 75%

The findings of the research can be used by engineers to test the effectiveness of their own hardstand deformation prediction method and provide advise on the benefits extra soil investigation might lead to.



Keywords: Crane hardstands, deformation analysis, differential settlement, cyclic loading, Hardening soil small strain, FEM-modeling, sensitivity analyses.

In this thesis, an automated buckling check method has been developed and validated for thin plated stiffened structures used in stressed skin topsides.

Thin plated stiffened structures are widely used in, for example, aircraft, bridges and ships. Recently, it has become competitive to use this type of construction to offshore topsides as well. Originally, topsides were built as a lattice structure, mainly for the oil and gas industry. Over the years, it was found that these lattice structures are sensitive to fluid and air leakage. Due to the later development of offshore wind farms with high voltage equipment, topsides were now also required as transformer houses for these farms. This necessitated topsides less sensitive to leakage, using a stressed skin structure.

Stiffened plated structures in compression are prone to fail by buckling. Therefore, each panel must be checked for every possible load case in the lifetime of the structure. There are three methods in which stiffened panels can be checked for buckling: full-scale experiments, FEA and by design code. Full-scale experiments are not cost-efficient because each topside is exposed to many different load conditions. Therefore, the only economically viable methods are FEA and design codes. Compared to non-linear plastic FEA, design codes are most economical and therefore the most cost-efficient choice for larger structures like topsides. However, the design code method yields more conservative results compared to non-linear plastic FEA.
Due to the use of many panels in a stressed skin topside, a demand has arisen for an automated application of the DNV-RP-C201 buckling standard for stiffened plated structures. This automated method opens up the possibility of stiffener placement optimization. This means that the stiffeners no longer need to be modelled in the design. In other words, during the design phase, non-stiffened panels can be modelled. At a later point in time, the optimization method can determine the number and type of stiffeners and stringers needed in the structure to ensure stability according to the DNV-RP-C201 design code.

Buckling analysis is dependent on a large set of variables and design considerations. The developed method sets clear boundaries for the applicability of the method and justifies the choices made.

Design codes have their limitation concerning assumptions which are not close to real conditions. Panels are subjected to uneven, distributed loads. Design codes provide rules for linear distributed loads over non-stiffened panels, but not for stiffened panels. For stiffened panels, because of the effective width method, an average stress distribution over a plate-stiffener is assumed. It was unclear whether large stress distributions over plate-stiffeners would cause a degrading effect on their ultimate resistance. Therefore, a validation study has been performed for uni-axially loaded stiffened panels. Non-linear plastic FEA has been used to determine the ultimate resistance.

From these “numerical experiments”, it can be concluded that the effective width method can be applied in most cases of stiffened panels. However, in the case of a plate slenderness between 3 and 4.28, large stress distributions can have a degrading effect on the ultimate resistance of the plate stiffener. Therefore, for plate of such slenderness, the maximum of a stress distribution should not exceed twice the minimum.

The stiffener optimization method developed in this thesis allows engineers to design stability-governed structures without modelling each individual stiffener. This enhances design flexibility and majorly simplifies the FE model. Later, the method can quickly generate a stiffener placement optimum, which would not be feasible by hand.

Fatigue is typically a governing limit state for maritime structures, and weld joints are the most critical locations. Various fatigue damage criteria have been developed involving either an intact or cracked geometry parameter, incorporating local or global information. In this thesis, the effective notch stress based total life fatigue damage criterion has been used in order to improve the accuracy of fatigue lifetime prediction and reduce the workload of engineers in the early design stage. First, the Battelle structural stress calculation procedure is clarified and examined with three models. A hot spot type A, B and C mesh convergence study are conducted. In order to quantify the influence of mesh quality, several ugly mesh models are tested with their good mesh counterparts. For validation purposes of the total life model, a large scale specimen fatigue test result has been used and the mesh quality investigations are included. The DNVGL based life time estimate is provided for the sake of comparison. Finally, several conclusions and recommendations are provided for future applications.

Offshore contractors use special cable laying vessels (CLV’s) in order to install subsea power cables, which transport offshore generated energy. Workability studies are performed to evaluate whether operations can be performed or not. These workability studies are subsequently a combination between operability assessments (performed in OrcaFlex months prior to operation) and forecasted weather windows. During the operability assessment, eventually limiting sea states are defined which are expressed in significant wave height (Hs), wave peak period (Tp) and incident wave angle relative to the vessel heading (a). If the forecasted weather windows exceed the predefined limiting sea states, operations cannot be executed. These current workability assessments are based on 1D JONSWAP spectra. This thesis contains an exploratory study of implementing a motion-based forecasting (MBF) method into workability studies, based on 2D wave spectra. This is done by focusing on the motions at the chute of the CLV, as this is where the subsea power cable leaves the CLV. Before MBF can be implemented, however, at first a specific limiting motion predictor needs to be identified that covers the cables integrity limits. Furthermore, this limiting motion needs to be quantified as well in order to compare this essentially composed new cable limit with MBF predicted chute motions. Subsequently, all cable integrity criteria need to be converted into this limiting motion to preserve the subsea power cables integrity. For normal cable lay operations, eventually all mechanical properties and cable limits are covered by three main cable integrity criteria. These are minimum bending radius (MBR), minimum bottom tension (BT) and maximum top tension (TT). By means of modelling a lot of various environmental loading conditions, the research described in this thesis shows that the chute z velocity is eventually indicated as a proper limiting motion predictor. Out of all investigated chute motions, chute z velocity (which represents the vertical velocity of the chute) shows the best correlations with the aforementioned cable integrity criteria. To determine workability by implementing motion based forecasting, this limiting chute z velocity needs to be quantified. The chute z velocity needs to account for all three main cable integrity limits, hence these limits are essentially converted into one single chute z velocity limit (which is essentially a new introduced cable limit). To quantify this limiting chute z velocity not the entire relation is of interest, but only the range close to breaching the cable integrity limits. Therefore, a percentile line method is introduced which is constructed on the 90th-percentile values per bin. Based on this research, it was found that binwidths must not exceed values of 0.5m/s to obtain robust results. However, no minimum amount of data points per bin was established as this varied for all assessed subsea power cables. Finally, workability studies of the current 1D JONSWAP (based on a single Hs −Tp sea state) method was compared to a 2D superimposed JONSWAP accounting for both swell and wind wave contributions. This comparison indicates that when determining workability based on more detailed 2D spectra, the workability study provides more smoothed results. This means, the higher chute z velocity peaks from the 1D total sea state are downscaled when simulating a 2D spectrum, whereas the lower chute z velocity peaks from the 1D total sea state are upscaled when implementing a 2D spectrum. The obtained motion-based chute z velocity forecasts indicate that optimization is possible by splitting the total sea states into both swell and sea waves contributions and accounting for wave spreading.