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.