Many navigation locks in the Netherlands under management and maintenance of Rijkswaterstaat need to be replaced or renewed in a sustainable way before 2050. In order to achieve this goal, Rijkswaterstaat is planning to renew as sustainable and cost-effective as possible. Most of the navigation lock gates that have been renewed in the last decades are made in steel, especially mitre gates. However, timber is a more sustainable material than steel to replace the navigation lock gates. The goal of this thesis is to find out why timber is scarcely used for the renewal of mitre gates with a navigation lock chamber wider than 12 metres and to extend the application of timber in an innovative way for the renewal of existing mitre gates to replace steel mitre gates.

First, the structural layout of the mitre gates was analysed. Further research has shown that the steel design of mitre gates is more profitable than the current timber design for lock chambers above 12 metres width, because all the existing timber mitre gates are made by solid timber beams, which have limited availability due to the required dimensions. Further, the mortise and tenon joint of the main girders and posts is one of the challenges and critical parts of timber structures. Recent innovations, such as timber lamination, crossed or not, increases the strength and stiffness characteristics and creates more freedom in the design of the cross section size and shape, which makes timber a construction material that could be more competitive with other often used construction materials, steel for example. Since the mitre gates need to withstand the loads in both vertical and horizontal directions, cross laminated timber can be efficient. In building engineering, laminated timber is usually glued, however, for hydraulic engineering, this is not possible yet as no adhesive is appropriate in a wet environment. It is therefore chosen to further investigate the possibility of applying mechanically jointed cross laminated timber in a mitre gate.

The eastern navigation lock of Sambeek is considered as a suitable case study location to investigate. This lock chamber has a width of 16 metres, a water retaining height of 8.44 metres and a maximum differential head of 4.2 metres. The results of the preliminary design for this mitre gate consists of a dowel cross laminated skin plate, semi-ellipse web plates and three layered laminated curved girders. The skin plate in the renewed design contains layers in vertical and horizontal directions to transfer the load in both directions. Furthermore, the skin plate contains diagonally orientated layers to replace the steel strut and tension bar. The girder of the mitre gate is curved to create the biggest stiffness halfway the width of the mitre gate and spare the used amount of timber sideways. The web of the redesign is the connector of the skin plate and the girder. The challenge of the mortise and tenon joint is solved by directly supporting the girder towards the lock chamber wall. This results in a skin plate of 6 layers; all with a thickness of 25 mm. The skin plate has 2 horizontally orientated, 2 vertically orientated and 2 diagonally orientated layers. The curved laminated girder has 3 lamellae each 100 millimetres thick and the distance to the skin plate and girder varies between 0 and 300 mm. In between the girder and skin plate, a web plate of 150 millimetres thick is constructed. The girder and web plate are repetitive elements with a centre to centre distance of 1.5 metres vertically.

To verify the preliminary redesign, the mitre gate is modelled in a finite element program. In this finite element program, the mitre gate is built up of beam elements, and the interaction of the timber elements and fasteners is simulated with springs. For the closed mitre gate, the global outcomes of the model and preliminary design are consistent, but the interaction between the fasteners and timber elements in the dowel cross laminated skin plate requires further research. Furthermore, it can be concluded that the use of cross laminated timber is an equivalent replacement of the steel strut and tension bar to resist the self-weight of the mitre gate.

Based on the performed research in this thesis, the renewed design of timber mitre gates is at an early stage but attainable for the future. The mitre gate with cross laminated timber skin plate works as efficient as the steel gate and is more sustainable. However, the challenge remains in the connection of the timber elements and further research is needed to make the design feasible. The development in the material and connection method would make timber mitre gates more attractive during the choice of design.