Analysis of a rolling FRP lock gate

Abstract

Fibre-reinforced polymers (FRPs) are becoming a more commonly used building material in many civil engineering applications including locks. One quality of FRPs is the fact that it has a high strength to weight ratio. By applying FRPs in rolling lock gate design, the self-weight of the gate could be significantly reduced. This in turn could lead to less wear-and-tear to the support carriages, mechanical parts and rails. Self-weight is also an important factor in the stability of a rolling lock gate. A minimum weight is required to counter the moment caused by horizontal loads during opening and closing. If FRPs were to be applied in rolling lock gates an optimization of lightweight versus stability will be required. The objective of this thesis is to investigate the technical feasibility of the FRP rolling lock gate and how the gates design is affected by the stability criteria. Also, the question remains if the FRP design can compete with traditional materials, for example steel.
To quantify the problem a case study was chosen: New Lock Terneuzen. A rolling lock gate is set to be constructed to improve the connection between Ghent-Terneuzen. The rolling gates will be very large, with a span of 55 m and a height of approximately 26 m.
Initially, the rolling gate is designed with a box shape. The global dimensions of the box gate are determined with a hand calculation based on the boundary conditions and design input from the chosen case study. Basic strength, deflection and stability checks are performed. The box gate is dimensioned in both FRP and steel. The following dimensions are found for the FRP box gate: Width of 8.96 m, with retaining plates: skin:280 mm, core: 200 mm and webs: skin: 200 mm, core: 200 mm.
The dimensions found with the hand calculation serve as input for a 3D model of the design. The model is created with Scia Engineer. With this software the gate is checked with finite element analysis. Some additional checks, fatigue and creep, are performed.
The box gate model is adjusted to resemble the gate during movement. This is achieved by changing the supports, leaving the top right corner unsupported. In addition to a 3D stability check of the designed box gate, the width between the supports, representing the carriage width, is varied (from 0.5 to 12 m) and the impact on the stability is evaluated. This impact is quantified by the required dead weight to guarantee stability.
All the results are used to come up with potential improvements or alternatives to the box gate design. The main objective being a gate with increased stability, which is again quantified by the overweight required. A number of ideas are discussed, where optimizing the shape of the gate is explored further.
It is found that the required dead weight to achieve stability increased for all evaluated shapes. The main reason is the distribution of the stabilizing moment, which is split up in a horizontal and vertical component. The shape changes result in an shift from horizontal to vertical, which in turn results in more dead weight required to meet the stability criteria.
The application of FRP in rolling gate design is technically feasible. However from a stability point of view it’s questionable if FRP is the better choice over traditional materials. In the chosen case study, the amount dead weight required to fulfil the stability criteria is significant, and the lightweight quality of FRP cannot be fully taken advantage of. Laminates are designed much thicker when compared to the dimensions required to meet strength and deflection criteria. In other words, material is added primarily for the sake of adding weight.

Reducing the required dead weight was proven to be much harder than anticipated. Even though
a wide base gives a larger arm for the vertical couple, which would lead to a smaller force at an equal moment, the required weight is not necessarily reduced. The applied loads, shape of the gate, location of supports and deflections all affect the distribution of loads over the supports, both horizontal and vertical, of the gate. In a structure of this scale, even small differences can have a significant impact on the stability of the gate and the dead weight required to achieve this stability. The required dead weight to meet the stability criteria must be brought down in order for FRP to be a viable option.