Repurposing wind turbine blades as main structural elements in traffic bridges

Abstract

Wind turbine blades have a service life of around 20 to 25 years and are then decommissioned while generally still having excellent structural performance and high-value material properties. Currently, the recycling options for the fibre-reinforced polymer (FRP) composite components that make up the blade are limited, so most blades are either landfilled or incinerated at the End-of-Life, essentially wasting these qualities. By repurposing the blades instead, the qualities can be preserved while also lowering the environmental impact of the new structure. This research focusses on repurposing decommissioned wind turbine blades as main structural elements in traffic bridges, where the focus is on the structural design and feasibility.

The possibilities for repurposing largely depend on the type, size and condition of the specific batch of blades. Based on literature research regarding the common features of blades that are soon to be decommissioned, a custom 38-meter-long blade model is developed. Next, a variety of design options including multi-membered bridge structures have been created and arranged in an overview. By combining these options with the findings from the literature study, several designs for ‘blade bridges’ are proposed, most of which have the potential to already be realised in the upcoming years. Some of these designs are only intended for pedestrians and cyclists, while others are intended for regular road traffic. The maximum allowable spans for these bridge designs are all between 15 and 20 meters, thus confirming the large potential for repurposing blades in bridges.

Based on the structural analysis of the blade bridge designs, it can be concluded that for blade bridges as pedestrian and bicycle bridges, the natural frequency is governing. A prerequisite is that the blade-to-support connections at the aerofoil parts are designed to prevent stress concentrations, but this should be easily achievable. For road traffic bridges, it is found that the deflections are of greater importance than the natural frequencies. Also, the blades in a road traffic bridge will be highly stressed, especially locally near the supports of the aerofoil parts. These local stresses are likely to be governing, making the connection design at these supports crucial. A thorough investigation of these local stresses is therefore recommended in a real-life blade bridge project.