Abstract
Cracks can occur in reinforced-concrete onshore wind turbine foundations due to factors such as the use of substandard concrete mix, mistakes in foundation design or multi-stage concrete pouring under challenging weather conditions. Cracks are routinely identified via above ground inspections and follow-on examination of excavated underground surfaces and are repaired, for example with resin injection and grouting. Their impact on the structure or the efficacy of the repair are often unknown as crack degradation during normal operating conditions is unexplored. In this work, sub-surface cracks in an onshore wind turbine foundation have been instrumented with fibre-optic based strain sensors in an attempt to determine severity and magnitude of deterioration over time. Here we determine cracks monitored show a small magnitude of deterioration over the initial 9-month period after sensor installation, suggesting that repair is not required. We propose a novel methodology for the classification of the types of deterioration evident in cracks as “reactive”, “permanent” and “behavioural”, and demonstrate methods to extract these types of deterioration. Such methods will continually be developed over time as further knowledge of crack behaviour is gained to determine appropriate limits and identify the optimal time to repair.
Highlights
Onshore wind turbines are becoming a focus of structural health monitoring (SHM), due to their hugely increasing role in renewable energy generation
During early stages of monitoring, we have found that cracks show a linear response to load, or equivalently, to the strain measured in the tower: ΔLa = Jp ∊T
The objective of this work is to identify if the cracks monitored are displaying any visible deterioration in data over the initial 9 month period, beginning in January
Summary
Onshore wind turbines are becoming a focus of structural health monitoring (SHM), due to their hugely increasing role in renewable energy generation. As of 2017, onshore wind energy makes up 22.5% of the world’s renewable capacity [1,2]. Support structures (usually gravity-based, reinforced concrete foundations) are the least monitored part of an onshore wind turbine despite being safety critical structures. Cracking of the concrete is of primary concern, as water ingress can cause corrosion to the steel reinforcement. This warrants the monitoring of any cracks in onshore wind turbine foundations to ensure an irreversible state is not reached
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