Concrete structures for the hydropower industry
Performance of data-based models for early detection of damage in concrete dams
A failure of a massive concrete dam could cause catastrophic consequences. The purpose of monitoring is to detect anomalies and damage at an early stage to prevent failure. Data-based models for anomaly detection are based on the hypothesis that the behaviour of an undamaged dam will follow an expected pattern, and deviation from this pattern is an indication of damage. In this study, simulations were used to create time series for an undamaged dam and three different damage scenarios at three different locations in the dam body. Three common data-based models were used to predict a dams crest displacements, both on the generated artificial data and the corresponding measurements from the dam. Prediction bands for future measurements were created, and the ten time-series were used to test the ability to detect damage. All models could detect instantaneous damage but struggle to detect progressive damage; the Neural network outperforms the two regression models. The choice of the mathematically optimal threshold limit leads to a large number of false alerts. Requiring three consecutive values outside the threshold before an alert is issued, increases the possibility to receive an early alert compared to the standard approach where observations are classified individually.
Assessing the structural safety of cracked concrete dams subjected to harsh environment
As the dams are aging and the design requirements continuously increase, complex analyses may be required that consider aspects previously excluded in the original design. Due to the harsh environment in cold regions with significant seasonal temperature variations, many concrete dams have cracked. The development of cracks may result in internal failure modes, where parts of the dam may fail. These internal failure modes are thereby primarily governed by the material failure of reinforcement and concrete. When assessing cracked hydraulic structures, how- ever, many design guidelines are based on global safety factors for stability failure modes, i.e. overturning and sliding, while the partial coefficient methods are used for the structural design related to material failures. By using a developed design methodology based on finite element analysis, all these failure modes but also combinations of different failure modes can be considered. The design methodology is presented and
implemented to assess the structural safety of a cracked concrete spillway section. The result provides support for dam owners on how to manage pillars of concrete dams subjected to extensive cracking.
Contact: Richard Malm (profile pages)
Assessment of frost damage in hydraulic structures using a hygro-thermo-mechanical multiphase model
An extension of a novel hygro-thermo-mechanical multiphase model for simulation of freezing of partially saturated air-entrained concrete on the structural scale to account for the effect of damage in the material is presented. The model is applied in an example which investigates the extent and severity of frost damage caused by extremely cold climate conditions in a typical concrete wall in a waterway constructed with air-entrained concrete. The results were concluded to comply with observations made in experimental work and testing of freezing air-entrained concrete under exposure conditions similar to those in hydraulic structures. Furthermore, the results indicate that the effect of short periods of time with high rates of freezing was rather small on the obtained damage. Additionally, increasing the depth of the boundary region with an initially high degree of water saturation on the upstream side had also a rather small effect on the damaged zone.