PIANC Smart Rivers 2022

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Abstract : *(250~1000 words)

One of the challenges in assessing the load-bearing capacity of existing solid hydraulic structures is the formal verification of concentrated loads for non-reinforced concrete. Due to the age band-width of such structures in Germany, this applies to hundreds of cases and especially low strength rammed concrete of older structures. Typical examples are recesses for inspection gates, show-casing partial loading. Although they cannot be formally verified using the current regulations, the BAW’s Code of Practice for the verification of existing structures (TbW*) allows more detailed investigation methods to be applied, e.g. probabilistic simulations. The research project aims to develop such a verification procedure and its underlying safety concept by a classification of structural markers. As a result, the necessity of complex subsequent reinforcements for such structures could be assessed.
The principle research motivations are twofold: 1st) higher loading capacity by numerical simulations with a more realistic material model compared to the linear calculations. Its appeal includes not only an extension of the linear material behaviour stipulated in typical verification calcula-tion, but notably the contribution of tensile strength in partial loading conditions. 2nd) a higher loading capacity by reproducing a “natural” 3D bandwidth of material characteristics in these simulations. The 3D bandwidth averages to higher material strengths than the 5 per cent quantile concept typically applied to material properties, whereas the probabilistic application of the 3D bandwidth encompasses the concrete’s broad spread of mixture and localization.

The non-linear material model chosen reproduces different damage and failure modes, including tension, and replicates the fracture pattern and forces of compression tests on cubes and cylin-ders over a range of low to middle strength concrete. As the material distribution of the structures is not known in such a detail as the simulations require, a probabilistic approach is chosen to counter these uncertainties: The robustness of different combinations of variations in material properties and spatial distributions is investigated in various scenarios with  3D random fields of the material characteristics. The resulting hundreds to thousands of simulations of individual cases enable the stochastic analysis of metamodels to deduce general probabilistic results. To generate these 3D distribution fields not only based on literature research, rebound-tests have been carried out on different structure parts of two weirs and a laboratory counterpart of rammed concrete. The analysis focused on distribution and autocorrelation characteristics tailored to the construction process induced concrete layers.
These layers are currently implemented in the distribution fields. As a demonstrator step, partial segments of a lock recess are simulated with randomly mapped 3D distribution fields. The results are analysed in view of failure indicators as well as their combinations to categorize failure and deduce the capacity probabilities for specific water levels (loading).

*TbW: German Federal Waterways Engineering and Research Institute (Ed.) (2016): BAW Code of Practice “Evaluation of the load bearing capacity of existing solid hydraulic structures” (TbW). Karlsruhe: German Federal Waterways Engi-neering and Research Institute

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