Thermo-mechanical experiments of RC structures correlated to distributed coda signals

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Assessment, maintenance, strengthening, and renewal of infrastructure buildings remain one core task of responsible authorities in Germany and worldwide. Functioning transport routes with unique bridges and tunnels form our economic backbone. Their importance requires prudent and far-sighted action. Today decisions and forecasts of residual structural lifetimes are increasingly based on long-term monitoring data.The global aim of RUB 2 is to enable and promote an application of non-destructive coda techniques to large RC structures like bridges and tunnels. The idea is twofold, namely first, to make structures transparent (“glass-like”) for significant inner damages and second, to enable structures to autonomously report to responsible authorities and “react” in cases of relevant damages following the idea of a future “cognitive building infrastructure”.To extend the range of application of damage detection and assessment by coda wave techniques step by step to realistic cases of non-destructive testing in monitoring praxis of RC structures, the project follows five steps in the second phase:First, pre-stressing is introduced to give pressure-induced versus tension-induced changes a decisive edge to enable recording of positive and negative strains and to establish direct correlation of coda properties and strains. Second, the impact of complex geometries and a loss of direct sight between ultrasonic transducers as well as damaged surfaces, imitated by surface roughness, shall be quantified in the coda.Third, spatial maps of damage probability obtained from correlation of the relative velocity change in the coda and strains will enable to generalize and transfer measured signal changes to arbitrary structures.These components are joined in an integral full-scale demonstrator (4th step), which will be used to prove that externally invisible losses of pre-stress by tendon rupture can be successfully detected and localized.Finally, the two reference structures, “Gänstorbrücke” at Ulm and the “Scheidplatz” subway station in Munich will be used to assess the practical applicability and performance of the coda-based monitoring method.