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

基础设施建筑的评估、维护、加固和更新仍然是德国和世界各地主管部门的核心任务。具有独特桥梁和隧道的功能运输路线构成了我们的经济支柱。它们的重要性要求采取审慎和有远见的行动。如今，结构剩余寿命的决策和预测越来越多地基于长期监测数据。RUB 2的全球目标是实现并促进无损尾波技术在桥梁和隧道等大型钢筋混凝土结构中的应用。这个想法是双重的，即第一，使结构透明（“玻璃状”）用于严重的内部损伤，根据未来“认知建筑基础设施”的设想，使结构能够自主地向主管当局报告并在相关损坏的情况下“做出反应”。在钢筋混凝土结构监测实践中进行破坏性测试，该项目在第二阶段遵循五个步骤：首先，引入预加应力，为压力引起的变化与张力引起的变化提供决定性优势，以便记录正应变和负应变，并建立直接相关性尾波属性和应变。第二，复杂几何形状的影响和超声换能器之间的直接视线损失以及由表面粗糙度模拟的受损表面，应在尾波中量化。从尾波相对速度变化和应变的相关性获得的损伤概率的空间图将能够将测量的信号变化概括和传递到任意结构。规模示范（第四步），这将被用来证明外部不可见的损失预应力筋断裂可以成功地检测和定位。最后，两个参考结构，“Gänstorbrücke”在乌尔姆和“Scheidplatz”地铁站在慕尼黑将被用来评估的实际适用性和性能的尾波为基础的监测方法。

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.