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

基础设施建筑的评估、维护、加强和更新仍然是德国和世界各地主管当局的一项核心任务。独特的桥梁和隧道构成了我们的经济支柱。它们的重要性要求采取谨慎和有远见的行动。今天，对剩余结构寿命的决策和预测越来越多地基于长期监测数据。RUB 2的全球目标是实现和促进非破坏性尾轴技术在大型RC结构（如桥梁和隧道）中的应用。这个想法是双重的，首先，使结构透明（“像玻璃一样”），以应对重大的内部损害；其次，使结构能够自主向主管部门报告，并在发生相关损害时做出“反应”，这是未来“认知建筑基础设施”的想法。为了逐步将尾波技术的损伤检测和评估应用范围扩展到RC结构监测实践中的实际无损检测案例，该项目在第二阶段遵循五个步骤：首先，引入预应力，使压力诱导与张力诱导的变化具有决定性的优势，从而能够记录正应变和负应变，并建立尾波特性与应变的直接相关性。其次，复杂的几何形状和超声波换能器之间的直接视线损失的影响，以及由表面粗糙度引起的损坏表面，应在结尾处量化。第三，由尾段相对速度变化与应变的相关性得到的损伤概率空间图，可以将测量到的信号变化推广并传递到任意结构。这些组件连接在一个完整的全尺寸演示器中（第4步），该演示器将用于证明由肌腱断裂引起的外部不可见的预应力损失可以成功检测和定位。最后，将使用乌尔姆的“Gänstorbrücke”和慕尼黑的“Scheidplatz”地铁站这两个参考结构来评估基于coda的监测方法的实用性和性能。

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.