Bridging the Gap by Means of Multiscale Structural Analyses

Occasionally, multiscale analyses of structures are somewhat indiscriminately regarded as a panacea for the improvement of the quality of structural analysis. The reason for this is that, contrary to conventional structural analyses, chemical, thermal, hygral, and poromechanical information from scales far below the macroscale of the respective heterogeneous material is used. However, multiscale analyses are based on assumptions which are not always supported by sufficient experimental evidence. This refers e.g. to the number of scales and phases inside so-called representative volume elements, the mathematical homogenization method for the transfer of information from a particular scale to the next higher one, and treatment of the conceptually challenging problem of homogenization of material failure. This situation elucidates the topicality of the present research project. Its ambitious goal is quantification of the added value of multiscale analyses, notwithstanding the explicit acknowledgment of the scientific progress that manifests itself in such analyses. The overriding research object is the 35.6 km long Hongkong Zhuhai Macao Bridge, presently under construction. For shipping, the bridge is interrupted by a 6.7 km long tunnel below the bottom of the sea, representing the actual research object. The topographical term Bridging the Gap corresponds to the mathematical bridging of several mechanical orders of magnitude in multiscale analyses of tunnel segments. In particular, this concerns the investigation (a) of the development of the temperature and the strain state in a reinforced-concrete segment shortly after casting and (b) of the mechanical behavior of (1) a segment after the outbreak of a fire, (2) the model of a long portion of the tunnel subjected to earthquake loads, and (3) the model of the connection of neighboring tunnel elements by means of shear keys. Multiscale analyses of these four structures and the preceding methodical developments will be carried out at TU Vienna. The results will be compared with results from experiments, performed by members of the College of Civil Engineering of Tongji University, Shanghai, ranked number one in China, to a lesser part on the building site, mainly however in world-class laboratories of this university. To quantify the added value of multiscale analyses, the results will also be compared with results from conventional structural analyses, carried out by a Chinese consulting firm at the planning stage of the building. These results and the test results will be placed at the disposal of the Viennese research team, free of charge. At planning of the project, the experimental boundary conditions had to be considered. Attention was paid to the greatest possible complementarity of the four experimental test groups. The uniqueness of the project arises from the trias of experiments, conventional structural analyses, and novel multiscale structural analyses of a remarkable civil engineering structure. i

The project "Bridging the gap by means of multiscale structural analysis" formed the framework for the successful cooperation between civil engineers from TU Wien and Tongji University, Shanghai, the leading Chinese university in the field of Civil Engineering. Eva Binder, Thomas Schlappal, Hui Wang and Jiao-Long Zhang worked on their doctoral theses under the supervision of University Professor Herbert Mang and Associate Professor Bernhard Pichler. Mr. Wang completed the first double-doctorate in the history of the two universities, in 2019. The second degree of this kind will be completed by Ms. Binder, in autumn 2020. The project was a career springboard for everyone involved. Eva Binder continues her academic career as a postdoc at Linnaeus University in Vaxjö, Sweden. Thomas Schlappal started a career in practical tunneling in Germany. Hui Wang applied successfully for the position of an "Assistant Professor" at the Shanghai Jiao Tong University, #47 in the global QS university ranking 2021. Jiao-Long Zhang applied successfully for the position of an "Assistant Research Fellow", a tenure track position at Tongji University. Bernhard Pichler has been appointed university professor for "Experimental Mechanics and Structural Analysis" at TU Wien. Herbert Mang received the "International Science and Technology Cooperation Award", the highest award granted by China to foreign scientists. From a scientific viewpoint, the added value of multiscale analysis was demonstrated using selected examples from concrete and reinforced concrete construction. Multiscale material analysis of cementitious materials was performed to identify previously unknown processes at the microstructure of these materials, which are responsible for their macroscopic behavior. For instance, in the field of thermal expansion, it was shown that nanoscopic calcium-silicate-hydrates, which are the products of the chemical reaction of water with cement, release water spontaneously and reversibly when heated. This decreases the underpressure in the pore water, which results from capillary tension, and the solid skeleton of the material expands in a macroscopically measurable fashion. These processes, described for the first time, were independently confirmed by nuclear magnetic resonance relaxometry experiments. Thus, multiscale material analysis has led to an essential scientific advance of knowledge in the field of basic research in material science. Multiscale structural analysis refers to structural analyses, carried out by means of modern multiscale material models. The performed analyses referred to hailstorms on concrete slabs used for highways, moderate fires in tunnels, and the high-dynamic increase of strength of specimens made of cementitious materials. In addition, new methods for structural analysis and innovative design guidelines were elaborated for reinforced concrete hinges and segmental tunnel linings, such as produced by tunnel boring machines. Thus, multiscale structural analysis has led to essential scientific advances of knowledge in the field of application-oriented basic research regarding engineering mechanics of reinforced concrete structures.