Multiscale structural analysis inspired by exceptional load cases concerning the immersed tunnel of the Hong Kong-Zhuhai-Macao Bridge

Abstract

This paper contains an assessment of the added value of multiscale material models for concrete in the context of macroscopic structural analysis of (steel-reinforced) concrete structures. Two examples are discussed. They are inspired by the possibility of car accidents inside the immersed tunnel of the Hong Kong-Zhuhai-Macao Bridge (HZMB). The first example deals with vehicles crashing into the tunnel wall. The high-dynamic strengthening effect of concrete is studied based on an engineering mechanics model. The structural nature of the dynamic strength increase factor (DIF) is demonstrated by means of high-dynamic strength values measured on mortar cylinders of different size. Furthermore, the evolution of the DIF as a function of hardening of concrete at material ages beyond 28 days is studied. A validated multiscale model for concrete renders a customized analysis for the specific concrete used for the aforementioned tunnel possible. It is found that the DIF decreases with progressive hardening of concrete at material ages beyond 28 days. The second example is inspired by tunnel fires as may happen after car accidents. The study refers to thermal stresses in steel-reinforced concrete beams subjected to sudden heating. The thermal expansion coefficient of the concrete of the tunnel is quantified by means of a multiscale model. It is used as input for linear thermo-mechanical Finite-Element simulations of steel-reinforced concrete beams. The essential macroscopic simulation results are temperature distributions and associated stress fields. They are employed for top-down quantification of microscopic stress states inside the cement paste and the aggregates. This allows for quantifying two sources of microstructural stress fluctuations: (i) the macro-to-micro stress concentration and (ii) the mismatch of microscopic thermal expansion coefficients. In both examples, the multiscale models for concrete have increased the informative content of the structural simulations.