Multiscale Modeling - Structural Analysis - Experiments
Herbert Mang, Technische Universität Wien
The lecture consists of a report about a joint research project of Tongji University, Shanghai, and Vienna University of Technology. Its title reads as “Bridging the Gap by Means of Multiscale Analysis”. It was inspired by the tunnel between the two parts of the Hongkong-Zhuhai-Macao Bridge, connecting cities on opposite sides of the mouth of the Pearl River into the South Chinese Sea. The project stretches over the time period 2015-2019 and is financially supported by the Austrian Science Fund and the China Scholarship Council. The project focuses on the use of modern multiscale material models for concrete in the context of structural analysis. It consists of four topics.
The first one deals with the increase of the high-dynamic strength of specimens made of concrete with increasing speed of loading. It is quantified by means of an engineering mechanics model. The structural nature of the dynamic strength increase factor (DIF) is verified with the help of a comparison of model predictions with results from laboratory tests. Furthermore, the evolution of the DIF as a function of hardening of concrete at material ages beyond 28 days is studied by combining the engineering mechanics model with a predictive multiscale material model for the quasi-static compressive strength of concrete.
The second topic is devoted to the thermal expansion of mature cement paste as a nonlinear function of the internal relative humidity. It is found that a temperature increase results in a quasi-instantaneous release of water by nanoscopic cement hydrates and vice versa. This yields a quasi-instantaneous change of the internal relative humidity and the effective pore underpressures. This amplifies the temperature-induced swelling (or shrinkage) observed at macroscopic material scales. The validated multiscale model is used as input for linear thermo-mechanical Finite-Element simulations of structures subjected to sudden temperature changes.
The third topic deals with reinforced concrete hinges subjected to eccentric compression. They exhibit a ductile failure behavior. This is analyzed by means of nonlinear three-dimensional Finite Element simulations. The required input parameters are identified based on experimental data from laboratory experiments. Parameter identification is supported by a multiscale model for tensile failure of concrete and linear-elastic two-dimensional Finite Element simulations. After parameter identification, bearing capacity tests by Schlappal et al. (2017) are simulated. The obtained results agree well with the experimental observations.
Multiscale structural analysis of segmental tunnel rings subjected to ground pressure is the last topic. The structural model combines analytical solutions of the linear theory of slender circular arches with interface models. Both unreinforced and bolted interfaces are analyzed. The interface models account for linear-elastic and ideally-plastic behavior of both concrete and steel. Elastic limits and bearing capacities of segmental tunnel rings are quantified as a function of the coefficient of lateral ground pressure. The simulations are validated by comparing numerical output with results from real-scale bearing capacity tests of segmented tunnel rings.
The presented examples underline the benefits resulting from the combination of modern multiscale and multiphysics material modeling, structural analysis, and innovative experiments both at material and structural scales.
Herbert Mang, Technische Universität Wien
The lecture consists of a report about a joint research project of Tongji University, Shanghai, and Vienna University of Technology. Its title reads as “Bridging the Gap by Means of Multiscale Analysis”. It was inspired by the tunnel between the two parts of the Hongkong-Zhuhai-Macao Bridge, connecting cities on opposite sides of the mouth of the Pearl River into the South Chinese Sea. The project stretches over the time period 2015-2019 and is financially supported by the Austrian Science Fund and the China Scholarship Council. The project focuses on the use of modern multiscale material models for concrete in the context of structural analysis. It consists of four topics.
The first one deals with the increase of the high-dynamic strength of specimens made of concrete with increasing speed of loading. It is quantified by means of an engineering mechanics model. The structural nature of the dynamic strength increase factor (DIF) is verified with the help of a comparison of model predictions with results from laboratory tests. Furthermore, the evolution of the DIF as a function of hardening of concrete at material ages beyond 28 days is studied by combining the engineering mechanics model with a predictive multiscale material model for the quasi-static compressive strength of concrete.
The second topic is devoted to the thermal expansion of mature cement paste as a nonlinear function of the internal relative humidity. It is found that a temperature increase results in a quasi-instantaneous release of water by nanoscopic cement hydrates and vice versa. This yields a quasi-instantaneous change of the internal relative humidity and the effective pore underpressures. This amplifies the temperature-induced swelling (or shrinkage) observed at macroscopic material scales. The validated multiscale model is used as input for linear thermo-mechanical Finite-Element simulations of structures subjected to sudden temperature changes.
The third topic deals with reinforced concrete hinges subjected to eccentric compression. They exhibit a ductile failure behavior. This is analyzed by means of nonlinear three-dimensional Finite Element simulations. The required input parameters are identified based on experimental data from laboratory experiments. Parameter identification is supported by a multiscale model for tensile failure of concrete and linear-elastic two-dimensional Finite Element simulations. After parameter identification, bearing capacity tests by Schlappal et al. (2017) are simulated. The obtained results agree well with the experimental observations.
Multiscale structural analysis of segmental tunnel rings subjected to ground pressure is the last topic. The structural model combines analytical solutions of the linear theory of slender circular arches with interface models. Both unreinforced and bolted interfaces are analyzed. The interface models account for linear-elastic and ideally-plastic behavior of both concrete and steel. Elastic limits and bearing capacities of segmental tunnel rings are quantified as a function of the coefficient of lateral ground pressure. The simulations are validated by comparing numerical output with results from real-scale bearing capacity tests of segmented tunnel rings.
The presented examples underline the benefits resulting from the combination of modern multiscale and multiphysics material modeling, structural analysis, and innovative experiments both at material and structural scales.
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