Tomáš Janda

Modeling of soil structure interaction during tunnel excavation: An engineering approach

Several advancements in the modeling of soil structure interaction in the light of tunnel excavation are discussed. The theoretical formulation as well as numerical implementation are presented such as to meet the following requirements: simplicity, reliability and practical applicability to make the resulting software product available for a direct use on the construction site. To that end a recently introduced 2D3D modeling of tunnel excavation incorporating the in situ measurements is effectively combined with a fully three-dimensional (3D) beam-like representation of a typical urban structure made of masonry or precast concrete. Both standard and advanced non-linear constitutive models can be adopted to account for a potential shear failure of a subsoil material during excavation consequently triggering the evolution of damage of an above-ground (upper) structure. A simple example is provided to illustrate the proposed approach.

µMech micromechanics library

A first micromechanical library, as far as we are aware ofMultiple inclusion problem based on polynomial Eshelby solution to the single inclusion problem.Consistent implementation of analytical homogenization schemes including a novel direct integration method. The paper presents the project of an open source C/C++ library of analytical solutions to micromechanical fields within media with ellipsoidal heterogeneities. The solutions are based on Eshelbys stress-free, in general polynomial, eigenstrains and equivalent inclusion method. To some extent, the interactions among inclusions in a non-dilute medium are taken into account by means of the self-compatibility algorithm. Moreover, the library is furnished with a powerful I/O interface and conventional homogenization tools. Advantages and limitations of the implemented strategies are addressed through comparisons with reference solutions by means of the Finite Element Method.

A jigsaw puzzle metamaterial concept

Abstract A concept of a planar modular mechanical metamaterial inspired by the principle of local adaptivity is proposed. The metamaterial consists of identical pieces similar to jigsaw puzzle tiles. Their rotation within assembly provides a substantial flexibility in terms of structural behavior, whereas mechanical interlocks enable reassembly. The tile design with a diagonal elliptical opening allows us to vary elastic properties from stiff to compliant, with positive, zero, or negative Poisson’s ratio. The outcomes of experimental testing on additively manufactured specimens confirm that the assembly properties can be accurately designed using optimization approaches with finite element analysis at heart.

Hierarchical stochastic model of terrain subsidence during tunnel excavation

In this contribution the Bayesian statistical method is applied to assess the expected probability distribution of the terrain subsidence in the course of tunnel excavation. The approach utilizes a number of simplifying assumptions regarding the system kinematics to arrive at a very simple model with just a few degrees of freedom. This deterministic model together with the intrinsic uncertainties of its parameters and measurement inaccuracies are used to formulate the stochastic model which defines a distribution of the predicted values of terrain subsidence. Assuming the measured data to be fixed, the stochastic model thus defines the likelihood function of the model parameters which is directly used for updating their prior distribution. This way the model parameters can be incrementally updated with each excavation step and the prediction of the model refined.

Numerical and Experimental Modal Analysis of Laminated Glass Beams

This paper presents a numerical and experimental modal analysis of laminated glass beams, i.e. a multilayer composite structure made of glass panes bonded to an interlayer foil. These polymer foils provide shear coupling of glass layers, damping of vibrations, and play a key role in post-breakage performance. In this contribution, three-layer beams with ethylene-vinyl acetate interlayer are investigated. Using a finite element discretization and the Newton method, we solve numerically a complex eigenvalue problem which is nonlinear due to the frequency/temperature-sensitive viscoelastic behavior of the interlayer. In our experimental investigations, a roving hammer test was carried out to identify the mode shapes, natural frequencies, and modal damping. The validation shows that there is a good agreement between the numerical predictions and experimental data in natural frequencies. However, the errors in loss factors can be high, because these values are very sensitive to the material properties of polymer, frequency, temperature, and boundary conditions. These effects are discussed in the concluding part of our study.

CORRELATION RELATIONSHIPS FOR THE HYPOPLASTIC MODEL FOR FINE GRAINED SOILS

The paper is concerned with our ongoing research effort devoted to the development of reliable computational tools for the calibration of advanced constitutive models of soils. At present, such software is available for the hypoplastic model of clays applicable to soft soils. This software provides a stepping stone for the determination of potential links between individual model parameters and fundamental characteristics of soils. Identifying such links would allow for tuning the model without performing time consuming experiments, particularly in the case of an initial design. Some preliminary results are presented in the paper.

VARIATIONALLY-BASED EFFECTIVE DYNAMIC THICKNESS FOR LAMINATED GLASS BEAMS

Laminated glass, consisting of glass layers connected with transparent foils, has found its applications in civil, automotive, or marine engineering. Due to a high contrast in layer properties, mechanical response of laminated glass structures cannot be predicted using classical laminate theories. On the other hand, engineering applications demand easy-to-use formulas of acceptable accuracy. This contribution addresses such simplified models for free vibrations of laminated glass beams, with the goal to determine their natural frequencies and modal damping properties. Our strategy is to approximate the complex behavior of a laminated structure with that of an equivalent monolithic beam. Its effective thickness is determined by the variational method proposed by Galuppi and Royer-Carfagni for static problems, which we extended for modal analysis. We show that this new approach overcomes inaccuracies of the currently used dynamic effective thickness model by Lopez-Aenlle and Pelayo.

An Additively Manufactured Modular Metamaterial Composed of a Single Cell

Preliminary outcomes on a novel modular additive manufacturing technology are presentedin this contribution. The capabilities of the proposed system to synthesize materials with conventionalor meta properties are explored. Two limiting and a single mixed compositions are tested in com-pression in order to reveal both, global and local behaviours of the conglomerates. The experimentalmeasurements are supported by DIC (Digital Image Correlation) observations.

Calibration of Hypoplastic Models for Soils

The paper is concerned with hypoplastic models for both coarse and fine grained soils. It concentrates on the description of models parameters and presents procedures for their evaluation based on actual laboratory tests. The sample of sand for the calibration of the hypoplastic model for coarse grained soil comes from the Třeboň basin. The sample was classified as Sa. The second sample was classified as saCl. This sample comes from the street Evropská in Prague and was used for the calibration of the hypoplastic model for fine grained soils. The classification was performed according to ČSN EN ISO 14688-2. Keywords: hypoplasticity, fine grained soils, coarse grained soils, calibration, parameters.