Günter Hofstetter

A Galerkin-type BE-FE formulation for elasto-acoustic coupling

The interactions between the vibrations of an elastic structure and the sound field in the surrounding fluid are taken into account by coupling a symmetric Galerkin formulation of the Boundary Element Method for acoustic radiation and scattering with a standard finite element formulation for the dynamic behavior of elastic structures.

A Symmetric Galerkin Formulation of the Boundary Element Method for Acoustic Radiation and Scattering

A symmetric Galerkin formulation of the Boundary Element Method for acoustic radiation and scattering is presented. The basic integral equations for radiation and scattering of sound are derived for structures, which may consist of a combination of a three-dimensional closed part and thin-walled parts. For the numerical solution of these integral equations a Galerkin-type numerical solution scheme is proposed. The evaluation of the weakly-singular and the hypersingular integrals, occurring in this formulation, is addressed briefly. An improved CHIEF-method is employed in order to prevent the singularity of the coefficient matrix of the algebraic system of equations at so-called irregular frequencies. Subsequently, an algorithm for the automatic determination of the number of nodal unknowns at intersections of thin-walled parts of a structure, or of thin-walled parts and the three-dimensional closed part of a structure, is described. The numerical study contains comparisons of analytical solutions for simple academic examples with the numerical results. In addition, a comparison of measured and computed results is presented for a structure, consisting of both a three-dimensional closed part and a thin-walled part.

Numerical modeling of concrete cracking

M. Jirasek: Damage and smeared crack models. - I. Carol, A. Idiart, C. Lopez, A. Caballero: Cracking and fracture of concrete at meso-level using zero-thickness interface elements. - A. E. Uespe, J. Oliver: Crack models with embedded discontinuities. - G. Hofstetter, C. Feist, H. Lehar, Y. Theiner, B. Valentini, B. Winkler: Plasticity based crack models and applications. - N. Moes: Crack models based on the extended finite element method. - G. Meschke, S. Grasberger, C. Becker, S. Jox: Smeared crack and X-FEM models in the context of poromechanics.

A comparison of elastic–plastic soil models for 2D FE analyses of tunnelling

Abstract Based on 2D FE analyses, simulating the excavation of a tunnel and subsequent lining with shotcrete, the impact of the employed soil model on the predicted displacements and stresses in the soil mass as well as on the predicted sectional forces in the shotcrete lining is investigated. In particular, four different soil models are considered: linear–elastic constitutive relations, the elastic–plastic models according to the Drucker–Prager and to the Mohr–Coulomb criterion as well as an elastic–plastic cap model. The computed results are compared with available field data for the vertical strains.

A 3D BOUNDARY ELEMENT METHOD FOR DETERMINATION OF ACOUSTIC EIGENFREQUENCIES CONSIDERING ADMITTANCE BOUNDARY CONDITIONS

A 3D boundary element method for the determination of the acoustic eigenfrequencies of car compartments, characterized by a unified treatment of Robin, Dirichlet, and Neumann boundary conditions, is presented. The drawback of frequency-dependent matrices of the eigenvalue problem is overcome by means of the Particular Integral Method. Thus, the standard numerical algorithms for the extraction of eigenvalues can be applied. The numerical study contains both a comparison of numerical results with analytical solutions of a simple problem with different types of boundary conditions and a comparison of numerical results of a large-scale problem with respective numerical results, computed on the basis of the finite element method. In addition, for the latter example, different numerical algorithms for the eigenvalue extraction are examined.

An Extended Damage Plasticity Model for Shotcrete: Formulation and Comparison with Other Shotcrete Models

The aims of the present paper are (i) to briefly review single-field and multi-field shotcrete models proposed in the literature; (ii) to propose the extension of a damage-plasticity model for concrete to shotcrete; and (iii) to evaluate the capabilities of the proposed extended damage-plasticity model for shotcrete by comparing the predicted response with experimental data for shotcrete and with the response predicted by shotcrete models, available in the literature. The results of the evaluation will be used for recommendations concerning the application and further improvements of the investigated shotcrete models and they will serve as a basis for the design of a new lab test program, complementing the existing ones.

Coupled material modelling and multifield structural analyses in civil engineering

In this paper, three research topics are presented referring to different aspects of multifield problems in civil engineering. The first example deals with long term behaviour of wood under multiaxial states of stress and the effect of moisture changes on the deformation behaviour of wood. The second example refers to the application of a three‐phase model for soils to the numerical simulation of dewatering of soils by means of compressed air. The soil is modelled as a three phase‐material, consisting of the deformable soil skeleton and the fluid phases – water and compressed air. The third example is concerned with computational durability mechanics of concrete structures. As a particular example of chemically corrosive mechanisms, the material degradation due to the dissolution of calcium and external loading is addressed.

Computational plasticity of reinforced and prestressed concrete structures

This paper contains a summary of a survey of computational mechanics of reinforced and prestressed concrete structures. It begins with a description of some very important experimental results. Subsequently, mathematical models for the simulation of the material behavior are reviewed briefly, followed by an exemplary overview over the finite element method (FEM) for reinforced and prestressed concrete structures. The apparent success of constitutive models for concrete, resting on the theory of plasticity, is based, to a great extent, on the excellent works of the late Prof. J. C. Simo, representing milestones of progress in computational plasticity. The survey is completed by two examples of numerical analyses of reinforced and prestressed concrete structures.

Influence of the Constitutive Model for Shotcrete on the Predicted Structural Behavior of the Shotcrete Shell of a Deep Tunnel

The aim of the present paper is to investigate the influence of the constitutive model for shotcrete on the predicted displacements and stresses in shotcrete shells of deep tunnels. Previously proposed shotcrete models as well as a new extended damage plasticity model for shotcrete are evaluated in the context of 2D finite element simulations of the excavation of a stretch of a deep tunnel by means of the New Austrian Tunneling Method. Thereby, the behavior of the surrounding rock mass is described by the commonly used Hoek–Brown model. Differences in predicted evolutions of displacements and stresses in the shotcrete shell, resulting from the different shotcrete models, are discussed and simulation results are compared to available in situ measurement data.

Plasticity based crack models and applications

Models for the numerical simulation of concrete cracking are traditionally based either on the smeared crack approach or the discrete crack approach.