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Viscoplastic material models for soil: new insight into the soil-support interaction in NATM tunnel excavations

Spira Y., Lackner R., Pichler Ch., Mang H. A.

Archives of Mechanics

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2005

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Vol. 57, nr 2-3

209--240

EN

In this paper, the benefits gained from advanced material modeling of soil for the numerical simulation of soil-support interaction in tunneling processes according to the New Austrian Tunneling Method (NATM) are illustrated by means of plane-strain Finite Element (FE) analyses. The studies performed encompass different types of soil (cohesive and granular) and two types of support means (shotcrete lining and jet-grouted soil). As regards the latter, the early-age behavior of the cement-based components is taken into account by means of a coupled chemomechanical approach. The obtained results provide an insight into the benefits gained from the employed support means during NATM tunneling in different geological conditions, serving as the basis in the day-to-day decision process at NATM construction sites. Additionally, effects of the changing geological conditions on the soil-support interaction are illustrated.

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Material modeling of concrete subjected to multiaxial loading: application to pull-out analyses

Pivonka P., Lackner R., Mang H. A.

Archives of Mechanics

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2001

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Vol. 53, nr 4-5

487-499

EN

This paper deals with the application of 3D-constitutive models for concrete to simulations of pull-out experiments [1]. Two different models are considered: The first material model is formulated within the framework of multi-surface plasticity. It consists of three Rankine yield surfaces for the simulation of cracking and a Drucker-Prager yield surface for the description of compressive failure of concrete. The Drucker-Prager surface is reformulated in order to account for the influence of confinement on the compressive strength and the ductility of concrete. The formulation of the second model, the Extended Leon Model (ELM) [4], is based on one yield function for description of compressive and tensile failure of concrete. It accounts for the influence of the Lode angle on the material strength. The simulation of ductile behavior of concrete is controlled by means of a pressure-dependent ductility function. The predictive capability of the models is demonstrated by means of a finite element (FE) analysis of a pull-out test [1]. The influence of confinement on the peak load and the failure mode is investigated.

3

Adaptive ultimate load analysis of RC shells

Lackner R., Mang H. A.

Computer Assisted Mechanics and Engineering Sciences

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2000

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Vol. 7, No. 4

641-666

EN

The aim of the present paper is a synthesis of both realistic modelling of the structural behavior of reinforced concrete (RC) shells and an adaptive finite element (FE) calculation tool suitable for the solution of nonlinear problems involving strain-hardening and softening plasticity. In the context of incremental-iterative analysis, an incremental error estimator is introduced. It is based on the rate of work. The reference solution required for error estimation is obtained by means of a recovery scheme applied to stress resultants. If the estimated error exceeds a prespecified threshold value, a new mesh is designed. Mesh generation is performed in the 2D parametric space of the shell. After mesh refinement, the state variables are transferred from the old to the new mesh and the calculation is restarted at the load level which was attained by the old mesh. The usefulness of the developed adaptive analysis scheme is demonstrated by a numerical analysis of an RC cooling tower.