SUMMARYA constitutive model for concrete, based on the smeared crack approach and formulated within the framework of the theory of plasticity, is extended by coupling damage due to tensile stresses with damage due to compressive stresses for mixed tension-compression loading and by introducing an isotropic scalar damage model for unloading and reloading. Additionally, a uniaxial model for tension stiffening is extended to reinforced concrete subjected to biaxial stress states. The constitutive model for plain and reinforced concrete is validated by means of test data taken from the literature and by laboratory tests on L-shaped panels.Finally, the validated material model is used to perform a non-linear FE-analysis of a permanent tunnel lining made of hexagonal precast concrete segments. During the construction work of the lining hairline cracks were detected on the inner surface of some precast segments, running parallel to the longitudinal axis of the tunnel lining. They were supposed to be mainly caused by the installation process of the lining. In order to gain more information about the origin of these cracks, a non-linear numerical analysis of the installation process of the lining is performed. The results of the numerical simulation, showing under which conditions cracks are initiated, are presented and discussed.

A constitutive model for concrete cracking, based on the smeared crack approach within the framework of the theory of plasticity, was verified by experiments on L-shaped structural members. The model is used for finite element ultimate load analyses of plain and reinforced concrete structures. The experimental investigations consisted of a series of L-shaped structural members, made of plain concrete and three series of reinforced L-shaped structural members with different layout of the reinforcement, which were loaded until failure. The comparison between experimental and computed results included the load at the initiation of cracking and the load-displacement curves in the pre- and post-peak regions. Additionally, the experimentally determined crack patterns were compared with the computed crack propagation and damage behaviour of the material.

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SUMMARYA numerical model within the framework of a non-symmetric strong discontinuity approach (SDA) suitable for fracture simulations of plain concrete is presented. The model is based on the fixed crack concept and is formulated within the framework of elements with embedded discontinuities. Discontinuity segments of individual elements are considered to form a C 0 -continuous surface. Enforcement of continuity of the crack surface across adjacent elements is established by the so-called partial domain crack tracking algorithm (PDTA). Orientation of individual crack segments is derived from a non-local strain field. Within the present work emphasis is put on the formulation for the three-dimensional case. The implications on the respective algorithms are highlighted. The capabilities of the model are shown by means of numerical examples.

Hygro-thermo-chemo-mechanical modelling of time-dependent concrete behavior requires the accurate determination of a large set of parameters. In this paper, the parameters of a multiphase model are calibrated based on a comprehensive set of experiments for a particular concrete of grade C30/37. The experiments include a calorimetry test, tests for age-dependent mechanical properties, tests for determining the water desorption isotherm, shrinkage tests, and compressive creep tests. The latter two were performed on sealed and unsealed specimens with accompanying mass water content measurements. The multiphase model is based on an effective stress formulation. It features a porosity-dependent desorption isotherm, taking into account the time-dependency of the desorption properties. The multiphase model is shown to yield excellent results for the evolutions of the mechanical parameters. The evolution of the autogenous shrinkage strain and evolutions of the creep compliances for loading at concrete ages of 2 days, 7 days, and 28 days are well predicted together with the respective mass water content evolution. This also holds for the evolution of the drying shrinkage strain, at least for moderate drying up to one year. However, it will be demonstrated that for longer drying times further conceptual thoughts concerning the coupled representation of shrinkage and creep are required.