Numerical Verification of Interaction between Masonry with Precast Reinforced Lintel Made of AAC and Reinforced Concrete Confining Elements

This paper describes results of numerical analyses of reinforced lintels made of autoclaved aerated concrete built into unconfined walls and walls confined with reinforced concrete. The combination of the Menétrey–Willam elastic-plastic failure criterion (M-W-3) and the Rankine criterion was used for numerical analysis of masonry. The parameters were determined by laboratory tests. Rebars were modelled using the Huber–Mises–Hencky yield criterion. The numerical model included interface elements att the interface between masonry units, at interfaces between reinforced concrete and masonry, and at interfaces between elements of test stands with a model using the Coulomb–Mohr (C-M) criterion. The majority of parameters of interface elements were assumed from laboratory tests. Results of numerical analysis were compared with laboratory tests. Results of numerical analysis and experiments were compatible in the range of load-carrying capacity of models and the failure method.

Numerical modelling of pore-fluid-enhanced thermal spallation in granitic rock

This paper considers numerically the effect of pore-fluid on thermal spallation of granitic rock. For this end, a numerical model based on the embedded discontinuity finite element approach to rock fracture and an explicit scheme to solve the underlying thermo-mechanical problem is developed. In the present implementation, a displacement discontinuity (crack) is embedded perpendicular to the first principal direction in a linear triangle element upon violation of the Rankine criterion. In the thermo-mechanical problem, the heating due to mechanical dissipation is neglected as insignificant in comparison to the external heat flux. This leads to an uncoupled thermo-mechanical problem where the only input from the thermal part to the mechanical part is thermal strains. This problem is solved with explicit time marching using the mass scaling to speed up the solution. Finally, the fluid trapped into the micro-pores is modelled as a material that can bear only volumetric compressive stresses. A thermal spallation problem of a rock sample under axisymmetry is simulated as a numerical example.

On Some Problems in Determining Tensile Parameters of Concrete Model from Size Effect Tests

The paper presents results of numerical simulations of size effect phenomenon in concrete specimens. The behaviour of in-plane geometrically similar notched and unnotched beams under three-point bending is investigated. In total 18 beams are analysed. Concrete beams of four different sizes and five different notch to depth ratios are simulated. Two methods are applied to describe cracks. First, an elasto-plastic constitutive law with a Rankine criterion and an associated flow rule is defined. In order to obtain mesh independent results, an integral non-local theory is used as a regularisation method in the softening regime. Alternatively, cracks are described in a discrete way within Extended Finite Element Method (XFEM). Two softening relationships in the softening regime are studied: a bilinear and an exponential curve. Obtained numerical results are compared with experimental outcomes recently reported in literature. Calculated maximum forces (nominal strengths) are quantitatively verified against experimental values, but the force – displacement curves are also examined. It is shown that both approaches give results consistent with experiments. Moreover, both softening curves with different initial fracture energies can produce similar force-displacement curves.

Size effect in concrete beams under bending – influence of the boundary layer and the numerical description of cracks

In the paper the size effect phenomenon in concrete is analysed. The results of numerical simulations of using FEM on geometrically similar un-notched and notched concrete beams under bending are presented. Concrete beams of four different sizes and five different notch heights under three-point bending test were simulated. In total 18 beams were analysed. Two approaches were used to describe cracks in concrete. First, eXtended Finite Element Method (XFEM) describing cracks as discrete cohesive ones with bilinear softening was chosen. Alternatively, an elasto-plastic constitutive law with Rankine criterion, associated flow rule and bilinear softening was defined. In order to ensure mesh-independent FE results, a non-local theory in an integral format as a regularisation technique was applied in the softening regime. In both approaches the influence of the decrease of the material parameters (mainly fracture energy) in the boundary layer on obtained maximum loads was studied. Additionally the influence of the averaging method in non-local plasticity was also examined. Obtained results were compared with experimental outcomes available in literature.

The ‘ I 3 ’ generalization of the Galileo–Rankine tension criterion

The paper presents a new tension failure criterion which generalizes the so-called Galileo–Rankine formulation. The criterion can be used as a component of the so-called perfectly no-tension model for masonry and cements as well as for establishing a tension cut-off in complex constitutive models for soils, granular materials and powders. The criterion is described by means of a very concise equation based on the third invariant of the stress tensor, approximating the boundaries of the compressive octant of the principal stress space. This sheds new light on the physical significance of the third invariant of the stress tensor. The new criterion has been validated against two known analytical solutions for no-tension materials and also effectively applied for solving two geotechnical and structural engineering problems. The proposed formulation allows for an efficient implementation in finite-element programmes, removing some of the numerical difficulties associated with the Galileo–Rankine criterion.