Hélène Dumontet

Prediction of the volume of concrete backfill materials excavated using a pick

Pick excavatability of controlled low-strength materials was experimentally studied to circumvent the fact that current classification systems or empirical excavatability criteria lack relevance (they do not refer to digging facilities and depend on the mix design and the granular skeleton of the material). Manual excavation is separated into two steps: the impact of the pick and decompaction. This was analysed by a mechanical approach. Energy is mainly consumed during the first step. A laboratory punching test was therefore proposed to evaluate excavatability (a confined cylindrical specimen was loaded by a cylindrical punch). Results were compared between the mechanised and the manual pick excavation tests on field trenches backfilled with air-entrained mortars or very lean concretes. These comparisons confirmed that a limited compressive strength was an indicator of excavatability. A model was proposed to evaluate the excavated volume by punching penetration for a given level of energy and a maximum size of aggregates in the material.

Modeling of Externally Prestressed Beams until Fracture in Non Linear Elasticity

In this paper, we present an analytical model to analyze reinforced and prestressed concrete beams loaded in combined bending, axial load and shear, in the frame of non linear elasticity. In this model, the equilibrium of the beam is expressed by solving a system of equations, governing beams equilibrium, based on the stiffness matrix of the beam, which connects the load vector to the node displacements vector of the beam. It is built from the stiffness matrix of the section which takes into account a variation of the shearing modulus (depending on the shear variation) instead of assuming a constant shearing modulus as in linear elasticity. For the internal tendons, the stiffness matrix is completed by the terms due to the prestress effect in flexural equilibrium and by the balancing of one part of the shear by the transverse component of the force in the inclined cables.

Modélisation numérique des structures élancées en béton armé

ABSTRACT Dimensioning of slender structures in reinforced concrete requires study of their global stability. This stability must take into account both types of non linearity: the physical one, which concerns the non linearity of concrete behaviour and the geometric one, which results from the study of the structure on its deformed configuration. The method described here is used to simulate numerically the ruin of reinforced concrete slender structures wich can occur by exceeding the strength of the more sollicited section or by instability. Accuracy of the numerical method developped is illustrated by the confrontation of numerical simulations results with analytical critical loads and experimental results. Otherwise this validation is reinforced by looking into results sensitivity regard to parametrs of numerical simulation.