Abstract

This study focuses on the improvement of composite slabs characterization throughout the use of advanced finite elements models. The accurate three-dimensional modelling of a full scale commercial steel sheet and concrete slab geometries enables the analysis of the composite slab micromechanics. The inclusion of the embossments depth and slope, the steel sheet thickness, the tilting angle, the length and width and spacing of embossments, and the profiling angle of the rib shape removes the need of simplifications for the complex phenomenon at the steel – concrete interface. The accuracy observed at the finite element models once compared with the laboratory specimens enables a new approach to describe the complex stress distributions in composite slabs. In particular, this study introduces a novel representation of the longitudinal shear strength t_u and a newly defined vertical normal stress σ_u between the steel and concrete that frequently define the overall composite slab bearing capacity. Subsequently, this study compares detailed stress diagrams and deformations from the finite elements models with experimental data obtained through piezoelectric gauges at the laboratory specimens.

Abstract

We analyze the relative importance of the selection of (1) the geostatistical model depicting the structural heterogeneity of an aquifer, and (2) the basic processes to be included in the conceptual model, to describe the main aspects of solute transport at an experimental site. We focus on the results of a forced-gradient tracer test performed at the “Lauswiesen” experimental site, near Tübingen, Germany. In the experiment, NaBr is injected into a well located 52 m from a pumping well. Multilevel breakthrough curves (BTCs) are measured in the latter. We conceptualize the aquifer as a three-dimensional, doubly stochastic composite medium, where distributions of geomaterials and attributes, e.g., hydraulic conductivity (K) and porosity (ϕ), can be uncertain. Several alternative transport processes are considered: advection, advection–dispersion and/or mass-transfer between mobile and immobile regions. Flow and transport are tackled within a stochastic Monte Carlo framework to describe key features of the experimental BTCs, such as temporal moments, peak time, and pronounced tailing. We find that, regardless the complexity of the conceptual transport model adopted, an adequate description of heterogeneity is crucial for generating alternative equally likely realizations of the system that are consistent with (a) the statistical description of the heterogeneous system, as inferred from the data, and (b) salient features of the depth-averaged breakthrough curve, including preferential paths, slow release of mass particles, and anomalous spreading. While the available geostatistical characterization of heterogeneity can explain most of the integrated behavior of transport (depth-averaged breakthrough curve), not all multilevel BTCs are described with equal success. This suggests that transport models simply based on integrated measurements may not ensure an accurate representation of many of the important features required in three-dimensional transport models.

Abstract

In practice, tunnels design uses analytical methods and numerical models. The last methods are because tunnels need solutions that provide a high level of security given their complexity and civil use. In this paper the study of the influence of the geometric and the mechanical soil properties on the tunnel displacements is presented, when it is used the finite element method (FEM) in two (2D) and three (3D) dimensions. Validation of results was through of the displacements comparison with an elastic analytical method. The constitutive model used was the Mohr-Coulomb and the soil parameters are of a soil in Mexico. Results shows a convergence towards a similar behavior for the elastic case and a difference when a perfect elasto-plastic behavior is considered in design. As fundamental conclusions, it is observed that it is possible to speed up the time using the 2D-FEM method, as well as the feasibility of quickly reviewing a 3D tunnel using a 2D program. '''Key words: '''Finite elements; two-dimensions; three-dimensions; tunnels.

Abstract