Fernando R. Contreras Medina

Boundary elements for the analysis of the seismic response of dams including dam-water-foundation interaction effects. II

Abstract A Boundary Element frequency domain approach that takes into account the dynamic interaction between solid and fluid regions, which was presented in a separate paper (part I), is used to study the seismic response of concrete gravity dams. Results for a particular dam geometry, two different soil profiles, and full and empty reservoir conditions are shown. The agreement with corresponding published results obtained by other authors using Finite Elements is very good. The BE approach is shown to be capable of modelling a larger variety of soil profiles than any of the previous FE approaches. The effects of several parameters of the model on the seismic response of the dam are studied to show the importance of the joint dam-water-foundation interaction effects and the importance of the correct representation of each one of the three regions involved. Particular attention is paid to the aspects related to the BE modelling of the problem. The use of artificial boundaries, where far-field boundary conditions are prescribed, for cases where the radiation conditions are not satisfied, has been shown to be effective.

A numerical approach for the design of multiscale fibre-reinforced cementitious composites

In the present work, a numerical framework for the design of new multiscale fibre-reinforced cementitious composites is presented. This is accomplished by covering three different length scales, namely the micro-, meso- and macroscale. At the microscale (here defined as ~1 mm), an enhanced fibre-reinforced lattice model is presented for the simulation of strain hardening cementitious composites. On the other hand, the analysis of fibre-reinforced concrete is performed at the mesoscale (~10 mm) by means of a novel lattice-particle model. The main variables in both models are the fibre dimensions (i.e. length and diameter), the fibre volume content and the fibre-matrix bond behaviour. Their contribution to the global mechanical properties is discussed in details. Finally, the structural characterisation of the fibre-reinforced cementitious composites (FRCC) is carried out by means of a hierarchical numerical homogenisation of the material behaviour, integrating the information obtained from lower scales into the macroscale problem (~1 m). The macroscopic response of the resulting material is characterised via three-point bending tests using a continuum damage plastic model. Although the described lattice models can be used independently as design tools in fibre cement-based composites at the micro- or mesoscale, the multiscale procedure described in this paper allows for the development of new types of FRCC by considering the effect of the multiple-scale fibre-reinforcement.

Comparative study of CSF neurofilaments in HTLV-1-associated myelopathy/tropical spastic paraparesis and other neurological disorders.

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a progressive CNS disease leading to corticospinal tract degeneration. Various degenerative diseases have increased neurofilament subunit concentration in cerebrospinal fluid (CSF), frequently showing hyperphosphorylation in neurofilaments. The aim of this study was to determine if there were elevated concentrations of neurofilament light subunit (NFL) and phosphorylated forms of neurofilament heavy subunit (PNFH) in HAM/TSP CSF. NF concentrations were compared with those of controls and patients with neurodegenerative diseases associated with other retroviruses (HIV-associated dementia, HAD) and a form of prion disease (familiar Creutzfeldt-Jakob, FCJD). Western blotting of CSF with antibodies against NFL showed two immunoreactive bands of 66 and 59 kDa, the latter probably corresponding to a partially degraded NFL form. The concentration of the 59-kDa form was not different in HAM/TSP compared with controls, but it was significantly increased in HAD and FCJD groups. ELISA assay for PNFH did not show differences among HAM/TSP, HAD, and control groups, while PNFH concentration was significantly elevated in FCJD. Our results show that CSF NFL and PNFH are not molecular markers of axonal damage for HAM/TSP probably due to the slow progression of this disease. NFL phosphorylation studies required previous immunoprecipitation from CSF for mass spectrometric analysis. This preliminary analysis indicated phosphorylation at S472 and at some other residues.

A lattice‐particle approach to determine the RVE size for quasi‐brittle materials

Purpose – The purpose of this paper is to determine the representative volume element (RVE) size for quasi‐brittle materials using a discrete approach, namely a lattice‐particle model.Design/methodology/approach – Different material samples are generated and subjected to study regarding its size, maximum aggregate size and boundary conditions. In order to determine the mechanical properties such as the elastic modulus, Poissons ratio or tensile strength, several tension tests are carried out. For this purpose, a lattice‐particle approach is used to model concretes fracturing behavior. The information provided by the previous simulations is implemented in a statistical analysis to determine the size of the RVE.Findings – The determination of the RVE size for quasi‐brittle materials is successfully achieved by means of a lattice‐particle model. Computed results show a good agreement with other results reported in the bibliography.Originality/value – Within a general multiscale framework, the determination...

Mesoscale Characterization of Fracture Properties of Steel Fiber-Reinforced Concrete Using a Lattice–Particle Model

This work presents a lattice–particle model for the analysis of steel fiber-reinforced concrete (SFRC). In this approach, fibers are explicitly modeled and connected to the concrete matrix lattice via interface elements. The interface behavior was calibrated by means of pullout tests and a range for the bond properties is proposed. The model was validated with analytical and experimental results under uniaxial tension and compression, demonstrating the ability of the model to correctly describe the effect of fiber volume fraction and distribution on fracture properties of SFRC. The lattice–particle model was integrated into a hierarchical homogenization-based scheme in which macroscopic material parameters are obtained from mesoscale simulations. Moreover, a representative volume element (RVE) analysis was carried out and the results shows that such an RVE does exist in the post-peak regime and until localization takes place. Finally, the multiscale upscaling strategy was successfully validated with three-point bending tests.

Experimental Fracture Behavior of Polypropylene Fiber Reinforced Concrete Specimens with Variable Width

This paper presents a study of the influence of polypropylene fiber reinforcement of concrete on the fracture behavior and edge effect in elements of variable width. Experimental results of fracture behavior of specimens with different cross sections are available. It has obtained more ductile behavior for specimens with trapezoidal sections (with increasing width) and inverted T-sections. Therefore, we analyze the influence of the fibers addition on the fracture behavior of these sections. Sections with gradual variation of wide and sudden change of width were analyzed. Results allow us to quantify the increase of ductility and fracture performance improvements produced by polypropylene fiber addition to concrete in these sections.

Periodismo y arte: dos caminos creativos entrecruzados

The main purpose of this article is the interpretation of the journalists creative process from the characteristics of art: originality, essentiality and purity. Moreover, this study shows the transfiguration of press messages in the context of postmodernism. For that reason we have examined the meaning of experience, rupture, tradition and realistic spirit in art and contemporary culture and also how the journalistic discourse has taken advantage of that.