Radioactividad natural en materiales de construcción

Some materials usually employed in building edification have been analyzed for their radioactive contents. The specific activities of all the gamma rays emisors present in fourteen differents samples have been determined. In all the cases, only low activities (under 2 Bq/g) have been found for these samples collected from the surroundings of Barcelona.Los radioisótopos contenidos en los materiales habitualmente empleados en construcción son analizados con espectrometría gamma. Se calculan las actividades específicas de los diferentes radioisótopos en catorce materiales seleccionados, provenientes de las cercanías de Barcelona, obteniéndose niveles de radioactividad bajos (inferiores a 2 Bq/g)

Guaranteed behaviour of shape memory alloys : After quench and long time effects in CuZnAl SMA

The use of Shape Memory Alloys (SMA) in critical "high tech" applications such as robotics and in continuous actuators needs an increased reliability and a guaranteed behaviour lasting several years. High resolution measurements enabled to quantify the time effects of aging near room temperature on the properties of CuZnAl SMA and to modelize the macroscopic behaviour. Some structural measurements showed small changes on the material structure

Ms-Evolution in Cu-Zn-Al SMA. Predictable Temperature and Time Actions on Parent Phase

Recently an increased interest has been noticed for order effects in Cu-based SMA. For instance, on the transformation temperature Ms values and its evolution after heat treatments and quench type effects. Usually, the experimental Ms values after quench fluctuate around ± 2 K. The interest for continuous actuators needs a more reduced and, in any case, predictable fluctuation domain. In this work, by using high resolution in temperature, time and resistance measurements on a Cu-Zn-Al alloy (1.48 e/a), the results establish a distribution of the evolution in two main actions : a relatively short time and a long time tail effects. Two temperature dependent time constants have been determined from the experiments, with different activation energies (13630 K and 10330 K). The two actions might be associated to different ordering processes. Furthermore, the experimental results allow to describe a representative model that can be used to predict the Ms evolution with temperature and time. The differences between simulated and experimental results for the Ms is about ± 0.15 K for temperature-time evolutions near room temperature

Built-form, mass and energy: Urban fabric performance

The link between urban form and building energy demand is a complex balance of morphological, constructive, utilization and climatic factor. Especially in the European compact city, where existing areas prevail on much more energy-efficient new settlements, it is evident that operative ways to transform efficiently the building stock have to be found. This paper explores the existence of a relation between built mass and energy demand depending on urban form. Focusing on the compact city of Mediterranean climate, tests on different case studies simulations are carried out. Results presented and discussed, point out that mass has strong relevance on energy demand and plays an important role in reducing energy consumptions. This paper is a preliminary report of an ongoing research study about one possible way to comprehend "metabolic rate" scaling law - The relationship between power and mass of a complex system in its process - concerning urban fabric. This knowledge-base could help verify the accordance with this rule on urban scale and give hints to conscious and effective built environment transformations towards more efficient conditions

Time Evolution in Static β-Phase and Dynamic β-Martensite Coexistence (Cu-Zn-Al SMA)

The application of a SMA implies an accurate knowledge about the eventual time - behavior of the alloys. The effects of quenching and micro-heatings were studied by calorimetric and resistance measurements and the β-martensite coexistence by stress - strain - temperature - time observations. Experimental analysis was performed using copper based single crystals (Cu-Zn-Al, e/a ≈ 1.48 e/a with Ms below room temperature). The phenomenological behavior establishes several time constants for each evolution. A change ΔT of temperature of the parent phase near 300 K induces an asymptotic time evolution on Ms near 11 per cent. The parent to martensite coexistence produces an evolution of the equilibrium temperature (near 0.5 K) linked to the existence of an interface

Shape Memory alloys as an effective tool to damp oscillations: study of the fundamental parameters required to guarantee technological applications

The SMA was studied for their macroscopic application in damping for civil engineering. The study is a synthesis and includes an outline of the models required for the SMA simulation and some case studies using the finite element analysis methods. This work is an overview that focuses in the mitigation of the oscillations in structures induced by earthquakes, and for a reduction of the oscillations amplitude in stayed cables under the action of rain, wind or traffic. The analysis needs the required conditions for each application determining the working conditions. The study includes the number of working cycles, the temperature effects and the cooling actions and, for instance, the action of the cycling frequency. The main target relates the appropriateness of the SMA for each purpose, and the suitability of the SMA device is always experimentally guaranteed. Furthermore, the applicability of the obtained results for SMA and the practical behavior of the SMA dampers were studied in international facilities. The paper includes appropriate suggestions for a correct preparation of the SMA dampers. This work outlines the effects of stress and temperature aging in NiTi, describes the particular structural effects between 18R and 6R, introduces a first attempt in the dynamic properties of the CuAlBe single crystals and summarizes some recent suggestions for damping using SMA.Fil: Torra, V.. No especifíca;Fil: Isalgue, A.. Universidad Politécnica de Catalunya; EspañaFil: Lovey, F.C.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Sade Lichtmann, Marcos Leonel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Fatigue laboratory tests toward the design of SMA portico-braces

A deeper understanding of the effectiveness of adopting devices mounting shape memory alloy (SMA) elements in applications targeted to the mitigation of vibrations is pursued via an experimental approach. During a seismic event, less than 1000 loading-unloading cycles of the alloy are required to mitigate the earthquake effects. However, the aging effects during the time of inactivity prior to the oscillations (several decades characterized by the yearly summer-winter temperature wave) should be considered in order to avoid and/or minimize them. In this paper, the results obtained by carrying out, in different laboratories, fatigue tests on SMA specimens are compared and discussed. Furthermore, the effects of seismic events on a steel structure, with and without SMA dampers, are numerically simulated using ANSYS. Under an earthquake excitation, the SMA devices halve the oscillation amplitudes and show re-centering properties. To confirm this result, an experimental campaign is conducted by actually installing the proposed devices on a physical model of the structure and by evaluating their performance under different excitations induced by an actuator

Mesoscale observations and yearly effects in Cu-Zn-Al shape memory alloys: Representative model and predictable damping effects

The use of the damping effect produced by the hysteresis cycle is one of the relevant applications in shape memory alloys. The experimental study at mesoscale level of the Cu-based alloys and in preliminary level of TiNi allows the development of a one-dimensional model that describes the response to the external thermodynamic forces, including the evolution associated to diffusion effects (phase coexistence and temperature-time on parent phase). The results furnished by the model establish the appropriate guarantee of the alloy properties for series of working cycles separated by long times in austenite phase, as scarce events (as in earthquakes). Using a simple case, the damping effect is visualized with the fluctuations imposed by summer-winter actions. the coexistence effects among the phases and the seasonal room temperature actions on parent phase