La importancia de las cosas insignificantes

Nombrado Doctor Honoris Causa en el acto del Día de la Universidad del curso 94/9

Comportamiento del hormigón a muy bajas temperaturas

Este trabajo se refiere al comportamiento de hormigones fabricados y curados a temperatura ambiente y que posteriormente son enfriados. En estos casos, el proyectista utiliza sólo datos para temperatura ambiente y considera que el incremento de resistencia que puede producirse al enfriar redunda en una mayor seguridad. El constructor también sigue los métodos de control y ensayo diseñados para temperatura ambiente, entre otros motivos, porque no dispone de una metodología y una normativa para estas circunstancias

Comportamiento de las armaduras activas después de un fuego

Después de un fuego, aunque una estructura no haya colapsado y ni siquiera se hayan producido daños aparentes, resulta imprescindible evaluar si sigue siendo segura, porque tanto las propiedades mecánicas de los materiales como la distribución de cargas pueden haberse visto afectadas. En los últimos años, el comportamiento a altas temperaturas de los materiales de construcción se ha caracterizado exhaustivamente con objeto de aplicarlo en el diseño de estructuras capaces de resistir el fuego. Sin embargo, apenas se ha prestado atención a la situación post-incendio. En este trabajo se ha estudiado el comportamiento de las armaduras activas después de sufrir un incendio; Se muestra que el fuego puede provocar daños no-visibles tanto en el material (deteriorando sus propiedades mecánicas) como en la distribución de cargas de la estructura (reduciendo la fuerza de pretensado al aumentar las pérdidas por relajación de los tendones). Ambos efectos pueden perjudicar la capacidad resistente de la estructura. Se aportan datos experimentales para estimar estos daños y ayudar en la evaluación de la seguridad estructural después del fuego

Fire-induced damage in presstressing steels

After a fire, even If no collapse happens, there Is a possibility of fire-Induced damage in the structure. Correct knowledge of residual properties of wires after fire Is of major importance for the assessment of the residual load-bearing capacity of a presfressed structure. This paper studies the non-vlslble fire-Induced damages In presfressed wires, Including the reduction of the prestress bads and the strength of steel wires produced by the exposure to high temperatures

The role of residual stresses in the performance and durability of prestressing steel wires

Residual stresses developed during wire drawing influence the mechanical behavior and durability of steel wires used for prestressed concrete structures, particularly the shape of the stress–strain curve, stress relaxation losses, fatigue life, and environmental cracking susceptibility. The availability of general purpose finite element analysis tools and powerful diffraction techniques (X-rays and neutrons) has made it possible to predict and measure accurately residual stress fields in cold-drawn steel wires. Work carried out in this field in the past decade, shows the prospects and limitations of residual stress measurement, how the stress relaxation losses and environmentally-assisted cracking are correlated with the profile of residual stresses and how the performance of steel wires can be improved by modifying such a stress profil

Análisis de las especificaciones de materiales utilizados para el hormigón pretensado a bajas temperaturas

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Improved cold-drawn eutectoid steel wires based on residual stress measurement and simulation: Part 2. optimization of mechanical properties

Cold-drawn eutectoid steel wires are used in prestressed concrete structures to provide compressive stresses to the concrete. For that purpose, they are loaded up to 60 to 70% of their tensile strength. Although the loading stress is lower than the elastic limit (around 85% of the tensile strength), failure may occur in service conditions due to stress corrosion. Wire failure reduces the load bearing capacity and may lead to catastrophic collapse of the prestressed structure. The risk of these failures can be increased by the presence of tensile residual stresses on the surface of the wires. Cold-drawing generates considerable residual stresses which, added to the service stresses, may seriously affect the mechanical properties and durability of the wires [1,2]. Until now, the measuring of residual stresses was considered more a scientific problem and even revealing their presence was a challenging task [3]. However, wire manufacturers were aware of the deleterious effect produced by the presence of tensile residual stresses at the surface of the wires after drawing. That is the reason why they consider residual stresses both dangerous and damaging, and hence attempt to reduce their influence by stress relieving treatments. But residual stresses may also have beneficial effects if we are able to obtain the desired profile. With the advent of powerful experimental techniques for measurement of residual stresses — such as neutron and X-ray diffractometers — and of faster computers to simulate numerically the wire drawing processes, this phenomenon is seen now in a new light. A significant research effort has been undertaken in recent years in order to understand, measure and control the residual stresses in cold-drawn wires [3-5]. In the first part of this paper [3], the advances on the measurement and simulation of residual stresses have been discussed. In this second part, the influence of residual stresses on the mechanical properties required by standards to this kind of wire (tensile, stress relaxation and stress corrosion tests) is reviewed. The control of residual stresses may play an important role in the design of new post-drawing treatments and the optimization of the performance of the wires