Carlos López-Colina

Influence of recycled aggregate quality and proportioning criteria on recycled concrete properties

This paper presents the results of experimental research using concrete produced by substituting part of the natural coarse aggregates with recycled aggregates from concrete demolition. The influence of the quality of the recycled aggregate (amount of declassified and source of aggregate), the percentage of replacement on the targeted quality of the concrete to be produced (strength and workability) has been evaluated. The granular structure of concrete and replacement criteria were analyzed in this study, factors which have not been analyzed in other studies. The following properties of recycled concretes were analyzed: density, absorption, compressive strength, elastic modulus, amount of occluded air, penetration of water under pressure and splitting tensile strength. A simplified test program was designed to control the costs of the testing while still producing sufficient data to develop reliable conclusions in order to make the number of tests viable whilst guaranteeing the reliability of the conclusions. Several factors were analyzed including the type of aggregate, the percentage of replacement, the type of sieve curve, the declassified content, the strength of concrete and workability of concrete and the replacement criteria. The type of aggregate and the percentage of replacement were the only factors that showed a clear influence on most of the properties. Compressive strength is clearly affected by the quality of recycled aggregates. If the water-cement ratio is kept constant and the loss of workability due to the effect of using recycled aggregate is compensated for with additives, the percentage of replacement of the recycled aggregate will not affect the compressive strength. The elastic modulus is affected by the percentage of replacement. If the percentage of replacement does not exceed 50%, the elastic modulus will only change slightly.

Simplified Models for the Material Characterization of Cold-Formed RHS

It is well known that the cold-forming process used to manufacture tubes causes an increase in both the yielding stress and the ultimate strength of the corner material in rectangular steel hollow sections. This may have a significant effect on the resistance of any structure built with those profiles. However, the mentioned material hardening can be difficult to take into account in the calculations for member design or to evaluate the connection resistance through the design formulation or when using numerical simulation models. As an attempt to face the above-mentioned problem, the present paper presents a comparison among simplified approaches that consider homogeneous material properties for the whole section. It has been carried out by comparing the results obtained from the finite element modelling of stub column tests in which the material properties based on the flat faces were considered for the whole profile.

The Influence of the Heat-Affected Zone Mechanical Properties on the Behaviour of the Welding in Transverse Plate-to-Tube Joints

Eurocode 3 establishes the component method to analytically characterize the structural joints between beam and columns. When one of the members involved in the joint is a hollow section (i.e., a tube) there is a lack of information for the specific components present in the joint. There are two different ways to bridge the gap: experimental testing on the actual beam column joints involving tubular sections; or numerical modelization, typically by means of finite element analysis. For this second option, it is necessary to know the actual mechanical properties of the material. As long as the joint implies a welding process, there is a concern related to how the mechanical properties in the heat-affected zone (HAZ) influence the behavior of the joint. In this work, some coupons were extracted from the HAZ of the beam-column joint. The coupons were tested and the results were implemented in the numerical model of the joint, in an attempt to bring it closer to the experimental results of the tested joints.

A web‐based training approach for the structural steel design

Fortunately the design processes of steel buildings across Europe is eventually covered by a unified code: The Eurocode 3: “Design of steel structures.” Nevertheless, although Eurocodes will soon become mandatory documents, designs will not be standardized because each country has a set of National Annexes which must be taken into account when designing in that particular country. Furthermore, every country also has its own body of non‐conflicting complementary information. A problem then arises when engineers need to produce designs in other European countries, either for a company based in one state or as individuals. Also, allowing engineers time out of the office for attendance at the intensive training courses which are required for earning experience on the new codes of design, frequently represents an obstacle for their employers. In an attempt to solve these problems, a strong trans‐national partnership has been working to develop an ICT‐supported, flexible training approach to allow designers to apply Eurocodes in accordance with the national regulations and practices of different member states. The resulting material in seven languages shows how to design a typical building according to the different national contexts. The developed portal incorporates facilities for course presentation, forums, blogs and on‐line translation. The students thought that the portal was an effective tool that helped them to improve the quality and efficiency of their studies. In their opinion the web‐course is well structured and they found the forum for discussion and the web‐based tutoring system very helpful.