Estruturas mistas no contexto da pré fabricação: alternativa à ligação viga-laje pré-fabricada.

O intenso processo de industrialização sofrido pela construção civil nos últimos anos está associado à busca por sistemas estruturais e/ou construtivos que visem à racionalização da construção, entre os quais se destacam os sistemas mistos de aço e concreto. Um sistema misto de aço-concreto visa extrair o máximo desempenho dos materiais. Para tanto, é necessário que se garanta a melhor interação possível entre os materiais. Nesse contexto, o comportamento das conexões entre os elementos de aço e concreto pré-fabricado, é um fator determinante na escolha do sistema construtivo. O presente trabalho apresenta e discute soluções para a conexão entre a viga metálica e a laje de concreto, tendo como enfoque as ligações por aderência. São apresentadas tanto soluções que utilizam conectores do tipo Pino, mais usuais, até às mais recentes soluções, no caso, as ligações por aderência, que tem se demonstrado bastante promissora em termos de resistência. Por fim, são apresentados resultados específicos de novas soluções para a conexão viga-laje, no contexto de uma solução pré-fabricada.The intense process of industrialization suffered by construction in recent years is associated with the search for structural and/or constructive systems aiming the rationalization of construction, among which stand out the composite systems of steel and concrete. A composite system of steel-concrete aims to extract maximum performance of materials. Therefore, it is necessary to ensure the interaction between these materials. In this context, the behavior of connections between elements of steel and precast concrete is a determining factor in the choice of the structural system. This paper presents and discusses solutions to the connection between the steel beam and concrete slab, with the focus on the connections by adherence. Are presented as solutions that utilize stud connectors, more usual, as the latest solutions, connections by adherence, which has been shown quite promising in terms of strength. Finally is presented specific results of new solutions for the beam-slab connection in the context of prefabrication

Experimental analysis of new interfaces for connections by adhesion, interlocking and friction.

The authors thank the federal agency CAPES and the Foundation for Research Support of the state of Sao Paulo, Brazil (FAPESP) for providing a PhD scholarship, and the University of Minho, in Portugal, for the international collaboration.This paper presents the results of an experimental program developed to investigate the behavior of an innovative technology for connections by adhesion, interlocking and friction in composite structures. Connections have a strategic importance for precast concrete and steel–concrete composite structures, since they determine the global structural behavior and affect the whole production process, fromexecution to assemblage and other services on site. Currently, however, steel–concrete composite connections are not completely adapted for their use in prefabricated slabs. In this way, the development of new types of connections is clearly necessary, where connections by adherence (or connections by adhesion, interlocking and friction) seem quite promising. To improve the knowledge in the field of connections by adherence, this paper proposes a new geometry of embossments in the steel and in the concrete surfaces associatedwith the use of a high performance mortar.Monotonic push-out tests are performed, and their results are presented and discussed. A satisfactory behavior of the proposed connection in terms of strength is observed, justifying further studies on the subject.CAPES, FAPES

Tests on composite beams using new connections by adherence

Cast in place concrete is often the cheapest solution in the context of conventional construction. However, prefabrication presents advantages in terms of execution time, quality of the structural elements and cost. Thus, the association of precast concrete elements and steel sections in a composite element can result in a high quality structure, executed with greater speed and economy of financial and material resources. Currently, steel to concrete composite connections are not completely adapted to prefabricated slabs and the use of connections by adhesion, interlocking and friction seem quite promising. To improve the knowledge in this field, this paper presents the development of full scale flexural tests of composite beams using new interfaces for these connections, and their results are interpreted and discussed. For comparison purposes, two beams with cast in place slab are tested. A satisfactory behavior in terms of strength is observed, in both cases investigated (cast in place and precast slab), justifying further studies on the subject.info:eu-repo/semantics/publishedVersio

Microfluidics: reframing biological enquiry

The underlying physical properties of microfluidic tools have led to new biological insights through the development of microsystems that can manipulate, mimic and measure biology at a resolution that has not been possible with macroscale tools. Microsystems readily handle sub-microlitre volumes, precisely route predictable laminar fluid flows and match both perturbations and measurements to the length scales and timescales of biological systems. The advent of fabrication techniques that do not require highly specialized engineering facilities is fuelling the broad dissemination of microfluidic systems and their adaptation to specific biological questions. We describe how our understanding of molecular and cell biology is being and will continue to be advanced by precision microfluidic approaches and posit that microfluidic tools - in conjunction with advanced imaging, bioinformatics and molecular biology approaches - will transform biology into a precision science

Hardened properties of self-compacting concrete - A statistical approach

This work presents a statistical study on the variability of the mechanical properties of hardened self-compacting concrete, including the compressive strength, splitting tensile strength and modulus of elasticity. The comparison of the experimental results with those derived from several codes and recommendations allows evaluating if the hardened behaviour of self-compacting concrete can be appropriately predicted by the existing formulations. The variables analyzed include the maximum size aggregate, paste and gravel content. Results from the analyzed self-compacting concretes presented variability measures in the same range than the expected for conventional vibrated concrete, with all the results within a confidence level of 95%. From several formulations for conventional concrete considered in this study, it was observed that a safe estimation of the modulus of elasticity can be obtained from the value of compressive strength; with lower strength self-compacting concretes presenting higher safety margins. However, most codes overestimate the material tensile strength. (C) 2010 Elsevier Ltd. All rights reserved.Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Spanish Ministry of Science and TechnologySpanish Ministry of Education and Science[MAT2003-5530]Spanish Ministry of Education and Science[PSS 11-2005

Variabilidade da aderência e das propriedades mecânicas do concreto auto-adensável

Esta pesquisa tem como objetivo estudar a variabilidade das propriedades mecânicas (resistência à compressão, módulo de elasticidade longitudinal e resistência à tração) e da resistência de aderência do concreto auto-adensável (CAA), com resistência à compressão do concreto de 50 MPa aos 28 dias, variando o tamanho máximo do agregado graúdo e sua fluidez. Os ensaios foram realizados em corposde- prova de 15 x 30 cm e em vigas padronizadas de acordo com o Rilem-Ceb-Fib (1973). De acordo com os resultados obtidos, pode-se concluir que a variabilidade do concreto auto-adensável é pequena para o módulo de elasticidade e para a resistência à compressão e grande para a resistência à tração por causa do modo de ruptura do modelo. Com relação à resistência de aderência, a variabilidade foi pequena mostrando que o concreto auto-adensável é material confiável com grande potencial de utilização no mercado da construção civil