No abstract

RESUMO Os materiais compósitos comumente apresentam delgadas regiões ou interfases localizadas entre a matriz e as inclusões. Estas interfases têm influência no comportamento efetivo do compósito. Em diversas aplicações, os compósitos estão sujeitos a variações significativas de temperatura e, consequentemente, a condutividade térmica efetiva desses materiais se torna parâmetro essencial para compreensão do seu comportamento. O objetivo desse trabalho é determinar a influência de interfases na condutividade térmica efetiva de compósitos reforçados com fibras unidirecionais distribuídas periodicamente, utilizando a formulação paramétrica da Teoria de Volumes Finitos. Para isso, são avaliados os efeitos da espessura e condutividade térmica da interfase, assim como do raio da fibra e de sua fração volumétrica. Compósitos com fibras naturais são apresentados dentre os exemplos analisados. Os resultados obtidos com a Teoria de Volumes Finitos são confrontados com outros encontrados por métodos numéricos ou experimentos. Desse modo, observa-se que a interfase possui mais influência quanto maior for a fração volumétrica de fibras e quanto menor o raio das mesmas. Quanto mais espessa a interfase, mais suas propriedades influenciam a condutividade térmica efetiva do compósito, quando a fração volumétrica de fibras é mantida constante. Conclui-se que os efeitos de interfase sobre o comportamento térmico de compósitos são de extrema importância e, consequentemente, eles precisam ser considerados para proporcionar predições consistentes e realísticas.

The use of fibre reinforced polymers (FRP) for increasing the strength of RC structures became a usual method. FRP presents easy application and demands low space and provide significant strength increase. Usually, the decision for FRP use is made in terms of applied loads and deflections. However, such quantities can vary significantly depending on the characteristics of the structural element e.g. span, effective depth and concrete resistance. Therefore, this paper aims to present an alternative control variable to analyse the behaviour of RC beams repaired with glass fibre reinforced polymer (GFRP), called damage. Such damage variable accounts for concrete cracking and it was experimentally measured before and after the application of GFRP. Note that the application of GFRP increased the ultimate load for all repaired beams. The damage values of such beams also increased when collapse was reached. Furthermore, it was observed that the collapse mechanism shifted to shear and did not occurred the failure of the GFRP.

<p class="Normal1">The inherent relation between the instability parameters α and γz is studied in this paper. Such parameters are simplified criteria widely used in structural design in Brazil to evaluate the necessity to consider the global second order effects. Thus, an analytical relation between the parameters α and γz is proposed through a simple example. For this, design values of α and γz of thirty reinforced concrete buildings and twenty-two masonry buildings were used. The obtained results prove the accuracy of the proposed formulation for both types of construction</p>

Structural design procedures are based on simplified hypotheses that attempt to approximate the actual behaviour. Depending on the adopted hypothesis, the design procedure may not satisfactorily describe the structural actual behaviour. Such condition occurs in the design of reinforced concrete pipes, where there are uncertainties related especially on the internal forces and the installation type of the pipe. Moreover, the main design hypothesis is that the cross section is plane and perpendicular to the deformed axis. Based on materials resistance principles it is known that this hypothesis is unsatisfactory to pipes with aspect ratio lower than ten. Note that the commercial reinforced concrete pipes usually present aspect ratio well below ten. In the light of the foregoing, the main objective of this paper is to analyse the accuracy of the design procedure for reinforced concrete pipes. Therefore, statistical processes were used to compare design values with experimental results. The comparisons in this paper showed that the design procedure results in oversized pipes.