Resumo Neste trabalho é apresentado um estudo sobre a ruptura do concreto por pry-out em conectores de cisalhamento tipo Crestbond com o objetivo de obter um modelo de cálculo que estima a resistência da conexão a esse modo de falha. As análises foram realizadas por meio de simulações numéricas capazes de reproduzir o referido modo de falha. Os resultados numéricos são comparados com os experimentais e discutidos em relação à força máxima atingida e o aspecto da fissuração típica do pry-out. O modelo de cálculo proposto apresentou boa correspondência com os resultados experimentais, com uma razão média Pteo/Pexp igual a 0,99 e um coeficiente de variação de 10%. Os valores encontrados nesse estudo sugerem que a expressão da Aprovação Técnica Alemã para outros conectores pode ser aplicada nos conectores Crestbond.

Abstract In this work, a study on failure by concrete pry-out in Crestbond shear connectors is presented. The study’s aim was the development of an expression that estimates the connection’s bearing capacity. The analyses were carried out through numerical simulations designed to reproduce the referred failure mode. Numerical and experimental results are compared and discussed in relation to the maximum force reached and the cracking aspect typical of concrete pry-out. The proposed equation corresponded well to experimental results, with a mean ratio Ptheo/Pexp equal to 0,99 and a coefficient of variation of 10%. The results found in this study indicate that the concrete pry-out expression in German Technical Approval Z-26.4-56 can also be applied to Crestbond shear connectors.

Abstract Carbon-black nanoparticles (CBN) have been incorporated into cement-based materials for improvement of mechanical or self-sensing properties. There is no previous research focused on the microstructural evaluation of effects of CBN on both parameters. In this work, mortars containing different CBN contents were produced, cured for 28 days, and subjected to electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Tests for determination of compressive strength, modulus of elasticity and piezoresistivity response were developed. SEM indicated that lower CBN contents refined the cementitious matrix, while higher contents increased the volume of voids. XRD and Raman spectroscopy indicated hydration improvements for CBN contents between 0.375% and 3%. The best mechanical improvements were provided by concentrations of CBN up to 3%. CBN contents of 5% and 6% provided the best sensing properties. The optimal concentration was found to be 5% of CBN, since it provided excellent piezoresistivity, without significant mechanical properties loss.

Resumo Nas últimas décadas, inúmeros estudos têm sido desenvolvidos a respeito de estruturas de pórticos preenchidos com alvenaria participante, comprovando o aumento de rigidez lateral proporcionado por esta. Neste trabalho, análise foi realizada, baseada em prescrições normativas que adotam o método da barra diagonal equivalente, com o objetivo de comparação aos resultados experimentais de ensaios de pórtico de aço preenchido com alvenaria de blocos de concreto. Duas das três normas técnicas estudadas sugeriram valores de rigidez lateral inferiores aos resultados experimentais, como condição de segurança ao dimensionamento. Sobre as forças de ruptura da alvenaria, os dois procedimentos analisados apresentaram valores próximos de força crítica, embora tenham apontado modos críticos de colapso distintos. O método da barra diagonal equivalente se mostrou uma ferramenta útil e simples para a consideração da alvenaria participante, devendo ser empregado em caso de ações horizontais reduzidas, prévias ao estágio inicial de fissuração do painel.

Abstract In the last decades, several studies have been developed regarding structures composed by frames infilled with masonry walls, proving the increase of lateral stiffness by the infill. In this work, an analysis was carried out, based on design codes which adopt the equivalent diagonal strut method, to compare theoretical results with experimental ones of tests performed on steel frames infilled with concrete block masonry. Two of the three assessed codes specify lateral stiffness smaller than that measured from experimental testing, as safety measures for design. Regarding the masonry ultimate loads, the two specifications analyzed yielded similar values of critical force, although they pointed out different failure modes. The equivalent diagonal strut method has been proved to be a simple and useful tool for considering masonry walls and it should be used in case of reduced horizontal loads, prior to initial cracks of the infill wall.

Degradation of mechanical properties and durability of reinforced concrete structures occur when they are subjected to fire situations, depending on the characteristics of the material, fire duration and the ways of fire extinguishing. Mechanical properties such as compressive strength, tensile strength and elasticity modulus are some examples of typically altered characteristics in concrete during high temperature exposure. Nevertheless, little is known about the advance of the carbonation front on fire-damaged concrete, which is a characteristic directly related to the durability of the structural system. For this purpose, the carbonation front was evaluated in specimens with characteristic strengths of 20 MPa and 35 MPa, subjected to high temperatures (200 °C, 500 ºC and 700 ºC) and different types of cooling (fast and slow). It was observed that the concrete durability is harmed by exposure to high temperatures and fast cooling. However, advance of the carbonation front was not verified in slow cooling situations.

O objetivo deste trabalho foi analisar a exatidão de estimativas de fatores de empilhamento obtidas através de fotografias digitais e de software especialmente desenvolvido para esta finalidade, em pilhas sobre caminhões. Para isto, foram utilizados seis caminhões com cinco pilhas cada um, pertencentes à ACESITA ENERGÉTICA Ltda. Após as análises, verificou-se que a diferença média entre os fatores obtidos pelo método fotográfico e os fatores reais foi da ordem de 3,2%, com tendência de superestimação dos fatores obtidos pelo método fotográfico. Pelo teste "t", verificou-se, também, que os fatores obtidos pelo método fotográfico diferiram dos fatores reais, principalmente devido ao mau empilhamento da madeira.

The objective of this work was to analyze the accuracy of piling factor estimates using digital photography and software especially developed for this purpose. Six trucks carrying five piles each, owned by ACESITA ENERGÉTICA Ltd., were used in this research. The analysis revealed that the average difference between the factors determined by the photographic method and the actual factors was approximately 3.2%, with a tendency for over estimation of the values obtained by the photographic method. The "t" test analysis suggested that the differences observed between these factors were mainly due to the the poor piling up of the wood.