Investigations into the fire resistance of high-strength concrete (HSC) is extremely important to optimize structural design in construction engineering. This work describes the influence of polypropylene fibers on the mechanical properties and durability of HSC at high temperatures (25, 100, 200, 400, 600 and 800 °C). HSC specimens with 2 kg/m³ composed of polypropylene fibers are tested in a temperature range of 25 to 800 °C, followed by microstructural analysis. In addition, a statistical analysis is designed to identify the effect of factors, namely temperature and polypropylene fibers, and their interactions on mechanical properties and water absorption, electrical resistivity, mass loss and ultrasonic velocity. Most of the properties are improved by the incorporation of fibers, obtaining highly predictable regression models. However, the polypropylene fibers reduce compressive strength but improve the residual mechanical properties up to 400 °C.

Recently, castellated columns have been increasingly used in buildings because of their flexibility, easy compatibility and potential savings due to less steel consumption. However, there is a lack of research related to the subject. In view of that, this work evaluates the influence of the opening type and size on the resistant capacity of the column, considering a nonlinear plastic analysis by the finite element method (792 simulations). For this, columns without openings were modeled to validate the methodology proposed. After validation, a nonlinear buckling analysis of castellated columns was performed. In this study, different cut patterns of the beam web are evaluated, as well as residual stresses, material and geometric imperfections, based on a statistical design. The loads obtained by castellated columns and columns without web are compared. Also, the resistance reduction factors associated with global buckling (χ) for castellated profiles are compared to the values proposed by ABNR NBR 8800 (2008). Furthermore, statistically, there are no differences between the opening types evaluated. Finally, in order to contribute to the design of castellated columns, equations based on regression models were found to predict the load capacity of these elements.

Wood is widely used in many sectors of civil construction as a structural material. Brazilian code ABNT NBR 7190:1997 Design of Timber Structures governs the method of project design as well as the characterization of wood for structural design. In this aspect the code considers wood as an orthoptic material, however is well known that the organic origin provides great anatomical complexity to its. This work aims to study the distribution of normal stresses in a Tauari wood beam subjected to the elastic regime, and to ascertain the current position of the Neutral Line during test. For this purpose, a four-point static bending test and subsequent compression and tension to the grain tests were performed to determine the modulus of elasticity and calculate the normal stresses by recording deformations and applying Hooke's Law. The data were statistically analyzed to define bests adjusts to Stress vs. Strain diagrams, and thus determine the location of the Neutral Line. It was verified that the position of the Neutral Line was a normal distribution variable, being located at 1,07cm above the geometric center of the board. Finally, the comparison between values of normal tension obtained experimentally and through the theoretical method was determined and similarities were verified in these data, being also plausible the theory for the calculation of the normal tensions of the wood beams, when it is in the elastic regime.

Resumo Para o dimensionamento correto de estruturas de madeira, as premissas da norma brasileira são de extrema valia como norte para os engenheiros estruturais, pois exibem valores padrão de resistência. Dessa forma, este estudo tem como objetivo analisar se o valor do módulo de elasticidade da classe C60 exibido na norma brasileira confere com os valores obtidos em ensaio de 23 espécies brasileiras, utilizando a metodologia Bootstrap com 1 milhão de simulações. Além disso, analisa-se, com modelos de regressão, se é possível estimar a propriedade de rigidez (E c0 ) dessas 23 espécies em função da densidade aparente. É possível concluir que a norma brasileira superestima o módulo de elasticidade das madeiras brasileiras, apresentado um valor quase 35% superior ao que realmente elas resistem, evidenciando que a norma necessita passar por revisão. Outro ponto é que os modelos de regressão não mostram significância, ou seja, com a densidade aparente não é possível estimar a propriedade de rigidez analisada.

The Brazilian code ABNT NBR 7190-1 (2022) presents different strength classes for hardwood and displays representative values for apparent density, compressive strength parallel to the grain and modulus of elasticity in parallel direction of fibers to help designers for an appropriate timber structure design. This research evaluated to check if the representative value of modulus of elasticity in parallel direction of fibers and apparent density of D20 strength class (native wood species) still represent a secure value for designers. Also, it was checked the possibility to estimate compressive strength parallel to the grain and modulus of elasticity in parallel direction of fibers as function of apparent density using regression models, aided by the analysis of variance. The results showed that the representative value of modulus of elasticity in parallel direction of fibers and apparent density for D20 is close to the obtained in the present research. The analysis of variance indicated the impossibility to estimate strength and stiffness properties as function of apparent density.

A crescente utilização da madeira na construção, devido às suas qualidades estruturais, estéticas e sustentáveis, destaca a importância de compreender suas propriedades elásticas para um dimensionamento preciso dos elementos estruturais. No entanto, a determinação desses parâmetros pode ser desafiadora devido à grande variabilidade das características físicas e mecânicas da madeira. Neste contexto, esta pesquisa investigou a necessidade de uma estimativa mais precisa do módulo de elasticidade transversal (G) da madeira. Com essa finalidade foi realizado um levantamento bibliográfico de estudos e normas que abordassem o módulo de cisalhamento (G) e sua relação com o módulo de elasticidade longitudinal (E), utilizada para o dimensionamento quando dados experimentais do G não estão disponíveis. Comparando diferentes propostas encontradas na literatura com a norma brasileira ABNT NBR 7190-1:2022, que estabelece G=E/16, foram identificadas discrepâncias significativas. Entre os métodos de ensaio destacados na literatura, a flexão e o ultrassom surgiram como os mais relevantes para prever o comportamento elástico da madeira. No entanto, a falta de equipamentos para ensaios de torção na madeira no Brasil, conforme indicado por normas, ressalta a necessidade de métodos alternativos, como o de flexão, que se mostram práticos e acessíveis para determinar o módulo de cisalhamento da madeira. Os resultados desta pesquisa têm implicações significativas para a engenharia prática e o avanço do conhecimento acadêmico sobre as propriedades da madeira. Ao reconhecer as complexidades na determinação dos parâmetros elásticos da madeira e explorar novas abordagens, é possível melhorar a segurança e eficiência das estruturas de madeira, beneficiando tanto a sociedade quanto a comunidade acadêmica.