Abstract Civil structures are, normally, subjected to gravitational and thermal loads. The association of the effects of these loads should be the object of analysis when the loss of stability of the slender columns was verifying. In the case of reinforced concrete structures, temperature variations induce internal stresses in addition to gravitational ones since they are caused by the difference in the thermal properties of steel and concrete. Since the structure is a slender system, its stiffness was divided into two parts. In the first one, the properties of the concrete were introduced, including cracking and creep, doing the equations obtained at the time-dependent mathematical process. In the second, the geometric, the construction imperfections and the internal efforts mobilized by the temperature variation were considered. Additionally, strains and thermal loads were considered together. At the end, the values of critical buckling loads for different moments of interest were determined.

RESUMO Em estruturas de wood frame, as ligações entre montantes e banzos tem como finalidade garantir a rigidez e o contraventamento necessários para essas construções, que são naturalmente flexíveis, quando submetidas aos esforços horizontais tais como vento e sismos. Este trabalho teve como objetivo avaliar a resistência ao cisalhamento de ligações de madeira para produção de painel de wood frame produzidos com madeira de eucalipto jovem (menos que 15 anos de idade), tendo em vista que o plantio de espécies desse gênero é mais abundante no país. Os tipos de ligações escolhidas para este estudo foram do tipo chapa de dente estampado, parafuso autoatarraxante e encaixe de madeira. Para cumprir esse objetivo, foram utilizados corpos de prova de madeira de Eucalyptus pellita com idade variando entre 7 e 10 anos (classe C20). Foram utilizados os procedimentos experimentais previstos no projeto de revisão de norma da ABNT PN 02:126.10-001-4 (ABNT, 2017). Os resultados indicaram que a ligação do tipo encaixe é a mais apropriada para a ligação entre banzos e montantes de painéis de wood frame produzidos com madeira de eucalipto jovem, por ter melhor resistência e maior rigidez ao cisalhamento quando comparada com as ligações com parafuso autoatarraxante à 90° e chapa de dente estampado.

ABSTRACT In wood frame structures, the frame connection plays an important role to guarantee stability for those constructions that are naturally flexible when subjected to shear during wind or earthquake. This work aimed to evaluate the shear strength of timber joints for wood frame shear wall produced with young eucalyptus wood (less than 15 years old), considering that the planting of species of this genus are more abundant in the country. The types of connections chosen for this study were metal plate, self-tapping screw, and rectangular mortise and tenon. To achieve this objective, 7 to 10 years old Eucalyptus pellita wood (class C20) was used to produce the specimens. The experimental procedures were provided by in the standard revision project ABNT PN 02:126.10-001-4 (ABNT, 2017). The results indicated that the mortise and tenon are the most suitable for frame to frame connection of wood frame shear wall due to its higher shear resistance and stiffness when compared to the self-tapping screw connected in 90° angle and metal plate.

Abstract The ultimate limit state of stability by equilibrium bifurcation, the limit states for stress and strain resulting from this condition were evaluated for an extremely slender real structure of reinforced concrete, with geometry varying along its length. The aspects related to nonlinearities of the material were considered through the recommendations on NBR 6118:2014, from the Brazilian Association of Technical Standards (ABNT). In the analytical solution, developed for stability analysis, all elements of the structural dynamics present in the system were taken into account, including the column self-weight. The critical buckling load was then dynamically defined to different instants of time. Reductions of 70% for the modulus of elasticity and 59% for the critical buckling force were found in analyses performed from zero and five thousand days. It was also possible to obtain the induced stresses on the homogenized cross-sections and those transferred to reinforcement steel bars.

ABSTRACT According to the study of mechanical properties, wood is an elastic or elastoplastic material that presents different structural behaviour when tensioned or compressed. From the viewpoint of elasticity, wood is considered anisotropic, or rather it is a material with elastic properties that vary with the direction considered. During tree growth, the internal structure of the solid material consisting of the wood becomes highly oriented and therefore anisotropic. To study the failure modes of wooden parts and to observe their anisotropy in this process, we performed a series of exploratory tests on models of beams, taking into account the different positions of fibers and growth rings and the different relationships between height and length for a specific specie of wood, in other words, a test with tangent, radial and inclined load applied to the fibers. The pieces were made of dicotyledonous wood that was first category and free of defects, making a total of nine samples in three groups. Failure by shearing and normal stresses was observed and was well characterized in terms of records left in the samples. In addition, when describing the failure modes, the results are discussed with the presentation of images and graphics for each case.

RESUMO A fluência é um fenômeno que pode ocorrer em estruturas de madeira por ser esse um material viscoelástico. A fluência pode alterar os parâmetros puramente elásticos determinados nos ensaios iniciais de caracterização da madeira, pois o seu comportamento depende da reologia do material, mesmo com um nível de tensão constante. Matematicamente, a fluência pode ser caracterizada por modelos onde a deformação elástica imediata é acrescida de uma deformação viscosa, resultando em uma função temporal. Por essa razão, o cálculo da frequência natural de vibração e a verificação da estabilidade de uma coluna esbelta devem incluir os efeitos redutores da rigidez tanto da força axial quanto da fluência. O primeiro pode ser considerado por meio da parcela geométrica e o segundo pela introdução, na parcela convencional, de um módulo de elasticidade variável com o tempo, obtido em relação ao modelo reológico adotado. Para avaliar os aspectos mencionados, foi realizada uma simulação numérica, considerando uma peça comprimida por uma força na extremidade livre equivalente a 10% da força crítica de Euler, mais o seu peso próprio, adotando-se um modelo reológico de três parâmetros para a variação do módulo de elasticidade. Os resultados indicaram diferenças de 60% e 50% para a frequência e para o módulo de elasticidade, além de definir o instante exato de colapso da coluna em caso de sua inobservância.

ABSTRACT Creep is a phenomenon that can occur in wooden structures since wood is a viscoelastic material. Creep may change the purely elastic parameters determined in wood characterization initial tests, as its behavior depends on the rheology of the material, even under a constant stress level. Mathematically, creep can be characterized by models in which the immediate elastic deformation is increased by a viscous deformation, resulting in a temporal function. For this reason, the calculation of the natural frequency of vibration and the stability verification of a slender column should include the reducing effects of stiffness both of axial force and creep. The first one can be considered through the geometrical portion and the second one by the introduction, in the conventional portion, of a variable elasticity modulus over time, obtained in relation to the adopted rheological model. A numerical simulation was performed to evaluate the aspects above, considering a bar compressed by a force at the free end equivalent to 10% of the Euler critical force, plus its own weight, adopting a rheological model with three parameters for the variation of the elasticity modulus. The results show differences of 60% and 50% for the frequency and elasticity modulus, besides defining the exact instant of column collapse in the case of its non-observance.

Abstract The theoretical analysis for the Brazilian test is a classical plane stress problem of elasticity theory, where a vertical force is applied to a horizontal plane, the boundary of a semi-infinite medium. Hypothesizing a normal radial stress field, the results of that model are correct. Nevertheless, the superposition of three stress fields, with two being based on prior results and the third based on a hydrostatic stress field, is incorrect. Indeed, this work shows that the Cauchy vectors (tractions) are non-vanishing in the parallel planes in which the two opposing vertical forces are applied. The aim of this work is to detail the process used in the construction of the theoretical model for the three stress fields used, with the objective being to demonstrate the inconsistency often stated in the literature.