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O presente trabalho teve como objetivo realizar o monitoramento do teor de umidade das madeiras de Apuleia leiocarpa, Clarisia racemosa e Buchenavia capitata submetidas à secagem ao ar no município de Rolim de Moura, RO. Para a avaliação, toras da madeira de cada espécie foram desdobradas em tábuas com faces tangenciais, das quais foram selecionadas 30 tábuas que foram submetidas à secagem ao ar no decorrer de um ano. As curvas de secagem e taxas de secagem foram determinadas a partir da pesagem periódica de amostras controladoras de umidade e das quais também foram avaliadas as contrações sofridas pela madeira. O teor de umidade mínimo atingido pelas madeiras no decorrer do período avaliado foi de 19,43, 21,57 e 25,72%, para B. capitata, A. leiocarpa e C. racemosa, respectivamente, que não pode ser considerado compatível para a maioria das possibilidades de uso da madeira. A maior taxa de secagem foi registrada para a madeira de menor densidade aparente (C. racemosa). O maior valor para o coeficiente de anisotropia foi registrado para a madeira de B. capitata (1,61), que apresentou a maior massa específica aparente (0,86 g.cm-3). A densidade da madeira influenciou o comportamento da mesma ao final do processo de secagem. O método de secagem ao ar livre, para as condições climáticas locais avaliadas não se mostrou eficiente para que as madeiras testadas atingissem um baixo teor de umidade final e, assim, recomenda-se o seu uso combinado com o método de secagem artificial. Palavras-chave: taxa de secagem, curva de secagem, métodos de secagem da madeira. BEHAVIOR OF THE THREE AMAZONIAN WOODS SUBMITTED TO AIR DRYING ABSTRACT This work aimed to carry out the monitoring of the moisture level of Apuleia leiocarpa, Clarisia racemosa and Buchenavia capitata woods, which were submitted to air drying in the city of Rolim de Moura, RO, Brazil. For the evaluation, wood logs of each species were outspread on boards with tangential faces, of which 30 boards were selected, and they were submitted to air drying in the course of a year. Drying curves and drying rates were determined based on periodic weighing of the controlling moisture samples, of which the contractions suffered by the wood were also evaluated. The minimum moisture levels reached by the woods during the study period were 19.43, 21.57 and 25.72% for para B. capitata, A. leiocarpa and C. racemosa, respectively, but these values cannot be considered compatible for most of the possibilities of use of wood. The highest drying rate was registered for the lowest density wood (C. racemosa). The highest value for the anisotropy coefficient was registered for B. capitata wood (1.61), which showed the highest apparent specific mass (0.86 g.cm-3) . The wood density has influenced its behavior at the end of the drying process. The method of air drying, for the local evaluated climatic conditions, has not proved to be effective to allow the researched woods to achieve a low level of final moisture. Therefore, we recommend its use combined with the artificial drying method. Keywords: drying rate, drying curve, drying methods of woods. DOI: http://dx.doi.org/10.14583/2318-7670.v04n01a07

In this paper we extend Kollár and Pluzsik’s thin-walled anisotropic composite beam theory to include multiple cells with open branches and booms, and present a finite element formulation utilizing the stiffness matrix obtained from this theory. To recover the 4x4 compliance matrix of a beam containing N closed cells we solve an asymmetric system of 2N+4 linear equations 4 times with unitary section loads and extract influence coefficients from the calculated strains. Finally, we compare 4x4 stiffness matrices of a multi-celled beam using this method against matrices obtained using the finite element method to demonstrate accuracy. Similarly to its originating theory, the effects of shear deformation and restrained warping are assumed negligible.

A wide number of applications in vibration analysis rely on estimation of modal properties, such as natural frequencies,\ud mode shapes, damping ratios and modal masses [1]. Identified modal parameters form an information\ud baseline for model updating [2], sensor placement, damage detection [3] and structural performance evaluation [4].\ud Thus, the relevance of modal testing keeps increasing, particularly for slender and wobbly structures such as long\ud bridges.\ud At the same time, modal identification often relies on expensive and difficult-to-operate technical equipment, such\ud as shakers or impact hammers. Other drawbacks of these methods include high sensitivity to non-linearities, timeconsumption\ud and susceptibility to human-structure interaction effects.\ud As a consequence, this work investigates the applicability of a new spectral approach for modal identification in\ud slender structures. The approach is fast, cost-effective and easy-to-perform. It questions if is it possible to identify\ud modal properties, with a reliability comparable to standard modal tests, using only a human induced excitation.\ud The identification process requires two main inputs: recordings of structural responses under passage of a given\ud pedestrian at a timed pacing rate; and the pedestrian’s walk forces at the same pacing rate (which can be recorded\ud with an instrumented treadmill). Validation of the methodology is illustrated with a 16.9 m long fiber reinforced\ud polymer footbridge, instrumented with accelerometers, on which standard modal tests have been performed.\ud One of the most significant aspects of the proposed approach is its probabilistic treatment of the identification\ud process, which allows to learn the modal properties from data, while accounting for their estimation variability and\ud measurement noise. Moreover, the human excitation is described with a power spectral density model, based on\ud recorded pedestrian walk forces. In essence, a complex Gaussian log-likelihood function of the dynamic response\ud power spectrum is established and then sampled with the Metropolis–Hastings [5] algorithm. Future developments\ud aim to also account for identification bias.\ud Results indicate that the pedestrian-based approach can identify natural frequencies and damping ratios with a\ud reliability comparable to reference values, obtained with an impact hammer modal test. On the other hand, modal\ud masses are biased relatively to reference values. However, it is noted that even on standard tests, modal masses\ud pose a challenging identification problem. Consequently, the pedestrian-based approach developed in this work is\ud believed to pave a new way for modal identification in structural dynamics.\ud [1] J. Brownjohn, P. Reynolds, S.-K. Au, D. Hester, and M. Bocian, “Experimental modal analysis of civil structures:\ud state of the art,” presented at the SHMII – 7th International Conference on Structural Health Monitoring of\ud Intelligent Infrastructure, 2015.\ud [2] A. Jesus, P. Brommer, R.Westgate, K. Koo, J. Brownjohn, and I. Laory, “Bayesian structural identification of a\ud long suspension bridge considering temperature and traffic load effects,” Structural Health Monitoring, pp. 1–14,\ud Sep. 2018.\ud [3] A. Jesus, P. Brommer, R.Westgate, K. Y. Koo, J. Brownjohn, and I. Laory, “Modular Bayesian damage detection\ud for complex civil infrastructure,” JCSHM, no. Current Advances in Structural Health Monitoring, Dec. 2018.\ud [4] A. Jesus, P. Brommer, Y. Zhu, and I. Laory, “Comprehensive Bayesian structural identification using temperature\ud variation,” Engineering Structures, vol. 141, pp. 75–82, Jun. 2017.