Mechanical behavior of dowel connection for timber-concrete composite rural bridges

This study focuses on the evaluation of the mechanical behavior of two types of connections for intended use in rural Timber‑Concrete Composite traffic bridges. The two connection types used were the “X” type connection – XD and the dowel type connection – PD. Firstly, static shear tests in small-scale specimens were performed in both connection types and higher results were obtained for the XD series, both for stiffness and load carrying capacity. Secondly, the PD connection was chosen, based on practical and economical aspects, for further testing also in small-scale specimens, including cyclic tests. The influence of the number of cycles in the connection stiffness and load carrying capacity was evaluated. It was concluded that the load carrying capacity increased after the application of a pre-defined number of load cycles and that the connection stiffness increased 80.6% and 34.1% after 10,000 and 1,000 cycles, respectively, for different applied load levels. Also the increase of load level in the cyclic tests affected the performance of the connection, leading to a decrease in stiffness

Effect of microwave treatment on drying and water impregnability of Pinus pinaster and Eucalyptus globulus

Wood is a material that has been used by humankind for a long time. However, wood researchers and industry have always been concerned about the issues during wood drying and the permeability problems of certain species. In this sense, microwave technology has been applied for wood drying and improving permeably. This paper investigates the microwave drying of two Portuguese wood species, Pinus pinaster sap and heartwood and Eucalyptus globulus heartwood using small clear specimens. The samples were grouped into six during each microwave treatment run according to their similarity of initial moisture content. Once the drying was completed, control and microwave -treated samples were impregnated with desalinated water to analyze their improvement in water absorption, and the compression strength parallel to the grain was analyzed. The results showed that each wood species behaves differently under microwave drying and initial moisture content. The impregnation results demonstrated that pine and eucalyptus microwave -treated heartwood samples improved their capability to absorb water. Finally, only the microwave -treated specimens of eucalyptus heartwood presented a decrease in the values of compression strength parallel to the grain compared to the control group. Therefore, MW treatment presents possibilities for further applications for the wood industry with supporting results

Fatigue design in reinforced concrete bridges according to Brazilian code

There has been an increase in the flow of freight vehicles commuting on Brazilian highways. Then, special attention to the structural performance of bridges regarding the fatigue in beams is needed. Brazil has neither normative metrology to study real data flow of vehicles, nor specific fatigue load train models and coefficients to the analysis and design of road bridges. The same load train that is used for general dimensioning, TB 450, is used for the fatigue verification. Hence, this work aims to verify if the current TB 450 is representative of the freight heavy vehicles with 2 to 9 axles concerning the effects of fatigue in the longitudinal reinforcement of beams of theoretical reinforced concrete bridges with two, three, and five beams. This verification is performed analyzing the stress variations found in the longitudinal reinforcement of vehicles with 2 to 9 axles and the TB 450. Based on the results, the longitudinal steel reinforcement was more susceptible to fatigue\u27s effects. Freight vehicles with 5, 6, 8 and 9 axles presented the most significant stress, therefore, they tend to cause more deleterious effects. Hence, the adoption of a Brazilian normative fatigue specific load train and coefficients is necessary to analyze pre-existing road bridges and design new ones most accurately

Alternative model to determine the characteristic strength value of wood in the compression parallel to the grain

Wood strength values are calculated based on the characteristic value, which corresponds to the 5 % percentile of a given probability distribution model. For a few number of samples (12 samples), the Brazilian standard ABNT NBR (7190) establishes an estimator of the characteristic compressive strength parallel to grain of the wood, which may provide a different result when compared with the characteristic value coming from a suitable probability distribution model. Considering the strength results in the parallel compression to the grain of 45 wood species of the hardwood group, Normal, LogNormal, Weibull and Exponential probability distribution models were used for each specie with the purpose of determining the one with the highest adhesion. Calculated the characteristic values by the best probability model distribution, an analysis of variance (ANOVA) was performed in the estimation of the characteristic value of compressive strength, making it possible to identify the most significant terms of the models as well as the quality of the adjustment obtained on such models. The proposed regression model (R2 adj= 96,56 %) proved to be equivalent to the empirical model of the Brazilian standard. The model proposed here only depends on the mean and the lowest value obtained from the compressive strength in the parallel direction to the grain

Estimativa da resistência característica à tração da madeira na direção paralela às fibras por meio de modelos probabilísticos

Para um dimensionamento de estruturas de madeiras dentro das exigências de segurança, a resistência paradeterminada solicitação mecânica é calculada com base em seu valor característico, correspondente ao percentilde de um determinado modelo de distribuição de probabilidades. A norma brasileira NBR 7190 [1]estabelece, para pequenas amostras, relações para estimar a resistência característica da madeira, que podemresultar em diferença significativa dos valores obtidos quando comparado a um modelo probabilístico adequado.Considerando os resultados da resistência à tração ( ) na direção paralela às fibras para 40 distintasespécies de madeira folhosas, com 480 determinações experimentais com teor de umidade padrão ( ),empregou-se funções densidade de distribuição de probabilidades (Normal, LogNormal, Weibull e Exponencial)para cada espécie visando determinar o modelo de maior aderência. Uma vez determinados os valores eos respectivos modelos para cada espécie, um modelo de regressão linear multivariável, fundamentado naanálise de variância (ANOVA) e dependentes do valor médio ( ̅), do coeficiente de variação ( ) e domenor ( ) e maior ( ) valor da resistência para cada espécie, é adotado com objetivo de estimar a resistênciaajustada com aqueles termos mais significativos, de modo a inferir na qualidade do estimador e,consequentemente, na confiabilidade da obtenção desta propriedade mecânica. Por fim, o modelo de regressãoaqui proposto é comparado a proposta da norma brasileira, a fim de avaliar a confiabilidade do modelo esua adequação na estimativa da resistência .Palavras-chave: madeiras tropicais, propriedades de resistência, valor característico

Carbon fiber-reinforced polymers as a tensile reinforcement of the Pinus elliotti and Manilkara huberi wood species

In wood structures, the elements subjected to bending stresses, such as the beams, present a fracture initiated in the tensile region, and under these conditions, the use of laminated composite materials is presented as an alternative solution in the form of repair or reinforcement. This research aimed to evaluate the influence of the use of carbon fibers laminated composites in tensile reinforcement in the direction parallel to grain of Pinus elliotti and Manilkara huberi wood species. The Viapol two-component epoxy adhesive was used in the lamination and fixation of the unidirectional carbon fiber in the wood species. Ten specimens with no defects (reference) and 10 specimens were prepared for each crack length (25 and 50mm) with and without the reinforcement (60mm × 50mm) by the laminated composite. The tensile tests were performed in accordance with the requirements of the Brazilian standard ABNT NBR 7190 (1997). From the results of the statistical analysis, the use of the carbon fiber composite was able to restore the tensile strength of the cracked samples (partial or total) in relation to samples without defects, demonstrating the potential of the laminates in carbon fibers as an alternative solution in repair for both wood species

Estimativa de propriedades da madeira Mandioqueira pela frequência natural de vibração e pela densidade aparente

Por ser um material anisotrópico e heterogêneo, o uso racional da madeira em estruturas requer o conhecimento de uma série de propriedades físicas e mecânicas. Parte das propriedades é obtida com o uso de equipamentos de grande porte, geralmente encontrados em poucos centros de pesquisas. A vibração transversal consiste em um método de ensaio não destrutivo utilizado na determinação da rigidez da madeira, em função agilidade proporcionada na realização dos ensaios. Essa pesquisa objetivou, com base na obtenção de dezessete propriedades entre físicas e mecânicas da madeira de Mandioqueira [Ruizterania albiflora (Warm.) Marc. -Berti, Vochysiaceae], espécie pouco conhecida na literatura nacional e internacional, avaliar a indicação de uso e relacionar suas propriedades físicas (estabilidade dimensional) e mecânicas (resistência e rigidez) com a densidade aparente e com a frequência natural do ensaio de vibração transversal por meio de modelos de regressão. Os resultados indicam o uso da madeira de Mandioqueira em estruturas, por apresentar propriedades equivalentes ou superiores às propriedades de outras comumente utilizadas na construção civil. Dos modelos de regressão, foram notadas fracas correlações entre a densidade e a frequência natural com as propriedades físico-mecânicas avaliadas, resultando em estimativas de baixa precisão. Entretanto, resultados mais abrangentes requerem maior número de espécies, e consistirão em objetivos de pesquisas futuras.Palavras-chave: Mandioqueira, caracterização, vibração transversal, correlação.

Numerical Modeling of the Load-Deformation Behavior of Doweled Softwood and Hardwood Joints

This article presents a nonlinear finite element model developed to simulate the load-deformation behavior of wood joints when loaded by a dowel-type fastener. Particular attention was paid to the initial load-deformation behavior that had a significant influence on the joint stiffness, a joint property with a large influence on the mechanical behavior of wood-based composite structures connected with semirigid joints. To obtain accurate predictions of joint deformation, the material models available in the literature were adapted and nonlinear deformations were taken into consideration during very early loading. The proposed model precisely describes the embedding behavior of different wood species and densities. Numerical results compared very well with those obtained in experiments. Based on this analysis, the recommendation is to obtain the material model inputs based on design values available in the literature

Non-Destructive Methodologies for Assessment of the Mechanical Properties of New Utility Poles

The application of non-destructive technologies for the assessment of mechanical properties has been increasingly used due to its reliable assessment of the condition of timber elements. The application of such methods is well established for sawn timber and small-diameter roundwood. However, regarding the assessment of the mechanical properties for roundwood with larger diameters, which are usually used for new utility poles, a fewer number of studies are available. This research considered three different methodologies for application in Maritime Pine utility poles: i) longitudinal vibration, ii) transverse vibration, and iii) ultrasound. The methodology with better results was chosen for use in the second stage of testing. Furthermore, mechanical tests were performed to compare and validate the results from the non-destructive tests. The moisture contents and densities were also determined. Simple and multiple linear regression analyses were performed between the visual, dynamic, and mechanical properties. The longitudinal vibration method achieved the best correlation within the non-destructive methods, while the ultrasound method had no noticeable correlation. The vibration frequency (f) (r = 0.51) showed a better correlation with the bending strength (MOR) than the dynamic modulus of elasticity (MOEdyn) (r = 0.45). The static modulus of elasticity (MOE) was the best property used to predict MOR because it presented the highest correlation (r = 0.79)

Mechanical behavior of dowel connection for timber-concrete composite rural bridges

This study focuses on the evaluation of the mechanical behavior of two types of connections for intended use in rural Timber-Concrete Composite traffic bridges. The two connection types used were the “X” type connection - XD and the dowel type connection - PD. Firstly, static shear tests in small-scale specimens were performed in both connection types and higher results were obtained for the XD series, both for stiffness and load carrying capacity. Secondly, the PD connection was chosen, based on practical and economical aspects, for further testing also in small-scale specimens, including cyclic tests. The influence of the number of cycles in the connection stiffness and load carrying capacity was evaluated. It was concluded that the load carrying capacity increased after the application of a pre-defined number of load cycles and that the connection stiffness increased 80,6% and 34,1% after 10000 and 1000 cycles, respectively, for different applied load levels. Also the increase of load level in the cyclic tests affected the performance of the connection, leading to a decrease in stiffness