Eduardo Chahud

Influence of wood moisture content on the modulus of elasticity in compression parallel to the grain

Brazilian Standard ABNT NBR7190:1997 for timber structures design, adopts a first degree equation to describe the influence of wood moisture content. Periodically, when necessary, the referred standard is revised in order to analyze inconsistencies and to adopt considerations according new realities verified. So, the present paper aims to examine the adequacy of its equation which corrects to 12% of moisture the values of rigidity properties obtained on experimental tests. To quantify the moisture influence on modulus of elasticity, it was applied tests of compression parallel to the grain for six specimens of different strength classes, considering nominal moisture of 12; 20; 25; 30%. As results, modulus of elasticity in the moisture range 25-30% showed statistically equivalents, and was obtained a first degree equation to correlate the studied variables which leads to statically equivalent estimations when compared with results by ABNT NBR7190:1997 equation. However, it was indicated to maintain the current expression for the next text of the referred document review, without prejudice to statistical significance of the estimates.

Stress Distribution in Tauari Wood Beam

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 Hookes 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.

Shear Strength of Joints in Glued Laminated Timber: Normative Verification of Bibliography Results

Wood has long been used by man for a wide range of purposes, including the production of furniture, civil construction and structural elements. Aiming the construction industry, the use of glued laminated timber proves to be an excellent alternative to constructive technology, allowing the production of elements with different shapes and sizes. It is important that the bonded wood presents resistance to the stresses imposed on its use. This way, the present study aims to make a comparative analysis of shear strength values of Glued Laminated Timber (also called glulam) through the analysis of studies done by several authors that used different types of wood and adhesives. The results found by these authors were verified based on the ASTM-D-5751 and the Brazilian standard ABNT NBR 7190. It was concluded that the glued joints analyzed obtained satisfactory resistance according to the American standard. However, the majority did not comply with the parameters required by the Brazilian standard.

Proof Load Test on Bridges and Viaducts: A Bibliography Analysis

This article aims at the study of proof load tests on bridges and viaducts, presenting the definitions and methods related to this test, in addition to describing the first load tests ever performed in Brazil. It evaluates the procedures of the Brazilian standards (NBR 9607:2013), comparing with the international regulations. The following topics present the importance and the way in which the load test is carried out, showing the risks of this test. Finally, this article explains the relevance of instrumentation and describes the most commonly used equipment: extensometer, inductive displacement transducer, deflectometer, clinometer, topography instruments, single-cell cell for measuring stationary forces and hydrostatic leveling system with pressure cell.

Pull Out Strength of Bonded-in Steel Rods Perpendicularly to the Grain in Corymbia citriodora and Pinus oocarpa Shiede Timber

The study of pull out strength of glued in rods perpendicularly to the grain is presented. Three types of resin were used in order to evaluate their efficiency. Additionally, the effects of the variation of the moisture content and of the glue line thickness were considered. The beams were made of wood from Corymbia citriodora, (ρ12% = 1000 kg/m3) and Pinus oocarpa Shiede (ρ12% = 550 kg/m3). The wood specimens (four samples for each type of test) were seasoned to the expected moisture contents of 12, 15, 18 and 22%. The anchorage length of the glued in rods was 80 mm, the hole diameters were 7.5, 8.5, 9.5 and 10.5 mm and their respective glue line thickness, 0.6, 1.1, 1.6 and 2.1 mm. The deformed reinforcing bars used as rods, with the minimum yield strength of 500 MPa, had nominal diameter of 6.3 mm. The obtained results confirmed the assumption that type of resin, moisture content, glue line thickness are strength determining factors, while density is less than others. The results are presented in a comparative form. The failure modes are discussed and the need of a broad understanding of resin behavior on wood was emphasized.

Production of Structural OSB with Cajueiro (Anacardium sp.) and Amescla (Trattinikia sp.) - A Preliminary Study

The purpose of this research is to demonstrate, in an original study, the potentiality of the use of Cajueiro (Anacardium sp.) and Amescla (Trattinikia sp.), two low density tropical wood species, for producing OSB (Oriented strand boards), structural panels that replace plywood for several building purposes. In those panels, wood strands can be disposed in a specific direction or in random distribution, in order to reach the desirable mechanical properties. In this case, the strands were oriented by a separator to generate layers in mass proportion 20:60:20 (outer, inner and outer layers). Then these pre-panels went to a pre-pressing to form the mattress. Finally, they were pressed at 100°C, by 10 minutes, under 4.5MPa pressure, using castor oil based bicomponent polyurethane resin as adhesive. They were produced eight panels (four with Cajueiro e four with Amescla), with nominal dimensions 350mm length, 350mm width and 10mm thickness. Results showed that these wood species can be used to produce OSB, mainly considering values obtained in mechanical tests, that are superior to OSB produced in Brazilian enterprises and can be classified as OSB/4, as recommended by European standard EN 300. Research should continue to be developed in order to reach more adequate performance in swelling and water absorption.