Evaluation and prediction of bending properties of glulam beams made from young plantation-grown Eucalyptus nitens

Oil palm timber used for load-bearing purposes such as glued laminated timber (GLT) needs to have clearly defined strength and stiffness values. Because the wood density (which correlates to elastomechanical properties) varies significantly within oil palm trunks, oil palm boards must be graded based on their density across the board width in order to homogenize and improve the properties of the final product. In this preliminary investigation, 20 beams of combined GLT with four different types of graded lamellas were produced and tested in a 4-point-bending test. The results show a correlation between density and bending strength. The characteristic strength values are achieved, and the elastomechanical properties of beams based on lamellas that are ripped lengthwise and edge-glued according to their density are higher compared to beams based on lamellas cut only according to their geometry. A correlation between bending strength and local MOE is determined. In summary, lengthwise ripping of oil palm boards according to their density across the board width as well as a grading according to density limit values is shown to improve the properties of combined GLT made from oil palm timber for load-bearing purposes.KeywordsGLTOil palm timberDensityGLT productionPropertiesBuilding products

This paper presents the results of extensive investigations on the lamination strength grading, the production and the mechanical properties of European beech (Fagus sylvatica L.) glued laminated timber (GLT). Based on the analysis of potential influencing parameters on strength and stiffness as well as subsequent tension tests parallel to the grain on single boards, a combined visual/machine approach for grading the raw material into tensile strength classes T50, T42, T33 and T22 was developed. Boards strength graded with the developed procedure were then finger-jointed by a Swiss GLT producer and the strength of the finger joints was investigated by means of tension and bending tests. The strength and durability of the bonding was investigated and verified by means of tensile-shear and delamination tests. It could be shown that the required finger-joint and bondline strengths for GLT of strength classes GL40 and GL48 can be achieved, but that the process parameters for finger jointing (in particular the geometrical properties of the finger joint profile) have to be optimized in order to be able to produce GLT of strength class GL55. Finally, an extensive experimental testing campaign was performed to investigate the mechanical properties of European beech GLT produced based on the strength grading rules and production techniques developed before. Bending, tensile and compressive parallel to the grain, as well as shear tests were carried out on GLT specimens of strength classes GL40, GL48 and GL55 in different sizes in terms of cross-section and length. Based on these investigations and complementing numerical simulations, characteristic strength and stiffness values and formulae for consideration of size effects in bending, tension and shear were determined.

The fiber-reinforced polymer is one kind of composite material made of synthetic fiber and resin, which has attracted research interests for the reinforcement of timber elements. In this study, 18 glued-laminated (glulam) beams, unreinforced or reinforced with internally embedded carbon fiber–reinforced polymer (CFRP) sheets, were tested under four-point bending loads. For the reinforced glulam beams, the influences of the strengthening ratio, the modulus of elasticity of the CFRP, and the CFRP arrangement on their bending performance were experimentally investigated. Subsequently, a finite element model developed was verified with the experimental results; furthermore, a general theoretical model considering the typical tensile failure mode was employed to predict the bending–resisting capacities of the reinforced glulam beams. It is found that the reinforced glulam beams are featured with relatively ductile bending failure, compared to the brittle tensile failure of the unreinforced ones. Besides, the compressive properties of the uppermost grain of the glulam can be fully utilized in the CFRP-reinforced beams. For the beams with a 0.040% strengthening ratio, the bending–resisting capacity and the maximum deflection can be enhanced approximately by 6.51 and 12.02%, respectively. The difference between the experimental results and the numerical results and that between the experimental results and analytical results are within 20 and 10%, respectively.

Theoretical and experimental studies on the bending properties of glued laminated timber manufactured with Chinese fir

Increasingly, efforts have been made to replace adhesives that contain formaldehyde in their formulation with others free of this substance in the production of engineered wood. It is known that the release of formaldehyde can cause serious problems to human health, potentially leading to death. As a result, the use of formaldehyde-free adhesives has gained prominence in industries. Furthermore, a major challenge in the use of wood products refers to their durability, which can be reduced by the attack of xylophagous agents. The use of preservative solutions is an alternative that mitigates this problem and guarantees greater durability to the material. Therefore, the objective of this work was to evaluate the mechanical properties of glulam beams produced with rubberwood treated with preservatives chromated copper borate (CCB) and pyrethroid using polyurethane as adhesive, a type of free-formaldehyde adhesive. The glulam beams were produced with 3 lamellas measuring 60 × 20 × 1200 mm, differentiated by the type of adhesive (polyurethane and resorcinol-formaldehyde), and by the presence or absence of preservative treatment. Specimens were obtained from the beams for characterization regarding resistance to normal compression, structural compression, and compression parallel to the fibers in dry and wet conditions. Among the properties evaluated, it was found that preservative treatments did not affect the compressive strength parallel to the fibers in beams produced with polyurethane, with values ​​of 33.77 and 31.61 MPa for those without treatment and treated with CCB, respectively, not showing significant differences. These results show the potential for using polyurethane as an adhesive in glulam beams.

Unprecedented widespread failure of welded moment connections in steel frames caused by the 1994 Northridge and the 1995 Kobe earthquakes have alarmed the engineering communities throughout the world. Beam-to-column connections in steel frames have been traditionally designed by using classical Euler-Bernoulli beam theory which leads to assumptions that the flanges transfer moment while the web connection primarily resists the shear force. The results of a recent finite element study at The University of Michigan have shown that stress distribution in the vicinity of moment connections drastically differs from the pattern assumed following the classical beam theory. This is in agreement with the boundary effect postulate expressed by the famous Saint Venants Principle. The finite element study has shown that the magnitude and direction of the principal stresses in the connection region are better approximated by using truss analogy rather than the classical beam theory. Accordingly, both the bending moment and the shear force are transferred across the connection near the beam flanges through diagonal strut action. Thus, the beam flange region of the traditionally designed connection is overloaded. This conclusion explains, to a large extent, the recently observed steel moment connection failures. This study uses the finite element analysis results and the truss analogy in order to establish a more realistic load path in the welded steel moment connections, a practical and more rational analysis and design procedure has been developed. The new connection design uses a combination of flange cover plates and vertical rib plates to carry the normal and shear stresses created by the truss action. The design procedure was successfully validated through cyclic load testing of a nearly full size specimen.

In this paper, based on the modi ed couple stress theory, the size-dependent dynamic behavior of circular rings on elastic foundation is investigated. The ring is modeled by Euler-Bernoulli and Timoshenko beam theories, and Hamilton's principle is utilized to derive the equations of motion and boundary conditions. The formulation derived is a general form of the equation of motion of circular rings and can be reduced to the classical form by eliminating the size-dependent terms. On this basis, the size-dependent natural frequencies of a circular ring are calculated based on the non-classical Euler-Bernoulli and Timoshenko beam theories. The ndings are compared with classical beam theories. Response of the micro-ring under application of static and dynamic loads is investigatedand compared with the classical theories. Results show that when the thickness of the ring is in the order of the length scale of the ring material, the natural frequencies evaluated using the modi ed couple stress are considerably more than those predicted based on the classical beam theories, while the defection and natural frequencies of the classical and non-classical beam theories approach one another for the rings with thickness much larger than the material length scale.

Glued laminated timber is a structural engineered product that requires precision and strict quality control in its manufacture. For ensure that produced elements properties are in compliance with regulatory requirements, final product must be tested under laboratory conditions. Determining factors in final glulam pieces cost are the type and the quantity of adhesive used in structural elements manufacture. This study aimed to investigate, aided by three point static bending tests and variance analysis (ANOVA), influence of glue lines (3, 5, 7) and lamellae (4, 6, 8) on strength (MOR) and stiffness (MOE) properties of glulam beams manufactured with <i>Pinus</i><i>oocarpa</i> (CCA treated) and bonded with Phenol Resorcinol resin (Cascophen RS-216-M). These beams presented nominal dimensions 90mm wide; 100mm height; and 1350mm length. For 100 mm fixed height, three beams configurations were tested (a) with four lamellae of 25 mm (3 glue lines); with 6 lamellae of 16,7 mm (5 glue lines) and 8 lamellae of 12.5 mm each (7glue lines), being fabricated 6 beams for experimental condition. In addition to investigating influence of glue lines and lamellae number, possibility of estimating MOE and MOR based on apparent density was also evaluated. ANOVA results showed no significance about glue lines number (or lamellae thickness) in strength and stiffness values, implying, for economic reasons, be configuration with four 25mm lamellae the best among tested beams. From regressions, apparent density was only significant in MOE estimating (R<SUP>2</SUP> = 46.90%), indicating not be possible to estimate the stiffness and strength values of the glued laminated timber evaluated by the apparent density.

The failure process of the Si-Ti-C-O fiber bonded ceramic material was investigated under tensile and flexural loading conditions. Tensile and three-point bending tests showed the significant difference between the failure modes caused under the two types of loading. The tensile failure process was calculated using a Monte-Carlo simulation method based on a shear-lag model. The calculation successfully predicted the distribution of the tensile strength of the Si-Ti-C-O fiber bonded ceramic material. The finite element method was employed for calculating the failure process of the Si-Ti-C-O fiber bonded ceramic material under three-point bend loading, where the statistic properties of the tensile strength obtained from the above Monte-Carlo simulation was taken into account. The calculated load-deflection response and failure process were in quite good agreement with the experimental data. Furthermore, the discrepancy in the distribution of the strength was calculated under tensile and three-point bend loading conditions ; the larger Weibull shape parameter and the smaller average value in the tensile strength than in the flexural strength were successfully assessed through the calculations. Finally, the effect of the interlaminar shear strength on the strength and its distribution was discussed under bend loading.

Development and structural behaviour of adhesive free laminated timber beams and cross laminated panels

Analytical and experimental investigation of the flexural and bond adhesive properties of thermally modified rubberwood and hybrid glulam beams with WPVC composites

Traditional in-place inclinometers are widely used for monitoring displacements inside a slope. However, these traditional inclinometers have several disadvantages such as electromagnetic interference, signal loss for long distance transmission, gravity dependence and poor durability. Scholars have proposed fibre Bragg grating (FBG)-based in-place inclinometers which can overcome these limitations. However, all such in-place inclinometers are based on the relative displacement between two tips of the rigid segment, but the deformation of the segment is not considered in the calculation, which is not consistent with the actual condition. The error of measurement is due to linear superposition. According to classical indeterminate beam theory, the authors developed a new type of FBG-based in-place inclinometers where the deformation of the segment is coordinated with the casings installed in boreholes. This type of FBG-based in-place inclinometer has been fabricated and calibrated in the laboratory. The measured displacement data are in good agreement with theoretical results obtained using equations derived by the authors based on classical beam theory. After the laboratory calibration, a series of FBG-based in-place inclinometers have been installed in one vertical borehole in a slope in China. Monitoring data of all FBG wavelengths have been collected in rainy and dry seasons, and have been analysed in this paper. It has been found that the slope moves quickly in the rainy season and remains stable in the dry season.

Approximate theory for locally loaded plane orthotropic beams

In the current paper, dynamic stability analysis of microbeams subjected to piezoelectric voltage is presented in which the microbeam is integrated with piezoelectric layers on the lower and upper surfaces. Both of the flutter and divergence instabilities of microbeams with clamped-clamped and clamped-free boundary conditions are predicted corresponding to various values of applied voltage. To take size effect into account, the classical Timoshenko beam theory in conjunction with strain gradient elasticity theory is utilized to develop nonclassical beam model containing three additional internal length scale parameters. By using Hamilton’s principle, the higher-order governing differential equations and associated boundary conditions are derived. Afterward, generalized differential quadrature method is employed to discretize the size-dependent governing differential equations along with clamped-clamped and clamped-free end supports. The critical piezoelectric voltages corresponding to various values dimensionless length scale parameter are evaluated and compared with those predicted by the classical beam theory. It is revealed that in the case of clamped-free boundary conditions, the both of flutter and divergence instabilities occur. However, for the clamped-clamped microbeams, only divergence instability takes place.

A size-dependent nonclassical Bernoulli–Euler beam model based on the strain gradient elasticity is proposed for piezoelectric nanowires. The governing equations and the corresponding boundary conditions are naturally derived from the variational principle. Different from the classical piezoelectric beam theory, the electric field–strain gradient coupling and the strain gradient elasticity are both taken into account. Static bending problem of a cantilever piezoelectric nanobeam is solved to illustrate the effect of strain gradient. The present model contains material length scale parameters and can capture the size dependent piezoelectricity and elasticity for nanoscale piezoelectric structures. The numerical results reveal that the deflections predicted by the present model are smaller than that by the classical beam theory and the effective electromechanical coupling coefficient is dramatic enhanced by the electric field–strain gradient coupling effect. However, the differences in both the deflections and effective EMC coefficient between the two models are very significant when the beam thickness is very small; they are diminishing with the increase of the beam thickness. This model is helpful for understanding the electromechanically coupling mechanism and in designing piezoelectric nanowires based devices.