Shear modulus of old timber

Selected wood properties were determined for 321 pieces of Scots pine (Pinus sylvestris) structural timber cut from three stands located in the north of Scotland that were approximately 80 years old at the time of felling. The dynamic modulus of elasticity (E d ) was determined for each piece of timber from measurements of stress wave velocity, made with a portable acoustic instrument, and bulk density. Four-point bending tests were conducted on the same samples of timber to determine global static modulus of elasticity (MOE G ) and modulus of rupture (MOR). Basic density was determined gravimetrically from smaller samples cut from each piece of timber. Each piece of timber was uniquely coded so that it could be linked back to a specific log, tree and stand.

2019

Regression trees, random forests, and generalized additive models (GAM) are statistical techniques often used in several disciplines, but rarely in wood technology. This study presented a novel approach to predicting the modulus of elasticity of Uruguayan pine timber by applying three statistical techniques and using visual parameters and non-destructive testing. For this purpose, two sample groups of beams (50 mm × 150 mm × 2800 mm) were selected from two commercial plantations, one comprised of 122 specimens from 14-year-old loblolly pine (Pinus taeda) and the second comprised of 111 specimens from 27-year-old slash pine (P. elliottii). The visual parameters and dynamic modulus of elasticity for each specimen were obtained and associated with their experimental static bending stiffness. The number of annual rings per centimeter, twist, crook, and knot size were the most relevant visual variables for the modulus of elasticity prediction. The inclusion of the dynamic modulus of elas...

The present study aims at investigating the effect of spatial distributions of defects on the mechanical properties of timber. It proposes to establish formalized method to link mechanics of composite materials (anisotropic solid) to the morphological structure of timber. A large database (200 full size beams) relative to maritime pine was created in order to obtain external images of structural components and their corresponding MOE and MOR determined experimentally. Parameters characterising the distribution of heterogeneities are extracted from image analysis of the lateral faces of beams. The main goal is to locate knots determining simultaneously the shape, the position and the size of each defect. When knots are localized, the correlation between several variables which take into account singularities and the bending strength is defined with two statistics methods: the linear regression and the non linear regression with neural network.

International Journal of Materials Engineering, 2014

This study aimed to present, with the aid of the four points static bending, conducted nondestructively, analytical methodology to determine the longitudinal (E) and shear modulus (G) of elasticity in lumber beams. The woods used were Manilkara spp and Pinus elliottii. Were used three different values to the form factor coefficient of the rectangular cross section, allowing evaluating the differences between the shear stiffness values obtained by wood species. The results of the analysis of variance indicated statistical equivalence between shear modulus of elasticity for the two wood species investigated, unless revealing significant the influence of the form factors used to determine the shear modulus of elasticity. The coefficients of the relationship between the modulus of elasticity (E=λ·G) obtained from the least squares method were equal to 37 and 33 to the woods Manilkara spp and Pinus elliottii, be revealing 85% and 65% higher respectively then the relationship (E=20·G) presented in the Brazilian standard ABNT NBR 7190. It is emphasized that these results may be different for the same or different wood species, justifying the use of this methodology in each work developed.

Acta Scientiarum. Technology, 2017

Improve quality of timber structures design is an aim that must be systematically sought by engineers in this area. An important topic that can contribute directly to be achieved in this subject is the more consistent knowledge related to structural properties of wood. Know values of longitudinal modulus of elasticity (E) and shear modulus (G) is essential for proper evaluation of plate structures performance, as example. It has been usual to adopt statistical equivalence for E and G values in plans longitudinal-radial and longitudinal-tangential, although experimental confirmation of this hypothesis is required. In this context, the aim of this work is to determine values of E LR , E LT , G LR and G LT , based on static bending tests, to five dicotyledonous species. Results showed statistical equivalence between the elastic properties in both plans, and the relation E = 35G was obtained for the five wood species here considered.

Engineering Structures, 2016

81 timber beams (14 of Spruce and 67 of Silver fir) were salvaged from different historical buildings. All the timber were visually graded, dynamically (vibration and acoustic methods were used) and statically (four point bending test) tested, to calculate the actual MOE/MOR. The results of the visual strength grading and dynamic tests were combined, in order to predict MOE and MOR on-site, or on reclaimed timber after their dismantling. For salvaged timbers, comparable results to those reported in literature for new solid timbers were obtained on MOE/MOR prediction, combining longitudinal vibration tests and wane extension (r 2 = 0.71 and 0.43 for MOE and MOR prediction respectively). Within this research, alternative simplified methods, for the MOE/MOR prediction, which are based on the stress wave velocity and wane extension, applicable on site, were proposed (r 2 = 0.57 and 0.29 for MOE and MOR prediction respectively). Since the results were obtained by testing a sample with large variability, adopting some simplifications, they can be used as a starting point for the assessment of MOE/MOR of timber directly on-site, or to evaluate the mechanical properties of reclaimed timber after their dismantling, to assess their potential reuse in timber structures.

Revista Árvore, 2023

To simplify the characterization of wood species, the Brazilian standard document ABNT NBR 7190-1 (2022) establishes the determination of mechanical properties employing the characteristic strength in the compression parallel to grain (f c0,k). This mechanical property is estimated using the linear relation given by the following expression f v0,k = 0.12•f c0,k. Brazilian and European standard documents support the estimation of f v0,k using relations among properties. However, the European guidelines in the EN 384 (2019) have used the conventional characteristic strength in the static bending test (f M,k). Thus, this study aimed to investigate the efficiency of the ratio f v0,k = 0.12•f c0,k for adopting 30 hardwoods. The variance analysis results demonstrate the divergence among the experimental outcomes and those values estimated using the relation cited. Therefore, regression models at two parameters were considered to obtain more accurate estimates of f v0,k by adopting f c0,k , and f M,k as independent variables. Regarding the results, the geometric (R 2 = 80.80%) and linear (R² = 74.19%) models were the most accurate for the estimates of f v0,k in terms of f c0,k , and f M,k , respectively. This fact evinces the good accuracy of the models under consideration, which may provide a more rigorous structural design compared to the correlation currently prescribed by the ABNT NBR 7190-1 (2022).

2011

The grading of structural lumber besides contributing for increasing the structure's safety, due to the reduction of the material variability, also allows its rational use. Due to the good correlation between strength and bending stiffness, the latter has been used in estimating the mechanical strength of lumber pieces since the 60's. For industrial application, there are equipment and techniques to evaluate the bending stiffness of lumber, through dynamic tests such as the longitudinal vibration technique, also known as stress wave, and the transverse vibration technique. This study investigated the application of these two techniques in the assessment of the modulus of elasticity in bending of Teca beams (Tectona grandis), from reforestation, and of the tropical species Guajará (Micropholis venulosa). The modulus of elasticity estimated by dynamic tests showed good correlation with the modulus measured in the static bending test. Meantime, we observed that the accuracy of the longitudinal vibration technique was significantly reduced in the evaluation of the bending stiffness of Teca pieces due to the knots existing in this species.

BioResources, 2020

Accurate estimation of average modulus of elasticity in compression parallel to the grain (Ec0) is of paramount importance for rational sizing of timber structures, given the use of this property in the estimation of stability of compressed parts (ultimate limit state, ULS) and in calculation of excessive strains (serviceability limit state, SLS). In Brazil, if values cannot be experimentally determined, ABNT NBR 7190 (1997) allows for estimation of Ec0 through relations to average modulus of elasticity both in tension parallel to the grain (Et0) (Ec0 = Et0) and in bending (EM) (Ec0 = EM/0.90). This research aimed to access the efficiency of these relations by testing 30 tropical wood species. The analysis of variance results showed that Ec0 and Et0 were statistically equal. However, Ec0 and EM/0.90 were not statistically equal, and the method of least squares resulted in a coefficient of 0.98, which was 8.89% higher than the one suggested by ABNT NBR 7190 (1997) and close to 1, thu...

BioResources