In this study, an experimental campaign was conducted to characterize the length effect on the elasticity and tensile strength of clear spruce wood parallel to the grain direction. Four groups of specimens of different lengths, cut from the same log, were tested under the same conditions under longitudinal tensile loading. The cross-sectional area of the specimens was selected as being constant and sufficiently small to exclude the effect of variations of the properties in the transverse direction. Local deformations along the lengths of the specimens were recorded during the tests in order to characterize the spatial variability of the elastic modulus. A connection between the mesostructure of the clear wood and its local elastic modulus was observed. Statistics concerning the elastic modulus, strength and strain to failure and the effect of length change on these properties were extracted. The strength statistics were also used to examine the accuracy of the classical Weibull size effect law. The correlations between the strength, the elasticity and the density were obtained. The results show a variability of approximately 20% in the local elastic modulus. Also, the variability of the effective elastic modulus decreases with increasing length. The mean value of the strength has an upper bound when the length approaches zero, in contrast to the Weibull law, while its variability remains virtually unchanged for different lengths.
Abstract Probabilistic tools are being used to understand the inherent uncertainty of FRP composites. Over the years different approaches have developed, focusing on behaviour and associated uncertainties at a micro-/meso-/macro-scale, each with specific advantages/limitations depending on the type, and scope, of the analysis being undertaken. Consideration of spatial variability, and associated random field modelling, of geometric and material/mechanical properties is believed to be an importan...
Last. Simon Hehl(Bern University of Applied Sciences)H-Index: 7
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Abstract Adhesively bonding timber structural elements provides new opportunities as it is well adapted for the nature of the material. Experimental and numerical investigations were carried out on full-scale double-lap joints composed of hardwood adherends (beech). Although beech is currently only rarely used as a construction material – due to the difficult processing and the lack of design methods – its abundant availability in Central Europe and its high mechanical resistance make it a promi...
Linear vibration welding of timber structural elements provides new opportunities to potentially achieve structural joints. This paper investigates to which extent welded joints can be considered for load-bearing structural joints. On the basis of a series of experimental and numerical investigations on a series of welded single-lap joints, failure modes were identified, and the associated failure criterion was quantified. A probabilistic method subsequently allowed accurately predicting the cap...
Last. Simon Hehl(Bern University of Applied Sciences)H-Index: 7
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The strength prediction of adhesively bonded timber joints is difficult due to the anisotropic and brittle nature of the adherends, the complex stress distribution as well as the uncertainties regarding the associated material resistance. This paper describes a probabilistic method for the strength prediction of balanced double lap timber joints. The method considers the statistical variation and the size effect in the strength of timber using a Weibull statistical function. The design method pr...
#1Thomas Tannert(Bern University of Applied Sciences)H-Index: 23
#2Frank Lam(UBC: University of British Columbia)H-Index: 20
Last. Till Vallée(Bern University of Applied Sciences)H-Index: 23
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Rounded Dovetail Connections (RDC) are a relatively new wood-to-wood connection concept that, despite the lack of design guidance in standards, has become popular in timber construction due to the widespread of modern milling machinery. Because of the anisotropic nature of wood and the complex stress-strain state in RDC, the question of their dimensioning is very complex. Experimental and numerical investigations were carried out on full scale RDC used to connect two timber members as joist to b...
#1M. R. Mitchell(UMass: University of Massachusetts Amherst)H-Index: 1
#2R. E. Link(UMass: University of Massachusetts Amherst)H-Index: 1
Last. Meghan T. Krupka(UMass: University of Massachusetts Amherst)H-Index: 1
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The natural variation of strength properties within brittle materials leads to the phenomenon of size effect which causes the expected strength of a material to decrease as the stressed volume increases. An important implication of size effect is that size adjustment parameters must be incorporated into multi-axial constitutive and failure models used in numerical simulations such as those made using the finite element method. These size adjustments are based on the sizes of the individual eleme...
Last. Bugao Xu(University of Texas at Austin)H-Index: 30
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This paper reports the evaluation tests on the reliability and validity of a 3-dimensional (3D) laser body scanner for estimation of body volume and % fat. Repeated measures of body imaging were performed for reproducibility analysis. Validity of the instrument was assessed by comparison of measures of body volume by imaging to hydrodensitometry, and body fat was compared to hydrodensitometry and dual energy X-ray absorptiometry. Reproducibility analysis showed little difference between within-s...
#1Thomas Tannert(Bern University of Applied Sciences)H-Index: 23
#2Frank Lam(Bern University of Applied Sciences)H-Index: 20
Last. Till Vallée(Bern University of Applied Sciences)H-Index: 23
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The strength prediction of rounded dovetail connections (RDCs), a relatively new connection for structural timber members, is difficult due to the anisotropic and brittle nature of the material, the complex stress distribution as well as the uncertainties regarding the associated material resistance. Experimental investigations were carried out to provide input and benchmark data for developing a method to predict RDC strength. Numerical analyses confirmed that the experimentally observed failur...
#1Sanjay R. Arwade(UMass: University of Massachusetts Amherst)H-Index: 20
#2Peggi L. Clouston(UMass: University of Massachusetts Amherst)H-Index: 12
Last. Russell Winans(UMass: University of Massachusetts Amherst)H-Index: 2
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This paper describes a model for the spatial variation of the elastic modulus of parallel strand lumber (PSL) that is based on bending experiments and also describes a validated stochastic computational model that incorporates orthotropic elasticity and uncertainty in strand geometry and material properties. The PSL exhibits significant variability both within members and between members, but this variability is less than that of equivalent sawn-wood members, and decreases with increasing member...
Timber is a renewable material that should be more used for sustainable construction. While the mechanical behavior and durability of some species have been widely studied in the past, few studies are available for the Ozigo (Dacryodes buettneri) specie. This paper deals with the spatial variability of Ozigo beams subjected to long-term loadings and different environmental conditions. These beams were previously subjected to long-term creep in three environments (air-conditioned, unsheltered, an...
Abstract The aim of this work is the investigation of mesoscale/local variability in mechanical properties of clear timber in the radial direction. Clear Norway spruce wood, Picea abies, was used for cutting specimens of different lengths with a small cross-sectional area of 4 × 4 mm2, in the radial direction of timber boards, and tested under tensile loading. In some boards, specimens were positioned regularly and, in some others, randomly, and local deformations in each specimen were measured ...
#1Chao Wu(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 29
#2Niloufar Vahedi(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 2
Last. Thomas Keller(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 45
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Abstract Balsa wood is an appropriate core material for structural sandwich applications due to its high strength- and stiffness-to-weight ratios. However, the mechanical properties vary considerably owing to the inherent scattering of natural wood materials. One approach to reduce this scatter and tailor the mechanical properties according to specific application needs is to recompose the natural material into a veneered material consisting of veneer layers of different grain orientations, whic...
#1Sung-Jun Pang(SNU: Seoul National University)H-Index: 5
#2Kyung-Sun Ahn(SNU: Seoul National University)H-Index: 1
Last. Jung-Kwon Oh(SNU: Seoul National University)H-Index: 7
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The aim of this study was to predict the withdrawal resistance of a screw in hybrid cross-laminated timber (CLT) composed of two types of lamina layers. A theoretical model to predict the withdrawal resistance was developed from the shear mechanism between a screw and the layers in hybrid CLT. The parameters for the developed model were the withdrawal stiffness and strength that occurs when a screw is withdrawn, and the penetration depth of a screw in layers of a wood material. The prediction mo...
Abstract The paper proposes a new model for the assessment of size effects affecting the fracture strength of brittle materials. The proposed model permits to accurately estimate the relation between the specimen strength, the initial defect size and to take into account the strength variation with respect to the tested volume. The proposed methodology is analytically defined and thereafter validated with the literature data obtained through tests on different types of brittle materials, and on ...
Characterising spatial variability, which is of utter importance in inspection and maintenance strategies, requires comprehensive spatially distributed databases. However, in real practice, spatially distributed inspection is costly and could damage the structure if a large number of destructive tests are carried out. Therefore, the first objective of this work is to propose a methodology to extract as much informations as possible from available spatially distributed databases, in order to char...
Abstract According to the Weibull theory for brittle materials, the mean experimental strength decreases with test specimen size. For the brittle parts of an organism this would mean that becoming larger in size results automatically in reducing strength. This unfavorable relationship was investigated for two porous, biological materials that are promising concept generators for crack deflective and energy dissipative applications in compressive overloading: the quasi-brittle coconut endocarp an...
Last. Tieying Li(TUT: Taiyuan University of Technology)H-Index: 5
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In traditional Chinese timber structures, few tie beams were used between columns, and the column base was placed directly on a stone base. In order to study the hysteretic behavior of such structures, a full-scale model was established. The model size was determined according to the requirements of an eighth grade material system specified in the architectural treatise Ying-zao-fa-shi written during the Song Dynasty. In light of the vertical lift and drop of the test model during horizontal rec...
#1Dapeng Hao(CUMT: China University of Mining and Technology)H-Index: 9
#2Gang Tang(CUMT: China University of Mining and Technology)H-Index: 11
Last. Kui Han(CUMT: China University of Mining and Technology)H-Index: 7
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Abstract In theory, the macroscopic fracture of materials should correspond with the thermodynamic limit of the fiber bundle model. However, the simulation of a fiber bundle model with an infinite size is unrealistic. To study the finite size effects of the fiber bundle model, fiber bundle models of various size are simulated in detail. The effects of system size on the constitutive behavior, critical stress, maximum avalanche size, avalanche size distribution, and increased step number of exter...