Effect of Location, Clone, and Measurement Season on the Propagation Velocity of Poplar Trees Using the Akaike Information Criterion for Arrival Time Determination

The purchase price of any forest plantation depends on the quality of its raw wood, and specifically, variables such as density, orientation of the fibers, bending strength, and bending MoE (Modulus of Elasticity). The elastic waves propagation velocity has become one of the most popular parameters to evaluate the wood in standing trees. This study had two objectives: (1) Show how this velocity is clearly affected by the clone, the location of the crop, and the measurement season of poplar crops; and (2) apply the Akaike information criterion to determinate the arrival time of the waves, on the basis of the entropy of the signals recorded by the piezoelectric sensors placed on the trunk of the tree.This work has been possible due to the financial support of the COMPOP_Timber project “Desarrollo de productos de ingeniería elaborados a base de tablones y chapas de chopo con inserciones de material compuesto para su uso en construcción”, BIA2017-82650-R. The authors thank to Antonio Aguilar and Chihab Abarkane, for his help during measurements in field, and Esther Merlo from MADERAS PLUS, for the analysis of results and methods

Effects of empowering leadership under boundary conditions in the hospitality industry

This study tests the positive effects of empowering leadership (ELSH) under boundary conditions in the hospitality industry. We propose the existence of an interactive process through which ELSH behaviors interact with employees’ personality type to condition their engagement, which in turn influences their extra-role service behavior. We use data from 294 employees and structural equation modeling. The results show that the interaction of ELSH with employees’ independent and interdependent personality is negatively related to their engagement. This decrease in engagement is then reflected in decreased extra-role service behaviors due to the positive relationship between engagement and extra-role service. These findings suggest that self-construal is a significant boundary condition capable of changing the positive relationship between ELSH and engagement to a negative one. Not considering this relationship when establishing a leadership strategy such as ELSH in the hospitality context could render efforts to achieve the goal of high-quality service ineffective.European Regional Development Fund (European Union)Spanish Government ECO2017-84138-PJunta de Andalucia A-SEJ-154-UGR18University of Granada/CBU

An insight into mechanical properties of heartwood and sapwood of large French Douglas-fir LVL

The French resource of large diameter Douglas fir is currently still growing, while these large diameter trees are complicated to process efficiently by the sawmilling industry. The rotary peeling process appeared to be particularly adapted as an alternative to the usual sawing. This primary processing method produces veneers used to make a wood engineered product material called Laminated Veneer Lumber (LVL). The manufacturing process of LVL enables the distribution of the resource defects, allowing for increased mechanical behaviour compared to the solid wood from which it comes from. The main objective of this study is to provide an insight into the principal Douglas-fir heartwood LVL mechanical properties such as longitudinal and shear moduli of elasticity, bending, shear and compressive strengths. Up to now, there was no study on LVL derived from this resource. This study focuses on heartwood because of its very interesting natural durability properties for constructive outdoor applications. Moreover, a comparison with structural timber properties and a comparable industrial engineering product, made of Norway spruce and called Kerto S was also achieved to place the material in terms of mechanical performance among the market. Globally, this Douglas-fir heartwood LVL showed high compressive and shear properties. Even though the bending properties were significantly lower than data from Douglas-fir LVL of the literature, they seemed appropriate for structural applications. A larger experimental campaign fully representative of the industrial process and dealing with larger samples will be needed to finally conclude on the characteristic values to be used in structural design

Pine Beams Retrofitted with FRP and Poplar Planks: Mechanical Behavior

The paper presents an experimental analysis of the bending behavior of pine beams (Pinus Sylvester) retrofitted with fiber reinforced plastic (FRP) and poplar planks used as external covering. Poplar wood was chosen because of its rapid growth in planted forests, its homogeneity and attributes for sustainable local development, and high CO2 absorption rate. Vibration tests were also conducted in order to evaluate the stiffness in a non-destructive way and compare it with that obtained by means of the destructive tests. Three types of reinforcement were compared, namely: basalt fabric (FB), carbon fabric (FC) and carbon laminate (LC). In addition, some pine beams were reinforced only with poplar planks and used as control specimens in order to evaluate the improvement provided by the FRP. It was observed that a strong delamination preceded the final breakage of beam. Moreover, the results indicated that stiffness is provided mainly by the poplar plank and not by the FRP, as was expected.This work was made possible thanks to the financial support of the COMPOP_Timber project “Desarrollo de productos de ingeniería elaborados a base de tablones y chapas de chopo con inserciones de material compuesto para su uso en construcción”, BIA2017-82650-R

BENDING, SHEARING, AND COMPRESSION PROPERTIES OF FAST GROWING FRENCH DOUGLAS FIR LVL

The French resource of large diameter Douglas fir is currently keeping growing, while these large diameter trees are complicated to process efficiently by the sawmilling industry. The rotary peeling process appeared to be particularly adapted as an alternative to the usual sawing. This primary processing method produces veneers used to make a wood engineering product material called Laminated Veneer Lumber (LVL). The manufacturing process of LVL enables the distribution of the resource defects, allowing for increased mechanical behaviour compared to the solid wood from which it comes from. The main objective of this study is to present the principal Douglas-fir heartwood LVL mechanical properties such as longitudinal and shear moduli of elasticity, bending, shear and compressive strengths. Up to now, there were no study on LVL derived from this resource. This study focuses on heartwood because of its very interesting natural durability properties for constructive outdoor applications. Moreover, a comparison with structural timber properties was also achieved to place the material in terms of mechanical performance among the market. Globally, this LVL material showed high compressive and shear properties. Nevertheless, even though the bending properties were significantly lower than data from Douglas-fir LVL literature, they are still quite acceptable for structural applications

Monitoring of Carbon Fiber-Reinforced Old Timber Beams via Strain and Multiresonant Acoustic Emission Sensors

This paper proposes the monitoring of old timber beams with natural defects (knots, grain deviations, fissures and wanes), reinforced using carbon composite materials (CFRP). Reinforcement consisted of the combination of a CFRP laminate strip and a carbon fabric discontinuously wrapping the timber element. Monitoring considered the use and comparison of two types of sensors: strain gauges and multi-resonant acoustic emission (AE) sensors. Results demonstrate that: (1) the mechanical behavior of the beams can be considerably improved by means of the use of CFRP (160% in bending load capacity and 90% in stiffness); (2) Acoustic emission sensors provide comparable information to strain gauges. This fact points to the great potential of AE techniques for in-service damage assessment in real wood structures.The experiments were supported by the companies DÁVILA Restauración de Monumentos and DRIZORO® S.A.U, under research contract No. 3546. The authors also gratefully acknowledge the important contribution of lab technicians David Jiménez and Ismael Romero

Temporal Acoustic Emission Index for Damage Monitoring of RC Structures Subjected to Bidirectional Seismic Loadings

This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinforced concrete (RC) structures subjected to bidirectional seismic loadings. Two waffle plates (bidirectional) supported by isolated square columns were tested on a shaking table with a progressive and increasing ground acceleration until the final collapse. Each specimen was subjected to a different loading history. A relevant delay in the beginning of the significant AE energy is observed as the peak value of the ground acceleration increases. Based on this result, a new AE temporal damage index (TDI), defined as the time difference between the onset of the significant AE activity and the onset of the loading that causes this AE activity, is proposed and validated by comparing it with the plastic strain energy released by the concrete, typically used as a reliable damage level indicator. Good agreement was observed for both specimens and seismic inputs.This research was supported by the regional government of Andalucía, Consejería de Innovación, Ciencia y Tecnología, Project TEP-02429, by the Spanish Ministry of Economy and Competitivity, research project reference MEC BIA2017 88814 R and received funds from the European Union (Fonds Européen de Dévelopment Régional)

Propriétés mécaniques en flexion de LVL de gros douglas

Selon un rapport rendu au Sénat le 26 juin 2019, le vieillissement du patrimoine des ponts du réseau routier est un problème à traiter en France. Le remplacement progressif d’environ 10% de ces ouvrages est à envisager dès à présent. Une des solutions proposées à la région Bourgogne-Franche-Comté est l’élaboration de ponts mixtes bois béton. Efficaces, comparativement plus légers, rapides de mise en œuvre, plus écologiques et économiques, ils permettent par ailleurs la valorisation d’essences locales dans des qualités relativement basses. Cela est rendu possible par le choix d’un procédé de première transformation, le déroulage, permettant la composition d’un matériau multiplis composite appelé lamibois, au comportement mécanique augmenté par rapport au bois massif dont il est issu. La thèse « Développement de produits lamellés issus du déroulage de douglas pour des ponts et autres solutions constructives mixtes bois-béton collés », effectuée au LaBoMaP de Cluny, vise à optimiser ce matériau dans la conception des poutres de tablier. Cela passe notamment par une répartition optimisée dans tout le matériau des défauts tels que la nodosité et la variation de pentes de fils. Cependant, avant toute étape d’optimisation, il est nécessaire d’étudier le comportement mécanique du LVL sans plis croisés constitué à partir d’une ressource représentative du douglas français (100 m3 de bois transformés issus de 3 communes de Corrèze : Larfeuil, Ambrugeat et Neuvic d’Ussel). Il n’y avait jusqu’alors pas d’étude d’ampleur sur le LVL issu de cette ressource. Certains résultats ont été présentés aux assises France Douglas. Ce court article présente les premiers résultats d’essais de flexion quatre points sur chant de poutres de duramen de douglas selon deux configurations géométriques. Seule la configuration sur chant est testée car elle est la configuration préférée dans son intégration par poutre à une structure pont