René Oum Lissouck

Intra-tree variability in the physical, mechanical and viscoelastic properties (E’, E’’, tan δ) of Tali wood ( Erythrophleum ivorense A. Chev.): towards optimized use in construction

Charly Julien Nyobe, Nicolas Stéphane Nyobe, René Oum Lissouck, Louis Max Ayina Ohandja

Wood Material Science and Engineering

Tali wood(: Erythrophleum ivorense A. Chev.), a key tropical species from the Congo Basin, is widely used in structures subjected to high mechanical loads. This study investigated the intra-tree variability of its physical, mechanical, and viscoelastic properties to optimize its structural applications. Samples were collected using a double stratification: three longitudinal positions (base, mid-height, top) and three radial positions (center, middle, periphery). Axial compression, four-point static bending, and dynamic viscoelastic tests (WAVET) were conducted to assess density, compressive strength, modulus of elasticity (MOE), modulus of rupture (MOR), storage modulus (E′), loss modulus (E″), and loss factor (tan δ). LMM and Tukey’s test showed that the means differed significantly according to radial and longitudinal positions. Mechanical and viscoelastic properties improved from the center to the periphery, with maximum values in the basal peripheral zone (B-P): density (920 kg/m³), compressive strength (80 MPa), MOR (129 MPa), MOE (20,100 MPa), and E′ (640 MPa). Conversely, central zones exhibited lower stiffness but higher damping (tan δ), linked to the transition from juvenile to mature wood. These findings support a differentiated use of Tali wood: peripheral zones for structural applications, and central zones for damping-oriented uses, promoting more efficient and sustainable valorization of tropical hardwoods.

• #bamboo properties and applications
• #construction engineering and safety
• #natural fiber reinforced composites
• #viscoelasticity

Moisture content-mechanical property relationships for two okan ( Cylicodiscus gabunensis ) substitutes

Charly Julien Nyobe, René Oum Lissouck, Nyobe Nicolas Stephane, Goumgang Tassile Rolande, Ayina Ohandja Louis Max

Wood Material Science and Engineering

The aim of this work was to study the relationship between the mechanical properties of Cameroonian tropical woods and the moisture content. The forests of the Cameroonian part of the Congo Basin abound in species that are highly solicited for structural applications. However, some species such as okan (Cylicodiscus gabunensis) are overexploited, leading to their disappearance. Bodioa (Anopyxis klaineana) and lotofa (Sterculia rhinopetala) can be used as okan substitutes, as they belong to the same mechanical group. Clear wood was prepared and divided into five groups. Each group was conditioned at a relative humidity and temperature to achieve moisture contents of 12%, 16%, 20%, 24% and 28%. These specimens were subjected to 4-point bending, tensile, compressive and double cantilever beam test. Modulus of elasticity (MOE), modulus of rupture (MOR), fracture toughness (GIC), Stress intensity factor (K), bulk density (Db), true density (Dt), tensile and compressive strength were determined. The results showed that moisture content had significant effects on all the mechanical properties measured on clear wood specimens. MOE, MOR, KIC and strengths decreased with increasing moisture content and Db, Dt, GIC increased with increasing moisture content.

• #botanical research and applications
• #polysaccharides composition and applications
• #leaf properties and growth measurement
• #water content

Development and Characterization of a Micro-Concrete Based on Wood Waste from Sawmills

Rachel Raïssa Ngono Mvondo, René Oum Lissouck, Sophie Grigoletto

Key engineering materials

An experimental study was carried out to evaluate the feasibility of using concrete compositions containing waste wood for structural and non-structural building applications. First, the inert and wood aggregates used in the composite design were characterized. Five compositions containing a reference, 50% and 100% of wood particles were then produced and characterized in terms of physical and mechanical performance (e.g., apparent density, abrasion, compressive strength, and flexural strength). The selected specimens were used for additional experimental tests. These included water absorption and thermal tests. Increasing wood waste content considerably lower compressive and flexural strengths while improving the thermal insulation quality of wood waste-cement composite. The durability assessment of selected compositions further showed that the abrasion resistance of manufactured specimen decreased by adding wood waste in the cement matrix while there was an increase of the capillarity absorption coefficients. It appears that the incorporation of waste wood particles into mortars decrease their thermal conductivities to 0.3 W/mK. The use of wood waste treated by a lime solution improves the studied properties.

• #innovations in concrete and construction materials
• #recycling and utilization of industrial and municipal waste in materials production
• #hygrothermal properties of building materials
• #characterization (materials science)

Non-linear analysis of the flexural-torsional stability of slender tropical glulam beams

Louis Elvis Bikanda, René Oum Lissouck, Morel Junior Angouah Massaga, Louis Max Ayina Ohandja

The Journal of Strain Analysis for Engineering Design

The main objective of this manuscript is to model the flexural-torsional buckling of slender tropical glulam beams using the finite element method. The non-linear approach to quantify both the buckling strength and the lateral geometrical features of wooden beams is proposed. A very rigorous methodology is used which is based on the kinematic Vlasov’s theory to determine the displacement field of the beam section by considering an updated Lagrangian description. For the finite element discretization, the Author develop a single wood element characterized by 14 degrees of freedom, i.e. seven degrees for each nodal point, and derive non-linear stiffness matrices by using the virtual works principle. The model is implemented in MatLab and the numerical results are compared with results based on the classical linear stability theory of slender wood beams. The selected case-studies are a cantilever beam and a beam on two supports.

• #tree root and stability studies
• #wood treatment and properties
• #bamboo properties and applications
• #beam (structure)

Investigation of green-glued laminated timber from the Congo Basin: durability, mechanical strength and variability trends of the bondlines

René Oum Lissouck, Rachel Raïssa Ngono Mvondo, François René Ateba, Régis Pommier

Southern Forests a Journal of Forest Science

The development of glulam may give complementary, added-value to an important part of the timber production in the Congo Basin. Nevertheless, the high humidity in which these timbers operate may cause problems such as cracks and severe deformations if they are not suitably bonded. Moreover, there is a lack of knowledge concerning the refined design of the bondlines of glulam assembling from the Congo Basin hardwoods. We investigated the durability, mechanical strength, and variability features of the bondlines, manufactured under higher moisture conditions. Eight hardwood species with very different properties were selected. A one-component polyurethane adhesive was used. Industrial gluing parameters were kept constant. Delamination, shear tests and analysis of bondlines thickness were carried out. Multivariate analysis and a goodness-of-fit test of the strength variability of the bondlines were performed. Optimum bondlines thicknesses were obtained. Their durability exhibited satisfactory trends up to a density of 750 kg/m3. The behaviour of the bondlines can operate in three homogeneous groups. In each of them, the variability of the shear strength can be properly modelled using a 3-parameter Weibull probability. Wood failure trends were in accordance with several international requirements. The density value of 750 kg/m3 appeared as critical for the compatibility between the shear strength, the durability and the bondlines thickness. The overall results showed the ability of several tropical timber species to be valorised in green-glulam applications. Moreover, the findings unlock new trends concerning a reliable and safe design of tropical glulam as a structural wood-based product.

• #bamboo properties and applications
• #wood treatment and properties
• #natural fiber reinforced composites
• #durability

Influence of mixing tropical timber species and material heterogeneities on the long-term stability of slender glulam beam columns

Martial Ourmama, René Oum Lissouck, Louis Max Ayina Ohandja

Wood Material Science and Engineering

Slender glulam beams are high value products that may be used differently concerning large span structures. They can be manufactured in developing countries without significant industrial resources by using two tropical timber species, while preserving emblematic species and promoting lesser known ones. The current Eurocode 5 design rules, based on the effective length method, are not adapted for designing such products, subjected to axial compression. An approach, based on a work-energy method, is investigated in this work. The goal of the paper is to provide a refined modeling of the long-term buckling strength of mixed and slender tropical glulam beam column, based on the finite element method. The variability of the rheological properties of the materials is considered, as well as the geometrical imperfection of the product, characterized by initial deflection. Variations of the glulam composition are also considered. Monte-Carlo simulations of the beam behavior over time are performed. Results provide for each glulam composition a set of analytic and decreasing evolution of the long-term buckling strength with time. The relative gap between the initial and final critical load can reach up to 18%. The possibility of optimizing the parameters that drive the long-term stability of beams is discussed. Moreover, the study may unlock a new standard design approach for the designers and engineers, aiming at guaranteeing the long-term safety of the slender and mixed glulam products.

• #bamboo properties and applications
• #wood treatment and properties
• #construction engineering and safety
• #deflection (physics)

Analysis of drying stresses in green-glued plywood of Bete (Mansonia Altissima) specie

Valentin Makomra, René Oum Lissouck, Régis Pommier, Anh Phan Ngoc, Denys Breysse, Louis Denaud and 1 more

Journal of Wood Science

Abstract The wood veneer dried artificially before gluing for the manufacture of plywood generally suffers several damages (cracks, deformations), decreasing the competitiveness of the process and limiting the use of nervous species of wood. The proposed solution is to glue them at the green state. However, during the drying process, superficial and internal cracks are observed. These cracks appear when stresses due to the anisotropic shrinkage of the plywood exceed the mechanical strength of the wood material. In the present study, the response of a 3-ply plywood of Bete ( Mansonia altissima ) glued at the green state is simulated in order to evaluate these stresses and deformations during drying using a finite element method program. The numerical results and associated experimental data make it possible to better analyze and understand the mechanical behavior of the plywood during drying in order to look for reliable plywood through new process.

• #wood treatment and properties
• #textile materials and evaluations
• #natural fiber reinforced composites
• #shrinkage

A decision support tool approach based on the Electre TRI-B method for the valorisation of tropical timbers from the Congo Basin: an application for glulam products

René Oum Lissouck, Régis Pommier, Franck Taillandier, Jean K Mvogo, Denys Breysse, Louis Max Ayina Ohandja

Southern Forests a Journal of Forest Science

An alternative approach to the formal management strategy of tropical timber species from the Congo Basin was investigated. It focused on the development of glulam, with an aim to specify a decision support model for the valorisation of tropical timber species considered for use in these products. There were 76 forest species analysed regarding ecological, engineering and social criteria according to their major uses. The Electre TRI-B multicriteria sorting method was used. The main result was a new and robust classification tool of timber species from the Congo Basin, corresponding to their multicriteria consensus degree. The potentials of the new grouping system were analysed. Species that meet a great majority of criteria were identified. They were highly suitable for sustaining the market position of glulam products. Implementing this strategy may significantly improve the management and increase the value of the timber species from the Congo Basin, while preserving endangered species.

• #global trade and competitiveness
• #forest management and policy
• #quality and supply management
• #electre

Clustering for preservation of endangered timber species from the Congo Basin forest.

René Oum Lissouck, Régis Pommier, Denys Breysse, Louis Max Ayina Ohandja, R. D. A. Mansié

JOURNAL OF TROPICAL FOREST SCIENCE

• #forest ecology and management
• #african botany and ecology studies
• #endangered species
• #agroforestry

Optimisation de l’utilisation du pin maritime

Franck Taillandier, Régis Pommier, Christophe Fernandez, Amadou Ndiaye, René Oum Lissouck

HAL (Le Centre pour la Communication Scientifique Directe)

International audience

• #urban and freight transport logistics
• #computer science

Green gluing of tropical wood Part III: X-Ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) analysis of Frake and Ayous green wood's Glue line

Emmanuel Njungab, René Oum Lissouck, Hyppolite Ntede Nga, Christine Labrugère, Régis Pommier, Louis-Max Ayina Ohandja and 1 more

DSpace (Centre National De La Recherche Scientifique)

Colloque avec actes et comité de lecture. Internationale.

• #wood treatment and properties
• #lignin and wood chemistry
• #plant surface properties and treatments
• #x-ray photoelectron spectroscopy