The aim of the present paper is to assess the non-destructive indicating properties of Slovenian beech (Fagus sylvatica) logs and correlate them with the mechanical properties of the final product, ...which is boards. Beech logs were visually graded according to the standard procedure and vibrational frequencies were measured. Logs were further on sawn into boards which were also non-destructively tested in wet and dry conditions. Finally, the boards were experimentally tested in tension. Special focus was directed towards visual parameters of the beech logs and their influence on the overall quality of the output material. The longitudinal natural frequencies of the logs were studied as potential indicating properties. The results showed that a majority of the visual log grading parameters do not result in good quality timber in terms of strength and stiffness properties, and only few are decisive for the final classification. The coefficient of determination of the static MOE vs. dynamic MOE of logs was r2=0.13, whereas vs. the MOE of wet boards was r2=0.49. Using a few visual characteristics in combination with dynamic measurements of logs and of wet boards could help to increase the yield of high quality beech wood.
The impact of climate change has become increasingly severe in forests, where droughts and strong winds on the one hand and extreme rainfall events on the other hand can damage forest ecosystems. To ...mitigate the effects of drought and enhance soil water retention capacity, three types of soil conditioners (SCs), labeled SC_R, SC_CG, and SC_ZZC, were developed as part of the European project ONEforest. All the conditioners are based on Xanthan gum and have different types and amounts of fillers with diverse cellulose fiber lengths. These can offer the potential to optimize the SC characteristics, e.g., water absorption, water retention, and mechanical stability. This paper focuses on the influence of fillers in the SCs on the geotechnical properties of forest soils from Ljubelj in the Alpine part of Slovenia (S1), Catalonia, northeastern Spain (S2), and Heldburg, Germany (S3). The results show an increase of 53% to 100% in the water absorption of treated soil. A less favorable impact of the SCs was found on the drained shear strength and the compressibility. The drained shear strength of untreated forest soils in a saturated state was S1 c′ = 4.4 kPa, φ′ = 33.5°; S2 c′ = 1.4 kPa, φ′ = 30.0°; and S3 c′ = 12 kPa, φ′ = 28.0°. The addition of SCs results in a reduction in the drained shear strength of saturated mixtures. The reduction depends on the dosage of added SC—whether it is a low (L) or a high (H) dosage. For instance, when the soil S1 was treated with a low dosage of the soil conditioner SC_R, it demonstrated a cohesion (c′) of 11 kPa and a friction angle (φ′) of 27.0°. However, increasing the dosage of the SC_R led to a decrease in both the cohesion and the friction angle for the same soil (c′ = 7.7 kPa, φ′ = 25.0°). Additionally, the type of soil conditioner also impacts the drained shear strength. Among the mixtures with a high dosage of the SC_R, SC_CG, or SC_ZZC, those containing the SC_CG with the longest fibers stand out, demonstrating the highest friction angle. Therefore, longer fibers can be a promising component of the SCs to reduce the negative influence of XG on the mechanical properties of treated soils.
This paper presents the formulation of strain-based finite elements for modelling composite beams with finger joints considering slip between the layers. The finite elements are derived according to ...Reissner beam theory based on the modified principle of virtual work where the displacements and rotations are eliminated from the problem and the axial deformation, shear deformation and curvature of the layers remain only functions to be approximated within the finite element. Lagrange polynomials are used as shape functions to approximate the deformations and various interpolation methods are applied to numerical examples, with the Lobatto integration scheme giving slightly better results than Equidistant. The experimentally measured mechanical properties needed as input data for the numerical model are given for the four glued laminated beech beams. The numerical model is thoroughly verified and validated. The results show that the presented finite element formulation is an efficient tool for practical and accurate calculations.
•New finite elements for composite beams with slip and finger joints are proposed.•Numerical model is validated and verified with experimental results.•The finite elements exhibit no slip and shear locking.
The paper presents the analytical model of a linear two-layer composite beam with partially debonded interlayer contact. The interlayer contact may be also locally fully debonded. The two-dimensional ...model is materially and geometrically linear, and the governing equations are based on Reissner beam theory. In the partially debonded interlayer contact, only axial slips are allowed. The finger joints are modelled as linear springs. The analytical solution is presented. The kinematic and equilibrium variables are evaluated along the simply supported beam. A parametric study was carried out to analyse the effect of the strength of finger joints and interlayer contact. In addition, different lengths and positions of the fully debonded area of the interlayer contact were analysed, and their effects on selected kinematic and equilibrium variables were observed and commented on. It was shown that the presence of the fully debonded interlayer contact and finger joints significantly affects the behaviour of the beam as well as the stiffness properties of the interlayer contact and finger joints.
This paper focuses on the development of a new mathematical model and its analytical solution for the analysis of finger-jointed Timoshenko–Ehrenfest glulam beams with interlaminar debonding and ...finger joint (FJ) flexibility. Consequently, an analytical solution for the mechanical behavior of finger-jointed elastic Timoshenko–Ehrenfest glulam beams with interlaminar debonding and flexibility of FJ is derived. In the illustrative examples, a simply supported Timoshenko–Ehrenfest glulam beam is analyzed, and the analytical results for various kinematic and equilibrium variables are given. Moreover, the parametric study showed that the mechanical behavior of a finger-jointed Timoshenko–Ehrenfest glulam beam is affected by the contact and FJ stiffnesses and the position of the FJ. Moreover, it is proven, that the effect of shear deformation on vertical deflections can be considerable, and can be up to aprroximately 60%.
Finger joints with standard geometries and adhesives used for joining coniferous wood are not sufficient in terms of strength when gluing beech wood. A numerical model of finger joined beech lamellas ...was prepared and simulations of tension tests were made. Parametric studies with multiple variables referring to geometrical properties of finger joints and two different types of applied adhesives were performed. The results showed a high influence of the finger joint geometrical parameters. Experimental tests on the tension strength of the finger joints were performed. To validate the numerical model, 20 mm long finger joints were produced and tested. Two types of adhesives were used, MUF and PRF. The finger joints were pressed under two different pressures. Prior to tension testing, the dynamic modulus of elasticity was measured with a strength grading machine and strength grade assignments were made. The influence of joining of the boards on the dynamic modulus of elasticity was analysed. The results of the tension tests of the finger joints showed a clear influence of the finger joint geometry, where highest strengths were obtained with longer and thinner fingers, while the influence of the adhesive seems to decrease with the length of finger joints.
COVID-19 has had disproportionate contagion and fatality in Black, Latino, and Native American communities and among the poor in the United States. Toxic stress resulting from racial and social ...inequities have been magnified during the pandemic, with implications for poor physical and mental health and socioeconomic outcomes. It is imperative that our country focus and invest in addressing health inequities and work across sectors to build self-efficacy and long-term capacity within communities and systems of care serving the most disenfranchised, now and in the aftermath of the COVID-19 epidemic.
The spread of COVID-19 in Italy resulted in the implementation of a lockdown that obligated the first time the general populace to remain at home for approximately two months. This lockdown ...interrupted citizens' professional and educational activities, in addition to closing shops, offices and educational institutions. The resulting changes in people's daily routines and activities induced unexpected changes in their thoughts, feelings and attitudes, in addition to altering their life perceptions. Consequently, the present study explores how young adults perceived their lives under lockdown during the final week of March 2020, when the reported number of daily coronavirus infections reached its peak in Italy. The research was carried out among 293 university students (234 women and 59 men) with an average age of 20.85 years old (SD = 3.23). The researchers asked participants to describe the emotions, thoughts and experiences that characterized their time under lockdown. The study analyzed specific narratives related to time and space using grounded theory methodology, which was applied using Atlas 8 software, leading to the creation of 68 codes. The study organized these codes into three specific categories: confined in the present, confined in the past, and striving toward one's goals. Finally, the researchers also created a core-category labeled "continuity of being." The results showed that the closure of open spaces caused a division in participants' perceptions of time continuity, with many viewing themselves as feeling fragmented and as living the present in a static and fixed way. Additionally, participants also saw the present as being discontinuous from the past, while, simultaneously, projecting toward the future and the changes it might bring. Finally, this study examined further implications surrounding individual projecting among young people in greater depth.
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