(1) The early assessment of wood quality, even while trees are standing, provides significant benefits for forest management, sales efficiency, and market diversification. Its definition cannot be in ...absolute terms but must always be linked to the material’s intended use. (2) In this contribution, a review of the scientific literature is given to discuss the visually evaluable attributes that define wood quality in standing trees, the applicability of the techniques used for their assessment, and the effectiveness of these attributes and technologies in predicting quality, to finally highlight future research needs. (3) The visual characteristics generally used to evaluate wood quality are linked to stem form and dimension, branchiness, and stem damage, but their assessment is challenging due to time and resource constraints. To address these challenges, laser-based and image-based techniques have been applied in field surveys. (4) Laser scanners offer detailed and accurate measurements. Photogrammetry, utilizing images to reconstruct 3D models, provides a cost-effective and user-friendly alternative. Studies have demonstrated the effectiveness of these tools in surveying the visible properties of stems and branches, but further development is necessary for widespread application, particularly in software development, with faster and more effective algorithmic advancements for automatic recognition and subsequent measurement of pertinent characteristics being critical for enhancing tool usability. (5) However, predicting wood quality from these surveys remains challenging, with a limited correlation between the visible tree characteristics assessed and the sawn product quality. Empirical studies evaluating products downstream in the forest-wood supply chain could provide valuable insights. In this sense, the implementation of traceability systems could facilitate the linkage between data on standing trees and the quality of the sawn product. Also, further research is needed to develop models that can accurately predict internal tree characteristics and their impact on product quality.
(1) The assessment of the mechanical properties of old timber is essential for the proper maintenance of wooden structures. (2) Among the non-destructive properties, the dynamic modulus of elasticity ...is one of the best predictors of the mechanical characteristics of the members, but it requires the determination of wood density to be determined. (3) Thus, wood density was estimated by drilling resistance measurements, developing species-specific prediction equations for silver fir, chestnut and poplar. (4) The estimated density was combined with the stress wave velocity propagating longitudinally through the wooden piece, and the dynamic modulus of elasticity was calculated. (5) Medium-high coefficient determinations (R2 from 0.79 to 0.94) were found for density estimation, and medium coefficient determinations (R2 from 0.53 to 0.60) were found for the estimation of the static modulus of elasticity using the dynamic modulus.
•New test methods to assess the quality of face bonding in CLT are presented and evaluated.•During shear test the specimens are loaded with a 45° angle to avoid rolling shear.•Practical applicability ...led to elect the most suitable method for inclusion in technical standards.•Shear and delamination results proved not to be correlated.•It is feasible to propose the coupling of accelerated aging procedures with shear tests.
The effectiveness of new shear test methods for evaluating the face-bonding quality of Cross-Laminated Timber (CLT) panels was examined by comparing experimental data and numerical modelling. The common characteristic of the specimens was the loading with angle of 45° with respect to the wood grain, in order to avoid rolling shear during test. In addition, the sampling methodology along the panel was investigated, as well as the relation between shear and delamination tests, and the possibility of coupling them using the same specimen. The results demonstrated that all the proposed shear test methods were effective for evaluating the quality of bonding among layers in CLT panels; however, the practical applicability of the methods led to elect the most suitable for inclusion in technical standards. Shear and delamination results proved not to be correlated, and the results showed that the size of the specimen is a crucial factor in determining the outcomes of delamination tests. Therefore, while it is feasible to propose the coupling of accelerated aging procedures with shear tests, the size of the samples need to be higher than the one tested here.
The study presents results of the characterization of Norway spruce (Picea abies Karst.) and fir (Abies alba Mill.) wood thermally modified by TERMOVUOTO® technology at temperatures in the range of ...160 to 220°C in vacuum conditions. Sixteen thermo-vacuum treatment tests were carried out using a pilot laboratory unit on 30-mm-thick spruce and fir boards in various combinations of the process parameters, i.e. temperature ( T ), duration ( t), and pressure ( p ). The treated material was characterized to reveal the changes of the physical-mechanical properties including color and durability. The treated wood showed an improved performance with relation to the dimensional stability and durability. The measured mechanical properties did not show any significant decrease. Analytical models, based on the existing correlations between wood properties and process parameters, were assessed, thus allowing the control of the process.
Round timber is often used for hydraulic engineering works, but the strength grading of round logs is not as well developed as that of sawn timber. The advantages of using defined strength classes, ...as well as the proper selection of the raw material, could be applicable to hydraulic works as well. In this study, the methods and rules developed for sawn timber were applied to the mechanical selection of oak round logs, paying particular attention to the issue of the simplicity of grading operations and the moisture content of the timber. Both the acoustic velocity and dynamic modulus of elasticity of oak logs were measured with different instruments before performing destructive bending tests; machine settings were derived for both properties and dry and wet grading operations were simulated to compare efficiency. The use of the dynamic modulus of elasticity makes machine grading more efficient. On the other hand, the use of acoustic velocity alone is feasible and makes the procedure much faster, even if wet grading resulted in very conservative estimations. The yields obtained were similar for lower grades, but to achieve higher strength classes, the dynamic modulus was preferable. For very fast and less expensive measurements, velocity could be considered an appropriate method, as an improvement over the use of unselected material.
Before round timber can be profitably used in construction, it needs structural characterization. The visual grading of Eucalyptus grandis poles was integrated with additional parameters developed by ...multivariate regression analysis. Acoustic velocity and dynamic modulus of elasticity were combined with density and pole diameter in the estimation of bending strength and stiffness. The best models achieved were used to group the visually graded material into qualitative structural classes. Overall, dynamic modulus of elasticity was the best single predictor; and adding density and diameter to the model improved the estimation of strength but not of stiffness. The developed parameters separated the material into two classes with very distinct mechanical properties. The models including velocity as a parameter did not perform as well. The strength grading of Eucalyptus grandis poles can be effectively improved by combining visual parameters and nondestructive measurements. The determination of the dynamic modulus of elasticity as a grading parameter should be preferred over that of acoustic velocity.
Near infrared spectroscopy (NIR) is a technique widely used for the prediction of different chemical-physical features of wood. In this study, the technique was used to assess its potential to ...predict the mechanical characteristics of wood. Castanea sativa samples of three different European provenances were collected and laboratory tests were performed to assess the mechanical properties of wood samples. Modulus of elasticity (MOE), load-deflection curve and modulus of rupture (MOR) were calculated by using INSTRON machine with three points bending strength with elastic modulus, while density (D) was calculated according to the current standard. Samples were then analysed by means of NIR spectroscopy. The raw spectra were pre-processed and regression models were developed. Variables selection techniques were used to improve the model performance. In detail, MOE regression model returned an error of 696.01 MPa (R2=0.78). Instead, MOR and D prediction models must be further investigated on a wider number of samples considering the high variability in physical characteristics of chestnut wood. The results demonstrated the possibility to use NIR technique for the prediction of the mechanical properties of wood providing useful indications in evaluation-screening processes. Indeed, the presence of the principal wood compounds (cellulose, hemicellulose and lignin) and their influence in the characterisation of mechanical stress reactions were confirmed.
•In historical wooden structures degradation due to insect attacks is common.•A software routine is presented to quantify degradation depth by drilling resistance.•The routine was optimized and ...verified on wooden beams with satisfactory results.•Drilling profiles were informative with degradation by cerambycids, but not with anobiid attacks.
The assessment of insect degradation on the surface of timber elements is a key point in evaluating the safety of wooden buildings. The depth and the degree of the insect attack are necessary data to determine the resistant section of the load-bearing elements.
To the aim, the resistance drilling is applied as non-destructive technique in the on-site inspection. Here, a routine is proposed and verified to automatically process the resistance data and to identify the presence of insect decay.
Twelve wooden beams disassembled from an old timber structure were used as experimental material: five to optimize the routine and seven to verify the output after the optimization. In total, 78 % of the measurements showed an error of less than 5 mm and 86 % less than 10 mm when compared to the determination made by an expert operator on the same drilling profiles. Comparing the non-destructive measurements with the cross-sections cut from the beams, the profiles seemed very informative when the degradation was caused by cerambycids, but less so with anobiid attacks.
The maintenance of historic wooden structures requires the assessment of the timber elements that compose them. The accurate knowledge of their mechanical performance is a fundamental aspect to ...guarantee conservation, safety, and usability. In this work, the assessment of the mechanical properties of timber was done by visual and machine strength grading. The visual grading rule developed for new wooden products was applied, as well as that established by the Italian standard for historic load-bearing structures. Machine grading was also performed by simulating the procedures applicable to the dismantled or in situ elements. The strength and stiffness values expected according to the different strength grading procedures were compared with the values obtained from destructive tests. As a result of visual grading, the modulus of elasticity was in line with the provisions of the standardization, while the characteristic strength was lower. With machine grading the yields were lower, but the characteristic strength values of the classes were respected, especially if combined with a visual inspection rejecting decayed or damaged pieces. The modulus of elasticity, however, was higher than that of the class, thus being underestimated.
•Prediction of the mechanical properties of historic load-bearing wooden structures is crucial for their conservation.•Visual and machine strength grading were applied on dismantled timber and verified through destructive tests.•Bending strength was lower than expected by applying the visual grading rules, the modulus of elasticity was in line.•The machine grading led to lower yields, but the characteristic strength of the classes were respected.
•In historical structures wooden elements often have very irregular cross-section.•Bending strength and stiffness were underestimated of 23% when calculated on rectangular cross-section.•The ellipse ...shaped cross-section determines an overestimation of mechanical properties of 30%•The octagonal cross-section can provide an excellent representation of irregular elements.•For average wane higher than 0.66, ellipse should be preferred to octagon.
The assessment and the mechanical evaluation of the wooden elements in historical buildings are prerequisites to guarantee their conservation and safety at the same time. The availability of reliable reference values for the mechanical properties of old timber is crucial and they must refer to a well-defined cross-section. This could be a huge problem when the structural elements are irregular, as frequently happens with historical timber.
A sample of 24 wooden elements dismantled from the roof of two buildings located in central Italy dated to the late nineteenth century and with very irregular cross-sections was used to investigate the geometry that best represents the actual cross-section for the mechanical characterization. Rectangular, elliptical and octagonal geometry patterns were defined and compared.
Bending strength and stiffness were underestimated of 23% on average when calculated on rectangular cross-section and overestimated of 30% on average when the ellipse was used as a reference. The representation by an irregular octagon proved to be an excellent schematization of the actual cross-section, with an average overestimation of just 1%.
For the tested elements, the value of 0.66 (2/3 of the side) of mean wane was identified as the threshold above which the elliptical representation should be preferred to the octagonal one. The data also suggested a sufficient representativeness of the rectangle for an average wane of less than 0.2 (1/5 of the side). The last conclusions, however, need further confirmation on a wider sample.
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