Needle penetration resistance (NPR) and screw withdrawal resistance (SWR) are widely used techniques for density estimation of woods integrated in timber structures. The moisture content (MC) influences these measurements and correction coefficients are needed to ensure the accuracy of results. The goal of the present paper was to scrutinize the relation between NPR and SWR measurements and MC in case of radiata pine, Scots pine, Salzmann pine, and maritime pine usually used in wood constructions, from which 25 specimens from each species were probed. The specimen’s MC ranged from 65.1 to 8.3%. Results show that NPR depth has a positive linear relationship with MC while the SWR force a negative one below the fiber saturation point (FSP). Above the FSP, the MC influence is less pronounced and less regular. MC correction factors of measurements below the FSP are proposed for the species studied.

Research Highlights: The novelty of this study is the development of an accurate wood density estimation method based on a relatively brand new semi-destructive testing technique (drilling chips extraction). This method is especially crucial in the assessment of existing timber structures. Background and Objectives: Probing, drilling, and coring are non-destructive and semi-destructive techniques commonly used for timber density estimation in existing timber structures. Most of these techniques show poor or medium accuracy or are so expensive or destructive. This paper aims to obtain accurate estimation models for wood density in existing structures using the easy to use drilling chips extraction technique. Materials and Methods: 300 specimens (95 × 65 × 200 mm³) from ten softwood and hardwood species covering a wide range of density (from 350 to 980 kg·m⁻³) were tested after conditioning. The Wood Extractor device based on the drilling chips extraction technique was used in the radial and the tangential direction. Mass of the chips collected (drilling residue) from each drill was recorded. Results: Density obtained from drilling residue was not statistically significantly different between radial and tangential directions avoiding take into account direction when measuring. The density obtained in the whole specimens is slightly higher than the density obtained by drilling residue being this difference uniformly through the range of densities studied. Two different estimation models were presented with high determination coefficients (96% and 97%) and low standard errors. These results were similar to those obtained by other authors using core drilling but causing less damage. Conclusions: Drilling chips extractor is a simple, reliable and inexpensive method to estimate density in existing structures with accuracy.

Detailed measurements of drying fissures were carried out on 28 pieces of gross cross-section structural Scots pine timber. Different parameters have been proposed to measure their magnitude: length, depth, thickness and slope of grain, as well as an index of area in the neutral axis plane (ratio of effective to total surface). The parameters of fissures have been related to bending strength, shear strength, modulus of elasticity and rupture energy obtained from mechanical tests, considering whether rupture is due to bending or shear. All of the fissures observed allows to classify the pieces as MEG according to the UNE 56544 standard. To quantify the magnitude of fissures the index of areas is proposed, while mechanical properties can be quantified by rupture energy. Analysis of the results does not show any relation between the fissures analyzed and the mode of failure, their magnitude and mechanical properties..

Time-of-flight (ToF) measurements were conducted on twelve 76×226-mm² in cross-section, 4.52-m long specimens of Norway spruce timber pieces from a dismantled 19^th-century building in Barcelona (Catalonia, Spain). Two commercially available acoustic devices were used: the USLab ultrasound device with conical 22 and 45 kHz sensors and the MicroSecond Timer (MST) stress wave device with spike sensors. ToF were obtained for the full-length (4.52 m) specimens in an end-to-end arrangement and for lengths of 0.5, 1, 1.5, 2, 3 and 4 m on the same surface and on opposite surfaces. The differences between the velocities obtained from end-to-end and semi-direct measurements were less than 4.5%. Apparent velocity dependence on length was observed in short-distance measurements. This could be corrected by determining a time lag (tL) from a linear regression between the ToF and the distance. Estimation of the modulus of elasticity (MOE) from the dynamic MOE (MOE_dyn) is acceptable (r²=0.45–0.69) depending on the measurement procedure, and the best results for in situ timber are obtained in edge surface velocity. Although modulus of rupture (MOR) estimation from MOE_dyn improves slightly when knottiness is included, it has low predictive capacity.

Density estimation by non-destructive or semi-destructive methods is applied mainly on softwood species. The instruments are expensive, the methods are complicated and the determination coefficients are low. In the present study, the simple core hollow drilling approach is revisited. Data of 600 cores or cylindrical specimens from 300 pieces of 10 different softwood and hardwood species were evaluated in the density range from 350 to 975 kg m⁻³. The data were obtained from complete pieces and from the cores from core drilling, while the difference between the two data sets is 1.7%. At higher densities, the differences are greater. A model was proposed concerning the piece density estimation with a determination coefficient of 0.98. It is concluded that core drill is a cheap and reliable method for density estimation and the data are equally reliable for radial (R) or tangential (T) probing. The cylindrical cores obtained are suitable for moisture content (MC) and species determination.