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.

The aim of this research is to evaluate the influence of the moisture content of wood on stress wave velocity, as a nondestructive technique for estimating the mechanical properties of gross cross-section Spanish Scots pine (Pinus sylvestris) lumber for structural use. 26 100 x 150 x 3000 mm pieces from Segovia, Spain, were tested with different moisture content values, from 35,5 to 9%. Measurements of longitudinal stress wave velocity were carried out during the natural drying process by using three commercial portable devices based on ultrasonic, acoustic and vibrational techniques. The results can be summarized as three percentage points of decreasing velocity per percentage point of increased wood moisture content in the range from 11,8 to 21,4%: 0,48% for ultrasonic, 0,50% for acoustic wave and 0,65% for longitudinal vibration.

The present study explores the possibility of using longitudinal ultrasound transmission to evaluate the bending strength and modulus of elasticity in structural timber made from the two species most commonly found in Spanish construction and rehabilitation works: Scots pine (Pinus sylvestris L.) and Laricio pine (Pinus nigra Arn.). An analysis of 1305 Scots pine and 852 Laricio pine beams shows that ultrasound transmission velocity alone can predict neither the bending strength nor the modulus of elasticity and that other predictive variables are required.A series of models are proposed based on ultrasound transmission velocity measurements, the relative size of the largest face and edge knots, length and density. After running models for each species individually and for the two jointly, a single model is found to be suitable for both. The models proposed explain from 63 to 73 per cent of bending strength and modulus of elasticity variability.

The ratio of juvenile wood (jW) to mature wood (mW) is relevant for structural wood applications because of their different properties. Near infrared-hyperspectral imaging (NIR-HI) indicates after calibration, the spatial distribution of jW and mW, and this approach is less time consuming than the established micro X-ray densitometry (μXRD). In the present study, a comparative detection of the jW and mW ofPinus sylvestrisL. was performed by NIR-HI and μXRD and the NIR-HI results were evaluated in combination with three chemometric approaches, namely, the principal component analysis (PCA), partitional k-means unsupervised classification (p-k-mUC) and partial least squares discriminant analysis (PLS-DA) in the range of 900–1700 nm. The best NIR-HI results can be obtained when the transition point of earlywood (EW) and latewood (LW) are assessed separately by PLS-DA. The presented results are useful for an automating data evaluation and simplified data collection.