In situ acoustic methods to estimate the physical and mechanical aging of oriented strand board

Following the success achieved in previous research projects usin non-destructive methods to estimate the physical and mechanical aging of particle and fibre boards, this paper studies the relationships between aging, physical and mechanical changes, using non-destructive measurements of oriented strand board (OSB). 184 pieces of OSB board from a French source were tested to analyze its actual physical and mechanical properties. The same properties were estimated using acoustic non-destructive methods (ultrasound and stress wave velocity) during a physical laboratory aging test. Measurements were recorded of propagation wave velocity with the sensors aligned, edge to edge, and forming an angle of 45 degrees, with both sensors on the same face of the board. This is because aligned measures are not possible on site. The velocity results are always higher in 45 degree measurements. Given the results of statistical analysis, it can be concluded that there is a strong relationship between acoustic measurements and the decline in physical and mechanical properties of the panels due to aging. The authors propose several models to estimate the physical and mechanical properties of board, as well as their degree of aging. The best results are obtained using ultrasound, although the difference in comparison with the stress wave method is not very significant. A reliable prediction of the degree of deterioration (aging) of board is presented

Wood Density and Moisture Content Estimation by Drilling Chips Extraction Technique

Producción CientíficaThe novelty of this study is the development of an accurate wood moisture content (MC) estimation method based on a relatively brand-new, non-destructive testing technique (drilling chips extraction). The method is especially important in the assessment of existing timber structures, where non-destructive testing (NDT) results are affected by wood MC and should be adjusted to a reference MC, usually 12%. In the assessment of timber structures, it is not possible to determine MC by oven drying method and this should be estimated. Electrical resistance and capacitance are the conventional methods used for MC estimation. This research work aims to present an accurate MC estimation method based on the drilling chips extraction technique. For that, 99 specimens (90 × 65 × 38 mm3) from three softwood and hardwood species covering a wide range of densities (from 355 to 978 kg m−3) were tested after conditioning at five different MCs (5%, 10%, 15%, 20%, 25%). The Wood Extractor device based on the drilling chips extraction technique was used. The mass of the chips collected (drilling residue) from each drill was recorded. The results show that the MC of the chips extracted was statistically significantly different than the MC of the specimen and cannot be directly used as MC determination. However, the chips MC can be used as an estimator of specimen MC with high determination coefficients (R2 from 71% to 86%). As the main result, models to estimate density directly adjusted to a reference 12% MC from the wet and dry mass of chips extracted were developed with an R2 of 98%. In sum, the drilling chips extractor is a dependable and straightforward method to estimate MC and density from only one measurement. Density adjusted to a reference 12% MC can be directly estimated from a single model.Ministerio de Economía, Industria y Competitividad (project BIA2014-55089-P)Asociación de Investigación Técnica de la Madera (projects AITIM-Fucovasa 2012–2013 and AITIMFucovasa 2014–2015

Wood Density Determination by Drilling Chips Extraction in Ten Softwood and Hardwood Species

Producción CientíficaResearch 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.Ministerio de Economía, Industria y Competitividad (project BIA2014-55089-P)Asociación de Investigación Técnica de la Madera (projects AITIM-Fucovasa 2012–2013 and ITIM Fucovasa 2014–2015

NDT to identify biological damage in wood

Nondestructive techniques are widely used to assess existing timber structures. The models proposed for these methods are usually performed in the laboratory using small clear wood specimens. But in real situations many anomalies, defects and biological damage are found in wood. In these cases the existing models only indicate that the values are outside normality without providing any other information. To solve this problem, a study of non-destructive probing methods for wood was performed, testing the behaviour of four different techniques (penetration resistance, pullout resistance, drill resistance and chip drill extraction) on wood samples with different biological damage, simulating an in-situ test. The wood samples were obtained from existing Spanish timber structures with biotic damage caused by borer insects, termites, brown rot and white rot. The study concludes that all of the methods offer more or less detailed information about the degree of deterioration of wood, but that the first two methods (penetration and pullout resistance) cannot distinguish between pathologies. On the other hand, drill resistance and chip drill extraction make it possible to differentiate pathologies and even to identify species or damage location. Finally, the techniques used were compared to characterize their advantages and disadvantages

The effect of moisture content on nondestructive probing measurements

When assessing existing timber structures it is not possible to obtain density as the ratio mass/volume, so nondestructive probing methods are used to predict density. As in other nondestructive techniques, moisture content influences measurements. The goal of this paper is to study the influence of timber moisture content on two nondestructive probing techniques (penetration resistance and pullout resistance). 25 large cross section specimens of laricio pine from Spain were measured. The moisture content ranged from 65.1% to 8.3%. Penetration depth decreases and screw withdrawal strength increases when moisture content decreases below the fiber saturation point. There are lineal tendencies in both techniques. No moisture content influence was found in measures above fiber saturation point

Madera aserrada de gran escuadría para uso estructural y sus particularidades

The size effect on mechanical properties of timber is described including the recent evolution of testing procedures and stress grading. Further, a specifi c research work on large cross section timber is explained. A total of 395 pieces of sawn timber from three species (Pinus sylvestris L., Pinus nigra subs. salzmanii (Dunal) Franco and Pinus radiata D. Don) with cross section between 150x200 y 200x250 mm, have been visually graded according to UNE 56544 standard obtaining its output and mechanical properties. The percentage of rejected pieces is too high (38 to 45%) and therefore, a modifi cation of standard specifications is proposed. The output is highly improved in the proposal of standard (rejected percentage of 11 to 17%) whereas the mechanical properties are not modified in practice.A similar procedure was applied to 85 timber pieces from old timber structures of building demolition of Pinus sylvestris L. and Pinus pinaster Ait. The percentage of rejected pieces is 52% in a visual grading according to the application of all grading parameters of the standard UNE 56544:2003. This procedure is not practical for existing structures and therefore, it is proposed the application of grading considering only the parameters of knots size and slope of grain. In that way the output is improved reducing the rejected percentage to 10%.En este artículo se realiza una exposición general del efecto del tamaño en las propiedades mecánicas de la madera y la evolución que han sufrido los procedimientos de ensayo y clasifi cación por esta razón. Además se expone un trabajo de investigación específi co sobre madera de gran escuadría. Sobre un total de 395 piezas de madera aserrada de tres especies (Pinus sylvestris L., Pinus nigra subs. salzmanii (Dunal) Franco y Pinus radiata D. Don) con secciones comprendidas entre 150x200 y 200x250 mm, se ha procedido a su clasifi cación de acuerdo con la norma UNE 56544:2003 determinando su rendimiento y propiedades mecánicas. El porcentaje de piezas que son rechazadas es demasiado elevado (38 a 45%) y por tanto se propone una modifi cación de las especifi caciones de la norma. Con la nueva propuesta de norma el rendimiento aumenta en alto grado (rechazo del 11 al 17%) sin que las propiedades mecánicas se vean afectadas significativamente.Por otro lado se ha seguido un procedimiento similar con 85 piezas de madera procedentes de estructuras antiguas en proceso de derribo de Pinus sylvestris L. y Pinus pinaster Ait. La clasifi cación de acuerdo con la norma UNE 56544:2003 da lugar a un 52% de rechazo aplicando estrictamente todos los parámetros de clasifi cación. Este procedimiento resulta poco viable en la práctica en el caso de estructuras existentes y por tanto, se propone la aplicación de una clasificación basada únicamente en los parámetros del tamaño de los nudos y de la desviación de la fi bra. De esta forma el rendimiento aumenta reduciendo el porcentaje de rechazo al 10%

Identification of Cryptotermes brevis (Walker, 1853) and Kalotermes flavicollis (Fabricius, 1793) Termite Species by Detritus Analysis

Producción CientíficaWe carried out morphological and dimensional analysis of the detritic elements deposited in the galleries of two termite species of the Kalotermitidae family present in Spain known as drywood termites (Cryptotermes brevis (Walker, 1853) and Kalotermes flavicollis (Fabricius, 1793)). This was in order to gauge the possibility of differentiating the species only on the basis of debris observation and analysis. Ten samples from six different geographical sources were analyzed and measured. Significant statistical differences were found between these two termite species in all measured parameters, and multivariate statistical models, able to predict species on the basis of dimensional measurements, were developed, with a degree of success higher than 75%. The most important dimensional differences were length and width, as well as the variable hexagonal shape of the cross-section of the detritic elements. The detritic elements of both species had a variable form of a hexagonal prism with slightly concave faces, and with pointed or rounded ends. Those of the Cryptotermes brevis species were significantly larger, less elongated, and had a smaller concavity on the faces of the prism. Color was found to be particularly variable in both species, and was not useful. Nevertheless, the debris of Kalotermes flavicollis was markedly “dirty” (mixed with other wood remains)

Análisis comparativo de procedimientos para la medición de las gemas y evaluación de su influencia en la determinación de las propiedades mecánicas de la madera de Pinus sylvestris L. de gran escuadría. Comparison of wanes measurement systems to evaluate their influence on the mechanical properties of large cross section timber of Pinus sylvestris L.

Las gemas se evalúan mediante la norma de clasificación visual (UNE 56544), pero su aplicación en estructuras existentes y grandes escuadrías resulta poco eficaz y conduce a estimaciones demasiado conservadoras. Este trabajo analiza la influencia de las gemas comparando la resistencia de piezas con gemas y piezas correctamente escuadradas. Se han analizado 218 piezas de pino silvestre con dimensiones nominales 150 x 200 x 4.200 mm, de las que 102 presentaban una gema completa a lo largo de toda su longitud y el resto estaban correctamente escuadradas. En las piezas con gema se ha medido la altura de la sección cada 30 cm (altura en cada cara y altura máxima). Para determinar la resistencia se han ensayado todas las piezas de acuerdo a la norma EN 408. Se ha comparado la resistencia obtenida para las piezas con gema, diferenciando si la gema se encuentra en el borde comprimido o en el borde traccionado, con las piezas escuadradas. Puede concluirse que la presencia de gemas disminuye la resistencia excepto si la gema se encuentra en el borde traccionado, en cuyo caso los resultados obtenidos han sido similares a los de las piezas escuadradas. The wanes on structural timber are evaluated according to the visual grading standard (UNE 56544), but its application on existing structures and large cross sections is ineffective and leads to conservative estimations. This paper analyzes the influence of the wanes by comparing the resistance of pieces with wanes and square pieces. 218 pieces of Scotch pine with nominal dimensions 150 x 200 x 4200 mm have been analyzed, 102 of them had a complete wane along its length and the rest were properly squared. The height of the cross section was measured every 30 cm (the height on each side and the maximum height) for the pieces with wane. The bending strength of all the pieces was obtained according to the EN 408 standard. The bending strength of the pieces with wane has been compared with the strength of the squared pieces, taking into account if the wane is positioned on the compressed edge or on the tensioned edge. It can be concluded that the bending strength of the pieces with wanes is lower than the one of squared pieces, except if the wanes are on the tensioned edge of the beam

Non-destructive methods to estimate physical aging of plywood

This paper studies the relationship between aging, physical changes and the results of non-destructive testing of plywood. 176 pieces of plywood were tested to analyze their actual and estimated density using non-destructive methods (screw withdrawal force and ultrasound wave velocity) during a laboratory aging test. From the results of statistical analysis it can be concluded that there is a strong relationship between the non-destructive measurements carried out, and the decline in the physical properties of the panels due to aging. The authors propose several models to estimate board density. The best results are obtained with ultrasound. A reliable prediction of the degree of deterioration (aging) of board is presented

Estado actual de la investigación sobre madera estructural en España

This article intends to show the current state of the research about structural timber in Spain. An ample compilation of information from people and institutions has been carried out. Information received has been so extensive that a hard work of synthesis has been necesary in order to offer a general and objective vision of the subject.In a few years a new legislative and normative frame has been implanted in Spain, defi ned by the Law of Arrangement of the Construction, the Construction Technical Code and the European Construction Products Directive. In this frame some challenges for the sector arise from the construction and the timber. It is the fi rst time that structural timber is framed within a norm of forced fulfillment, which it supposes not only a challenge but the putting in value of all its potential like structural material.In this frame research necessities have been increased, as well as development and innovation, and it is demostrated by several research iniciatives started in our country, with a clear vocation to respond to the necessities arisen in the sector and to satisfy the raised requirements of security in the norm. In this work, using the compiled information, the research lines on structural timber at the moment in Spain are summarized, as well as their presence in means of national or international diffusion or their direct applications in the industry.Este artículo pretende dibujar un panorama sobre el estado actual de la investigación en torno a la madera estructural desarrollada actualmente en España. Se ha realizado una amplia recopilación de información entre personas e instituciones. La información recibida ha sido tan extensa que ha sido necesaria una difícil labor de síntesis para ofrecer una visión general y objetiva.En poco tiempo ha sido implantado en España un nuevo marco legislativo y normativo defi nido por la Ley de Ordenación de la Edifi cación, el Código Técnico de la Edificación y la Directiva Europea de Productos de la Construcción. En este marco surgen algunos retos para el sector de la construcción a los que la madera no resulta ajena. La madera estructural se enmarca por primera vez en una normativa de obligado cumplimiento, lo que supone no sólo un reto sino la puesta en valor de todo su potencial como material estructural.En este marco se han disparado las necesidades de investigación, desarrollo e innovación, y así lo demuestran las muchas líneas de investigación abiertas en nuestro país, con una clara vocación de responder a las necesidades surgidas en el sector y de satisfacer los requisitos de seguridad planteados en la normativa. En este artículo, con la información recopilada se resumen las líneas de investigación sobre madera estructural que se están desarrollando actualmente en España, así como su presencia en medios de difusión nacional o internacional o sus aplicaciones directas en la industria