Evaluation of the influence of visual parameters on wave transmission velocity in sawn chestnut timber

Non-destructive, visual evaluation and mechanical testing techniques were used to assess the structural properties of 374 samples of chestnut (Castanea sativa). The principal components method was applied to establish and interpret correlations between variables obtained of modulus of elasticity, bending strength and density. The static modulus of elasticity presented higher correlation values than those obtained using non-destructive methods. Bending strength presented low correlations with the non-destructive parameters, but there was some relation to the different knot ratios defined. The relationship was stronger with the most widely used ratio, CKDR. No significant correlations were observed between any of the variables and density.

Clasificación de madera estructural de gran escuadría de Pinus sylvestris l. mediante métodos no destructivos

Esta Tesis Doctoral aborda el estudio de algunas técnicas no destructivas para la clasificación de madera de pino silvestre (Pinus sylvestris L.) de procedencia española y de gruesa escuadría para uso estructural. Para la estimación del módulo de elasticidad y de la resistencia se han aplicado técnicas basadas en la propagación de una onda a través de la madera: onda de ultrasonidos (Sylvatest) o de impacto (Microsecond Timer) en dirección longitudinal, o vibración en dirección longitudinal y transversal (PLG). Para la estimación de la densidad se han utilizado métodos puntuales basados en el penetrómetro (Pilodyn) y en la resistencia al arranque de un tornillo. Las variables obtenidas han sido relacionadas con los resultados de la clasificación visual y con las propiedades de la madera determinadas mediante ensayo mecánico. Además, se ha estudiado la influencia de la humedad de la madera en la velocidad de propagación de la onda para definir factores de corrección a los equipos comerciales utilizados en esta Tesis Doctoral. La muestra de estudio está formada por 244 piezas procedentes de El Espinar, Segovia, con dimensiones nominales 150 x 200 x 4000 mm (218 piezas) y 100 x 150 x 3000 mm (26 piezas). De todas las piezas se tomaron datos de dimensiones, contenido de humedad y clasificación visual según la norma UNE 56544. En las primeras 218 vigas se aplicaron las técnicas de ultrasonidos, onda de impacto y vibraciones, se determinó la densidad de cada pieza completa y se ensayaron según la norma UNE-EN 408 para obtener el módulo de elasticidad global (en todos los casos) y local (en un porcentaje), así como de la tensión de rotura. Se extrajeron tres rebanadas para los ensayos puntuales y para el cálculo de la densidad. En las otras 26 piezas se repitieron los ensayos (transmisión de onda, vibración y clasificación visual) durante el proceso de secado natural, desde que la madera se encontraba húmeda (en torno al 40 %) hasta la humedad de equilibrio higroscópico (en torno al 9%). Respecto a la clasificación visual no se han observado diferencias significativas entre la calidad MEG o las rechazadas. Se han estudiado las consecuencias del secado (principalmente las deformaciones) y no se ha encontrado justificación para que estos defectos penalicen la clasificación. Para la densidad, el mayor R2 obtenido ha sido de un 47% a partir del uso combinado de los dos equipos puntuales (penetrómetro y arranque de tornillo). Para el módulo de elasticidad y la tensión de rotura, la mejor relación se ha obtenido a partir de la técnica de vibración longitudinal, con unos coeficientes de 79% y un 52% respectivamente. Se ha estimado que el aumento de un punto porcentual en el contenido de humedad de la madera produce una pérdida de velocidad de onda del 0,58% para Sylvatest y Microsecond Timer, y del 0,71% para PLG. Estos valores son generalizables para un rango de humedades entre 9 y 25 %. Abstract This Doctoral Thesis approach the study of some non-destructive techniques as a classification method for structural use of Scots pine wood of Spanish origin with large cross section. To estimate the modulus of elasticity and strength have been used techniques based on the propagation of a wave through the timber: ultrasonic wave (Sylvatest) or stress wave (Microsecond Timer) in longitudinal direction, or vibration in longitudinal and transversal direction (PLG). Local probing methods have been applied to estimate the density, based on penetrometer (Pilodyn) and the screw withdrawal resistance meter. The different variables obtained were compared with the results of the visual grading and the values of the properties of the wood determined by the standardized test of the pieces. Furthermore, the influence of the moisture content of the wood on the velocity of propagation of the waves through the timber has been analyzed in order to establish a correction factor for the commercial devices used in this Doctoral Thesis. The sample tested consists of 244 pieces from El Espinar, Segovia, with nominal dimensions 150 x 200 x 4000 mm (218 pieces) and 100 x 150 x 3000 mm (26 pieces). Data collection about dimensions, moisture content and visual grading according to the UNE 56544 standard were carried out on all the pieces. The first 218 pieces were tested by non destructive techniques based on ultrasonic wave, stress wave and vibration, the density was measured on each piece and bending test according to the UNE-EN 408 standard was carried out for calculating the global modulus of elasticity (all the pieces) and the local one (only a representative group), as well as the bending strength. Three slices were removed for implementing the local probing and to calculate the density. In the other 26 pieces the tests (wave transmission, vibration and visual grading) were repeated during the natural drying process, from wet timber (around 40 % moisture content) up to the equilibrium moisture content (around 9%). Regarding the visual grading no significant differences were observed between MEG or rejected pieces. The effects of drying (deformations) have been studied, and justification for the specification hasn't been found. To estimate the density, the greater R2 obtained was 47% by using both penetrometer and screw withdrawal. For the modulus of elasticity and bending strength, the best relationship has been found with the longitudinal vibration, with coefficients of 79% and 52% respectively. It has been estimated that an increase of a point of the moisture content of the wood produces a decrease on the velocity obtained from ultrasonic or stress wave of 0,58%, and 0,71 % for the one obtained from vibration. Those values can be generalized for a range of moisture content from 9 to 25 %.

Analysis of wave attenuation and shore protection of a bulk carrier ship performing as a detached floating breakwater

Análisis de la atenuación del oleaje por un carguero funcionando como dique flotante y aplicación a dos casos de protección portuaria y costera. The effectiveness of a bulk carrier working as a detached floating breakwater to protect a stretch of coast and form salients or tombolos is assessed in this paper. Experiments were conducted in the Madrid CEDEX facilities in a 30 m long, 3 m wide, 1/150 scale flume. The bulk carrier ship is 205 m long, 29 m wide and 18 m in height with a draught of 13 m, and has been subjected to irregular waves with significant heights from 2 m to 4 m and peak periods from 6 s to 12 s at a depth of 15 m, all prototype dimensions. Three probes were placed between the wave paddle and the ship to record incident and reflected waves and four probes were placed between the ship and the coastline to measure the transmitted waves. Transmission, reflection and dissipation coefficients (Ct, Cr, Cd) were calculated to determine wave attenuation. Results show good shelter in the lee of the ship with values of Ct under 0.5 for peak periods from 6 s to 11 s. In addition, forces on the mooring chains were measured showing maximum values of about 2000 tons at a 10 speak period. Finally, two analytical models were used to determine the shoreline’s response to the ship’s protection and to assess the possible forming of salients or tombolos. According to the results, salients - but not tombolos - are formed in all tests.