Mechanical Characteristics of Historical Beams of Picea Abies Wood: Assessment by Ultrasound
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Mechanical Characteristics of Historical Beams of Picea Abies Wood: Assessment by Ultrasound Javier Ramón Sotomayor-Castellanos and José María Villaseñor-Aguilar Universidad Michoacana de San Nicolás de Hidalgo. Ciudad Universitaria, Morelia, Michoacán. 58130 México. e-mail: [email protected] ABSTRACT Five historical full-size wood structural beams of Picea abies were tested with ultrasound. The speed of ultrasound, the modulus of elasticity, the moisture content and the wood density were measured for each specimen. The speed of the ultrasound waves in the radial, tangential and longitudinal directions was 1,769 m/s, 1,599 and 5,713 m/s respectively. The modulus of elasticity in the radial, tangential and longitudinal directions was 1,353 MPa, 1,069 MPa and 13,863 MPa respectively. The moisture content was on average 11.92% and the density was on average 422 kg/m3. Wood parameters such as density and orthotropic directions had influence in ultrasound measurements. In spite of local weakness in the beams, they had enough strength to be considered full structural members. INTRODUCTION The structural elements of the historical wood structures frequently present geometrical deformations, biological decay and weathering, and sometimes it is difficult to identify the wood species. The moisture distribution in wood elements is complex, and the members are submitted to environmental variations of humidity and temperature. During the service life of the wood structural element, the members are exposed to environmental variations of humidity and temperature causing cyclic stresses in the wood. In an old wooden frame, frequently the structural connections between the wooden members have relative weaknesses. Also, the joints of the structures with the walls or foundations sometimes are in a deplorable state. This is frequently the technical diagnostic after an inspection of the historical wood structures. However, the structure continues functioning safely and giving the appropriate service. An important fact is that the structural status of the mechanical condition of the structure does not reduce its historical and cultural value. Following the recommendation of [1] and in order of respecting the authenticity of the building in these days, it is necessary to perform an appropriate scientific method to analyze the structure. The modulus of elasticity of the wood beams can be calculated using the speed of propagation of the ultrasound waves. When the ultrasound technique is used to assess the modulus of elasticity of the wood beams, it is important to consider the form and function of the anatomical components of the wood [2]. The density and moisture content of wood influence the velocity of ultrasound in wood [3]. Indeed, it has been proved that below the fiber saturation point, ultrasound velocity decreases rapidly and linearly with increasing moisture [4]; whereas above the fiber saturation point changes in velocity were rather gradual and curvilinear with marked differences in velocity patterns between temperatures below
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