Friction Coefficients of Chestnut (Castanea sativa Mill.) Sawn Timber for Numerical Simulation of Timber Joints

Abstract

This study focuses on the friction characteristics of chestnut sawn timber (Castanea sativa Mill.) of Spanish origin. The values of both the static and dynamic friction coefficients were determined, as this knowledge is of interest for the numerical simulation of the stress transmission in joints of timber structures. Therefore, two sets of tests were carried out combining different orthotropic orientations. Firstly, timber-to-timber tests were assessed to obtain the coefficients applicable to carpentry joints; secondly, timber-to-steel friction was also evaluated to determine the coefficients needed for mechanical joints with metal plates and dowels. The results presented a conventional behavior of friction, i.e., a maximum static value before sliding and a subsequent decrease. For timber-to-timber tests, global mean values of μs = 0.47 and μk = 0.36 were found, and the results were slightly higher than those obtained between pieces with the same orthotropic orientation and sliding direction. Regarding timber-to-steel tests, the resulting friction coefficients, as well as the difference existing between the static and dynamic values were lower (μs = 0.19 and μk = 0.17) compared to the timber-to-timber sets. The use of these results in numerical studies would allow for closer simulations in which chestnut wood is involved in friction. In addition, the values provided herein could be included as new data in standards that already consider other wood species.

Frictional Behavior of Chestnut (Castanea sativa Mill.) Sawn Timber for Carpentry and Mechanical Joints in Service Class 2

“…The oscillations observed in Figure 3 are illustrative of the stick-slip phenomenon. However, the fluctuation manifested with reduced intensity compared to similar tests conducted at lower moisture levels [30,31]. This reduction aligns with findings by [29,39], highlighting that higher moisture weakens the stick-slip behavior between the wood surfaces.…”

“…Firstly, this method allows for the application of a normal load (N) to the upper face of the specimen through a distribution plate connected to a load bridge and counter-balance device while controlling the sliding speed. Similar to other research works [30,31,37,38], this study employed a 0.5 MPa load and an 8 mm•min −1 speed to simulate conditions encountered in practice while also effectively preventing the occurrence of inertial forces. Moreover, this method enables the measurement of both displacement and the necessary force (F) required to produce sliding by means of an LVDT (Linear Variable Differential Transformer) displace-ment sensor and load cell sensor, respectively.…”

“…In the absence of a specific European standard test for determining the friction coefficient of wood and drawing upon the general recommendations provided by the American standard ASTM G115-10 [35], the authors developed and validated a test procedure based on a direct shear machine [36]. The proposed method adapts common geotechnical equipment to facilitate the placement and contact of the surfaces to be tested (i.e., specimens were positioned in the device by their largest surface area, ensuring that sliding occurred along the longest dimension), thereby facilitating both accurate experimental conditions as well as the application and recording of the necessary variables.…”

“…The results arising from the experimental program would provide a comprehensive database to be used as an input for precise engineering calculations, such as those carried out in numerical simulations, that would allow for a more accurate volumetric optimization of this natural resource. Additionally, in combination with previous findings by the authors on timber-to-timber and timber-to-steel tests at a 12% moisture content [30,31], this program would be used to validate the interpolation approach suggested for softwoods within the 12-18% moisture content range for hardwoods.…”

Bending strength prediction and finite element analysis of larch structural beams

“…The support was set as fixed support. The boundary condition between the support and the specimens was set as frictional so that it could slide because it was a roller point, and the coefficient of friction was set to 0.5 (Villar-García et al 2022). Because a bending test causes large deflection values, the large deflection option is set to on.…”