Abstract
The assessment of existing timber structures requires the determination of the mechanical properties of the individual timber members, which is often obtained by visual grading combined with information of small clear wood specimens. The purpose of this work is to present the results obtained in a multi-scale experimental evaluation of 20 old chestnut (Castanea sativa Mill.) beams, aimed at defining the correlations between bending modulus of elasticity (MOE) in different scales of timber members in combination with visual grading. The results of bending tests, according to EN 408:2010 (2010), were statistically analyzed to obtain correlations of bending MOE between and within different scales size. The results of visual inspection according to UNI 11119:2004 (2004) regarding the presence and distribution of defects were considered for variation analysis of MOE, evidencing a significant variance between samples of different visual strength grades. Strong correlations within the same phase (coefficient of determination r2 from 0.82 to 0.89) and moderate to high correlations for different phases (r2 from 0.68 to 0.71) were found for bending MOE. Cumulative distribution functions for global MOE remained similar throughout the experimental phases. Moreover, percentage of segments attributed to a specific visual grade is given for each member and compared between scales.
Highlights
The assessment of existing timber structures requires the determination of the mechanical properties of the individual timber members and joints
As mentioned by Branco et al (2010), if the visual grading is based on the evaluation of local defects but the result is the assignment of a specific strength class to the entire timber element, this leads to a loss in evaluating local defects
In Phase 3, after the visual inspection and g rading, timber sawn boards were subjected to bending tests in elastic regime according to EN 408:2010 (2010), the height was chosen to be the smaller cross section dimension (h = 4 cm) in order to establish a consistent measurement of the stiffness parameters, expressed by the bending modulus of elasticity (MOE), with size variation
Summary
The assessment of existing timber structures requires the determination of the mechanical properties of the individual timber members and joints. Strength grading of existing timber members is made by indirect prediction of the mechanical properties using visual inspection and non-destructive testing. The correlations between properties are higher for small-clear specimens and lower for large members (Kasal 2010) In this context, the purpose of the present work is to address the correlation of bending MOE in different scales size of a timber element. It is intended to investigate the interest of visual inspection for variation analysis of MOE between and within different scales size, regarding the presence of defects and its distribution. For these purposes, a multi-phase experimental campaign, conducted to twenty old chestnut beams, and its results are presented and analyzed
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