Visual grading of timber elements in service

The UNI 11119/2004 standard indicates some classification rules based on the observation of physical or defective characteristics of existing timber structural elements in service, to attribute the analysed elements to a strength class. This standard, in addition to requiring the measurement of the cross-section of the wooden element, proposes a classification based on some significant structural features. The wooden element is inspected on at least three sides, it must be free of opaque coatings (paintings, varnishes, …), and some parameters are quantitatively defined such as: presence of cracks, presence of material decay, presence and dimensions of bevels, single and grouped knots, inclination of the grain. For assignment to a specific category (I, II or III) it is necessary that all the characteristics and/or defects fall within the specified limits for each one, the element being alternatively unclassifiable. Starting from a category attribution, the standard therefore reports, for timber elements of different wood species, the maximum stresses that can be adopted for the application of the allowable stress method and the average values ​​of flexural elastic modulus which should be used for the calculation of deformations of the structure in serviceability limit states.
Reference standards: UNI 11119:2004; UNI 11035:2022.