This paper investigates the tensile strength and stiffness of low quality beech sawn timber. In addition, the influences of visual and physical characteristics of the beech boards on the mechanical performance were analysed. Visual characteristics like knots, pith or fibre deviation as well as density and dynamic modulus of elasticity were examined regarding their influence on the tensile strength and stiffness of the beech boards. The subsequent destructive testing was performed according to EN 408on 214 beech boards with two different cross sections. Correlation analyses regarding non-destructive and destructive parameters indicate possibilities and limits of strength grading in terms of beech sawn timber. This paper complements many investigations of the last years focusing mainly on the mechanical behaviour of middle and high quality beech sawn timber and glulam. As a large proportion of beech sawn timber is low quality material, a better understanding of its behaviour may lead to higher yield in combination with economic benefits as well as to more reliable strength grading and more efficient material use. @en

Generally, for structural timber the main properties are listed in a strength class system. In Europe EN 338 (2016) lists available strength class and their respective characteristic properties. Depending on the product application the bending or the tension properties are of main interest. For glulam lamellas, tension classes are preferred as through tension classes the mechanical properties of glulam can be better predicted. Also, machine grading allows for a better prediction of tensile properties compared to bending properties. So far, tension grades were regulated in EN 14081- 4. Due to the increased demand on glulam products, the grades were recently analysed, and a tensile class table was introduced in EN 338 (2016). The new strength profiles are the preferred option for glulam production. The requirements for softwood glulam are regulated in EN 14080 (2013). So far, no tension classes exist for hardwoods. The EN 338 lists for hardwood specimens only so-called “D” classes based on the bending strength. The other properties, like tension strength, are assigned by the default on the safe side using the equations listed in EN 384. For those classes, the ratio tension strength to bending strength is declared on the safe side 0.6. However as shown by Burger & Glos (1997) for higher quality timber higher ratio can be expected. New tensile classes for hardwoods would allow utilising the properties of hardwoods more efficiently. Whereas the old European standards EN 1194 and EN 14080 (2005) did not regulate species, the most recent version of EN 14080 (2013) is restricted to softwoods only. This means that hardwood glulam producers in Europe face additional costs for obtaining approvals for their products. @en

For the production of lamellas for GLT or CLT visually or machine strength graded timber is required. Visual grading allows only for a limited number of classes while reject rates tend to be high. The present paper shows the potential of an evolutionary algorithm NSGA-II optimizing the boundaries of multiple visual grading criteria in a reliable way. The optimization routine is applied to optimize the boundaries of the visual grading criteria given in DIN 4074-1 and DIN 4074-5. Destructive and non-destructive test data of 1515 specimens of Norway spruce (Picea abies) and 704 specimens of European beech (Fagus sylvatia) tested in tension were analysed. The optimization aims at: a) a maximization of the yield; 2) grade timber to the desired strength classes. Using this optimization routine for both beech and spruce higher yield figures compared to the grading according to DIN 4074 can be obtained while the desired characteristic strength are being reached.@en

Medium dense hardwoods (HWs) show higher tensile strength (TS) values than softwoods (SWs). These advantages cannot be utilised effectively because HW grading is not well developed. The aim of the present paper was to analyse the utilisation potential of European ash (Fraxinus spp.) and maple (Acer spp.) grown in Central Europe, which were graded by different methods. The visual grading characteristics of 869 HW boards were determined and the dynamic modulus of elasticity (MOE dyn ) and X-ray attenuation (XRA) were measured by an industrial scanner. The specimens were subsequently tested in tension according to EN 408:2010 and according to German visual grading rules show strength values of 28 MPa and 30 MPa, respectively. Machine strength grading and for a combination of manually assessed boards and MOE dyn give rise to higher strength data. MOE dyn , in particular, results in lamella data with 62 MPa for ash and 42 MPa for maple. There is good agreement with recently presented HW tensile profiles. Machine grading with a multisensor system allows better strength prediction compared to the MOE dyn or visual strength grading. Best performance is achieved by a combined grading approach. @en

Medium dense hardwoods (HWs) show higher tensile strength (TS) values than softwoods (SWs). These advantages cannot be utilised effectively because HW grading is not well developed. The aim of the present paper was to analyse the utilisation potential of European ash (Fraxinus spp.) and maple (Acer spp.) grown in Central Europe, which were graded by different methods. The visual grading characteristics of 869 HW boards were determined and the dynamic modulus of elasticity (MOE dyn ) and X-ray attenuation (XRA) were measured by an industrial scanner. The specimens were subsequently tested in tension according to EN 408:2010 and according to German visual grading rules show strength values of 28 MPa and 30 MPa, respectively. Machine strength grading and for a combination of manually assessed boards and MOE dyn give rise to higher strength data. MOE dyn , in particular, results in lamella data with 62 MPa for ash and 42 MPa for maple. There is good agreement with recently presented HW tensile profiles. Machine grading with a multisensor system allows better strength prediction compared to the MOE dyn or visual strength grading. Best performance is achieved by a combined grading approach. @en

The usage of hardwoods for engineered wood products, such as glulam, requires defined mechanical properties reflecting the actual tensile strength of the material. Currently, the European strength class system EN 338 only covers profiles for hardwoods tested in bending. In this study, the material properties of medium-density hardwoods are analysed with the focus on a total of 3663 European ash (Fraxinus excelsior) and European beech (Fagus sylvatica) specimens tested in different loading modes (tension, compression, bending, and shear). The relationships between the material properties—tensile strength, stiffness, and density—are analysed on grouped data of both graded and ungraded specimens. As a result, a tailored ratio of tensile strength to tensile MOE and density is given, which allows to utilize a higher tensile strength of hardwoods (ft,0,k over 30 N/mm²) compared to softwoods. Furthermore, the relationship of the test values and the derived values is checked. The equations for deriving the compression and bending strength from tensile strength are verified based on available data. For tensile and compression strength perpendicular to the grain and for shear strength of both beech and ash, higher strength values than the ones listed in EN 338 are possible. The relationship between the mechanical properties are combined to tensile strength profiles for hardwoods.@en

The usage of hardwoods for engineered wood products, such as glulam, requires defined mechanical properties reflecting the actual tensile strength of the material. Currently, the European strength class system EN 338 only covers profiles for hardwoods tested in bending. In this study, the material properties of medium-density hardwoods are analysed with the focus on a total of 3663 European ash (Fraxinus excelsior) and European beech (Fagus sylvatica) specimens tested in different loading modes (tension, compression, bending, and shear). The relationships between the material properties—tensile strength, stiffness, and density—are analysed on grouped data of both graded and ungraded specimens. As a result, a tailored ratio of tensile strength to tensile MOE and density is given, which allows to utilize a higher tensile strength of hardwoods (ft,0,k over 30 N/mm²) compared to softwoods. Furthermore, the relationship of the test values and the derived values is checked. The equations for deriving the compression and bending strength from tensile strength are verified based on available data. For tensile and compression strength perpendicular to the grain and for shear strength of both beech and ash, higher strength values than the ones listed in EN 338 are possible. The relationship between the mechanical properties are combined to tensile strength profiles for hardwoods.@en