lnu.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Publications (10 of 75) Show all publications
Briggert, A., Olsson, A. & Oscarsson, J. (2020). Prediction of tensile strength of sawn timber: definitions and performance of indicating properties based on surface laser scanning and dynamic excitation. Materials and Structures, 53, 1-20, Article ID 54.
Open this publication in new window or tab >>Prediction of tensile strength of sawn timber: definitions and performance of indicating properties based on surface laser scanning and dynamic excitation
2020 (English)In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 53, p. 1-20, article id 54Article in journal (Refereed) Published
Abstract [en]

The presence of wood irregularities such as knots are decisive for the mechanical properties of sawn timber, and efficient utilisation of timber requires methods by which grade determining properties can be predicted with high accuracy. In the glulam and sawmilling industries today, there is a potential and a need for more accurate prediction methods. This paper concerns the performance of a set of indicating properties calculated by means of data from surface laser scanning, dynamic excitation and X-ray scanning, the latter used to obtain boards’ average density. A total number of 967 boards of Norway spruce originating from Finland, Norway and Sweden were used to determine statistical relationships between the indicating properties and the grade determining properties used to grade sawn timber into T-classes. Results show that the indicating properties give coefficients of determination to tensile strength as high as 0.70. Furthermore, results also show that laser scanning of boards with sawn surface finish give basis for almost as accurate grading as what scanning of planed boards do. The results imply that more accurate grading of timber into T-classes is possible by application of a new set of indicating properties. This paper is part one of a series of two papers. In the second paper, two models to derive settings and calculate yield in different strength classes using the indicating properties presented herein are compared and discussed.

Place, publisher, year, edition, pages
Springer, 2020
Keywords
Laser scanning, Fibre direction, Dynamic modulus of elasticity, Grading of timber, Norway spruce
National Category
Other Civil Engineering
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-94130 (URN)10.1617/s11527-020-01460-5 (DOI)
Funder
Knowledge Foundation, 20150179
Available from: 2020-05-04 Created: 2020-05-04 Last updated: 2020-05-26Bibliographically approved
Briggert, A., Olsson, A. & Oscarsson, J. (2020). Prediction of tensile strength of sawn timber: models for calculation of yield in strength classes. Materials and Structures, 53, 1-15, Article ID 55.
Open this publication in new window or tab >>Prediction of tensile strength of sawn timber: models for calculation of yield in strength classes
2020 (English)In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 53, p. 1-15, article id 55Article in journal (Refereed) Published
Abstract [en]

In Europe, strength classes for structural timber and glulam lamellae are defined by minimum requirements of characteristic values of the grade determining properties (GDPs). To fulfill these minimum requirements of characteristic values in the daily production at sawmills, indicating properties (IPs) to GDPs are calculated for each board and based on predetermined limits of the IPs (settings) boards are assigned to the graded class, or rejected. The aims of this paper is to address and discuss two different grading procedures/models that can be applied when settings for IPs that reflects a local board property are derived and to show how the yield in different T-classes depend on the model applied. It is not always that a board’s weakest cross-section is evaluated in a destructive test. An IP representing a local board property can therefore be determined either as the lowest property of the tested part of the board or as the lowest property along the whole board when applied to derive settings. Results presented in this paper show that too low settings and too large yields are obtained when the latter IP is employed. Similarly, IPs reflecting a global board property, like axial dynamic MOE, also give too low settings and too high yield in strength classes. This paper is the second and closing part of a series of two paper on prediction of GDPs and procedures for grading sawn timber into T-classes.

Place, publisher, year, edition, pages
Springer, 2020
Keywords
Grading of timber, Laser scanning, Fibre direction, Dynamic modulus of elasticity, Norway spruce
National Category
Other Civil Engineering
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-94131 (URN)10.1617/s11527-020-01485-w (DOI)
Funder
Knowledge Foundation, 20150179
Available from: 2020-05-04 Created: 2020-05-04 Last updated: 2020-05-26Bibliographically approved
Lukacevic, M., Kandler, G., Hu, M., Olsson, A. & Füssl, J. (2019). A 3D model for knots and related fiber deviations in sawn timber for prediction of mechanical properties of boards. Materials & design, 166, 1-18, Article ID 107617.
Open this publication in new window or tab >>A 3D model for knots and related fiber deviations in sawn timber for prediction of mechanical properties of boards
Show others...
2019 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 166, p. 1-18, article id 107617Article in journal (Refereed) Published
Abstract [en]

Increased use of wood has led to complex timber constructions and new types of engineered wood products. In simulations, however, mainly simplified models are used to describe this material with its strongly varying properties. Therefore, reliable prediction tools for mechanical properties of wooden boards are needed. Those varying properties mainly originate from knots and fiber deviations. Thus, we use fiber directions on board surfaces to reconstruct knots within boards. Combined with a fiber deviation model we assess our model with experiments on different levels: fiber directions on surfaces, strain fields and bending stiffness profiles.

This model now better describes fiber patterns near knots and knot clusters. Also, we showed that accurate modeling of the pith is important to avoid large regions of incorrect fiber deviations. Furthermore, modified knot stiffness properties were successfully used to consider pre-cracked knots. Finally, we obtained multiple bending stiffness profiles, where we showed that even local effects can be simulated accurately.

We anticipate our tool to be a starting point for improving strength grading models, where effects of knot configurations can be studied more easily than with experiments alone. Furthermore, the presented improvements will render the simulation of realistic failure mechanisms in wooden boards more likely.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-80009 (URN)10.1016/j.matdes.2019.107617 (DOI)000458260700015 ()2-s2.0-85060758980 (Scopus ID)
Available from: 2019-01-29 Created: 2019-01-29 Last updated: 2019-10-17Bibliographically approved
Habite, T., Olsson, A. & Oscarsson, J. (2019). Automatic detection of pith location along boards of Norway spruce on the basis of data from optical scanning of longitudinal surfaces. In: CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019: . Paper presented at CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019 (pp. 64-64). Växjö: Lnu Press
Open this publication in new window or tab >>Automatic detection of pith location along boards of Norway spruce on the basis of data from optical scanning of longitudinal surfaces
2019 (English)In: CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019, Växjö: Lnu Press , 2019, p. 64-64Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Different mechanical and physical properties of wood are related to the location of pith. Norway spruce wood from the centre of logs, close to the pith, is characterized by lower longitudinal MOE, larger spiral grain angle, and larger longitudinal shrinkage coefficient than what wood farther away from the pith is [1]. Thus, knowledge of pith location along timber boards may play an important role in both appearance grading and in assessment of mechanical properties such as strength [2]. The current work aims to develop an algorithm which is capable of automatically estimating the pith location of Norway spruce boards, along the boards’ length direction, by utilizing optical scanning of longitudinal surfaces. The initial step of the algorithm is to identify defect free sections along the timber board. This is done by utilizing data from tracheid effect scanning of the four sides of the timber board. Thereafter, a continuous wavelet transform (CWT), similar to fast Fourier transform, is applied on grey scale images from scanning, to analyse the variation of light intensity across the four surfaces at selected positions along the board. Obtained local frequencies correspond to the local annular ring pattern on surfaces. Then, assuming that annular growth rings are concentric circles with the pith in the centre, detected local annular ring wavelengths (using CWT) and artificial annual ring wavelengths corresponding to different hypothetical locations of pith are compared, and an optimization procedure is used to identify the location of pith that minimizes the discrepancy between the detected and artificial sets of annular ring wavelengths. Figure 1 shows grey scale images of short segments of longitudinal surfaces, graphs of the detected local annual ring widths, and a photograph of the board cross section where the determined location of pith is marked out. Preliminary results reveal that data from optical scanners and the suggested method allow for accurate detection of annular ring width and location of pith along boards.

Place, publisher, year, edition, pages
Växjö: Lnu Press, 2019
Keywords
Fibre orientation - modeling and grading of wood
National Category
Wood Science Building Technologies
Research subject
Technology (byts ev till Engineering); Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89351 (URN)978-91-88898-64-7 (ISBN)
Conference
CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019
Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2020-02-24Bibliographically approved
Bader, T. K., Füssl, J. & Olsson, A. (Eds.). (2019). CompWood 2019 - Computational Methods in Wood Mechanics -: From Material Properties to Timber Structures: Book of Abstracts.. Paper presented at CompWood 2019 - Computational Methods in Wood Mechanics - From Material Properties to Timber Structures, June 17-19, 2019, Växjö, Sweden. Växjö: Linnaeus University Press
Open this publication in new window or tab >>CompWood 2019 - Computational Methods in Wood Mechanics -: From Material Properties to Timber Structures: Book of Abstracts.
2019 (English)Conference proceedings (editor) (Refereed)
Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2019. p. 110
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-90446 (URN)978-91-88898-64-7 (ISBN)
Conference
CompWood 2019 - Computational Methods in Wood Mechanics - From Material Properties to Timber Structures, June 17-19, 2019, Växjö, Sweden
Available from: 2019-12-09 Created: 2019-12-09 Last updated: 2019-12-19Bibliographically approved
Habite, T., Olsson, A. & Oscarsson, J. (2019). Detection of Pith Location of Norway Spruce Timber Boards on the Basis of Optical Scanning. In: Xiping Wang; Udo H. Sauter; Robert J. Ross (Ed.), Proceedings, 21st international nondestructive testing and evaluation of wood symposium: Freiburg, Germany. Paper presented at 21st International Nondestructive Testing and Evaluation of Wood Symposium, Freiburg, Germany, September 24-27, 2019 (pp. 268-275). Madison, U.S.A: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory
Open this publication in new window or tab >>Detection of Pith Location of Norway Spruce Timber Boards on the Basis of Optical Scanning
2019 (English)In: Proceedings, 21st international nondestructive testing and evaluation of wood symposium: Freiburg, Germany / [ed] Xiping Wang; Udo H. Sauter; Robert J. Ross, Madison, U.S.A: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory , 2019, p. 268-275Conference paper, Published paper (Refereed)
Abstract [en]

Optical scanners are used in the woodworking industry to detect various defects, such as dead and live knots, cracks, and fibre distortions, which are important for the visual appearance grading of wood. Data from scanning is also used to assess mechanical properties such as bending and tensile strength, for the purpose of machine strength grading of sawn timbers. Knowledge of annular ring width and location of pith in relation to board cross-sections, and how these properties vary in the longitudinal direction of boards, is relevant for many purposes, such as assessment of shape stability and mechanical properties of timber. Therefore, the purpose of the present research is to evaluate possibilities to determine annular ring width and location of pith on the basis of scanning of surfaces parallel to the longitudinal board direction. The first step of this novel method is to identify clear wood sections, free of defects along boards. Then time-frequency analysis is applied to assess the variation of light intensity over surfaces of these sections, such that local wavelengths, related to the annular ring width patterns are detected on all four surfaces around the board. Finally, the location of pith is calculated by comparing annular ring width distributions on the different surfaces, and assuming that annular rings are concentric circles with the pith in the centre. Results indicate that optical scanners and the suggested method allow for accurate detection of annular ring width and location of pith along boards.

Place, publisher, year, edition, pages
Madison, U.S.A: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, 2019
Series
General Technical Report ; FPL-GTR-272
Keywords
pith location, annual ring width, continuous wavelet transform
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering); Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89385 (URN)
Conference
21st International Nondestructive Testing and Evaluation of Wood Symposium, Freiburg, Germany, September 24-27, 2019
Available from: 2019-10-02 Created: 2019-10-02 Last updated: 2020-02-24Bibliographically approved
Olsson, A., Briggert, A. & Oscarsson, J. (2019). Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect. European Journal of Wood and Wood Products, 77(6), 1063-1077
Open this publication in new window or tab >>Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect
2019 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 77, no 6, p. 1063-1077Article in journal (Refereed) Published
Abstract [en]

Finger joints in structural timber and glulam lamellae are often used to enable production of long members or to allow forre-connection of parts of a member after removal of weak sections. According to the European Standard EN 15497, certainmargins are required between knots and a finger joint in structural timber, which means that a considerable amount of clearwood becomes waste when finger joints are applied. The purpose of this paper was to investigate the possibility of reducingthe quantity of waste using different criteria for placement of finger joints. The investigation was based on (1) applicationof methods of colour scanning and tracheid effect scanning to detect knots and grain disturbance on board surfaces, and (2)interpretation of the requirements of EN 15497 regarding where finger joints may be placed. The standard’s requirementwhen producing finger joints is that the minimum distance between a knot and a finger joint is three times the knot diameter.The standard allows for the minimum distance between a knot and a finger joint to be shortened to 1.5 times the diameterwhen the local fibre orientation is measured. Utilizing this in simulated production resulted in reduction of waste from 7.4to 4.0%, when using finger joints simply to produce timber of long lengths. If finger joints are also used to re-connect partsof members after removal of weak sections, even larger savings can be made. Furthermore, it is concluded that knowledgeof fibre orientation obtained from scanning could be used not only to decrease the waste in production but also to increasethe quality of finger joints.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-89702 (URN)10.1007/s00107-019-01465-0 (DOI)000490859500002 ()
Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2020-05-04Bibliographically approved
Gečys, T., Bader, T. K., Olsson, A. & Kajėnasa, S. (2019). Influence of the rope effect on the slip curve of laterally loaded, nailed and screwed timber-to-timber connections. Construction and Building Materials, 228, 1-13, Article ID 116702.
Open this publication in new window or tab >>Influence of the rope effect on the slip curve of laterally loaded, nailed and screwed timber-to-timber connections
2019 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 228, p. 1-13, article id 116702Article in journal (Refereed) Published
Abstract [en]

Timber-to-timber connections with different types of screws and nails were experimentally investigated with the aim to quantify the contribution of their axial resistance to their slip and their lateral load bearing capacity, which is the so-called rope effect in dowel-type timber connections. Five different types of screws, including partly threaded and double-threaded screws, as well as three types of nails, including smooth round nails, twisted square-sectioned and grooved nails, were used in the experimental investigations in order to cover a broad range of axial resistance of fasteners. Their behavior was tested in single shear and double shear timber-to-timber connections. In addition to connection testing, system and material properties were experimentally determined. This gave input to design equations and allowed for a comparison of the mechanical model in the European design standard for timber structures, Eurocode 5, with experiments. Experiments indicate that the initial slip modulus in the quasi-elastic domain is not influenced by withdrawal capacity of the fastener, while it shows pronounced influence on load-carrying capacity and the nonlinear shape of the slip curve of the connection at larger deformations. Rope effect strongly depends on fastener properties. High axial resistance of fasteners leads to highly non-linear slip curves and design equations tended to underestimate strength including the rope effect up to a displacement limit of 15 mm. Experimentally observed failure modes were well in line with the theoretical failure modes predicted by the design model. The provided experimental results are motivation for improvement of design models and development of analytical and numerical models that account for nonlinear effects in the complex load transfer mechanism.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Rope effect; Dowel-type connection; Nonlinear slip; Ductility; Stiffness
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89192 (URN)10.1016/j.conbuildmat.2019.116702 (DOI)000497886100010 ()
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-12-13Bibliographically approved
van Blokland, J., Olsson, A., Oscarsson, J. & Adamopoulos, S. (2019). Prediction of bending strength of thermally modified timber using high-resolution scanning of fibre direction. European Journal of Wood and Wood Products, 77(3), 327-340
Open this publication in new window or tab >>Prediction of bending strength of thermally modified timber using high-resolution scanning of fibre direction
2019 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 77, no 3, p. 327-340Article in journal (Refereed) Published
Abstract [en]

The market share of thermally modified wood (TMW) has increased in Europe during the past few years as an environmentally friendly and durable building product. However, TMW products of today are not permitted for use in structural applications, because the reduction in strength that is caused by thermal treatment cannot be accounted for. The purpose of this paper was to investigate the bending properties of thermally modified timber (TMT) of Norway spruce, and to explore possibilities to predict the bending properties of TMT. A sample of 100 boards from a 2X-log sawing pattern of 100 logs was thermally modified according to the ThermoWood® process, while the mirror 100 boards served as an unmodified control sample. Two non-destructive methods were employed: (1) a novel method based on scanning of fibre directions to obtain the lowest edgewise bending modulus of elasticity (MOE) along a board, and (2) a conventional excitation method to determine the first axial resonance frequency used to calculate the axial dynamic MOE. Finally, the boards were bent to failure according to European standard EN 408. Despite the fact that bending strength was reduced by 42% due to thermal treatment, the type and location of failure in TMT remained related to the presence of knots. Prediction of bending strength based on local fibre direction and axial dynamic MOE, gave coefficients of determination of 0.51 for the thermally modified boards and 0.69 for the control boards, whereas axial dynamic MOE alone gave 0.46 and 0.57, respectively. These results indicate that although Norway spruce TMT has lower bending strength compared to unmodified timber, predictions of the bending strength can be made with good accuracy.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
axial dynamic excitation, fibre angle, four-point bending, grade determining properties, machine strength grading, ThermoWood®, tracheid effect
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-80374 (URN)10.1007/s00107-019-01388-w (DOI)000463863700001 ()2-s2.0-85064163799 (Scopus ID)
Funder
Swedish Research Council Formas, 942-2015-722Stora Enso
Available from: 2019-02-11 Created: 2019-02-11 Last updated: 2019-10-17Bibliographically approved
van Blokland, J., Adamopoulos, S., Olsson, A. & Oscarsson, J. (2018). Bending properties and strain fields around knots in thermally modified timber. In: Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz and Brigitte Junge (Ed.), : . Paper presented at 9th European Conference on Wood Modification (ECWM), 17-18 September 2018, Bugers’ Zoo, Arnhem, The Netherlands.
Open this publication in new window or tab >>Bending properties and strain fields around knots in thermally modified timber
2018 (English)In: / [ed] Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz and Brigitte Junge, 2018Conference paper, Published paper (Refereed)
Abstract [en]

Thirty-two (32) boards of Norway spruce with cross-sectional dimensions of 145×45 mm2 were first tested non-destructively in a four-point static bending test, were then thermally modified according to the ThermoWood® process, and were finally tested destructively in the mentioned test set up. For one of these boards, the 2D strain fields occurring due to pure bending were recorded, both before and after thermal modification, over the surface of a knotty part of the board using a non-contact optical deformation measurement system. The objectives were to get more insight into the static bending behaviour of thermally modified timber (TMT), specifically with regard to the local and global modulus of elasticity (MOE) and their respective relationship to bending strength, and the strain development around a cluster of knots. The bending strength was significantly reduced by thermal treatment, whereas the effect on the MOEs was limited. Linear regression analyses demonstrated that bending strength of TMT can be predicted by employing stiffness as indicating property. Strain field measurements showed that at the examined levels of loading the quantity and distribution of strains in a knotty area were not influenced by thermal modification. It was therefore suggested that the influence of thermal modification on global stiffness, as well as on local stiffness around knots, is limited.

Keywords
four-point bending, modulus of elasticity, Norway spruce, strain measurement, strength prediction, ThermoWood®
National Category
Wood Science Building Technologies
Identifiers
urn:nbn:se:lnu:diva-77974 (URN)
Conference
9th European Conference on Wood Modification (ECWM), 17-18 September 2018, Bugers’ Zoo, Arnhem, The Netherlands
Note

Ej belagd 190524

Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2019-10-17Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6410-1017

Search in DiVA

Show all publications