Ändra sökning
Avgränsa sökresultatet
1234567 1 - 50 av 339
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Verbist, Maxime
    et al.
    ISISE, University of Minho, Campus de Azurém, Guimarães, Portugal.
    Nunes, Lina
    LNEC, Structures Department, Lisboa, Portugal;cE3c, Centre for Ecology, Evolution and Environmental Changes, Azorean Biodiversity Group and University of the Azores, Angra do Heroísmo, Portugal.
    Jones, Dennis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. DJ Timber Consultancy Ltd., Neath, United Kingdom.
    Branco, Jorge M.
    ISISE, University of Minho, Campus de Azurém, Guimarães, Portugal.
    11 - Service life design of timber structures2019Ingår i: Long-term Performance and Durability of Masonry Structures: Degradation Mechanisms, Health Monitoring and Service Life Design / [ed] Bahman Ghiassi and Paulo B. Lourenço, Elsevier, 2019, s. 311-336Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Wood has been widely used by humans for millennia as a construction material and can be easily found in everyday life, anywhere around the world. Since wood is a natural, sustainable, and organic composite material, it can be affected by several wood-deteriorating agents under suitable climate exposure conditions, which may threaten the long-term performance of timber structures in their service life. In that context, this chapter covers the background, guidelines, and current research that can help engineers and architects when designing timber structures. It provides extended knowledge about different wood-deteriorating agents, the natural durability of wood, and the use class concept. Based on this, durability models can be established, taking into account the potential presence over time of wood deterioration agents and allowing design for improved service life. Preventive measures and protection systems can be defined from the beginning, whereas on-site monitoring and maintenance of timber structures should be continuously performed.

  • 2.
    Myronycheva, Olena
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Poohphajai, Faksawat
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. innoReNew, Slovenia.
    Sehlstedt-Persson, Margot
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Vikberg, Tommy
    RISE Research Institutes of Sweden, Skellefteå, Sweden.
    Karlsson, Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Junge, Helmut
    ABiTEP GmbH, Berlin, Germany.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Application of GRAS Compounds for the Control of Mould Growth on Scots Pine Sapwood Surfaces: Multivariate Modelling of Mould Grade2019Ingår i: Forests, ISSN 1999-4907, E-ISSN 1999-4907, Vol. 10, nr 9, artikel-id 714Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Research Highlights: In this study, the Generally Recognised as Safe (GRAS) compounds were applied in order to study mould-fungi growth on dried Scots pine sapwood. Background and Objectives: The transition to the use of more sustainable wood-material may be possible by applying GRAS compounds that can control and prevent contamination by primary colonising mould fungi. Materials and Methods: Kiln-dried sawn timber was treated with three different GRAS compounds, and different fungal inoculation methods applied in order to investigate differences in the development of fungal communities. Results: Substances based on potassium silicate significantly reduced fungal growth and mould contamination on the studied wood surfaces. By combining wood-surface treatments with GRAS compounds, fungal-area size as predictors and mould grade as response, a partial least squares (PLS) model that makes it possible to predict mould grade on wood surfaces was developed. The PLS model is a key component in the development of a smart grading-systems equipped by e.g. high-speed digital cameras for the early detection of fungal attack on wood surfaces in different applications. However, the measurements based on chemical characterisation should be the next step to take in order significantly to enhance the model and increase the range of robust applications. In the current study, a multivariate model describing the influence of each fungal-covering area on mould grade was presented for the first time.

  • 3.
    Cool, Julie
    et al.
    University of British Columbia.
    Fredriksson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Avramidis, Stavros
    University of British Columbia.
    Automatic knot detection in coarse resolution cone-beam CT images of softwood logs2019Ingår i: Forest products journal, ISSN 0015-7473Artikel i tidskrift (Refereegranskat)
  • 4.
    Myronycheva, Olena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Characterization of Mould Fungi Growth on Scots Pine Sapwood Surfaces2019Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 5.
    Jones, Dennis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    COST FP1303 “performance of bio-based building materials”2019Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, nr 1Artikel i tidskrift (Refereegranskat)
  • 6.
    Blomqvist, Lars
    et al.
    Linnӕus University, Department of Building Technology, Växjö, Sweden. RISE, Research Institute of Sweden.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. Department of Wood Processing and Biomaterials, Czech University of Life Sciences Prague, Prague, Czech Republic.
    Distortion in laminated veneer products exposed to relative-humidity variations: Experimental studies and finite-element modelling2019Ingår i: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, nr 2, s. 3768-3779Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A shortcoming of the laminated bending process is that the product may become distorted after moulding. This study focused on the influence of fibre orientation deviation for individual veneers on the distortion of a moulded shell. The distortion of 90 cross-laminated shells of the same geometrical shape, consisting of seven peeled birch veneers, were studied under relative humidity variation. All the veneers were straight-grained in the longitudinal-tangential plane, but to simulate a deviation in fibre orientation, some of the individual veneers were oriented at an angle of 7° relative to the main orientation of the other veneers in the laminate. A finite element model (FEM) was applied to study the possibility of predicting the results of a practical experiment. The study confirms the well-known fact that deviation in fibre orientation influences shape stability. The results also show how the placement of the abnormal veneer influences the degree of distortion. From this basic knowledge, some improvements in the industrial production were suggested. However, the FE model significantly underestimated the results, according to the empirical experiment, and it did not show full coherence. The survey shows the complexity of modelling the behaviour of laminated veneer products under changing climate conditions and that there is a great need to improve the material and process data to achieve accurate simulations. Examples of such parameters that may lead to distortion are density, annual ring orientation in the cross section of the veneer, the orientation of the loose and tight sides of the veneer, and parameters related to the design of the moulding tool.

  • 7.
    Zhu, Zhaolong
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. Nanjing Forestry University, Coll Mat Sci & Engn, Nanjing, Jiangsu, China.
    Buck, Dietrich
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Guo, Xiaolei
    Nanjing Forestry University, Coll Mat Sci & Engn, Nanjing, Jiangsu, China.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Cao, Pingxiang
    Nanjing Forestry University, Coll Mat Sci & Engn, Nanjing, Jiangsu, China.
    Effect of Cutting Speed on Machinability of Stone–Plastic Composite Material2019Ingår i: Science of Advanced Materials, ISSN 1947-2935, E-ISSN 1947-2943, Vol. 11, nr 6, s. 884-892Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This research examined the orthogonal cutting of stone–plastic composite with diamond cutting tools. The objective was to quantify features relating to machinability, including cutting forces, cutting heat, chip formation, and machining quality with respect to cutting speed. The conclusions are as follows. An increased cutting speed promotes a decrease in the resulting force, causes cutting temperature to increase, makes the cutting processes more stable, and reduces the surface roughness. Chip-breaking length increases with an increase in cutting speed, and chip morphology changes from particle, to curve, to helical, and finally, to flow chips. Overall, a higher cutting speed is more suitable for machining stone–plastic composite materials: it not only increases the stability of cutting process, but also improves the final product of stone–plastic composite by promoting production of a smoother surface.

  • 8.
    Cao, Pingxiang
    et al.
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China.
    Zhu, Zhaolong
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China.
    Buck, Dietrich
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Xiaolei, Guo
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Wang, Xiaodong Alice
    Department of Wood and Forest Sciences, Laval University, Quebec, Canada.
    Effect of rake angle on cutting performance during machining of stone-plastic composite material with polycrystalline diamond cutters2019Ingår i: Journal of Mechanical Science and Technology, ISSN 1738-494X, E-ISSN 1976-3824, Vol. 33, nr 1, s. 351-356Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study investigates the effect of rake angle on cutting performance during machining of stone-plastic composite material with diamond cutters. To that end, an orthogonal cutting experiment was designed, in which stone-plastic composite material was planed by a polycrystalline diamond (PCD) cutter to produce chips. The features studied include cutting forces, cutting heat, chip formation and cutting quality. The conclusions are as follows: Firstly, increased rake angle causes frictional force and resulting force to decrease, promoting an increase in normal force. Secondly, during planing, cutting heat is primarily distributed in the chips, with less retained in the cutting edge, and the least retained in the machined surface. The temperatures of both cutting edge and chip decline with an increase in rake angle. Thirdly, as rake angle increases, chip morphology changes from segmental to curved and then to particle chips, with chip-breaking lengths first increasing and then decreasing. Finally, an increased rake angle leads a more stable cutting process and improved cutting quality. Therefore, with the precondition of blade strength, a diamond cutter with a larger rake angle can be used to machine stone-plastic composite to improve production quality by forming a smoother machined surface.

  • 9.
    Xiong, S.
    et al.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterial and Technology, Umeå, Sweden.
    Martín, C.
    Umeå University, Department of Chemistry, Umeå, Sweden.
    Eilertsen, L.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterial and Technology, Umeå, Sweden. Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology, Umeå Plant Science Center, Umeå, Sweden.
    Wei, M.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterial and Technology, Umeå, Sweden. Guangxi University, College of Agronomy, Nanning, China.
    Myronycheva, Olena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. Swedish University of Agricultural Sciences, Department of Forest Biomaterial and Technology, Umeå, Sweden.
    Larsson, S.H.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterial and Technology, Umeå, Sweden.
    Lestander, T.A.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterial and Technology, Umeå, Sweden.
    Atterhem, L.
    Biosteam AB, Burträsk, Sweden.
    Jönsson, L.J.
    Umeå University, Department of Chemistry, Umeå, Sweden.
    Energy-efficient substrate pasteurisation for combined production of shiitake mushroom (Lentinula edodes) and bioethanol2019Ingår i: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 274, s. 65-72Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hot-air (75 -100°C) pasteurisation (HAP) of birch-wood-based substrate was compared to conventional autoclaving (steam at 121 °C) with regard to shiitake growth and yield, chemical composition of heat-pretreated material and spent mushroom substrate (SMS), enzymatic digestibility of glucan in SMS, and theoretical bioethanol yield. Compared to autoclaving, HAP resulted in faster mycelial growth, earlier fructification, and higher or comparable fruit-body yield. The heat pretreatment methods did not differ regarding the fractions of carbohydrate and lignin in pretreated material and SMS, but HAP typically resulted in lower fractions of extractives. Shiitake cultivation, which reduced the mass fraction of lignin to less than half of the initial without having any major impact on the mass fraction of glucan, enhanced enzymatic hydrolysis of glucan about four-fold. The choice of heating method did not affect enzymatic digestibility. Thus, HAP could substitute autoclaving and facilitate combined shiitake mushroom and bioethanol production.

  • 10.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Turesson, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Huber, Johannes Albert Josef
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Finite element analysis of bending stiffness for cross-laminated timber with varying board width2019Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    ross laminated timber (CLT) is a wood panelling building system that is used in construction, e.g. for floors, walls and beams. Because of the increased use of CLT, it is important to have accurate simulation models. CLT systems are simulated with one-dimensional and two-dimensional (2D) methods because they are fast and deliver practical results. However, because non-edge-glued panels cannot be modelled under 2D, these results may differ from more accurate calculations in three dimensions (3D). In this investigation, CLT panels with different width-to-thickness ratios for the boards have been simulated using the finite element method. The size of the CLT-panels was 3.0 m × 3.9 m and they had three and five laminate layers oriented 0°–90°–0° and 0°–90°–0°–90°–0°. The thicknesses of the boards were 33.33, 40.0, and 46.5 mm. The CLT panel deformation was compared by using a distributed out-of-plane load. Results showed that panels with narrow boards were less stiff than wide boards for the four-sided support setup. The results also showed that 2D models underestimate the displacement when compared to 3D models. By adjusting the stiffness factor k88, the 2D model displacement became more comparable to the 3D model.

  • 11.
    Kaiser, Alex
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Larsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    From file to factory: Innovative design solutions for multi-storey timber buildings applied to project Zembla in Kalmar, Sweden2019Ingår i: Frontiers of Architectural Research, ISSN 2095-2635, E-ISSN 2095-2643, Vol. 8, nr 1, s. 1-16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A “file-to-factory” process of computer technology is a way to both maximise efficiency throughout the building process, increase a building׳s performance, and be able to add interesting architectural possibilities throughout the design phase. The authors investigate a novel approach that produces a set of building trajectories rather than a set of buildings, yet yields a series of build-able examples of those trajectories. This paper evaluates how this series of stacked multi-storey timber buildings can be both incorporated within a file-to-factory process, and give rise to creating new innovative solutions throughout the entire design and manufacturing process. This process is applied to a real Swedish project called Zembla. It redefines the notion of sprawl, turning it into a progressive tactics for linking the city fabric to rural areas. It is a post-sustainable file-to-factory-produced timber ground-scraper; soaring above ground and water, suggesting a new way of making city-sized buildings for the future. A plug-in grid-shell structure is designed to contain a minimal amount of timber elements, beams make up the lattice, cross-laminated panels add structural support, surfaces come together to form the living capsules. Having the structure undulate across the topography and touching the ground in as few places as possible uses the dichotomy between landscape and urbanism, bringing the city to the people living in less densified areas. Each living unit is customised to its topological conditions within the grid.

  • 12.
    Sekan, Alona S.
    et al.
    Institute of Food Biotechnology and Genomics, National Academy of Science of Ukraine, Kyiv, Ukraine.
    Myronycheva, Olena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Karlsson, Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Gryganskyi, Andrii P.
    LF Lambert Spawn Co., Coatesville, PA, USA.
    Blume, Yaroslav
    Institute of Food Biotechnology and Genomics, National Academy of Science of Ukraine, Kyiv, Ukraine.
    Green potential of Pleurotus spp. in biotechnology2019Ingår i: PeerJ, ISSN 2167-8359, E-ISSN 2167-8359, Vol. 7, artikel-id e6664Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background

    The genus Pleurotus is most exploitable xylotrophic fungi, with valuable biotechnological, medical, and nutritional properties. The relevant features of the representatives of this genus to provide attractive low-cost industrial tools have been reported in numerous studies to resolve the pressure of ecological issues. Additionally, a number of Pleurotus species are highly adaptive, do not require any special conditions for growth, and possess specific resistance to contaminating diseases and pests. The unique properties of Pleurotus species widely used in many environmental technologies, such as organic solid waste recycling, chemical pollutant degradation, and bioethanol production.

    Methodology

    The literature study encompasses peer-reviewed journals identified by systematic searches of electronic databases such as Google Scholar, NCBI, Springer, ResearchGate, ScienceDirect, and ISI Web of Knowledge. The search scheme was divided into several steps, as described below.

    Results

    In this review, we describe studies examining the biotechnological feasibility of Pleurotus spp. to elucidate the importance of this genus for use in green technology. Here, we review areas of application of the genus Pleurotus as a prospective biotechnological tool.

    Conclusion

    The incomplete description of some fungal biochemical pathways emphasises the future research goals for this fungal culture.

  • 13.
    Olofsson, Linus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Broman, Olof
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Holistic-Subjective Automatic Grading of Sawn Timber: Sensitivity to Systematic Changes2019Ingår i: International Wood Machining Seminar, 2019Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Holistic-subjective automatic grading of sawn timber by a partial least squares (PLS) regression model required training of the model. This study tests the sensitivity towards systematic changes of a specialized PLS model, trained on a selected type of material suitable for a specific paneling product, when used to grade sawn timber systematically different than the material it was trained on. A sawmills automatic scanning system used cameras to measure knot and bark features on 900 planks. Each plank was split into three boards, and each board was shaped into an indoor paneling product and manually graded as desirable or undesirable at a planing mill. The plank grade was decided as the majority of the board-grade outcome. The knot and bark measurements were used to create a large set of feature variables for each plank that was correlated to the plank’s grade by PLS regression. Of the 900 available planks, 434 planks sawn from top logs were used as a class-balanced specialistic training set, with half of the planks resulting in a majority of desirable boards. The regression model trained on the class-balanced specialistic training set was used to grade a test set of 282 planks, containing 64 planks that by manual classification of automatically captured images were determined to be sawn from butt logs and were systematically different from the training material. The PLS model’s grading accuracy of the planks sawn from top logs was 76%, compared to 70% for the plank sawn from butt logs. The grading outcome resulted in a higher proportion of both delivered planks from the sawmill and received desirable planks by the planing mill when grading planks from top logs as compared to planks from butt logs. The results indicated that a specialistic PLS model should not be used for a generalistic use-case.

  • 14.
    Olofsson, Linus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Broman, Olof
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Holistic-subjective automatic grading of sawn timber: Sensitivity to systematic changes.2019Ingår i: Proceedings of the 24th International Wood Machining Seminar, IWMS 24. / [ed] Schajer, G, Corvallis: Oregon State University (OSU) , 2019, s. 154-167Konferensbidrag (Refereegranskat)
  • 15.
    Turesson, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Impact of board width on in-plane shear stiffness of cross-laminated timber2019Ingår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 196, artikel-id 109249Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Board width-to-thickness ratios in non-edge-glued cross laminated timber (CLT) panels influence the in-plane shear stiffness of the panel. The objective is to show the impact of board width-to-thickness ratios for 3- and 5-layer CLT panels. Shear stiffnesses were calculated using finite element analysis and are shown as reduction factors relative to the shear stiffnesses of edge-glued CLT panels. Board width-to-thickness ratios were independently varied for outer and inner layers. Results show that the reduction factor lies in the interval of 0.6 to 0.9 for most width-to-thickness ratios. Results show also that using boards with low width-to-thickness ratios give low reduction factors. The calculated result differed by 2.9% compared to existing experimental data.

  • 16.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Turesson, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Björnfot, Anders
    Faculty of Engineering, Department of Manufacturing and Civil Engineering, Norwegian University of Science and Technology, Gjøvik, Norway.
    In-plane Shear Modulus of Cross-laminated Timber by Diagonal Compression Test2019Ingår i: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, nr 3, s. 5559-5572Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cross-laminated timber (CLT) is an engineered wood material that is used in the construction industry, e.g., for floors, walls, and beams. In cases where CLT-elements are used as shear walls, the in-plane-stiffness is an important property. For non-edge glued CLT, in-plane shear stiffness is lower than for edge-glued CLT. To evaluate the non-edge glued CLT panel’s in-plane shear modulus, the diagonal compression test and finite element (FE) simulation was used. FE-models with both isotropic and orthotropic material models were used to calculate the shear stiffness. The FE models using pure shear loads were used as a reference to determine the correct value of the shear modulus. To verify the FE simulations, diagonal compression tests were conducted on 30 CLT samples. A calibration formula was derived using the least square method for calculation of shear modulus. The formula gave accurate results. The results showed that FE simulations can reproduce the same shear stiffness as tests of non-edge glued 3-layer and 5-layer CLT panels.

  • 17.
    Sehlstedt-Persson, Margot
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Hansson, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Couceiro, José
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Vikberg, Tommy
    RISE.
    Konditionering av virke vid olika fuktkvoter: studier i tomograf2019Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Fuktförändringar i virke under pågående konditionering har aldrig tidigare studerats i tomograf.

    Resultat av denna labbstudie av diffusionsbaserad, icke-kondenserande jämviktskonditionering vid olika fuktkvotsnivåer sammanfattas enligt följande: (Notera att torkningsspänningar inte utvärde­rats i denna studie utan enbart fuktförändringar.)

    • Studien styrker industriella erfarenheter att konditionering ”tar bättre” på virke nedtorkat till lägre fuktkvot jämfört än om fuktkvoterna är högre.
    • Försöken ger en god fingervisning om hur länge konditionering bör pågå för en viss önskad medel­fuktkvotshöjning i ett industriellt vanligt förekommande klimat 70 °C och psykrometer­skillnad 2° vilket motsvarar en jämviktsfuktkvot på 16,8%. Vill man ex höja medelfuktkvoten från 10 – 12% visar resultaten att 4 timmars konditionering är tillräckligt för furuvirket. Att i samma klimat höja medel­fuktkvoten 2% vid högre startfuktkvoter (mellan 14–23%) har inte i något fall varit möjligt för vare sig gran eller furu under de 8 timmar som konditionering pågick. Det är också viktigt att påpeka att konditioneringsklimatet i dessa labbförsök har uppnått börvärden mycket snabbt (figur 3) vilket inte är fallet vid stora virkeslaster i industriskala där basningskapacitet och blåsdjup påverkar tid till uppnådda börvärden.
    • Vad gäller fuktkvotsskillnad nära ytorna ses generellt en utplaning av fuktförändringar i samtliga försök efter 3–4 timmar.
    • Fuktkvotsnivån spelar roll för den inledande fuktkvotsförändringen inom tvärsnittet: ju torrare virke desto snabbare förändring.
    • När konditioneringen startar är fuktvandringen i splintved effektivare än i kärnved vilket sannolikt förklaras av splintvedens högre diffusivitet.
    • Vad gäller eventuella skillnad mellan träslag är det inte möjligt att dra några slutsatser.
    • Metodstudien visar att upplösningen i tomografen är tillräcklig för att kunna utvärdera fuktkvotsförändringar nära virkesytorna i ca 3 mm tjocka skal.
  • 18.
    Zhaolong, Zhu
    et al.
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing.
    Buck, Dietrich
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Guo, Xiaolei
    College of Materials Science and Engineering, Nanjing Forestry University.
    Pingxiang, Cao
    College of Materials Science and Engineering, Nanjing Forestry University.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Machinability of stone-plastic materials during diamond planing2019Ingår i: Applied Sciences: APPS, ISSN 1454-5101, E-ISSN 1454-5101, Vol. 9, nr 7, artikel-id 1373Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper investigated the machinability of a stone–plastic composite (SPC) via orthogonal cutting with diamond cutters. The objective was to determine the effect of cutting depth on its machinability, including cutting forces, heat, chip formation, and cutting quality. Increased cutting depth promoted an increase in both frictional and normal forces, and also had a strong influence on the change in normal force. The cutting temperatures of chips and tool edges showed an increasing trend as cutting depth increased. However, the cutting heat was primarily absorbed by chips, with the balance accumulating in the cutting edge. During chip formation, the highest von Mises strain was mainly found in SPC ahead of the cutting edge, and the SPC to be removed partially passed its elastic limit, eventually forming chips with different shapes. Furthermore, the average surface roughness and the mean peak-to-valley height of machined surfaces all positively correlated to an increase in cutting depth. Finally, with an increase in cutting depth, the chip shape changed from tubular, to ribbon, to arc, to segmental, and finally, to helical chips. This evolution in chip shape reduced the fluctuation in cutting force, improving cutting stability and cutting quality.

  • 19.
    Huber, Johannes Albert Josef
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Modelling Alternative Load Paths in Platform-Framed CLT Buildings: A Finite Element Approach2019Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Timber has become more popular as a construction material during recent years. Engineered wood products, such as glued laminated timber and cross-laminated timber, have enabled the construction of multi-storey buildings. Tall buildings with many occupants need to resist a disproportional collapse in case of unexpected exposures, e.g. accidents or terrorism. Structural robustness can improve the collapse resistance of a building. The literature about robustness is comprehensive concerning concrete and steel buildings, but it is rather limited regarding timber.

    A robust building can mobilise alternative load paths in the structure after the removal of bearing building components. Alternative load paths rely primarily on the connections between components. For timber buildings, few investigations exist to evaluate the alternative load paths after a removal. Analyses usually do not take into account non-linear effects which could influence the capacity of alternative load paths, such as damage of single fasteners, friction,  timber crushing and brittle failure. In particular, the alternative load paths in platform-framed cross-laminated timber buildings are not well understood.

     The goals of this thesis are to i) review the concept of robustness in general and determine the state of the art concerning timber buildings in particular, ii) develop a method to analyse the alternative load paths in a platform-framed CLT building taking into account relevant non-linearities, iii) use the method to elicit the alternative load paths in a building after a wall removal, and iv) study the effects of probabilistic variations of model parameters.

     The thesis first introduces tall timber buildings and then presents a summary of structural robustness in a collapse resistance framework. The summary includes established analysis methods and specific considerations for timber, whereof a detailed review is provided in Paper I. Paper III additionally provides results of a survey on contemporary practices of professionals around the world concerning robustness.

     In the subsequent chapter, the studied 8-storey case building made of platform-framed cross-laminated timber is described including the modelling abstractions. Additionally, the setup of a validation experiment for the modelling approach is described. The following chapter introduces the modelling approach for an alternative load path analysis after a wall removal. The approach is based on the finite element method using the commercial software Abaqus. The deterministic part of the approach includes a non-linear static pushdown analysis of single storeys in a bay and elicits the alternative load paths and their capacity. Finite connector elements in the model substitute single fasteners including their elastic, plastic, damage and rupture behaviour. The 3D models of the walls and floors account for timber crushing, brittle failure and contact friction. A simplified non-linear dynamic model of the entire bay uses the pushdown results as inputs and evaluates the collapse progression among storeys after a sudden element removal. The probabilistic part of the approach models the uncertainty of the input parameters of the dynamic model by varying the parameter values in a Monte Carlo simulation, to evaluate the probability of a collapse.

     Paper II applies the approach for a simple pushdown of a single storey and Paper IV applies the pushdown and the dynamic analysis to elicit the alternative load paths after a single wall removal. The thesis shows furthermore the results of a double wall removal in the example building and the results of the Monte Carlo analysis for the single and double wall removal.

     For the assumed removals, the developed approach could identify the alternative load paths, determine their capacities and estimate the probability of a collapse under probabilistic variations. The approach might be used to classify various removal scenarios in platform-framed multi-storey cross-laminated timber buildings specifically and predetermine design solutions which could provide a desired level of robustness. The approach might be generalised for multi-storey timber buildings of various construction types.

  • 20.
    Olofsson, Linus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Broman, Olof
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Skog, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Fredriksson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Multivariate product adapted grading of Scots pine sawn timber for an industrial customer, part 1: Method development2019Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rule-based automatic grading (RBAG) of sawn timber is a common type of sorting system used in sawmills, which is intricate to customise for specific customers. This study further develops an automatic grading method to grade sawn timber according to a customer’s resulting product quality. A sawmill’s automatic sorting system used cameras to scan the 308 planks included in the study. Each plank was split at a planing mill into three boards, each planed, milled, and manually graded as desirable or not. The plank grade was correlated by multivariate partial least squares regression to aggregated variables, created from the sorting system’s measurements at the sawmill. Grading models were trained and tested independently using 5-fold cross-validation to evaluate the grading accuracy of the holistic-subjective automatic grading (HSAG), and compared with a resubstitution test. Results showed that using the HSAG method at the sawmill graded on average 74% of planks correctly, while 83% of desirable planks were correctly identified. Results implied that a sawmill sorting station could grade planks according to a customer’s product quality grade with similar accuracy to HSAG conforming with manual grading of standardised sorting classes, even when the customer is processing the planks further.

  • 21.
    Olofsson, Linus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Broman, Olof
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Skog, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Fredriksson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Multivariate Product Adapted Grading of Scots Pine Sawn Timber for an Industrial Customer, Part 2: Robustness to Disturbances2019Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Holistic-subjective automatic grading (HSAG) of sawn timber by an industrial customer's product outcome is possible through the use of multivariate partial least squares discriminant analysis (PLS-DA), shown by part one of this two-part study. This second part of the study aimed at testing the robustness to disturbances of such an HSAG system when grading Scots Pine sawn timber partially covered in dust. The set of 308 clean planks from part one of this study, and a set of 310 dusty planks, that by being stored inside a sawmill accumulated a layer of dust, were used. Cameras scanned each plank in a sawmill's automatic sorting system that detected selected feature variables. The planks were then split and processed at a planing mill, and the product grade was correlated to the measured feature variables by partial least squares regression. Prediction models were tested using 5-fold cross-validation in four tests and compared to the reference result of part one of this study. The tests showed that the product adapted HSAG could grade dusty planks with similar or lower grading accuracy compared to grading clean planks. In tests grading dusty planks, the disturbing effect of the dust was difficult to capture through training.

  • 22.
    Turesson, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Björnfot, Anders
    Department of Manufacturing and Civil Engineering, Faculty of EngineeringNorwegian University of Science and TechnologyGjøvikNorway.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Tomasi, Roberto
    Faculty of Science and Technology, Division of Buildings, Architecture, and Environmental EngineeringNorwegian University of Life SciencesÅsNorway.
    Picture frame and diagonal compression testing of cross-laminated timber2019Ingår i: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 52, nr 4, artikel-id 66Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Currently, no appropriate standard exists that describes how to determine the in-plane shear stiffness for cross-laminated timber (CLT) panels, meaning that, there is a lack of appropriate and reliable test methods. In this paper, two gross shear test methods are evaluated: a picture frame test and a diagonal compression test, which are intended to measure the shear stiffness of a whole CLT panel. This evaluation aimed to compare the shear modulus, the amount of compression/tension in the diagonal directions of the panels and the deformations of both sides of the panels. The picture frame test and diagonal compression test provides a bi- and uniaxial pre-stress, respectively. A total of 30 non-edge glued CLT panels were tested, 17 3-layer and 13 5-layer panels. The shear modulus for the 3- and 5-layer non-edge-glued panels were measured as 418 and 466 MPa, respectively, in the picture frame test. In the diagonal compression test, the shear modulus was measured to substantially higher values of 530 and 626 MPa for the 3- and 5-layer panels, respectively. In the picture frame test, panels were equally stretched along one of the diagonals as they were compressed along the other diagonal, which was not the case for panels in the diagonal compression test. The test results also showed that measuring only one side incurs a risk of over- or under-estimating the in-plane shear modulus. Compared with results from the literature, the picture frame test seems to be a more reliable test method than the diagonal compression test.

  • 23.
    Gaff, Milan
    et al.
    Czech University of Life Sciences Prague (CULS).
    Babiak, Marián
    Czech University of Life Sciences Prague (CULS).
    Kačík, František
    Czech University of Life Sciences Prague (CULS), Technical University in Zvolen.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Turčan, Marek
    Czech University of Life Sciences Prague (CULS).
    Hanzlíka, Peter
    Czech University of Life Sciences Prague (CULS).
    Vondrová, Veronika
    Czech University of Life Sciences Prague (CULS).
    Plasticity properties of thermally modified timber in bending: the effect of chemical changes during modification of European oak and Norway spruce.2019Ingår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 165, s. 613-625Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The plasticity of thermally modified European oak (Quercus robur L.) and f thermally modified Norway spruce (Picea abies Karst. (L.)) timber was evaluated in bending, and the plastic properties were related to the changes in chemical composition of the wood after modification. The objective was to gain new knowledge about the properties of materials in the plastic region of the force-deformation diagram in bending. A new software was developed (MATESS) and used to identify important characteristics of the material. This software eliminates shortcomings in current standards, such as simplifications in the evaluation of data when sufficiently sensitive measuring equipment is not available. The characteristics studied were: modulus of rupture (MOR), plastic potential (PP) chord modulus (CHM), the moduli of plasticity (EE), and the moduli of plasticity (EMV, EP). Extractives, lignin, cellulose, holocellulose, and hemicelluloses were analysed chemically to reveal the patterns that occur during the loading of the specimens. Thermal modification has different effects on the mechanical properties of oak and spruce, especially on CHM, EMV and EP, due to their different contents and structures of their chemical components. A strong correlation (r > 0.90) between hemicellulose content and MOR and Pp values was found for both species. The coefficients of determination indicated a very low dependence (r2 < 0.1) of MOR, PP, CHM, EE, EMV and EP, on the average density.

  • 24.
    Couceiro, José
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Lindgren, Owe
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Hansson, Lars
    Department of Ocean Operations and Civil Engineering, Norwegian University of Science and Technology (NTNU), Ålesund, Norway.
    Söderström, Ove
    c Professor Emeritus of Building Materials, Stockholm, Sweden.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Real-time wood moisture-content determination using dual-energy X-ray computed tomography scanning2019Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The estimation of the pixel-wise distribution of the moisture content (MC) in wood using X-ray computed tomography (CT) requires two scans of the same wood specimen at different MCs, one of which is known. Image-processing algorithms are needed to compensate for the anisotropic distortion that wood undergoes as it dries. An alternative technique based on dual-energy CT (DECT) to determine MC in wood has been suggested by several authors. The purpose of the present study was to evaluate the hypothesis that DECT can be used for the determination of MC in real time. A method based on the use of the quotient between the linear attenuation coefficients (μ) at different acceleration voltages (the so-called quotient method) was used. A statistical model was created to estimate the MC in solid sapwood of Scots pine, Norway spruce and brittle willow. The results show a regression model with R2 > 0.97 that can predict the MC in these species with a RMSE of prediction of 0.07, 0.04 and 0.11 (MC in decimal format) respectively and at MC levels ranging from the green to the totally dry condition. Individual measurements of MC show an uncertainty of up to ±0.4. It is concluded that under the conditions prevailing in this study, and in studies referred to in this paper, it is not possible to measure MC with DECT.

  • 25.
    Huber, Johannes Albert Josef
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Simulation of Alternative Load Paths After a Wall Removal in a Platform-Framed Cross-Laminated Timber Building2019Ingår i: CompWood 2019 Book of Abstracts / [ed] Tomas K. Bader, Josef Füssl, Anders Olsson, 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    An increasing number of multi-storey timber buildings use cross-laminated timber (CLT) for their bearing structure. Platform-framed CLT buildings consist of vertical repetitions of floors resting upon one-storey tall walls, squeezing-in the floor panels between the walls. Tall buildings need to be structurally robust because many lives would be at stake in case of a disproportionate collapse. Robustness is the ability of a system to survive the loss of components. For collapse resistance, it poses the last line of defence, after an unforeseen exposure (e.g. accident, terrorism) has already occurred and after the exposed components could not resist failure. A robust building offers alternative load paths (ALPs) which come into action when a part of the bearing structure has been removed [1].

    Many alternative load path analyses (ALPA) have been conducted for tall concrete and steel buildings using the finite element method (FEM), but for timber, ALPA are still scarce. ALPs depend on the behaviour of the connections after a loss [1]. Studies on timber so far have accounted for connections in a simplified manner by lumping their aggregate behaviour into single points. Our goal is to elicit the ALPs after a wall removal in a platform-framed CLT building, study their development and quantify their capacity, to determine whether they can prevent a collapse.

    We investigated a corner bay of an 8-storey platform-framed CLT building (see Figure 1) and removed a wall at the bottom storey. We studied the ALPs of each storey by pushing down the walls above the gap in a non-linear quasi-static analysis in the FE software Abaqus. We accounted for contact and friction, considered plastic timber crushing, and accounted for brittle cracking in the panels. We modelled single fasteners with connector elements which simulated the elastic, plastic, damage and rupture behaviour. We recorded the force-displacement curves, i.e. pushdown curves, for each storey and used them to conduct a dynamic analysis of the entire bay in a simplified model, as suggested by [2].

    The results show that the structure could engage the following ALPs after a wall removal: I) arching action in the outer floor panels, II) arching action of the walls, III) quasi-catenary action in the floor panels, and IV) hanging action from the roof panels. The ALPs were limited by various parameters, but they sufficed to resist a collapse of the bay. We observed that the inter-storey stiffness influenced the load-sharing among storeys, which affected the structural robustness. In the compressed connections, friction, and not the fasteners, transferred most of the horizontal loads. Future research should test the squeezed-in platform joint experimentally, to quantify its capacity for transverse shear loads. We also advise to assess the inter-storey stiffness to estimate the capacity for load-sharing among storeys.

  • 26.
    Johansson, Marie
    RISE.
    Olsson, Jörgen
    RISE.
    Ylmén, Peter
    RISE.
    Nord, Tomas
    Linköpings Universitet.
    Dorn, Michael
    Linneuniversitet.
    Frühwald Hansson, Eva
    Lunds Universitet.
    Serrano, Erik
    Lund Universitet.
    Broman, Olof
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Jonsson, Gustav
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Brännström, Mattias
    Renewinn.
    Slutrapport: Framtidens biobaserade byggande och boende.2019Rapport (Övrigt vetenskapligt)
  • 27.
    Huber, Johannes Albert Josef
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Structural robustness and timber buildings: a review2019Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, nr 2, s. 107-128Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Timber buildings are increasing in their dimensions. Structural robustness is imperative for all buildings and specifically important for tall buildings. Lives can be saved if disproportionate collapse can be avoided after a catastrophic event (e.g. accident, terrorism). The literature about robustness is comprehensive concerning concrete and steel buildings, but is rather limited regarding timber. This paper reviews robustness in general and robustness of timber buildings in particular. Robustness is an intrinsic structural property, enhancing global tolerance to local failures, regardless of the cause. A deterministic approach to assess robustness is to remove certain load-bearing elements from the structure and compare the consequences to given limits. Design methods for robustness may be direct by assessing effects of local failure, or indirect by following guidelines. For robust timber buildings, the connections are the key aspects. Usually, metal connectors may provide the required joint ductility. For robust light timber-frame construction, rim beams may be designed. For timber posts and beams and cross laminated timber, guidance regarding robustness is scarce, but in some aspects they seem to be similar to steel frames and precast concrete. Future research should assess the capacity of connections, and evaluate the adequacy of seismic connectors for robust timber buildings.

  • 28.
    Neyses, Benedikt
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Surface Densification of Solid Wood: Paving the Way Towards Industrial Implementation2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Surface densification of a piece of solid wood results in an increase in density and in hardness in the whole or a part of the densified material, and is one of the ways of improving the properties and value of low-density wood species. Despite efforts for many years, mass commercialisation of either bulk- or surface-densified wood products has not yet been achieved. Most of the previously tested densification methods have limitations in terms of processing speed and integration into the largely continuous wood processing chain, which leads to high production costs. Established methods to eliminate the set-recovery rely either on technologically complex close-system methods or on open-system methods that require relatively long periods of high energy input. For this reason, impregnation with adhesives is used in almost all commercially available densified wood products, and none of them have risen above their status of being niche products.

    Based on this background, three objectives for this project were formulated: (1) the development of a method for selecting the most suitable wood species for surface densification, (2) showing that surface densification can be carried out in a continuous manner at high process speeds, (3) and researching a fast open-system method to reduce the set- recovery.

    The method developed for selecting the most suitable wood species for surface densification was based on Lean principles, and it confirmed the suitability of previously studied wood species, such as Scots pine, spruce and poplar. In addition, several suitable alternatives from different parts of the world and from different types of forest were identified. This suggests a high potential for establishing such wood products on a global market level.

    Two studies using a continuous roller press showed that solid wood can be successfully surface-densified at process speeds of up to 80 m min-1, and that some defects, such as knots, are acceptable in the raw material, but the problem of set-recovery could not however be solved.

    A screening experiment testing different open-system approaches to reduce the set-recovery highlighted the potential of a novel method using ionic liquids as a plasticiser prior to the surface densification of solid Scots pine. The set-recovery could be reduced to 10%, with the time of high energy input being less than 10 minutes. The Brinell hardness was increased by a factor of 2.7 over that of undensified wood. A study with thermo-gravimetric analysis and digital image correlation showed that the set-recovery almost exclusively happens in the transition zone between the densified and undensified wood cells, where there is less penetration of the ionic liquids.

    The work accomplished in this project has successfully addressed several gaps in the field of wood densification, firstly, by employing a continuous surface densification process using a roller press, and secondly, by developing and studying a fast open-system pre-treatment with ionic liquids, which greatly reduces the set-recovery. Research will continue on a new band press, facilitating a swift transfer of knowledge between small- scale studies and the continuous surface densification of production-size wooden boards.

  • 29.
    Garskaite, Edita
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Karlsson, Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Stankeviciute, Zivile
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Aivaras, Kareiva
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Jones, Dennis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Surface hardness and flammability of Na2SiO3 andnano-TiO2 reinforced wood composites2019Ingår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, nr 48, s. 27973-27986Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this study was to explore an effect of the combined inorganic materials on the wood hardness and flame-retardancy properties in a concept of sustainable material management. Herein, the reinforcement of Scots pine (Pinus sylvestris L.) sapwood with sodium silicate and TiO2 nanoparticles via vacuum-pressure technique is reported. Pyrolysis of modified wood was studied by TG-FTIR analysis; the results showed that maximum weight loss for the modified wood was obtained at 40–50 °C lower temperatures compared to the reference untreated wood. The Gram–Schmidt profiles and spectra extracted at maxima absorption from Gram–Schmidt plots indicated chemical changes in wood–inorganic composites. SEM/EDS analysis revealed the presence of Na–O–Si solid gel within the wood-cell lumen and showed that TiO2 was homogeneously distributed within the amorphous Na–O–Si glass-forming phase to form a thin surface coating. EDS mapping further revealed the higher diffusivity of sodium into the cell wall compared to the silicon compound. The presence of amorphous sodium silicate and nano-TiO2 was additionally confirmed by XRD analysis. FTIR spectra confirmed the chemical changes in Scots pine sapwood induced by alkalization. Brinell hardness test showed that the hardness of the modified wood increased with the highest value (44% increase in hardness) obtained for 10% Na2SiO3–nTiO2 modified wood. The results showed good correlation between TG and flammability test; limiting oxygen index (LOI) values for the wood–inorganic composites increased by 9–14% compared to the untreated wood.

  • 30.
    Mpidi Bita, Hercend
    et al.
    Wood Science, University of British Columbia, Canada.
    Huber, Johannes Albert Josef
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Voulpiotis, Konstantinos
    Institute of Structural Engineering, ETH Zurich, Switzerland.
    Tannert, Thomas
    Wood Engineering, University of Northern British Columbia, Canada.
    Survey of contemporary practices for disproportionate collapse prevention2019Ingår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 199, artikel-id 109578Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper summarises contemporary practices and implementations of the existing codes and guidelines with respect to disproportionate collapse prevention. Here, focus is given to structural robustness, defined as the ideal method to decrease the probability of disproportionate collapse in buildings following an initial damage. The results from a global survey with 171 participants (mainly structural engineers) are presented. By comparing practices applied to different structural materials (steel, concrete and timber) and in different regions (Canada, USA, Europe, Australia/New Zealand), areas of improvements for the existing codes and guidelines as well as further research are identified. The results emphasise the importance of including specific recommendations for structural robustness in building codes, applicable to high importance and high occupancy structures. A performance-based approach is preferable, rather than prescriptive requirements, for practical and economic solutions. In addition, the obtained responses highlight the need to further develop the existing indirect and direct methods for disproportionate collapse prevention and structural robustness to include material-specific considerations.

  • 31.
    Sehlstedt-Persson, Margot
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Vikberg, Tommy
    RISE.
    Scheepers, Gerhard
    RISE.
    Temperaturdifferens ”ΔT” mellan virkesyta och luft under pågående torkning som möjlig styrparameter i virkestorkning.: Mätningar i labb och industriskala.2019Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Målsättningen med denna studie har varit att utvärdera frågeställningen om tempe­ratur­differensen mellan lufttemperatur och virkesyta (ΔT), kan användas adaptivt i en FB kanal för att detektera övergång från torkning i kapillär till diffusionsfas. Man eftersträvar att så mycket kapillärt vatten som möjligt ska avgå i zon 1 innan virket går in i zon 2 för att inte fuktkvoten ska bli för hög i uttagsänden.

    Inledningsvis utfördes ett antal grundläggande försök i labbmiljö följt av en mer omfattande mätning i industriskala vid J-G Anderssons i Linneryd. Vid Linneryds­försöket gjorde även termografimätningar. Slutligen gjordes ett långtidsförsök vid Norra Timbers anläggning i Kåge med beröringsfri IR-sensor för mätning av yttemperatur på långsidorna av passerande virkestaplar.

    Slutsatser av grundläggande försök i CT-lab

    Utvärderingen av försök på enbitsnivå pekar mot att ΔT signalen har god potential att kunna användas för att detektera när fibermättnad nås i virket. I kanaler med stora virkeslaster med varierande fuktinnehåll måste dock yttemperaturmätningar göras på medelvärden av större ytor. Nästa steg var industriella mätningar i kanal där dock ingen kontinuerlig fukt­kvots­bestäm­ning var möjlig att göra.

    Slutsatser av industrimätningar i Linneryd

    Mätningar av virkets yttemperatur, lokalt torkklimat, lufthastighet, fuktkvot och ΔT i prover placerade i olika positioner i en virkesstapel med 22x100 mm granbräder under torkning i en 2 zons FB kanal, visar överensstämmande resultat.  Nivåerna på ΔT i nedblåsningsschaktet visar tydligt om proven var kvar i kapillärfas eller inte. Höga nivåer på ΔT som i centrala de­lar­na av paketen i höjdled  innebär att proverna fortfa­rande var i kapillärfas. Låga nivåer på  ΔT, som på kanterna av mittpaketet, innebär att kapillär­fasen har passerats. I positioner där slutfuktkvot blev  betydligt högre än målfuktkvot (centrum i toppaket) var ΔT nivån hög i ned­blås­ningsschaktet. Detta virke skulle med fördel ha haft längre tid i zon 1. Virket på kan­terna var redo för övergång till zon 2. I praktiken görs dock naturligtvis drag­ningar för en hel stapel i taget.

     

    Termografibilderna ger en ögonblicksbild av torkningsläget i en virkelast och har potential att vara ett komplement till befintliga mätmetoder. Industrimätningarna visar att det är möjligt att ta bra värmebilder i nedblåsningsschaktet i en FB kanal. Att ha en permanent värmekamera i nedblåsningsschaktet ställer dock krav på kylning av kameran som inte klarar höga tempe­raturer.

    Slutsatser från långtidsförsök vid Norra Timbers anläggning i Kåge

    Två pyrometrar riktade att mäta yttemperatur på de två översta paketen på passerande vagnar installerades i en gångdörr vid nedblåsningsschaktet i en FB kanal. Beräknat ΔT tycks kunna utgöra värdefull processdata för att styra torkens dragningstid.

    Yttemperaturmätningar med pyrometer är en relativt robust metod som fungerar bra i en virkestork. Ingen rengöring behövdes under de fyra månaderna som mätningen pågick.

  • 32.
    Gaff, Milan
    et al.
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague,Suchdol, Czech Republic.
    Kačík, František
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague,Suchdol, Czech Republic.Department of Chemistry and Chemical Technologies, Faculty of Wood Sciences and Technology, Technical University in Zvolen, Zvolen, Slovakia.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague,Suchdol, Czech Republic.
    Babiak, Marián
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague,Suchdol, Czech Republic.
    Turčani, Marek
    Department of Forest Protection and Entomology, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Suchdol, Czech Republic.
    Niemz, Peter
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague,Suchdol, Czech Republic.
    Hanzlík, Peter
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague,Suchdol, Czech Republic.
    The effect of chemical changes during thermal modification of European oak and Norway spruce on elasticity properties2019Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 220, s. 529-538Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The elasticity in bending of European oak (Quercus robur L.) and Norway spruce (Picea abies (L.) Karst.) timber was evaluated before and after thermal modificationand related to the changes in chemical composition of the wood as a result of the modification. A new software was developed (MATESS) and used to identify characteristic points on the force-deformation diagram. The modulus of elasticity(MOE), stress at the limit of proportionality (LOP) and elastic potential (PE) were used to describe the wood properties. Extractives, lignin, cellulose, holocellulose, and hemicelluloses were analysed to reveal the patterns that occur during the loading of the specimens. Thermal modification lowers the mechanical properties (MOE, LOP and PE) of oak and spruce wood, and the reduction increases with increasing modification temperature. Changes in chemical composition of thermally modified wood show a strong relationship to the reduction in elasticity properties for bot species.

  • 33.
    Gaff, Milan
    et al.
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic.
    Kačík, František
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic;Department of Chemistry and Chemical Technologies, Faculty of Wood Sciences and Technology, Technical University in Zvolen, Zvolen, Slovakia.
    Gašparík, Miroslav
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic.
    Todaro, Luigi
    School of Agricultural, Forestry, Food and Environmental Sciences, University of Basilicata, Potenza, Italy.
    Jones, Dennis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Corleto, Roberto
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic;School of Agricultural, Forestry, Food and Environmental Sciences, University of Basilicata, Potenza, Italy.
    Makovická Osvaldová, Linda
    Department of Fire Engineering, Faculty of Security Engineering, University of Žilina, Žilina, Slovakia.
    Čekovská, Hana
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic.
    The effect of synthetic and natural fire-retardants on burning and chemical characteristics of thermally modified teak (Tectona grandis L. f.) wood2019Ingår i: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 200, s. 551-558Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article deals with the effect of various temperatures of thermal modification and fire retardants on selected burning characteristics and chemical wood components of teak (Tectona grandis L. f.) wood. The thermal modification was carried out at temperatures 160 °C, 180 °C and 210 °C. Subsequently, thermally modified wood was treated by natural (arabinogalactan) and synthetic (ammonium phosphate) fire retardants. The effect of thermal modification as well as fire retardant was detected by burning characteristics such as weight loss, burning rate, maximum burning rate, ratio of the maximum burning rate and time to reach maximum burning rate. The chemical changes caused by the influence of these factors were determined by changing the content of cellulose, hemicelluloses, holocellulose, lignin and extractives. The relationship between burning characteristics and chemical changes in the thermally modified wood was analyzed using Spearman’s correlation. The results showed that the thermal modification of teak wood had a negative effect on its ignition and burning properties. Synthetic fire retardant had the highest retardation effect in all cases. The natural fire retardant caused a better retardation effect on thermally modified wood at temperature 180 and 210 °C. The relative content of lignin, extractives and cellulose increased, while the amount of holocellulose and particularly hemicelluloses decreased.

  • 34.
    Vikberg, Tommy
    et al.
    RISE.
    Sehlstedt-Persson, Margot
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Tryckfall över värmebatteri i virkestork: resultat av tre års mätningar. Slutrapport.2019Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Möjligheterna att utföra behovsstyrt underhåll på virkestorkar istället för enligt ett underhållschema vore önskvärt. En av underhållsåtgärderna som är svåra att schemalägga i tiden är rengöring av värmebatterierna eftersom graden av nedsmutsning i stor del beror på råvaran, utomhusklimatet och sågutrustningen. I detta projekt mättes det statiska tryckfallet över värmebatteriet i 1:a-zon i en två zons kanaltork. Mätningen pågick under tre års tid och målet var att få till stånd en mätning som indikerar när det är dags att rengöra värmebatteriet. Projektets slutsatser är:

    • Det är möjligt att mäta graden av spånpålimning på värmebatterierna genom att mäta tryckfallet över värmebatteriet.
    • Tryckfallsmätning kan tjäna som indikator för när det är lämpligt att rengöra värmebatteriet.
  • 35.
    Markström, Emillia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Kuzman, Manja Kitek
    Biotechnical Faculty, Wood Science and Technology, University of Ljubljana, Ljubljana, Slovenija.
    Bystedt, Anders
    RISE Bioeconomy, RISE Research Institutes of Sweden, Skellefteå, Sweden.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. Department of Wood Processing and Biomaterials, Czech Universty of Life Sciences Prague, Suchdol, Czech Republic.
    Use of wood products in multi-storey residential buildings: views of Swedish actors and suggested measures for an increased use2019Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many studies have shown that wooden buildings in general have a lower climate impact than buildings built of conventional materials such as concrete and steel. In Sweden, however, only about 10% of the multi-dwelling buildings are built with timber frames. The goal of this empirical study is to provide a broad picture of the views of Swedish actors regarding the use of wood products in multi-storey residential buildings and suggest measures for an increased use. A questionnaire concerning the use of wood products in construction was sent out to Swedish developers, main contractors, and architects and 100 answers were received. The study shows that the views of the groups of actors differ in some respects and factors that may either facilitate or be obstacles to an increased use of wood products were identified and discussed.

  • 36.
    Sehlstedt-Persson, Margot
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Vikberg, Tommy
    RISE.
    Utveckling av industriell virkestorkning: Slutrapport2019Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Projektet har behandlat ett antal delstudier kopplat till virkestorkning inom följande områden : ADAPTIVITET, FUKT­DYNAMIK och TORKNINGSKVALITET. Projektet har bidragit till att steg har tagits mot målet att uppnå en mer självstyrande och automatiserad torkningsprocess, en mer optimerad och energieffektiv torkningsprocess samt bättre och jämnare torkningskvalitet som samman­taget minskar torkkostnader genom att:

    ADAPTIVITET identifiera olika mättekniska- och återkopplade signaler som kan användas i simulatorer och styrsystem: ”ΔT” principens möjlighet att adaptivt förlänga dragtider i en FB-kanal, termograferingens diagnostiska möjlighet att få en momentan överblick över rumslig fukt­kvots­spridning i en torkande virkeslast samt difftrycksmätningens potential att signalera rengöringsbehov för att undvika försämrad lufthastighet och värmeöverföring i en kanal.

    FUKTDYNAMIK öka förståelsen för virkets fuktdynamik genom att i tomografstudier visa på möjligheten att optimera diffusionsdriven jämviktskonditionering vid olika fuktkvotsnivåer och på så sätt effektivisera tid och energianvändning i torkar. Fuktförändringar under pågående kondi­tio­nering har aldrig tidigare studerats i tomograf.

    i tomografstudier visa hur övergången mellan kapillär och diffusionsfas genom  ΔT tydligt kan identifieras

    genom CT-studier ge ökad förståelse och förbättrat underlag för fuktdynamisk modellering i kapillär och diffusionsfas.

    TORKNINGSKVALITET förbättra torkningskvalitet genom bättre målfuktkvotsträff och mindre fuktkvotsspridning genom de ovan nämnda adaptiva metodernas potential.

    visa att en kombination av torkning med efterföljande hyvling och behandling med mögel­hämmare kan åstadkomma en produktgrupp av splintvedsbrädor av furu, contorta och gran med god och likvärdig mögelbeständighet.

    Studierna som avrapporteras övergripande i denna rapport har utförts inom delprojekt 3 inom ramen för projektet ”TiiN, TräInnovation i Norr”.

    Samtliga delstudier avrapporteras separat i följande TCN- rapporter.

    TCN-rapport: Temperaturdifferens ”ΔT” mellan virkesyta och luft under pågående torkning som möjlig styrparameter i virkestorkning. Mätningar i labb och industriskala. Margot Sehlstedt-Persson, LTU, Tommy Vikberg, RISE, Gerhard Scheepers, RISE.

     

    TCN-rapport: Värmekameramätningar i virkestorkar. Gerhard Scheepers, RISE.

     

    TCN-rapport: Mögeltest av torkade furu, gran och contorta bräder: Sammanfattning av “Mould susceptibility of dried boards of Contorta pine, Scots pine and Norway spruce A comparative study” Faksawat Poohphajai, februari 2018. Margot Sehlstedt-Persson, LTU.

     

    TCN-rapport: Konditionering av virke vid olika fuktkvoter – studier i tomograf. Margot Sehlstedt-Persson, Lars Hansson, José Couceiro samtliga LTU, Tommy Vikberg RISE.

     

    TCN-rapport: Tryckfall över värmebatteri i virkestork - resultat av tre års mätningar. Tommy Vikberg, RISE och Margot Sehlstedt-Persson, LTU. 

  • 37.
    Scheepers, Gerhard
    RISE.
    Värmekameramätningar i virkestorkar: Förstudie2019Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Det är möjligt att ta bra värmebilder i en virkestork. Värmebilderna ger en mer komplett uppfattning om torkningsläget. En förutsättning är dock att fönstret har hunnit värma upp och håller en temperatur högre än daggpunkt för att undvika kondens.

    Kärnved och splint är lätt att identifiera på färskt virke. Variationer över en stapel syns och ytfuktkvot kan uppskattas. Mängden information som värmebilderna förmedlar gör det möjligt att studera ytfuktvariationer inom en bräda eller planka, variationer mellan bräder, variationer mellan paket, processpecifika effekter (t.ex. reverseringar), osv. Med långvariga mätningar i en kammartork skulle även fuktkvotsutvecklingen över tid i olika positioner i stapeln kunna studeras.

    Slutsatsen är att värmekameran är ett bra komplement till befintliga mätmetoder som fördelaktigt kan användas ihop med t.ex. provbitar, som kan agera som referenspunkter i värmebilden.

  • 38.
    Raudoniene, Jolanta
    et al.
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Skaudzius, Ramunas
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Zarkov, Aleksej
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Selskis, Algirdas
    Center for Physical Sciences and Technology, Vilnius, Lithuania.
    Karlsson, Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Kareiva, Aivaras
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Garskaite, Edita
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Wet-chemistry synthesis of shape-controlled Ag3PO4 crystals and their 3D surface reconstruction from SEM imagery2019Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 345, s. 26-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simple chemical solution-based synthesis route has been developed to prepare uniform and shape-controllable Ag3PO4 crystals. Tetrapod- and cube-shaped crystals having a size of about 9–10 μm were prepared from AgNO3 and NH4H2PO4 precursors, and pseudo-octahedral (equiaxial) crystals were prepared from AgNO3 and (NH4)2HPO4. TEM analysis revealed Ag3PO4 crystals to be electron beam sensitive materials, which under a voltage of 200 kV decompose to the metallic Ag, thereby demonstrating the difficulty in determining crystal facets and structural defects using conventional electron diffraction studies. UV–Vis diffuse reflectance spectroscopy was used to study the correlation between structural and optical properties of surfaces of Ag3PO4 crystals. Furthermore, a spatial 3-dimentional (3D) reconstruction of Ag3PO4 surface structures was performed from SEM images. The reconstruction produced realistic 3D mesh models, insomuch that the 3D reconstructed structures provided extra information about the examined crystals. Results suggested that the proposed synthesis route and performed spatial reconstruction of Ag3PO4 had the potential for simulating processing conditions to produce various microcrystals and explore material surface structures and reconstruction of microstructures.

  • 39.
    Couceiro, José
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    X-ray computed tomography to study moisture distribution in wood2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    X-ray computed tomography (CT) has been used as an analysing tool for different features in wood research since the beginning of the1980s, but it can also be used to study wood-water interactions in different ways, such as by determining wood moisture content (MC). The determination of wood MC with CT requires two CT images: one at the unknown moisture distribution and a second one at a known reference MC level, usually at oven-dry condition. The two scans are then compared, and the MC is calculated based on the differences between the images. If the goal is to determine the MC in local regions within the wood volume, e.g. when studying moisture gradients in wood drying, wood shrinkage must be taken into account during the data processing of the images. The anisotropy of wood shrinkage creates an obstacle, however, since the shrinkage is not uniform throughout the wood specimen. The technique is thus limited in two ways: it cannot measure MC in local regions and it cannot do it in real time.

    The objective of this thesis was to study methods to overcome these two limitations. The work explores up to three different methods to estimate local MC from CT images in real time. The first method determines shrinkage for each pixel using digital image correlation (DIC) and is embedded in a broader method to estimate the MC, which verified against a reference. It involves several steps in different pieces of software, making it time-consuming and creating many sources of possible experimental errors. The determination of shrinkage within this method is further explored to enable the implementation of all steps in a unique piece of software. It is shown that it is possible to calculate MC through this method with a root mean square error of prediction of 1.4 percentage points for MC between 6 and 25%.

    The second method studied succeeds in determining the MC distribution in research applied to wood drying, but the calculation of shrinkage differs from the previous method: instead of calculating shrinkage in the radial and tangential directions, it does so by using the displacement information generated from the spatial alignment of the CT images. Results show that the algorithm can provide consistent data of internal MC distribution of wood at the pixel level that entail continuing researching wood drying processes with an improvement in the accuracy of the MC determination. It represents an improvement regarding the first method because the calculation is fast and highly automatized in a single piece of software.

    The third method studied is the application of dual energy CT (DECT) to moisture. DECT would provide means for MC calculation at the pixel level and, potentially, in real time, which would mean an important breakthrough in wood drying research. Previous research shows promising results, but its implementation in medical CT, the tool used throughout this work, has shown poor predicting ability. Nevertheless, further research is encouraged.

    The work done in this thesis proves that it is possible to measure local distribution of MC in wood using CT with accuracy and precision. It also shows that further research could potentially provide a means for MC estimation in real time.

  • 40.
    Huber, Johannes Albert Josef
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    A Review of Structural Robustness with Focus on Timber Buildings2018Ingår i: 40th IABSE Symposium: Tomorrow’s Megastructures, International Association for Bridge and Structural Engineering (IABSE) , 2018, artikel-id S32-17Konferensbidrag (Refereegranskat)
    Abstract [en]

    With an increasing number of storeys, timber buildings require closer attention to structuralrobustness. If a building can survive unforeseen events (e.g. accidents, terrorism), lives can be saved.The literature appears to be rather limited concerning robustness of timber buildings. This paperaims to give a brief review on robustness in general and design guidelines for timber in specific. Theresults indicate that connection design is a key aspect for robustness. Like in seismic design, by usingthe ductile capacity of connectors, the brittleness of timber can be controlled. For light timber-framebuildings, more guidelines exist than for posts and beams and cross-laminated timber, which bothseem to be similar to steel frames and precast concrete respectively regarding robustness.

  • 41.
    Jones, Dennis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Kutnar, Andreja
    University of Primorska, Andrej Marušič Institute, Muzejski trg 2; SI-6000 Koper, Slovenia.
    A review of wood modification across Europe as part of COST FP14072018Ingår i: Proceedings of ECWM9 - The 9th European Conference on Wood Modification / [ed] Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz, Brigitte Junge and Jos Gootjes, Arnhem: SHR B.V. Nieuwe Kanaal 9b 6709 PA Wageningen , 2018, s. 24-31Konferensbidrag (Refereegranskat)
  • 42.
    Atashipour, Seyed Rasoul
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. Department of Architecture and Civil Engineering, Division of Structural Engineering, Chalmers University of Technology.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Challamel, Noël
    Université de Bretagne Sud, UBS – Institut Dupuy de Lôme, Centre de Recherche.
    A weak shear web model for deflection analysis of deep composite box-type beams2018Ingår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 155, s. 36-49Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Deep box-type beams, consisting of framing members and sheathings, are sensitive to shear deformations and hence appropriate refined theories or complicated magnification factors are needed to be used to obtain accurate results. For sheathings or webs between the framing members that are weak in shear, additional shear deformations occur corresponding to the relative axial displacement between the framing members. These sandwich-type or partial interaction-type of in-plane shear behaviour between the framing members, needs to be taken into account, especially when the web shear stiffness is very low. The composite box-type beam treated here is composed of three framing members with sheathings on both sides. To incorporate effects of the sheathings shear deformations between the framing members on the deflection, the sheathings, here called web interlayers, are modelled as shear media with equivalent slip moduli corresponding to a partially interacting composite beam model. Governing equilibrium equations of the model are obtained using the minimum total potential energy principle and solved explicitly. The obtained results are compared with those based on different conventional beam theories and 3-D finite element (FE) simulations. It is shown that the model is capable of predicting accurately the deflection for a wide range of geometry and property parameters. It is demonstrated that the deflection of such deep box-type beams can be expressed as the summation of three different effects, namely bending deformations, conventional shear deformations in the framing members and sheathings, and additional in-plane shear deformations or shear slips of the weak web causing relative axial displacements between the framing members.

  • 43.
    Wei, Hong
    et al.
    Nanjing Forestry University, Faculty of Material Science and Engineering.
    Guo, Xiaolei
    Nanjing Forestry University, Faculty of Material Science and Engineering.
    Zhu, Zhaolong
    Nanjing Forestry University, Faculty of Material Science and Engineering.
    Cao, Pingxiang
    Nanjing Forestry University, Faculty of Material Science and Engineering.
    Wang, Baojing
    Nanjing Forestry University, Faculty of Material Science and Engineering.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Analysis of Cutting Performance in High Density Fiberboard Milling by Ceramic Cutting Tools2018Ingår i: Wood research, ISSN 1336-4561, Vol. 63, nr 3, s. 455-466Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to study the cutting performance of TiC reinforced Al2O3 ceramic cutting tools in milling high density fiberboard, the effects of cutting parameter on the cutting forces, tool wear and cutting quality were investigated. Under the condition of same average chip thickness, feed per tooth and geometry angles, firstly, the change rate of maximum cutting forces were higher than that of average cutting forces at two different cutting speeds, and the cutting forces at high speed cutting was less than that at low speed cutting. Secondly, the flank wear at high speed cutting was more pronounced than that at low speed cutting, whose abnormal wear were pull-out of grain, cracking, chipping and flanking. Thirdly, the machining quality at high speed cutting was better than that at low speed cutting. Fourthly, the tendencies of cutting forces, tool wear and surface roughness relative to cutting length were similar, but the change rates were different, especially at the initial stage. Finally, high speed cuttingare plausible to use in HDF processing, which not only improves machining quality, but also promotes production efficiency.

  • 44.
    Kitek Kuzman, Manja
    et al.
    University of Ljubljana, Wood Science and Technology.
    Haviarova, Eva
    Purdue University.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Architects perception of modified wood: a parallel study in selected countries of Europe2018Ingår i: ECWM9 - The 9th European Conference on Wood Modification. / [ed] Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz, Brigitte Junge and Jos Gootjes, Wageningen: SHR Wageningen, The Netherlands , 2018, s. 82-90Konferensbidrag (Refereegranskat)
  • 45.
    Kitek Kuzman, Manja
    et al.
    University of Ljubljana, Wood Science and Technology.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Haviarova, Eva
    Purdue University.
    Architects´perception of EWPs and modified wood in contemporary timber architecture2018Ingår i: Proceedings of WCTE 2018, Republic of Korea: National Institute of Forest Science , 2018, s. 1-6Konferensbidrag (Refereegranskat)
  • 46.
    Huber, Johannes Albert Josef
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Assessment of Connections In Cross-Laminated Timberbuildings Regarding Structural Robustness2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cross-laminated timber makes timber buildings with an increasing number of storeys achievable. Withmore storeys, structural robustness needs more attention to make a building survive unforeseen events (e.g. accidents,terrorism) and save lives. For steel and concrete buildings, design methods for robustness focus on connection details.The assessment of joints in cross-laminated timber buildings regarding robustness is rather limited in the literature. Theobjective of this paper is to conduct an initial assessment of the connectors after the removal of a wall in a platformcross-laminated timber building. We used the finite element method and the component method for the analysis of acase building. The results indicate that the wall-to-wall and the floor-to-floor connectors may fail at low deflectionlevels leading to high shear loads in the floor panel above the removed wall, which might induce cracking. The removalanalysis was only partially completed, but we identified an indication of the deformation behaviour of the case building.Testing and refined modelling of the connections is needed in the future to verify the results. This study may facilitatefuture investigations regarding robustness of multi-storey cross-laminated timber buildings.

  • 47.
    Kitek Kuzman, Manja
    et al.
    University of Ljubljana, Wood Science and Technology.
    Haviarova, Eva
    Purdue University, Department of Forestry and Natural Resources, West Lafayette, IN, USA.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Collaborative housing for elderly: clever co-living concepts2018Ingår i: COST Action CA 16121 “From sharing to caring”: International interdisciplinary Seminar Socio-technical aspects of the circular and colaborative economy University Rovira i Virgili, Tarragona, 16th March, 2018, s. 51-54Konferensbidrag (Refereegranskat)
  • 48.
    Ekatarina, Siderova
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Karlsson, Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Composition of monosaccharides in aqueous extracts of thermally modified wood.2018Ingår i: ECWM9 - The 9th European Conference on Wood Modification / [ed] Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz, Brigitte Junge and Jos Gootjes, Wageningen: SHR Wageningen, The Netherlands , 2018, s. 575-580Konferensbidrag (Refereegranskat)
  • 49.
    Pahlberg, Tobias
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Thurley, Matthew
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Popovic, Djordje
    Jönköping University.
    Hagman, Olle
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Crack detection in oak flooring lamellae using ultrasound-excited thermography2018Ingår i: Infrared physics & technology, ISSN 1350-4495, E-ISSN 1879-0275, Vol. 88, s. 57-69Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Today, a large number of people are manually grading and detecting defects in wooden lamellae in the parquet flooring industry. This paper investigates the possibility of using the ensemble methods random forests and boosting to automatically detect cracks using ultrasound-excited thermography and a variety of predictor variables. When friction occurs in thin cracks, they become warm and thus visible to a thermographic camera. Several image processing techniques have been used to suppress the noise and enhance probable cracks in the images. The most successful predictor variables captured the upper part of the heat distribution, such as the maximum temperature, kurtosis and percentile values 92–100 of the edge pixels. The texture in the images was captured by Completed Local Binary Pattern histograms and cracks were also segmented by background suppression and thresholding.

    The classification accuracy was significantly improved from previous research through added image processing, introduction of more predictors, and by using automated machine learning. The best ensemble methods reach an average classification accuracy of 0.8, which is very close to the authors’ own manual attempt at separating the images (0.83).

  • 50.
    Couceiro, José
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Hansson, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. Department of Ocean Operations and Civil Engineering. Norwegian University of Science and Technology (NTNU), Ålesund, Norway.
    Ahec, Ambroz
    University of Ljubljana.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    CT-scanning of the drying process of Eucalyptus nitens.2018Ingår i: Proceedings of 21st International Drying Symposium. / [ed] Cárcel JA, Polo GC, García-Pérez JV, Mulet A, Rosselló C.,, Valencia: Editorial Universitat Politècnica de València , 2018, s. 1269-1276Konferensbidrag (Refereegranskat)
    Abstract [en]

    The drying of Eucalyptus nitens is a troublesome process as the species is extremely prone to drying defects. This paper reports ongoing research toimprove the understanding of surface checking and cell collapse in Chilean grown Eucalyptus nitens during drying. Computed tomography (CT) scanning was used as a powerful tool for studying the internal changes in the wood-material during the drying process. Different levels of temperatures have been tested with the same equilibrium moisture content (EMC) conditions and low air velocity. The results confirm that a low drying temperature and a low air velocity, which results in a slow rate of drying, reduce internal cell collapse and surface checking .

1234567 1 - 50 av 339
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf