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Enquist, Bertil
Publications (10 of 51) Show all publications
Akter, S., Bader, T. K. & Enquist, B. (2018). Failure envelope for interaction of stresses perpendicular to the grain with rolling shear stress in wood. In: 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK: . Paper presented at 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK.
Open this publication in new window or tab >>Failure envelope for interaction of stresses perpendicular to the grain with rolling shear stress in wood
2018 (English)In: 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK, 2018Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

The orthotropic material property in combination with ductility in compression, brittleness in shear and tension, very low shear modulus in radial-tangential (RT) plane etc. requires anisotropic stress failure criteria, as well as their evolution with increasing strains. Three- dimensional failure criteria have been proposed for this purpose, but their validation in the RT plane with interaction of rolling shear stresses has attracted less attention. Corresponding stress interactions are however important for modelling of engineered wood-based products under compression perpendicular to the grain when taking into account influence of the annual ring structure.

The work aims at defining failure envelopes for stresses perpendicular to the grain with rolling shear stress interaction based on experimental investigations performed on Norway spruce. The experimental set-up was realized in a biaxial testing frame and consisted of stiff steel plates to transfer load from the testing machine to wood specimen. Mechanical grips prevented rotation and uplifting of the specimen in case of pure shear and tensile loading, respectively. In addition to conventional linear variable differential transformers, a digital image correlation system was used to measure strain fields on the surface of wood specimens and steel plates. Measurements of dog-bone shaped specimens were carried out along different stress interaction paths by displacement controlled loading.

The experimental dataset was then compared with commonly used phenomenological failure criteria, namely Tsai-Hill, Tsai-Wu [1], Norris [2] and Hoffman, as well as with regression equations from previous works [3].Experiments revealed that the stress-strain relationship under compression, shear, and biaxial loading differs in radial and tangential directions. None of the three-dimensional stress failure criteria provided good prediction of experiments under compression and rolling shear, but experimental data was closer to the regression equation proposed in [3].

National Category
Building Technologies
Identifiers
urn:nbn:se:lnu:diva-76228 (URN)
Conference
6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK
Available from: 2018-06-20 Created: 2018-06-20 Last updated: 2018-09-11Bibliographically approved
Bader, T. K., Vessby, J. & Enquist, B. (2018). Path dependence in OSB sheathing-to-framing nailed connection revealed by biaxial testing. Journal of Structural Engineering, 144(10), Article ID 04018197.
Open this publication in new window or tab >>Path dependence in OSB sheathing-to-framing nailed connection revealed by biaxial testing
2018 (English)In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 144, no 10, article id 04018197Article in journal (Refereed) Published
Abstract [en]

OSB sheathing-to-wood framing connection, as typically used in light-frame shear walls, was experimentally examined in a novel biaxial test setup with respect to possible path dependence of the load-displacement relation. The connection with an annular-ringed shank nail was loaded under displacement control following nine different displacement paths within the sheathing plane, which coincided at a number of points. In intersection points, resultant connection force, its orientation and work performed on the connection system to reach the specific point were calculated and compared. Evaluation of experiments revealed significant path dependence with respect to orientation of force resultants at path intersection points. However, magnitude of the forces and the work carried out showed relatively small dependence of the displacement path undertaken. Comparison of uniaxial connection tests with the European yield model demonstrated strong contribution of withdrawal resistance of the ringed shank nail to its lateral strength. Results of this type are a valuable basis to build better models when simulating such connections in wood structures.

Place, publisher, year, edition, pages
Reston, VA: American Society of Civil Engineers (ASCE), 2018
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-70762 (URN)10.1061/(ASCE)ST.1943-541X.0002112 (DOI)000441685500001 ()2-s2.0-85051250090 (Scopus ID)
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2019-08-29Bibliographically approved
Bader, T. K., Schweigler, M., Hochreiner, G., Eberhardsteiner, J., Serrano, E., Dorn, M. & Enquist, B. (2016). Experimental Assessment of the Load Distribution in Multi-Dowel Timber Connections. In: 17th International Conference on Experimental Mechanics, Rhodes, Greece, July 3-7, 2016: . Paper presented at 17th International Conference on Experimental Mechanics, Rhodes, Greece, July 3-7, 2016.
Open this publication in new window or tab >>Experimental Assessment of the Load Distribution in Multi-Dowel Timber Connections
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2016 (English)In: 17th International Conference on Experimental Mechanics, Rhodes, Greece, July 3-7, 2016, 2016Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

An integrative, hierarchically organized testing procedure for the quantification of the load distribution in multi-dowel timber connections is presented herein. The use of contactless deformation measurement systems allowed the combination of test data from single dowel and multi-dowel connections, which gave access to the loads acting on each dowel over the full loading history. As a consequence of the anisotropic material behavior of wood, a nonuniform and progressively changing load distribution among the dowels was found.

National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-56261 (URN)
Conference
17th International Conference on Experimental Mechanics, Rhodes, Greece, July 3-7, 2016
Available from: 2016-08-31 Created: 2016-08-31 Last updated: 2018-05-17Bibliographically approved
Bader, T. K., Schweigler, M., Hochreiner, G., Enquist, B., Dorn, M. & Serrano, E. (2016). Experimental characterization of the global and local behavior of multi-dowel LVL-connections under complex loading. Materials and Structures, 49(6), 2407-2424
Open this publication in new window or tab >>Experimental characterization of the global and local behavior of multi-dowel LVL-connections under complex loading
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2016 (English)In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 49, no 6, p. 2407-2424Article in journal (Refereed) Published
Abstract [en]

The thorough experimental characterization of a dowel-type connection under various combinations of bending moments and normal forces is presented in this study. Double-shear steel-to-timber connections with 12 and 20 mm steel dowels were tested in a 4-point bending test set-up. The load, between the connected steel and wood beams, was transferred by the dowels themselves and also via an additional (passive) contact device, which introduced an eccentric normal force in the timber beam. The behavior of the connections was studied at the global scale of the connection and at the local scale of the individual dowels. A non-contact deformation measurement system was used to assess the changes of the location of the center of relative rotation over the entire loading. At the same time, the head deformations of the individual dowels could be measured, giving a direct indication about the force distribution among the dowels. Due to reinforcement, connections behaved distinctly ductile with a global relative rotation of up to 3°. Pre-stressing of the contact device by a force of 40 kN yielded an even stiffer behavior. For the particular configurations tested herein, the center of rotation was found to be close to the vertical axis of symmetry of the joint and close to the top row of the dowels. Moreover, the superimposed vertical shift of the center of relative rotation in case of a delayed normal force could be quantified. © 2015 RILEM

Keywords
Bending moment and normal force, Center of relative rotation, Dowel connection, Ductility, Reinforcement, Timber, Bending moments, Deformation, Rotation, Wooden beams and girders, 4-point bending tests, Center of rotation, Dowel-type connection, Experimental characterization, Force distributions, Normal forces, Relative rotation, Fasteners
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-46196 (URN)10.1617/s11527-015-0657-8 (DOI)000376646900026 ()2-s2.0-84936806518 (Scopus ID)
Available from: 2015-09-10 Created: 2015-09-10 Last updated: 2018-04-25Bibliographically approved
Bader, T. K., Schweigler, M., Serrano, E., Dorn, M., Enquist, B. & Hochreiner, G. (2016). Integrative experimental characterization and engineering modeling of single-dowel connections in LVL. Construction and Building Materials, 107, 235-246
Open this publication in new window or tab >>Integrative experimental characterization and engineering modeling of single-dowel connections in LVL
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2016 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 107, p. 235-246Article in journal (Refereed) Published
Abstract [en]

In order to be able to realistically and consistently elucidate and subsequently simulate the load displacement behavior of single-dowel connections, the material behavior of the individual components, namely steel dowels and wood, needs to be investigated. The behavior of slotted-in, single-dowel steel-to-laminated veneer lumber (LVL) connections with dowel diameters of 12 and 20 mm is thoroughly discussed here in relation to steel dowel and LVL properties. In addition to connection tests at different load-to-grain directions of 0, 45 and 90, the corresponding embedment behavior of LVL was tested up to dowel displacements of three times the dowel diameter. The material behavior of steel dowels was studied by means of tensile and 3-point bending tests and accompanying finite element simulations. A pronounced nonlinear behavior of the single-dowel connections was observed for all load-to-grain directions. In case of loading perpendicular to the grain, a significant hardening behavior was obvious. Due to the anisotropic material properties of wood, enforcing a loading direction of 45 to the grain resulted in an additional force perpendicular to the load direction which was quantified in a novel biaxial test setup. Thus, a comprehensive and consistent database over different scales of observations of dowel connections could be established, which subsequently was exploited by means of engineering modeling. The comparison of experimental and numerical data illustrates the potential of the engineering modeling approach to overcome drawbacks of current design regulations, which are unable to appropriately predict stiffness properties of dowel connections. Moreover, the quasi-elastic limit of dowel connections was calculated and discussed by means of the model. (c) 2016 Elsevier Ltd. All rights reserved.

Keywords
Dowel connection, Engineering modeling, Anisotropy, Ductility, Stiffness, Reinforcement, Laminated veneer lumber
National Category
Civil Engineering
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-51061 (URN)10.1016/j.conbuildmat.2016.01.009 (DOI)000370308000024 ()2-s2.0-84954319869 (Scopus ID)
Available from: 2016-03-18 Created: 2016-03-18 Last updated: 2018-05-17Bibliographically approved
Bader, T. K., Schweigler, M., Hochreiner, G., Serrano, E., Enquist, B. & Dorn, M. (2015). Dowel deformations in multi-dowel LVL-connections under moment loading. Wood Material Science & Engineering, 10(3), 216-231
Open this publication in new window or tab >>Dowel deformations in multi-dowel LVL-connections under moment loading
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2015 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 3, p. 216-231Article in journal (Refereed) Published
Abstract [en]

The aim of the experimental study presented herein is the assessment and quantification of the behavior of individual dowels in multi-dowel connections loaded by a bending moment. For this purpose, double-shear, steel-to-timber connections with nine steel dowels arranged in different patterns and with different dowel diameters were tested in four-point bending. In order to achieve a ductile behavior with up to 7° relative rotation, the connections were partly reinforced with self-tapping screws. The reinforcement did not influence the global load–deformation behavior, neither for dowel diameters of 12 mm nor for 20 mm, as long as cracking was not decisive. The deformation of the individual dowels was studied by means of a non-contact deformation measurement system. Thus, the crushing deformation, that is, the deformation at the steel plate, and the bending deformation of the dowels could be quantified. In the case of 12 mm dowels, the bending deformation was larger than the crushing deformation, while it was smaller in the case of 20 mm dowels. Moreover, dowels loaded parallel to the grain showed larger bending deformations than dowels loaded perpendicular to the grain. This indicates that the loading of the individual dowels in the connection differs depending on their location.

Place, publisher, year, edition, pages
Taylor & Francis, 2015
Keywords
bending moment, Dowel connection, ductility, load distribution, reinforcement, timber, Bending moments, Crushing, Deformation, Fasteners, Deformation behavior, Four point bending, Load distributions, Parallel to the grains, Relative rotation, Self-tapping screws, Timber connections, Bending (deformation)
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-46194 (URN)10.1080/17480272.2015.1070372 (DOI)000368739700002 ()2-s2.0-84942191975 (Scopus ID)
Available from: 2015-09-10 Created: 2015-09-10 Last updated: 2018-04-25Bibliographically approved
Hu, M., Johansson, M., Olsson, A., Oscarsson, J. & Enquist, B. (2015). Local variation of modulus of elasticity in timber determined on the basis of non-contact deformation  measurement and scanned fibre orientation. European Journal of Wood and Wood Products, 73(1), 17-27
Open this publication in new window or tab >>Local variation of modulus of elasticity in timber determined on the basis of non-contact deformation  measurement and scanned fibre orientation
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2015 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 73, no 1, p. 17-27Article in journal (Refereed) Published
Abstract [en]

During the last decade, the utilization of non-contact deformation measurement systems based on digital image correlation (DIC) has increased in wood related research. By measuring deformations with DIC systems, surface strain fields can be calculated. The first aim of this study concerns the possibility to detect detailed strain fields along the entire length of a wooden board subjected to pure bending and the potential of using such strain fields to determine a bending modulus of elasticity (MOE) profile along a board. Displacements were measured over 12 subareas along a flat surface of the board. For each such area, a separate local coordinate system was defined. After the transformation of locally measured coordinates to a global system, high resolution strain fields and a corresponding bending MOE profile were calculated. A second method in establishing bending MOE profiles is to use fibre angle information obtained from laser scanning and a calculation model based on integration of bending stiffness over board cross sections. Such profiles have recently been utilized for accurate strength grading. A second aim of this study was to investigate the accuracy of the bending MOE profiles determined using the latter method involving fibre angle information. Bending MOE profiles determined using the two described methods agree rather well. However, for some patterns of knot clusters, the local bending MOE, calculated on the basis of fibre angles and integration of bending stiffness, is overestimated. Hence, this research adds knowledge that may be utilized to improve the newly suggested strength grading method.

Place, publisher, year, edition, pages
Springer, 2015
National Category
Construction Management
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-38089 (URN)10.1007/s00107-014-0851-3 (DOI)000347688100002 ()2-s2.0-84920552031 (Scopus ID)
Available from: 2014-11-07 Created: 2014-11-07 Last updated: 2018-01-09Bibliographically approved
Bolmsvik, Å., Enquist, B. & Linderholt, A. (2015). Stiffness and damping evaluation of Elastomers in different setups. In: Proceedings of the Internoise 2015 conference: . Paper presented at The 44th Internoise Congress, Implementing Noise Control Technology, 9-12 August, 2015, San Francisco. Society of Experimental Mechanics (SEM)
Open this publication in new window or tab >>Stiffness and damping evaluation of Elastomers in different setups
2015 (English)In: Proceedings of the Internoise 2015 conference, Society of Experimental Mechanics (SEM) , 2015Conference paper, Published paper (Refereed)
Abstract [en]

In timber buildings, elastomers are commonly used to decrease the sound transmission between apartments. Detailed properties of the elastomers are needed in order to model them in a correct yet computational efficient manner. In earlier studies, dynamic experiments have been made on elastomer strips half embedded. However, the sidewise effects need to be further evaluated. In this study, the elastomers are evaluated quasi-statically in different directions, having continuous as well as intermittent distributions, being plane supported or half embedded. An FE-model has been developed using data stemming from the quasi-static tests together with damping estimates stemming from vibrational tests.

Place, publisher, year, edition, pages
Society of Experimental Mechanics (SEM), 2015
Keywords
stiffness, damping, evaluation, elastomers, wooden buildings
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-45738 (URN)2-s2.0-84947598452 (Scopus ID)
Conference
The 44th Internoise Congress, Implementing Noise Control Technology, 9-12 August, 2015, San Francisco
Available from: 2015-08-17 Created: 2015-08-17 Last updated: 2016-08-12Bibliographically approved
Dorn, M., Kozłowski, M., Serrano, E. & Enquist, B. (2014). Development of large-scale load-bearing timber-glass structural elements. In: WCTE 2014 - World Conference on Timber Engineering: Proceedings. Paper presented at WCTE 2014, World Conference on Timber Engineering, Quebec City, Canada, August 10-14, 2014.
Open this publication in new window or tab >>Development of large-scale load-bearing timber-glass structural elements
2014 (English)In: WCTE 2014 - World Conference on Timber Engineering: Proceedings, 2014Conference paper, Published paper (Refereed)
Abstract [en]

The building industry demands ever more effective structural elements with a multitude of requirements at the same time. There is increasing interest for load-bearing glass elements which can be deployed in timber structures, e.g. in the outer façade or as column or beam elements within the building. In an on-going research project, the materials glass, timber and the adhesive combining the former have to be selected to fit each other but also suit the application. The mechanical properties are studied individually as well as in combined small-scale specimens experimentally. Furthermore,large-scale tests on beams and shear walls are performed. This is accompanied by numerical analysis to study a wide range of dimensions and variations as well as specific design situations. The final output of the project will be prototypes to beused in showcase projects.

Keywords
timber-glass composites, integrated structures, shear wa
National Category
Construction Management
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-37275 (URN)2-s2.0-84924944175 (Scopus ID)
Conference
WCTE 2014, World Conference on Timber Engineering, Quebec City, Canada, August 10-14, 2014
Projects
LBTGC - Load bearing timber glass composites
Funder
VINNOVA, 2011-02266
Available from: 2014-09-25 Created: 2014-09-25 Last updated: 2016-12-07Bibliographically approved
Vessby, J., Enquist, B. & Källsner, B. (2014). Directional dependency in an OSB sheathing-to-framing mechanical connection. In: : . Paper presented at WCTE, World Conference on Timber Engineering, Quebec City, 10-14 August.
Open this publication in new window or tab >>Directional dependency in an OSB sheathing-to-framing mechanical connection
2014 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Nailed connections are commonly employed for connecting sheathings to the framing used in shear walls. Although many aspects of such connections have been investigated thoroughly within the research community generally, the effect the loading direction has on connections of this sort has been much less investigated. In the present study experimental tests were carried out for determining in detail the effects the loading has on different sheathing-to-framing connections. The results obtained indicated the degree of loading to which a nail fastened to an oriented strand board (OSB) sheathing is subjected to not be strongly affected by which of the two main loading directions is involved, but that the effects of loading direction are found to be much greater if the timber element in question is also included in the testing carried out. The dependency of the loading effect on the loading direction at different loading stages and for different directions - parallel to the fibres, perpendicular to them, at some angle between these two main directions - was investigated here.

National Category
Building Technologies
Identifiers
urn:nbn:se:lnu:diva-34452 (URN)2-s2.0-85067780115 (Scopus ID)
Conference
WCTE, World Conference on Timber Engineering, Quebec City, 10-14 August
Available from: 2014-05-28 Created: 2014-05-28 Last updated: 2019-08-27Bibliographically approved
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