| 1. |
|
|
| 2. |
- Bader, Thomas K., 1980-, et al.
(författare)
-
Dowel deformations in multi-dowel LVL-connections under moment loading
- 2015
-
Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 10:3, s. 216-231
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 3. |
- Bader, Thomas K., 1980-, et al.
(författare)
-
Experimental Assessment of the Load Distribution in Multi-Dowel Timber Connections
- 2016
-
Ingår i: 17th International Conference on Experimental Mechanics, Rhodes, Greece, July 3-7, 2016.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
| 4. |
- Bader, Thomas K., 1980-, et al.
(författare)
-
Experimental characterization of the global and local behavior of multi-dowel LVL-connections under complex loading
- 2016
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:6, s. 2407-2424
-
Tidskriftsartikel (refereegranskat)abstract
- 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
|
|
| 5. |
- Bader, Thomas K., et al.
(författare)
-
Integrative experimental characterization and engineering modeling of single-dowel connections in LVL
- 2016
-
Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 107, s. 235-246
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 6. |
- Schweigler, Michael, et al.
(författare)
-
Static and dynamic properties of connections in timber-frame structures : BOOST + FBBB project
- 2018
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Connections play an important role in timber frame structures, especially when approaching the market of multi-story buildings. Two questions faced by practitioners were studied: for the first is the deformation behavior of such structures, where connections between wall and floor elements play an important role for the global stability of the timber structure. For the second is the sound transmission within elements of high importance, particularly timber building systems face challenges. For that reason, the static and dynamic behavior of such connections was studied in a joined experimental program. Two different building systems were investigated in 13 different test setups of how a floor and wall elements were connected to each other. By adjusting connection elements, the influence of various parameters on the dynamic and static behavior was studied. Sound/vibration transmission over the wall-floor connection was the special interest of the dynamic study. The floor element was excited by a shaker, and the response of floor and wall element was measured by accelerometers. This allowed to identify eigenfrequencies and eigenmodes as well as the damping of the structure and the insertion loss over the connection, respectively. Distinct differences between the building systems of the different producers were seen, while adjustments within building systems influenced only slightly the dynamic behavior. For the static part of the study, the moment-rotation behavior of the wall-floor connection was investigated. Variations of connection designs and layouts were tested to better understand the load-transfer and the mechanical interaction using different connectors and connector arrangements. The nailed connection between vertical studs and the bottom rail of the wall element was identified as a soft point when loaded by a horizontal force perpendicular to the plane of the wall element. Using screws this connection showed a substantial improvement of the connection strength. Further adjustments on the connector arrangements showed only partly influence on connection stiffness and strength.
|
|
| 7. |
- Akter, Shaheda T., et al.
(författare)
-
A numerical study of the stiffness and strength of cross-laminated timber wall-to-floor connections under compression perpendicular to the grain
- 2021
-
Ingår i: Buildings. - : MDPI AG. - 2075-5309. ; 11:10
-
Tidskriftsartikel (refereegranskat)abstract
- The use of cross-laminated timber (CLT) in multi-story buildings is increasing due to the potential of wood to reduce green house gas emissions and the high load-bearing capacity of CLT. Compression perpendicular to the grain (CPG) in CLT is an important design aspect, especially in multi-storied platform-type CLT buildings, where CPG stress develops in CLT floors due to loads from the roof or from upper floors. Here, CPG of CLT wall-to-floor connections are studied by means of finite element modeling with elasto-plastic material behavior based on a previously validated Quadratic multi-surface (QMS) failure criterion. Model predictions were first compared with experiments on CLT connections, before the model was used in a parameter study, to investigate the influence of wall and floor thicknesses, the annual ring pattern of the boards and the number of layers in the CLT elements. The finite element model agreed well with experimental findings. Connection stiffness was overestimated, while the strength was only slightly underestimated. The parameter study revealed that the wall thickness effect on the stiffness and strength of the connection was strongest for the practically most relevant wall thicknesses between 80 and about 160 mm. It also showed that an increasing floor thickness leads to higher stiffness and strength, due to the load dispersion effect. The increase was found to be stronger for smaller wall thicknesses. The influence of the annual ring orientation, or the pith location, was assessed as well and showed that boards cut closer to the pith yielded lower stiffness and strength. The findings of the parameter study were fitted with regression equations. Finally, a dimensionless ratio of the wall-to-floor thickness was used for deriving regression equations for stiffness and strength, as well as for load and stiffness increase factors, which could be used for the engineering design of CLT connections.
|
|
| 8. |
- Aquino, Caroline D., et al.
(författare)
-
Influence of test methodology on the characterization of the parallel-to-grain timber embedment strength and foundation modulus of dowels
- 2024
-
Ingår i: Wood Material Science & Engineering. - : Taylor & Francis Group. - 1748-0272 .- 1748-0280.
-
Tidskriftsartikel (refereegranskat)abstract
- A reliable determination of the embedment strength and foundation modulus of timber elements is critical for the design and safety assessment of joints in timber structures. However, the existence of various test configurations for characterising the embedding properties of large diameter steel fasteners in timber elements poses challenges in directly comparing and utilising available test data. This paper aims to provide an insight into the influence of embedment property test methods, comparing experimental results from different test setups within the guidelines of the EN 383 and ASTM D 5764-97a standards for European softwood species, Scots pine wood (Pinus sylvestris) and Norway spruce (Picea abies). In addition to the test guidelines, the thickness of the specimen and the application of the load was evaluated within the protocols. A comprehensive statistical analysis was performed to identify statistically significant differences between the groups evaluated. The results of the analysis revealed disagreement between the standards in the evaluation of the strength of the embedding, highlighting the potential bias inserted by the experimental setup and protocol. Furthermore, it was proven that the thickness of the specimens influences both the embedding strength and the foundation modulus of the wood species tested. Finally, no distinctions were observed between tensile and compressive loading within the guidelines of the EN 383 standard.
|
|
| 9. |
- Aquino, Caroline, et al.
(författare)
-
Influence of Test Methods on the Parallel to Grain Embedment Strength and Foundation Modulus Characterization
- 2023
-
Ingår i: Proceedings from the 13th World Conference on Timber Engineering 2023. - Oslo, Norway : World Conference on Timber Engineering (WCTE). - 9781713873297 - 9781713873273 ; , s. 3667-3674
-
Konferensbidrag (refereegranskat)abstract
- Different test setups have been reported in the literature for the determination of the embedment strengthin timber elements. These variances hinder a straightforward comparison between available test data. It is difficult todetermine if the source of variability lies in intrinsic timber properties or is related to the test protocol used. This paperaims to provide a better insight into the influence of embedment strength test methods, comparing experimental resultsfrom different test setups within the guidelines of EN 383 and ASTM D 5764-97a for Scots pine wood (Pinus sylvestris)and Spruce (Picea Abies). A robust statistical analysis was performed to identify statistically significant differencesbetween the groups evaluated. The analysis of the parallel to grain embedment strength showed that the results differedbetween standards, pointing out the potential bias inserted in the embedment properties given their evaluation method.Moreover, the thickness of the specimen tests also proved to influence the yield and ultimate embedment strength for thewood species tested.
|
|
| 10. |
- Bader, Thomas K., 1980-, et al.
(författare)
-
Berechnungsmodell für das Last-Verformungsverhalten von Stabdübelgruppen im Ingenieurholzbau
- 2014
-
Ingår i: Berichte der Fachtagung Baustatik-Baupraxis 12. - München : Technischen Universität, München. - 9783000412561 ; , s. 113-121
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In diesem Beitrag wird ein Berechnungsmodell für das Last-Verformungsverhalten von Stabdübelgruppen vorgestellt, mit dem lokale Verbindungsmittelkräfte und Verbindungsmitteldeformationen mit zugehörigen globale Schnittgrößen und Relativverformungen konsistent berechnet werden können. Grundlage dafür bildet das Last-Verformungsverhalten des Einzeldübels, das mit Hilfe eines baustatischen Modellierungsansatzes hergeleitet wird. Ein wesentlicher Eingangsparameter dieses Modells ist die Lochleibungsfestigkeit von Holz, die für beliebige Kraft-Faserrichtungen experimentell untersucht wurde. Mit Hilfe des vorgestellten Berechnungsmodells für Stabdübelgruppen können die Tragfähigkeit einer Verbindung unter einer beliebigen Kombination von Normalkraft, Querkraft und Momentenbeanspruchung und die zugehörige Relativverformung berechnet werden. Mit dem vorgestellten Berechnungsmodell kann der lastfallabhängige Einfluss einer Verbindung auf Schnittgrößen-Verformungsinteraktionen direkt in der baustatischen Berechnung von Holzkonstruktionen berücksichtigt werden.
|
|
