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Block Shear Failure Mode of Axially Loaded Groups of Screws

https://research.thinkwood.com/en/permalink/catalogue1512
Year of Publication
2016
Topic
Connections
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Solid-sawn Heavy Timber
Author
Mahlknecht, Ursula
Brandner, Reinhard
Augustin, Manfred
Year of Publication
2016
Country of Publication
Austria
Format
Conference Paper
Material
Glulam (Glue-Laminated Timber)
Solid-sawn Heavy Timber
Topic
Connections
Mechanical Properties
Keywords
Self-Tapping Screws
Block Shear Model
Stiffness
Strength
Bending Stresses
Axially-Loaded
Language
English
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 22-25, 2016, Vienna, Austria p. 362-371
Summary
Self-tapping screws are efficient and flexible fasteners, applicable for many types of connections. Investigations on axially loaded groups of screws pointed out, that small spacing between the screws lead to block shear failure mode. So far, block and plug shear failure mode are only analysed for laterally loaded fasteners. Corresponding models cannot be simple transferred to primary axially loaded screws, because of their load insertion continuously along the effective thread featuring a thread-fibre angle perpendicular or with an angle to grain. Results gained by means of two different test configurations, with constant 90° thread-fibre angle but different configurations of group of screws and support conditions are presented. A block shear model is presented, and for mean values for stiffness and strength properties as model parameters are discussed together with values for parameters related to the force distribution over the effective thread length for the first test configuration. Agreement between model and test results was found on a conservative basis. As outlook, considerations of additional bending stresses as well as parameter optimisation are seen as prerequisites and next steps for further model improvement and practicality.
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Withdrawal Properties of Threaded Rods Embedded in Glued-Laminated Timber Elements

https://research.thinkwood.com/en/permalink/catalogue217
Year of Publication
2016
Topic
Connections
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Author
Stamatopoulos, Haris
Organization
Norwegian University of Science and Technology
Year of Publication
2016
Country of Publication
Norway
Format
Thesis
Material
Glulam (Glue-Laminated Timber)
Topic
Connections
Mechanical Properties
Keywords
Withdrawal Properties
Threaded Rods
Finite Element Model
Language
English
Research Status
Complete
Summary
There is a complete lack of guidelines for the estimation of the withdrawal stiffness of threaded rods with larger diameters. Moreover, Eurocode 5 imposes a limitation to the angle between the rod-axis and the grain direction (a = 30°) without taking into account that splitting may be prevented by reinforcement. The lack of knowledge of proper design, documentation of mechanical behaviour, design guidelines and design codes for threaded rods are barriers for the development of timber connections with these fasteners. The withdrawal properties (capacity and stiffness) of axially loaded threaded rods were investigated in the present thesis by use of experimental, analytical and numerical methods. An overview of the background information and research on withdrawal of screws and threaded rods is presented in Part I of the present thesis. Part II consists of 4 appended papers where the findings of this Ph.D. project are presented. Part III consists of 3 appendices where some analytical remarks together with the detailed experimental and numerical results are presented. According to experimental observation, the specimens exhibited high withdrawal capacity and stiffness (without initial soft response). Based on the experimental results, the necessary input parameters for the analytical method were quantified. In particular, simple expressions for the mean and 5%-percentile withdrawal strength, the shear stiffness and the brittleness were developed. In general, the analytical estimations and the experimental results were in good agreement. Numerical estimations overestimated stiffness especially for small angles and short embedment lengths; however this overestimation was smaller in the case of longer rods. Finally, the experimental results from tests with pairs of rods showed that the effectiveness per each rod was quite high, despite the fact that rods were placed with small edge distances and spacings.
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Group Action of Axially-Loaded Screws in the Narrow Face of Cross Laminated Timber

https://research.thinkwood.com/en/permalink/catalogue1496
Year of Publication
2016
Topic
Mechanical Properties
Connections
Material
CLT (Cross-Laminated Timber)
Author
Brandner, Reinhard
Year of Publication
2016
Country of Publication
Austria
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Connections
Keywords
Axially-Loaded
Self-Tapping Screws
Withdrawal Properties
Stochastic Approach
Load-Displacement Curves
Language
English
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 22-25, 2016, Vienna, Austria p. 209-218
Summary
Withdrawal properties of axially-loaded groups of screws in the narrow face of cross laminated timber (CLT) are investigated by means of a stochastic approach based on a single screw model which provides a complete stochastic description of the load-displacement curve. Different group dimensions and configurations are analysed, featuring screws with equal or different thread-fibre angles. The stochastic approach is successfully verified by tests. Influences caused by shortcomings in assembling and by screws penetrating knots as well as gaps are addressed. Suggestions, relevant for the development of CLT system connectors and for practical applications, are made.
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Effect of Rod-to-Grain Angle on Capacity and Stiffness of Axially and Laterally Loaded Long Threaded Rods in Timber Joints

https://research.thinkwood.com/en/permalink/catalogue1371
Year of Publication
2018
Topic
Connections
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Author
Cepelka, Martin
Arne Malo, Kjell
Stamatopoulos, Haris
Publisher
Springer Berlin Heidelberg
Year of Publication
2018
Country of Publication
Germany
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Topic
Connections
Mechanical Properties
Keywords
Threaded Rods
Axial Loads
Lateral Loads
Rod-to-Grain
Joints
Boundary Conditions
Load-to-Rod
Language
English
Research Status
Complete
Series
European Journal of Wood and Wood Products
ISSN
1436-736X
Summary
Long threaded rods have recently been widely used as a reinforcement of glued laminated timber in perpendicular to the grain direction. The recent research has thus focused mainly on the withdrawal properties of the threaded rods in the axial direction. Utilizing their large withdrawal stiffness and strength, the threaded rods can also effectively be used as connectors in moment resisting timber joints. Yet, in joints, the threaded rods are often imposed to a non-axial loading, due to inclination of the rod axis to the grain as well as loading direction different from the rod axis. No design models are currently available for the combined axial and lateral loading of the threaded rods. In the present work, the effects of the rod-to-grain and load-to-rod angles on capacity and stiffness of the threaded rods are investigated by use of experiments and finite element models. Based on those, analytical expressions for determining stiffness and capacity of axially and laterally loaded threaded rods are proposed, intended as a basis for practical joint design. Furthermore, effect of various boundary conditions applied at the rod-ends is studied.
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Design of Timber Members Subjected to Axial Compression or Combined Axial Compression and Bending Based on 2nd Order Theory

https://research.thinkwood.com/en/permalink/catalogue115
Year of Publication
2015
Topic
Design and Systems
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Application
Columns
Author
Frangi, Andrea
Steiger, René
Theiler, Matthias
Organization
International Network on Timber Engineering Research (INTER)
Year of Publication
2015
Country of Publication
Germany
Format
Conference Paper
Material
Glulam (Glue-Laminated Timber)
Application
Columns
Topic
Design and Systems
Mechanical Properties
Keywords
Bending
Buckling
Codes
Compression
Deformation
Monte Carlo
Simulation
Structural
Testing
Language
English
Conference
INTER 2015
Research Status
Complete
Notes
August 24-27, 2015, Sibenik, Croatia
Summary
The paper examines the behaviour of structural timber members subjected to axial compression or combined axial compression and bending. Based on experimental and numerical investigations, the accuracy of the existing approach in Eurocode 5 for the design of timber members subjected to axial compression or combined axial compression and bending is assessed and modifications are suggested. By means of extensive experimental investigations, a data base was created for the validation of calculation models and for the assessment of design concepts. In order to assess the behaviour of timber members subjected to axial compression or combined axial compression and bending, strain-based calculation models were developed. The investigations indicate that the existing approach of Eurocode 5 based on 2nd order analysis can lead to an overestimation of the load-bearing capacity. Hence, a modified design approach was developed which agrees with the results of the Monte Carlo simulations very well and thus ensures a safe and economical design of timber members subjected to compression or combined compression and bending.
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Finite Element Modelling of the Cyclic Behaviour of CLT Connectors and Walls

https://research.thinkwood.com/en/permalink/catalogue1653
Year of Publication
2016
Topic
Mechanical Properties
Seismic
Connections
Material
CLT (Cross-Laminated Timber)
Application
Walls
Author
Aranha, Chrysl
Branco, Jorge
Lourenço, Paulo
Flatscher, Georg
Schickhofer, Gerhard
Year of Publication
2016
Country of Publication
Austria
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Application
Walls
Topic
Mechanical Properties
Seismic
Connections
Keywords
Shear Tests
Axial Tests
Cyclic Loads
Force-Displacement Curves
Numerical Model
Language
English
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 22-25, 2016, Vienna, Austria p. 3533-3540
Summary
The characterization of the behaviour of connectors used in Cross-laminated Timber (CLT) structures is an important aspect that needs to be considered in their seismic design. In this paper, the data from shear and axial tests conducted on connectors have been used to define their force-displacement curves under cyclic loads using the SAWS model in OpenSees. The component curves were then incorporated into the corresponding wall models and the results were compared with their experimental counterparts, in order to determine the validity of the finite element model. Thereby, the non-linear behaviour was restricted to the connectors while the walls themselves were composed of linear orthotropic shell elements. The models were found to provide a good estimate of the initial stiffness and maximum load capacity of the wall specimens. The effects of vertical loading and the presence of openings were determined based on analyses run on the calibrated model.
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Prediction of Withdrawal Resistance for a Screw in Hybrid Cross-Laminated Timber

https://research.thinkwood.com/en/permalink/catalogue2687
Year of Publication
2020
Topic
Connections
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Pang, Sung-Jun
Ahn, Kyung-Sun
Kang, Seog Goo
Oh, Jung-Kwon
Publisher
SpringerOpen
Year of Publication
2020
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Topic
Connections
Mechanical Properties
Keywords
Self-Tapping Screws
Withdrawal Resistance
Screw
Withdrawal Stiffness
Withdrawal Strength
Connections
Language
English
Research Status
Complete
Series
Journal of Wood Science
Summary
The aim of this study was to predict the withdrawal resistance of a screw in hybrid cross-laminated timber (CLT) composed of two types of lamina layers. A theoretical model to predict the withdrawal resistance was developed from the shear mechanism between a screw and the layers in hybrid CLT. The parameters for the developed model were the withdrawal stiffness and strength that occurs when a screw is withdrawn, and the penetration depth of a screw in layers of a wood material. The prediction model was validated with an experimental test. Screws with two different diameters and lengths (Ø6.5 × 65 mm and Ø8.0 × 100 mm) were inserted in a panel composed of solid wood and plywood layers, and the withdrawal resistances of the screws were evaluated. At least 30 specimens for each group were tested to derive the lower 5th percentile values. As a result, the developed model predictions were 86–88% of the lower 5th percentile values of hybrid CLT from the properties of the lamina layer. This shows that the withdrawal resistance of hybrid CLT can be designed from the properties of its layer.
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Withdrawal of Pairs of Threaded Rods with Small Edge Distances and Spacings

https://research.thinkwood.com/en/permalink/catalogue1395
Year of Publication
2017
Topic
Mechanical Properties
Connections
Material
Glulam (Glue-Laminated Timber)
Author
Stamatopoulos, Haris
Malo, Kjell Arne
Publisher
Springer Berlin Heidelberg
Year of Publication
2017
Country of Publication
Germany
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Topic
Mechanical Properties
Connections
Keywords
Threaded Rods
Withdrawal Capacity
Stiffness
Language
English
Research Status
Complete
Series
European Journal of Wood and Wood Products
ISSN
1436-736X
Summary
An experimental investigation on withdrawal of pairs of screwed-in threaded rods embedded in glued-laminated timber elements is presented in this paper. Specimens with varying angles between the rod axis and the grain direction (a = 15°, 30°, 60°, 90°) and 2 different configurations with respect to edge distances and spacings were tested. The diameter and the embedment length of the rods were 20 and 450 mm, respectively. The threaded rods were embedded in a row perpendicular to the plain of the grain. The edge distances and spacings were smaller than the minimum requirements according to Eurocode 5. The withdrawal capacity of pairs of rods was compared to the withdrawal capacity of single rods and the effective number, n ef , was found to be in the range 1.72–1.94, despite the small edge distances and spacings. Based on the experimental results obtained, a simple approximating expression was derived for n ef . An analytical model based on Volkersen theory with an idealized bi-linear constitutive relationship was used to estimate the withdrawal capacity and stiffness. The analytical estimations were in good agreement with the experimental results. Finally, the withdrawal stiffness was estimated by use of finite element simulations. The numerical estimations for the withdrawal stiffness were also in good agreement with the experimental results.
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Numerical Modelling of Steel-to-Timber Joints and Connectors for CLT Structures

https://research.thinkwood.com/en/permalink/catalogue1604
Year of Publication
2016
Topic
Connections
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Izzi, Matteo
Rinaldin, Giovanni
Fragiacomo, Massimo
Polastri, Andrea
Year of Publication
2016
Country of Publication
Austria
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Topic
Connections
Mechanical Properties
Keywords
Strength
Shear Tests
Steel-to-Timber
Joints
Nails
Hysteretic Model
Stochastic Approach
Language
English
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 22-25, 2016, Vienna, Austria p. 2032-2040
Summary
The mechanical behaviour of steel-to-timber joints with annular-ringed shank nails is investigated using numerical modelling and a component approach. These joints are used in Cross-Laminated Timber (CLT) buildings to anchor metal connectors such as hold-downs and angle brackets to the timber panels. At first, a general hysteresis model is introduced, where a single fastener joint is schematized as an elasto-plastic beam embedded in a non-linear medium with a compression-only behaviour. A second hysteresis model is then presented, where the mechanical behaviour of the joint is simulated by a non-linear spring with three degrees of freedom. Both models are calibrated on the design rules prescribed by the reference standards. Moreover, average strength capacities are determined from the corresponding characteristic values assuming a standard normal distribution and suitable coefficients of variation. As first applicative examples of the proposed models, shear tests are simulated on single steel-to-timber joints with annular-ringed shank nails and on a connection made of an angle bracket and sixty nails. The scatter of mechanical properties in steel-to-timber joints is also taken into account in the simulations and a stochastic approach is proposed, demonstrating acceptable accuracy.
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Probabilistic Models for the Withdrawal Behavior of Single Self-Tapping Screws in the Narrow Face of Cross Laminated Timber (CLT)

https://research.thinkwood.com/en/permalink/catalogue1388
Year of Publication
2018
Topic
Connections
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Brandner, Reinhard
Ringhofer, Andreas
Grabner, Martin
Publisher
Springer Berlin Heidelberg
Year of Publication
2018
Country of Publication
Germany
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Topic
Connections
Mechanical Properties
Keywords
Axial Load
Self-Tapping Screws
Withdrawal
Probabilistic Model
Language
English
Research Status
Complete
Series
European Journal of Wood and Wood Products
ISSN
1436-736X
Summary
Cross laminated timber (CLT) and self-tapping screws have strongly dominated the latest developments in timber engineering. Although knowledge of connection techniques in traditional light-frame structures can be applied to solid timber constructions with CLT, there are some product specifics requiring additional attention; for example in positioning of fasteners, differentiation in the side face and narrow face of the panels and the influence of potential gaps. The load–displacement behaviour of single, axially-loaded self-tapping screws positioned in the narrow face of CLT and failing in withdrawal was investigated. For the first time a multivariate probabilistic model was formulated together with models relating the parameters with the thread-fibre angle and the density. Different types and widths of gaps, initial slip and / or delayed stiffening as well as softening after exceeding of the maximum load can be considered. Beyond the scope of this contribution, the probabilistic model is seen as a worthwhile basis for investigations into the withdrawal behaviour of primary axially loaded, compact groups of screws positioned in timber products and subjected to withdrawal failure.
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10 records – page 1 of 1.