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Design of Shear Reinforcement for Timber Beams

https://research.thinkwood.com/en/permalink/catalogue1109
Year of Publication
2013
Topic
Connections
Design and Systems
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Dietsch, Philipp
Kreuzinger, Heinrich
Winter, Stefan
Year of Publication
2013
Country of Publication
Germany
Format
Conference Paper
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Connections
Design and Systems
Keywords
Shear
Reinforcement
Fractured
Unfractured
Language
English
Conference
CIB-W18 Meeting
Research Status
Complete
Notes
August 26-29, 2013, Vancouver, Canada p.193-209
Summary
The use of glulam beams with changing depth offers the possibility to adapt the section modulus to the bending moment. In the case of single-span beams under uniformly distributed load, however, a change in beam depth will lead to a contrary effect for the shear stresses, see Figure 1. Curved and pitched cambered beams feature not only high utilization rates in bending but also areas of high tension stresses perpendicular to the grain and shear parallel to the grain stresses, two stress components for which timber features only small capacities as well as brittle failure modes. Out of 245 cases of damaged or failed large-span timber structures, evaluated in [1], several failures document the possibility of a shear fracture (full separation) developing in grain direction from the curved part towards the supports, partly followed by a failure of the beam in flexural tension due to a change in stress distribution resulting from the change in section modulus. Reinforcements against tension stresses perpendicular to the grain in form of fully threaded screws or threaded rods can be considered state of the art [2], [3]. With respect to their application as shear reinforcement, not many research results are yet available [4], [5], resulting in a lack of experimentally validated design approaches. Within this paper, approaches to design shear reinforcement for glulam beams in the unfractured and the fractured state are presented, validated and discussed. The moment of failure, i.e. the transition from the unfractured to the fractured state is characterized by dynamic effects. This situation is not covered in this paper. A possible approach is given in [1]. The same applies to the subject of moisture induced stresses, resulting from the reinforcement restricting the free shrinkage or swelling of the glulam beam.
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Dynamic Effects in Reinforced Timber Beams at Time of Timber Fracture

https://research.thinkwood.com/en/permalink/catalogue2303
Year of Publication
2015
Topic
Design and Systems
Application
Beams

Effects of Changes in Moisture Content in Reinforced Glulam Beams

https://research.thinkwood.com/en/permalink/catalogue1173
Year of Publication
2014
Topic
Moisture
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Author
Dietsch, Philipp
Kreuzinger, Heinrich
Winter, Stefan
Year of Publication
2014
Country of Publication
Canada
Format
Conference Paper
Material
Glulam (Glue-Laminated Timber)
Topic
Moisture
Mechanical Properties
Keywords
Reinforcement
Threaded Rods
Moisture Induced Stresses
Finite Element Method
Moisture Content
Language
English
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 10-14, 2014, Quebec City, Canada
Summary
Reinforcement in glulam beams in form of screws or rods can restrict the free shrinkage or swelling of the wood material. The objective of the project presented was to evaluate the influence of such reinforcement on the magnitude of moisture induced stresses. For this purpose, experimental studies were carried out in combination with analytical considerations on the basis of the finite-element method. Taking into account the influence of relaxation processes, the results indicate that a reduction of timber moisture content of 3 - 4 % around threaded rods, positioned perpendicular to the grain, can lead to critical stresses with respect to moisture induced cracks. In addition, a substantial mutual influence of adjacent reinforcing elements has been identified. A reduction of the distance between the reinforcement thus results in a lower tolerable reduction of timber moisture content around the reinforcement.
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Shear Properties of Cross Laminated Timber (CLT) under In-Plane Load: Test Configuration and Experimental Study

https://research.thinkwood.com/en/permalink/catalogue180
Year of Publication
2015
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Brandner, Reinhard
Dietsch, Philipp
Dröscher, Julia
Schulte-Wrede, Michael
Kreuzinger, Heinrich
Sieder, Mike
Schickhofer, Gerhard
Winter, Stefan
Organization
International Network on Timber Engineering Research (INTER)
Year of Publication
2015
Country of Publication
Croatia
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Keywords
Diaphragms
Failure Mechanisms
Shear Strength
In-Plane Shear Test
Language
English
Conference
INTER 2015
Research Status
Complete
Notes
August 24-27, 2015, Sibenik, Croatia
Summary
Consolidated knowledge of CLT properties under in-plane shear is crucial for typical structural applications such as wall and floor diaphragms, cantilevered CLT walls and CLT used as (deep) beams, in all cases potentially featuring holes or notches. The current technical approvals for CLT products contain differing regulations to determine their load-carrying capacities in-plane. Generally they imply a verification of the torsional stresses in the cross-section of the cross-wise glued elements as well as a verification of the shear stresses proportionally assigned to the boards of the top and cross layers. The basis of theoretical and practical considerations are the following three basic failure scenarios for a CLT-element under in-plane shear: (i) gross-shear (longitudinal shearing in all layers), (ii) net-shear (transverse shearing in all layers in weak direction), and (iii) torsion failure in the gluing interfaces between the layers
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