Wood microstructure – A cellular composite

Published Date
2015, Pages 3–26, doi:10.1016/B978-1-78242-454-3.00001-9

Author 
M.P. Ansell

Abstract

Wood possesses a cellular, three-dimensional microstructure and is described as a natural composite material with orthotropic elastic properties. The mechanical properties of the wood cell wall, comprised of primary and secondary cell wall layers, are dictated by the orientation of stiff cellulose microfibrils in a matrix of hemicellulose and lignin. The hemicelluloses are closely associated with the cellulose microfibrils and these carbohydrate polymers are encrusted with non-carbohydrate lignin, affording protection from moisture and microbial organisms. The orientation of microfibrils has a direct influence on elastic properties of the wood cell wall and varies as a function of position in the tree and within annual rings. Numerous models of the wood cell wall have explored this relationship. Bound water content in the cell wall also affects mechanical properties together with swelling and shrinkage. The chapter concludes by presenting expanded forms of Hooke’s law for both wood (3D) and balanced veneers (2D), which are directly related to the wood composite microstructure.

Keywords

Wood microstructure

Microfibril angle

Chemical composition

Modelling the wood cell wall

Elastic properties of wood.

---

Figure 1.1.

Figure 1.2.

Figure 1.3.

Figure 1.4.

Figure 1.5.

Figure 1.6.

Figure 1.7.

Figure 1.8.

Figure 1.9.

Figure 1.10.

Figure 1.11.

Figure 1.12.

Figure 1.13.

Figure 1.14.

Figure 1.15.

Figure 1.16.

Figure 1.17.

Figure 1.18.

Figure 1.19.

Figure 1.20.

For further details log on website :
http://www.sciencedirect.com/science/book/9781782424543

Performance evaluation of traditional timber joints under cyclic loading and their influence on the seismic response of timber frame structures

Published Date
30 November 2016, Vol.127:321–334, doi:10.1016/j.conbuildmat.2016.09.122

Author 

Elisa Poletti ^a,,

Graça Vasconcelos ^a

Jorge M. Branco ^a

Aikaterini M. Koukouviki ^b

aISISE, Department of Civil Engineering, University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal

bCivil Engineer

Received 29 January 2016. Revised 20 August 2016. Accepted 28 September 2016. Available online 7 October 2016. 

Highlights

• Joints govern the behaviour of a timber structures.
• •
  Joints constitute the dissipative mechanism of timber structures for seismic events.
• •
  The quality of the joint (presence of gaps) greatly alters the response of a joint.
• •
  Strengthened joints present significantly higher stiffness and dissipative capacity.

Abstract 

Timber joints represent the governing part of a timber structure, particularly when assessing its seismic response. In order to better assess the seismic capacity of traditional timber frame structures, particularly timber-framed shear walls, pull-out and in-plane cyclic tests were carried out on their joints (half-lap joints). The aim is to better understand the influence of the joints on the walls and their influence on failure mechanisms and capacity.

Their seismic characterisation was obtained via the analysis of the hysteretic behaviour and dissipative capacity of both unreinforced and retrofitted joints (using self-tapping screws, steel plates and GFRP sheets).

Results show that all strengthening techniques were able to improve the dissipative and load-bearing capacity, but care should be taken into not over-stiffening the joints, as it would lead to an overly rigid structure.

Keywords

Half-lap joint

Seismic retrofitting

Self-tapping screws

GFRP

NSM

Steel plates

Dissipative capacity

---

Fig. 1.

Fig. 2.

Fig. 3.

 Table 1

Table 1.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.

Fig. 9.

Fig. 10.

Fig. 11.

Fig. 12.

Fig. 13.

Fig. 14.

Fig. 15.

Fig. 16.

• ⁎ 
  Corresponding author.
  
  

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0950061815004717

Self-tapping screws and threaded rods as reinforcement for structural timber elements – A state-of-the-art report

Published Date
30 October 2015, Vol.97:78–89, doi:10.1016/j.conbuildmat.2015.04.028
Special Issue: Reinforcement of Timber Structures

Author 

Philipp Dietsch ^a,,

Reinhard Brandner ^b,

aChair of Timber Structures and Building Construction, Technische Universität München, Germany

bInstitute of Timber Engineering and Wood Technology, Graz University of Technology, Austria

Received 6 January 2015. Revised 9 April 2015. Accepted 11 April 2015. Available online 8 May 2015.

Highlights

• Description of advantages of self-tapping screws as reinforcing elements.
• •
  Description of state-of-the-art in application and design approaches.
• •
  Extensive background information for all approaches described.
• •
  Results of German background literature summarized in English.

Author

In timber engineering, self-tapping screws, optimized primarily for axial loading, represent the state-of-the-art in fastener and reinforcement technology. Their economic advantages and comparatively easy handling make them one of the first choices for application in both domains. This paper focuses on self-tapping screws and threaded rods applied as reinforcement, illustrating the state-of-the-art in application and design approaches in Europe, in conjunction with numerous references for background information. With regard to medium to large span timber structures which are predominately erected by using linear timber members, from e.g. glued laminated timber, the focus of this paper is on their reinforcement against stresses perpendicular to grain as well as shear. However, latest findings with respect to cross laminated timber are included as well.

Keywords

Self-tapping screws

Rods

Reinforcement

Glued laminated timber

Cross laminated timber

Stresses perpendicular to the grain

Shear stresses

---

Fig. 1.

Fig. 2.

Fig. 3.

 Table 1

Table 1.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.

Fig. 9.

Fig. 10.

Fig. 11.

Fig. 12.

Fig. 13.

Fig. 14.

Fig. 15.

Fig. 16.

• ⁎ 
  Corresponding author.
  
  

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0950061815004717