Timber Properties

4 Key excerpts on "Timber Properties"

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  eBook - PDF

  An Introduction to Timber Engineering

  Pergamon Series of Monographs on Furniture and Timber

  • H. J. Andrews, Jack Kape(Authors)
  • 2014(Publication Date)
  • Pergamon

    (Publisher)

  CHAPTER 2 Timber as a Structural Material TIMBER is one of the very few living natural materials found widely distributed throughout the World, and in such vast quantities in many cases that its potential is not fully appreciated. If timber had resulted from a recent scientific discovery possessing all its natural characteristics, it would have a resounding effect in the construction industry, and in fact may well have delayed the advances made by other materials in this field. This new material can be made available in vast quantities and is able to reproduce each year more than that extracted for normal usage. It is competitive in cost and possesses unique strength characteristics in its ability to withstand shock treatment and retain permanent resilience. It is a natural insulating material, can be obtained in large sizes, and is readily worked into items of unique and exceptional beauty. Timber will stand up to considerable abuse and when properly used has an indefinite life. Left in its natural state, it possesses a wide variety of unique grain designs which when treated result in natural and enduring patterns. It can be painted and for this purpose provides a smooth surface; it is a material which can be worked with the simplest of tools; and its scrap value' is directly related to the size of pieces remaining after completing its first use. It possesses a useful weight-strength ratio superior to steel and concrete and is 9 A N I N T R O D U C T I O N T O T I M B E R E N G I N E E R I N G 10 more versatile in its application than any other known form of structural material. Timber has remained a primary construction material for thousands of years and the simple reason for this is that no other competitive material is as versatile or possesses all the advantages to be found in timber. Physical Properties A tree grows in size by the growth and development of new cells —myriads of new cells —direcdy under the bark and at the tips of the branches and roots.

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  eBook - PDF

  Timber Construction Manual

  • Jeff D. Linville(Author)
  • 2012(Publication Date)
  • Wiley

    (Publisher)

  1.8 CONCLUSION Timber construction encompasses several different structural systems and mate-rials, giving the designer flexibility to meet his structural and architectural needs. This chapter has presented an overview of timber construction including com-mon wood materials and structural systems. Additional guidance has been given regarding economy, durability, seasoning, handling, storage, and erection of 1.8 CONCLUSION 41 timber materials and systems. Where appropriate, references to other sources of information have been included. Chapter 2 presents fundamental information regarding the properties of wood. An understanding of these basic wood properties will enable a designer to maxi-mize the benefits of the timber members and systems while minimizing potential weaknesses and problems. Chapters 3 through 15 include detailed information regarding the structural design of timber components and connections using the Allowable Stress Design (ASD) methodology. Chapter 16 provides an overview of Load and Resistance Factor Design (LRFD). Chapters 17–19 discuss the design of timber bridges using both LRFD and ASD provisions. Chapter 20 cov-ers the topic of fire safety in timber construction. Appendices include additional design examples and supplemental information. CHAPTER 2 WOOD PROPERTIES 2.1 INTRODUCTION Wood is a cellular organic material made up primarily of cellulose, which com-prises the cells and lignin,which bonds the cells together. Wood cells are hollow and vary from about 0.04 to 0.33 in. in length and from 0.0004 to 0.0033 in. in diameter. Most cells are elongated and are oriented vertically in the growing tree, but some, called rays, are oriented horizontally and extend from the bark toward the center of the tree. 2.1.1 Hardwoods and Softwoods Trees are divided into two classes: hardwoods, which have broad leaves, and softwoods or conifers, which have needle-like or scale-like leaves.

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  eBook - PDF

  Timber

  Structure, Properties, Conversion and Use

  • H.E. Desch, J.M. Dinwoodie(Authors)
  • 2016(Publication Date)
  • Red Globe Press

    (Publisher)

  There are however a number of other physical properties, as distinct from mechanical properties (see Chapter I I), which are of secondary importance in many general timber applications, and of particular importance in a few specialised areas. This collection of prop-erties is covered in this chapter. 10.1 Thermal properties of wood 10. 1. 1 Thermal conductivity Thermal conductivity (A or k) of a material is a measure of its ability to transmit heat and is defined as the quantity of heat in joules which will flow through one square metre of the mate-rial one metre thick in one second where there is a one degree Celsius difference in temperature between its surfaces. It is therefore quantified in units of W /m K (W =Watts= joules/second; K = degrees Kelvin). Thus the smaller the value, the greater the resistance of the material to the passage of heat. Dry wood is one of the poorest conductors of heat and this characteristic renders wood emi-nently suitable for internal wall panelling, wall sheathing in timber frame house construction, wall cladding and as handles of cooking uten-sils. This outstanding performance of wood is due in part to the low conductivity of the actual cell wall materials, and in part to the cel-lular nature of wood which in its dry state con-tains within the cell cavities a large volume of air -one of the poorest conductors known. The cellular structure of wood also partly explains why heat is conducted about two to 96 three times as rapidly along, compared with across the grain and why, in association with variation in cell-wall thickness, heat is conducted more rapidly in high-density compared with low-density woods. A range of A values is presented in Table IO.I, illustrating the marked effects of density and grain orientation. This table also contains information on other materials in order to permit a direct comparison between timber and timber products and competing materials of construction.

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  eBook - ePub

  Current Perspectives and New Directions in Mechanics, Modelling and Design of Structural Systems

  Proceedings of The Eighth International Conference on Structural Engineering, Mechanics and Computation, 5-7 September 2022, Cape Town, South Africa

  • Alphose Zingoni(Author)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  There are different species of both the hardwood and softwood spread all over the tropical regions of the world. The mechanical properties of these wood are mostly responsible for their strength and use.

  One of the very important properties of engineering material is its microstructures. The mechanical and microstructural properties of hardwood were investigated by

  Wikete et al. (2010)

  , the microstructure-stiffness relationship for hardwood was observed through macroscopic mechanical experiments. Particularly, the large cylindrical vessels that run through the stem direction, the work was able to classify hardwood into ‘ring-porous’ and diffuse-porous’ as a result of what was observed in the experiment.

  This research aims to investigate the effect of wood microstructures on the mechanical properties of some selected tropical hardwood. Since several of these tropical hardwood species was not been listed in Table 14 of BS 5268-2 (2002) . The need to study these five tropical species arose because they are readily available and commonly used for construction and furniture purposes, but with very little information on their mechanical and microstructural properties to the best of our knowledge.

  2     Experimental Set Up

  Five samples of mature hardwood species were obtained from Malaaka village, in Abeokuta, Ogun State Nigeria. The local and botanical names for each tree species are African Mahogany (Afzelia africana), West African Albizia (Albizia zygia), Salt and Oil wood (Cleistopholis patens), African Birch (Anogeissus leiocarpus) and Beechwood (Gmelina arborea).

  2.1     Sawing and seasoning

  The sawn wood was arranged in an open environment protected from rain and the ground. It was arranged in such a way that air freely circulate it and was left in this state for 2 months (air seasoning).

  2.2     Moisture contents

  The sample was weighed after the period of seasoning and then dried in an oven at a temperature of 103 ± 2 °C (217 ± 4 °F) for 3 days until the weight was constant. The loss in weight expressed as a percentage of the final oven-dry weight was taken as the moisture content of the specimens

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