Short Notes: Timber | Short Notes for Civil Engineering - Civil Engineering (CE) PDF Download

 Page 1


CHAPTER 7 
TIMBER 
Timber denotes wood, which is suitable for building or carpentry or 
various other engineering purposes like for construction of doors, 
windows, roofs, partitions, beams, posts, cupboards, shelves etc 
Uses of timber: 
(i) Used in the form of piles, posts, beams, lintels, door/window 
frames and leaves, roof members etc 
(ii) Used for flooring, ceiling, paneling and construction of 
partition walls 
(iii) Used for form work for concrete, for the timbering of 
trenches, centring for arch work, scaffolding, transmission 
poles and fencing 
(iv) Used in wagon and coach building, marine installations and 
bridges 
(v) Used in making furniture of agriculture implements, sports 
goods, musical instruments, well curbs, mortar bodies, carts 
and carriages, railway sleeps, packing cases etc 
7.1 Classification of trees 
Depending upon their mode of growth trees may be divided in 
the following two categories 
(i) Endogeneous trees – These trees grow inwards and fibrous 
mass is seen in their longitudinal sections. Timber from 
Page 2


CHAPTER 7 
TIMBER 
Timber denotes wood, which is suitable for building or carpentry or 
various other engineering purposes like for construction of doors, 
windows, roofs, partitions, beams, posts, cupboards, shelves etc 
Uses of timber: 
(i) Used in the form of piles, posts, beams, lintels, door/window 
frames and leaves, roof members etc 
(ii) Used for flooring, ceiling, paneling and construction of 
partition walls 
(iii) Used for form work for concrete, for the timbering of 
trenches, centring for arch work, scaffolding, transmission 
poles and fencing 
(iv) Used in wagon and coach building, marine installations and 
bridges 
(v) Used in making furniture of agriculture implements, sports 
goods, musical instruments, well curbs, mortar bodies, carts 
and carriages, railway sleeps, packing cases etc 
7.1 Classification of trees 
Depending upon their mode of growth trees may be divided in 
the following two categories 
(i) Endogeneous trees – These trees grow inwards and fibrous 
mass is seen in their longitudinal sections. Timber from 
Timber                                                                              
  
these trees has very limited engineering applications Ex: 
bamboo, cane , palm etc 
(ii) Exogeneous trees: These increases in bulk by growing 
outwards and used for engineering purposes. 
 Exogeneous trees are further sub divided into two groups  
a) conifers  b) deciduous 
a) Conifers or evergreen trees: These trees having pointed, 
needle like or scale like leaves and yield soft wood 
b) Deciduous trees: The trees having flat broad leaves and 
leaves of those trees fall in autumn and new ones appear 
in spring season. Timber for engineering purpose is 
mostly derived from deciduous trees. These trees yield 
hard wood. 
Ex: ash, beach, oak, sal, teak, shishum and wallnut 
Comparison of softwood and hard wood 
S.No. Item   Soft wood        Hard wood 
1. Annual rings  Distinct  Indistinct 
2. colour   light   dark 
3. fire resistance  poor   more 
4. modullary rays Indistinct  distinct 
5. Structure  resinous and           non-resinous  
split easily      & close grained 
6. weight   light   heavy 
7. strength  strong for direct     equally strong 
    Pull & weak for      for resisting 
    Resisting thrust      tension,compr 
    or shear      -ession & shear 
Page 3


CHAPTER 7 
TIMBER 
Timber denotes wood, which is suitable for building or carpentry or 
various other engineering purposes like for construction of doors, 
windows, roofs, partitions, beams, posts, cupboards, shelves etc 
Uses of timber: 
(i) Used in the form of piles, posts, beams, lintels, door/window 
frames and leaves, roof members etc 
(ii) Used for flooring, ceiling, paneling and construction of 
partition walls 
(iii) Used for form work for concrete, for the timbering of 
trenches, centring for arch work, scaffolding, transmission 
poles and fencing 
(iv) Used in wagon and coach building, marine installations and 
bridges 
(v) Used in making furniture of agriculture implements, sports 
goods, musical instruments, well curbs, mortar bodies, carts 
and carriages, railway sleeps, packing cases etc 
7.1 Classification of trees 
Depending upon their mode of growth trees may be divided in 
the following two categories 
(i) Endogeneous trees – These trees grow inwards and fibrous 
mass is seen in their longitudinal sections. Timber from 
Timber                                                                              
  
these trees has very limited engineering applications Ex: 
bamboo, cane , palm etc 
(ii) Exogeneous trees: These increases in bulk by growing 
outwards and used for engineering purposes. 
 Exogeneous trees are further sub divided into two groups  
a) conifers  b) deciduous 
a) Conifers or evergreen trees: These trees having pointed, 
needle like or scale like leaves and yield soft wood 
b) Deciduous trees: The trees having flat broad leaves and 
leaves of those trees fall in autumn and new ones appear 
in spring season. Timber for engineering purpose is 
mostly derived from deciduous trees. These trees yield 
hard wood. 
Ex: ash, beach, oak, sal, teak, shishum and wallnut 
Comparison of softwood and hard wood 
S.No. Item   Soft wood        Hard wood 
1. Annual rings  Distinct  Indistinct 
2. colour   light   dark 
3. fire resistance  poor   more 
4. modullary rays Indistinct  distinct 
5. Structure  resinous and           non-resinous  
split easily      & close grained 
6. weight   light   heavy 
7. strength  strong for direct     equally strong 
    Pull & weak for      for resisting 
    Resisting thrust      tension,compr 
    or shear      -ession & shear 
Structure of tree: From the visibility aspect, the structure of a tree can 
be divided into two categories  
1. Macro structure 
2. Micro structure 
I. Macro structure: The structure of wood visible to the naked 
eye or at a small magnification is called macro structure. Fig 
7.1 shows the macro structure of exogenous tree. 
 
Fig 7.1 Micro structure of exogenous tree 
(i) Pith: The innermost central portion or core of the tree 
is called pith or medulla 
(ii) Heart wood: The inner annual rings surrounding the 
pith is known as heart wood. It imparts rigidity to tree 
Page 4


CHAPTER 7 
TIMBER 
Timber denotes wood, which is suitable for building or carpentry or 
various other engineering purposes like for construction of doors, 
windows, roofs, partitions, beams, posts, cupboards, shelves etc 
Uses of timber: 
(i) Used in the form of piles, posts, beams, lintels, door/window 
frames and leaves, roof members etc 
(ii) Used for flooring, ceiling, paneling and construction of 
partition walls 
(iii) Used for form work for concrete, for the timbering of 
trenches, centring for arch work, scaffolding, transmission 
poles and fencing 
(iv) Used in wagon and coach building, marine installations and 
bridges 
(v) Used in making furniture of agriculture implements, sports 
goods, musical instruments, well curbs, mortar bodies, carts 
and carriages, railway sleeps, packing cases etc 
7.1 Classification of trees 
Depending upon their mode of growth trees may be divided in 
the following two categories 
(i) Endogeneous trees – These trees grow inwards and fibrous 
mass is seen in their longitudinal sections. Timber from 
Timber                                                                              
  
these trees has very limited engineering applications Ex: 
bamboo, cane , palm etc 
(ii) Exogeneous trees: These increases in bulk by growing 
outwards and used for engineering purposes. 
 Exogeneous trees are further sub divided into two groups  
a) conifers  b) deciduous 
a) Conifers or evergreen trees: These trees having pointed, 
needle like or scale like leaves and yield soft wood 
b) Deciduous trees: The trees having flat broad leaves and 
leaves of those trees fall in autumn and new ones appear 
in spring season. Timber for engineering purpose is 
mostly derived from deciduous trees. These trees yield 
hard wood. 
Ex: ash, beach, oak, sal, teak, shishum and wallnut 
Comparison of softwood and hard wood 
S.No. Item   Soft wood        Hard wood 
1. Annual rings  Distinct  Indistinct 
2. colour   light   dark 
3. fire resistance  poor   more 
4. modullary rays Indistinct  distinct 
5. Structure  resinous and           non-resinous  
split easily      & close grained 
6. weight   light   heavy 
7. strength  strong for direct     equally strong 
    Pull & weak for      for resisting 
    Resisting thrust      tension,compr 
    or shear      -ession & shear 
Structure of tree: From the visibility aspect, the structure of a tree can 
be divided into two categories  
1. Macro structure 
2. Micro structure 
I. Macro structure: The structure of wood visible to the naked 
eye or at a small magnification is called macro structure. Fig 
7.1 shows the macro structure of exogenous tree. 
 
Fig 7.1 Micro structure of exogenous tree 
(i) Pith: The innermost central portion or core of the tree 
is called pith or medulla 
(ii) Heart wood: The inner annual rings surrounding the 
pith is known as heart wood. It imparts rigidity to tree 
Timber                                                                                             
  
(iii) Sap wood: The cuter annual rings between heart 
wood and cambium layer is known as sap wood 
(iv) Cambium layer: Thin layer of sap between sap wood 
and inner bark is known as cambium layer 
(v) Inner bark: The inner skin or layer covering the 
cambium layer is known as inner bark 
(vi) Outer Bark: The outer skin or cover of the tree is 
known as outer bark 
(vii) Medullary rays: The thin radial fibres extending 
from pith to cambium layer are known as medullary 
rays 
II. Micro structure: The structure of wood apparent only at 
great magnifications is called micro structure under micro 
scope, it becomes evident that the wood consists of living and 
lead cells of various sizes and shapes. 
7.2 Defects in Timber: 
Defects occurring in timber are grouped into the following 
divisions. 
a) Defects due to conversion: During the process of converting 
timber to commercial form, the following defects may occur. 
(i) Chip mark: mark or sign placed by chip on finished 
surface of timber 
(ii) Diagonal grain: Due to improper sawing of timber 
Page 5


CHAPTER 7 
TIMBER 
Timber denotes wood, which is suitable for building or carpentry or 
various other engineering purposes like for construction of doors, 
windows, roofs, partitions, beams, posts, cupboards, shelves etc 
Uses of timber: 
(i) Used in the form of piles, posts, beams, lintels, door/window 
frames and leaves, roof members etc 
(ii) Used for flooring, ceiling, paneling and construction of 
partition walls 
(iii) Used for form work for concrete, for the timbering of 
trenches, centring for arch work, scaffolding, transmission 
poles and fencing 
(iv) Used in wagon and coach building, marine installations and 
bridges 
(v) Used in making furniture of agriculture implements, sports 
goods, musical instruments, well curbs, mortar bodies, carts 
and carriages, railway sleeps, packing cases etc 
7.1 Classification of trees 
Depending upon their mode of growth trees may be divided in 
the following two categories 
(i) Endogeneous trees – These trees grow inwards and fibrous 
mass is seen in their longitudinal sections. Timber from 
Timber                                                                              
  
these trees has very limited engineering applications Ex: 
bamboo, cane , palm etc 
(ii) Exogeneous trees: These increases in bulk by growing 
outwards and used for engineering purposes. 
 Exogeneous trees are further sub divided into two groups  
a) conifers  b) deciduous 
a) Conifers or evergreen trees: These trees having pointed, 
needle like or scale like leaves and yield soft wood 
b) Deciduous trees: The trees having flat broad leaves and 
leaves of those trees fall in autumn and new ones appear 
in spring season. Timber for engineering purpose is 
mostly derived from deciduous trees. These trees yield 
hard wood. 
Ex: ash, beach, oak, sal, teak, shishum and wallnut 
Comparison of softwood and hard wood 
S.No. Item   Soft wood        Hard wood 
1. Annual rings  Distinct  Indistinct 
2. colour   light   dark 
3. fire resistance  poor   more 
4. modullary rays Indistinct  distinct 
5. Structure  resinous and           non-resinous  
split easily      & close grained 
6. weight   light   heavy 
7. strength  strong for direct     equally strong 
    Pull & weak for      for resisting 
    Resisting thrust      tension,compr 
    or shear      -ession & shear 
Structure of tree: From the visibility aspect, the structure of a tree can 
be divided into two categories  
1. Macro structure 
2. Micro structure 
I. Macro structure: The structure of wood visible to the naked 
eye or at a small magnification is called macro structure. Fig 
7.1 shows the macro structure of exogenous tree. 
 
Fig 7.1 Micro structure of exogenous tree 
(i) Pith: The innermost central portion or core of the tree 
is called pith or medulla 
(ii) Heart wood: The inner annual rings surrounding the 
pith is known as heart wood. It imparts rigidity to tree 
Timber                                                                                             
  
(iii) Sap wood: The cuter annual rings between heart 
wood and cambium layer is known as sap wood 
(iv) Cambium layer: Thin layer of sap between sap wood 
and inner bark is known as cambium layer 
(v) Inner bark: The inner skin or layer covering the 
cambium layer is known as inner bark 
(vi) Outer Bark: The outer skin or cover of the tree is 
known as outer bark 
(vii) Medullary rays: The thin radial fibres extending 
from pith to cambium layer are known as medullary 
rays 
II. Micro structure: The structure of wood apparent only at 
great magnifications is called micro structure under micro 
scope, it becomes evident that the wood consists of living and 
lead cells of various sizes and shapes. 
7.2 Defects in Timber: 
Defects occurring in timber are grouped into the following 
divisions. 
a) Defects due to conversion: During the process of converting 
timber to commercial form, the following defects may occur. 
(i) Chip mark: mark or sign placed by chip on finished 
surface of timber 
(ii) Diagonal grain: Due to improper sawing of timber 
(iii) Torn grain: Due to falling of tool small impression is 
formed 
(iv) Wane: Presence of original rounded surface on the 
manufactured piece of timber 
b) Defects due to fungi: The attack of timber by fungi when 
moisture content of timber is above 20% and presence of air and 
warmth for the growth of fungi the following defects are caused 
(i) Blue stain: Sap of wood is stained to bluesh colour 
(ii) Brown rot: Decay or disease of timber by removal of 
cellulose compounds from wood and wood assumes the 
brown colour 
(iii) Dry rot: Convert the wood into dry powder form 
(iv) Heart rot: This is formed when branch has come out of a 
tree and the tree becomes weak and gives out hallow 
sound when struck with a hammer  
(v) Sap stain: The sap wood looses its colour because of feed 
on cell contents of sap wood. 
(vi) Wet rot: Caused chemical decomposition of wood of the 
timber and timber converts to grayish brown powder 
known as wet rot. 
(vii) White rot: Attack lignin of wood and wood assumes the 
appearance of white mass