TIMBER - Civil Engineering short notes and previous year questions

TIMBER

Timber denotes wood which is suitable for building or carpentry and for various engineering and other purposes

PROCESSING OF TIMBER 

1. FELLING OF TREE 

• Age of tree for felling : 50 - 100 years 

• Season for felling 

• Hilly area : mid-summer 

• Plane area : mid-winter 

2. SEASONING OF TIMBER 

• Freshly felled tree moisture content : 50 % 

• optimum moisture content : 8 - 12% 

• Free moisture : moisture present in cell cavities 

• Bound moisture : moisture present in cell wall 

• Fiber saturation point : point at which no more moisture present in cell cavities 

i. NATURAL SEASONING 

• Arranged in stacks size 1.5 x 3m 

• Seasoning time : 2 - 4 years 

ii. ARTIFICIAL SEASONING 

• Kiln Seasoning : 3 to 12 days. 

• Chemical Seasoning : 30 to 40 days. 

• Electric Seasoning : 5 to 8 hours. 

iii. WATER SEASONING : 2 - 4 weeks

CLASSIFICATION OF TIMBER 

WR.TO SEASONING 

1. NON REFRACTORY TIMBER : no defects after seasoning , deodar, smule 

2. MODERATELY REFRACTORY : have small cracks , mango, rosewood, teak 

3. HIGHLY REFRACTORY : severe damage , axle wood, sal 

TYPES OF CONVERSION 

1. ORDINARY/ SLAB/BASTARD/FLAT SAWING 

• circumferential shrinking is the greatest due to the evaporation of moisture, 

• as sapwood shrinks much more than heartwood. 

• Thus rectangular pieces of wood become curved after sawing, called cupping. 

2. QUARTER SAWN TIMBER 

• Saw cuts are at right angles 

3. TANGENTIAL SAWING 

• Saw cuts are tangential to annual rings 

4. RADIAL/RIFT SAWING 

• High labor cost

DEFECTS IN TIMBER DEFECTS DUE TO CONVERSION 

1. CHIP MARK : marks placed by chips on the finished surface 

2. DIAGONAL GRAIN : due to improper sawing 

3. TORN GRAIN : depression made on finished surface by falling of tools 

4. WANE : presence of original rounded surface on manufactured wood

DEFECTS DUE TO FUNGI 

1. BLUE STAIN : color change to blue 

2. SAP STAIN : sap color change to brown 

3. WET ROT : due to alternate wetting and drying 

4. DRY ROT : wood converted to dry powder 

5. WHITE ROT : lignin become white in color 

6. BROWN ROT : cellulose changes to brown color 

7. HEART ROT : formed when a branch has come out of the tree

DEFECTS DUE TO NATURAL FORCES 

1. BURL/ BURR/ EXCRESCENCE : tree has received shock or injury in young age 

2. CALLUS : soft tissue which covers the wound 

3. CHEMICAL STAIN : discolouring 

4. COARSE GRAIN : annual rings widen, tree grows rapidly , makes wood soft 

5. DRUXINESS : presence of white spots 

6. FOXINESS : red , yellow tinge due to over maturity 

7. KNOT : 

• roots or base of small branches of tree 

i. Pin knot : < 6.5 mm 

ii. Small knot : 6.5 - 20 mm 

iii. Medium knot : 20 - 40 mm 

iv. Large knot : > 40 mm 

8. RIND GALS : 

• Curved swelling resulted from the growth of sap wood layers on wound, 

• left by falling or cut off branch in an irregular manner 

9. TWISTED FIBER : twisting of young tree by fast blowing wind 

10. UPSET : due to improper felling of the tree 

11. WIND CRACK : exterior surface crack due to fast blowing wind 

12. DEADWOOD : timber obtained from dead standing trees 

13. WATER STAIN : discoloring due to contact with water 

 14. SHAKE 

• The partial or complete separation between adjoining layers of tissues 

• Caused due to the shrinkage of wood 

• Types 

i. CUP SHAKE : small curved cracks on annual rings 

ii. HEART SHAKE : cracks in direction of medullary rays 

iii. RING SHAKE : cup shake covering the entire ring 

iv. STAR SHAKE : cracks extending from bark towards the sap wood 

v. RADIAL SHAKE : combination of star shake , heart shake , ring shake 

DEFECT DUE TO INSECT 

1. BEETLES : creates pinhole 2 mm dia 

2. MARINE BORERS : 25mm dia, 60mm length 

3. TERMITES : aka white ants 

DEFECTS DUE TO SEASONING 

1. BOW : curvature in the direction of length 

2. CUP : curvature in the transverse direction 

3. CHECK : crack which does not extent from one end to other 

4. SPILT : crack which extent from one end to other 

5. CASE HARDENING : exposed surface harden quickly than interior 

6. COLLAPSE : reduction in size of the timber 

7. TWIST : spirally distorted 

8. WARP : piece of timber bends out of shape 

9. HONEY COMPING :cracks develop in the interior portion of timber 

10. RADIAL SHAKE

MARKET FORMS OF TIMBER 

1. LOG : trunk after removal of branches 

2. END : short pieces of batten 

INDUSTRIAL FORMS OF TIMBER 

1. VENEERS : think sheets of superior wood , 0.4 - 0.6 mm 

2. PLYWOOD 

• combination of veneers and fiber 

• Layers placed perpendicular based on direction of grain 

• Expressed in thickness or no of plies 

3. FIBER BOARD / PRESSED BOARDS : wood fibers are placed between steel plates and pressed ( 8 - 12 mm ) 

4. IMPREG TIMBER : timber fully or partially covered with veneers using resin 

5. CUMPREG TIMBER : /// to impregg except pressure is applied while curing 

6. BLOCK BOARD : board having core made of strips of wood not exceeding 25 mm in width 

7. LAMIN BOARD : : board having core made of strips of wood not exceeding 7 mm in width 

8. HARD BOARD : made of wood pulp , 3 mm thick 

PREVIOUS YEAR REPEATED QUESTIONS BASED ON TIMBER