Timber testing laboratories

 Timber testing laboratories

  1. Specific gravity 
  2. Volumetric shrinkage
  3. compressive strength 
  4. Tension Test
  5. Bending test
  6. Density -moisture relationship 

Specific gravity:

  •  The specimen of 50mm x 50mm x150mm is taken and its weight is measured.
  • The specific gravity of the timber is G=(W/V)(100/(100+M).where W=weight of the specimen ;v=volume of the specimen ;m=moisture content; specific gravity of good timber should be approximately 1.54
Volumetric shrinkage 
  • The specimen is weighted initialy and the volume is determined 
  • the specimen is kept in and oven at 1030 +-20'C untile approximately constant weight is reached.
  • volumetric shrinkage of the timber =(Vi-Vf)/Vi
  • Moisture content in percentage =(Wi-Wf)/Wi
  • Oven Dry specific gravity G=Wf /Vf
  • where Vi and Wi are initial volume and weight respectively Vf and Wf are final (oven dry sample's) volume and weight respectively .   
Compressive strength:
  • The specimen 50 x 50 x 200mm is used with grains generally perpendicular to the direction of the application of load (That is Perpendicular to 200mm side )
  • A load of 2,5 KN is initially applied to set the specimen.
  • deformation under compression is then measured over a central gauge length of 150mm. The final reading at maximum load is taken .
  • compressive strength of good timber at 15% moisture is 30 to 80 Mpa
Tension Test 
  • The test specimen with cross section 7mm x 7mm is used for this test , with the grains along the length of the specimen 
  • The specimen is gripped in UTM and the load is applied at constant rate of 2.5mm per minute till maximum load is applied 
  • The tensile strength of the specimen is the ratio of maximum load to the cross sectional area of the specimen 
  • the tensile strength of timber parallel to the fiber is of the order of 80 to 190 Mpa .
Bending test 
  • A test specimen in the form of a beam of 50 x 50 x 100mm is used for this test, with the grains parallelly to the length of the specimen.
  • Two point load are applied at a constant rate of 3mm per minute till crack the tension zone seen 
  • the bending strength of the specimen is calculated based on simple bending equation 
  • bending strength of various timber various from 40 to 100 MPa
Density moisture relationship 
  • The relation between density and moisture content of the wood.
  • For structural timber 10 to 20% 
  • Timber used for flooring 7 to 12% 
  • For building frames 13 to 20%

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