### Timber testing laboratories

** Timber testing laboratories**

- Specific gravity
- Volumetric shrinkage
- compressive strength
- Tension Test
- Bending test
- 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 .

- 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

- 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 .

- 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

- 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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