Biology and Life Sciences

Biology and Life Sciences

Grade (Design) Stresses for Boswellia papyrifera (Gafal) Wood Grown in Blue Nile State. Sudan

Pages: 12  ,  Volume: 15  ,  Issue: 1 , October   2018
Received: 01 Nov 2018  ,  Published: 08 November 2018
Views: 130  ,  Download: 0


# Author Name
1 Elamin Elhadi Elamin
2 Tageldin H. Nasroun


Timber is a natural and very variable material affected by many factors. This makes it important to determine mechanical properties by standard methods using small clear specimens. As clear wood is not available for use, it is important to apply all the necessary reduction factors to reach design stresses for structural sizes and the appropriate duration of load. Unlike other Man-made materials wood is also an anisotropic material, ie properties differ in the different directions to the grain. Both static bending and compression parallel to the grain tests were carried out according to standard procedures. Test results gave short duration ultimate stresses for clear wood (without defects). The basic stresses for the two properties were derived first by using two reduction factors to the mean ultimate stresses from test results to cater for wood variability, safety and duration of load. The Factors influencing strength were studied for grading the timber according to the size of strength reducing defects. This was followed by assigning a strength ratio to each grade. Grade (or design) stresses were then calculated by multiplying basic stress by the strength ratio for each grade. These Results revealed that the basic stress for bending for gafal wood was 10.8 MPa and 13.6 MPa for compression parallel to the grain. Grade (design) stresses in MPa, for the two properties were as follows: Grade 1 Grade 2 Grade 3 Grade 4 For Bending 8.64 7.02 5.40 4.32 For compression 10.53 8.55 6.58 5.26 These results indicate that gafal wood with its low density and low strength values can only be used for light constructions as columns and non-load bearing members in wood frame buildings. This procedure will be followed for structural timbers with higher strength which can be used for heavy constructions.



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