Page 65 - ROHANA_Journal_No_11-2019-ok

Research Journal of the University of Ruhuna, Sri Lanka- Rohana 11, 2019

Characteristic bending strength should be reduced by modification factors to derive
the grade bending stresses (Department of Communities and Local Government

2008). According to BS 5268-2, the modification factor for sections less than 72 mm

in depth and for short term loads are 0.856 and 0.571 respectively. Table 1 shows
the grade bending stresses calculated for clear and finger jointed timber specimens.

Table 1: Bending test results.

Bending strength Grade stress

Species Clear Finger Strength Clear Finger
2
2
(N/mm ) Jointed Reduction (N/mm ) Jointed
2
2
(N/mm ) % (N/mm )
Teak 26.02 23.20 10.84 13.97 10.4
Satin 27.94 25.28 9.5 24.12 20.93
Mahogany 24.59 16.64 32.34 8.93 7.72
Jak 30.58 17.49 42.82 8.53 8.4
Kumbuk 25.77 13.26 48.54 16.87 11.53
Grandis 29.39 16.09 45.25 8.92 7.74
Pine 20.86 16.8 19.43 9.08 8.8
Source: Author compiled

35 Clear Timber
Specimen
AVERAGE BENDING STRENGTH /(N/mm²) 20
30
Finger Jointed
Timber Specimen
25
15
10
5

0
Jak
Kumbuk
Satin
Teak
Mahogani
TIMBER SPECIES Grandis Pinus

Source: Author compiled

Figure 9: Comparison of the average bending strength of different timber
species

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