16 Types of pile
logs but the centre-line of a sawn timber pile must not deviate by more than 25 mm from a
straight line throughout its length. This is similar to the end to end centroid deviation
allowed in BS EN 14081-2: 2005 for rectangular structural timber.
The requirements of BS8004 for working stresses in timber piles merely state that
these should not exceed the green permissible stresses in BS5268-2 for compression
parallel to the grain for the species and grade of timber being used. The Code suggests
that suitable material will be obtained from stress grades SS and better. Grade stresses in
accordance with BS5268-2 are shown in Table 2.1, for various classes of softwood and
hardwood suitable for piling work. The working stresses shown in Table 2.1 for the hard-
woods are considerably higher than those of the comparable grades of softwood. It
should be noted that the stresses in Table 2.1 are for dry timber. Timber piles are usually
in a wet environment when the multiplying factors shown in Table 2.2 should be used to
convert the dry stress properties to the wet conditions. When calculating the working
stress on a pile, allowance must be made for bending stresses due to eccentric and lateral
loading and to eccentricity caused by deviations in the straightness and inclination of a
pile. Allowance must also be made for reductions in the cross-sectional area due to
drilling or notching and to the taper on a round log. Eurocode 5 (EC5) BSEN 1995-1:
2004 Design of timber structures: Part 1-1 provides common rules on stresses which will
be relevant to timber piling.
As a result of improved ability to predict and control driving stresses, BSEN 12699
allows the maximum compressive stress generated during driving to be increased to 0.8
Table 2.1Grade stresses and moduli of elasticity of some softwoods and tropical hardwoods suitable
for bearing piles
BS5268: Part 2: 2002 (values in N/mm^2 )
Standard Grade Bending Tension Compression Compression Shear Modulus of elasticity
name parallel parallel parallel perpendicular parallel
to grain to grain to grain to grain to grain' Mean Minimum
British larch SS 7.5 4.5 7.9 2.1 0.82 10 500 7000
Douglas fir SS 6.2 3.7 6.6 2.4 0.88 11 000 7000
Pitch pine SS 10.5 6.3 11.0 3.2 1.16 13 500 9000
Western red cedar SS 5.7 3.4 6.1 1.7 0.63 8500 5500
(imported) GS 4.1 2.5 5.2 1.6 0.63 7000 4500
Douglas fir-larch SS 7.5 4.5 7.9 2.4 0.85 11 000 7500
(Canada and USA) GS 5.3 3.2 6.8 2.2 0.85 10 000 6500
Greenheart HS 26.1 15.6 23.7 5.9 2.6 21 600 18 000
Jarrah HS 13.8 8.2 14.2 3.1 2.0 12 400 8700
Opepe HS 17.0 10.2 17.6 3.8 2.1 14 500 11 300
Teak HS 13.7 8.2 13.4 3.1 1.7 10 700 7400
Notes
- Stresses applicable to timber 300 mm deep (or wide).
' When the specifications specifically prohibit wane at bearing areas, the SS grade and HS grade comperssion perpendicular to
the grain stress may be multiplied by 1.33 and used for all grades.
SS denotes special structural grade (visually stressed graded).
HS denotes special structural grade (machine stress graded).
All stresses apply to long-term loading.