EI 02G001
CEMP-E
01 July 1997
The axial compression of a pile is given by the equation
Dp = ((Qb + "sQs)L + (Qb + Qs)(Lt-L))/(AbEp)............(1)
where
Dp
=
settlement from axial deformation of the
shaft, m or ft
Qb =
design load at the pile toe, kN or kips
"s =
distribution factor for load along the pile
length = 0.5 to 0.67; normally assume 0.5
Qs =
design load taken by shaft friction, kN or
kips
L
=
embedded length, m or ft = 16.159m or 53 ft
Lt
=
total pile length = 25.9m (85')
Ab
=
toe bearing area, m2 or ft2 = .258 m2 or
2.78 ft2
Ep
=
pile modulus of elasticity = 20,682,000 kPa
(432,000 kips/ft2)
A rough estimate of Qs may be made by assuming that Qs = Qsu, since nearly all
shaft resistance will be mobilized before significant toe resistance, unless the
pile toe is bearing on a hard stratum. Qb is then estimated by subtracting Qsu
from the design load Qd. If Qb and Qs are each assumed to take half of the load
or 267 kN (60 kips), then
Dp = 0.00218m (0.0072')...........(2a -- Qb = Qs = 267 kN)
If the design load of 534 kN (120 kips) is assumed to be taken totally by shaft
Dp = 0.00178m (.0058').................(2b -- Qs = 534 kN)
Figure 5-10. Computation of axial pile compression.
5-16
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