Civil Engineering Reference
In-Depth Information
The piles of offshore structures are exposed to static and cyclic loading, and
the loads will be axial and lateral. So all of these load effects should be con-
sidered in the pile design.
4.6.1 Pile Capacity for Axial Loads
On the basis of API RP2A (2007), the ultimate static axial capacity (QI)ofan
open-ended pipe pile in compression is given by the equation:
Q
t
=
Q
f
+
Q
s
+ f
small values fromQ
fi
or Q
sp
g
(4.11)
⋅
⋅
Q
t
=
f
A
s
+
A
a
Q
+
A
p
:
q
(4.12)
Where A
p
is the area of pile or
Q
t
=
f
⋅
⋅
A
s
+
A
a
Q
+
fA
si
(4.13)
where Q
t
= the total pile resistance, Q
f
= total outside shaft resistance, Q
s
= end-
bearing capacity of the annulus, Q
fi
= total inside shaft resistance, Q
sp
= bearing
capacity of the soil beneath the plug, f = unit skin friction capacity (in kPa),
A
s
= outside surface area of pile (in m
2
), q = unit end-bearing capacity (in kPa),
A
a
= the area of the pile annulus (in m
2
)andA
si
= inside surface area of pile (in m
2
).
In computing pile loading and capacity, the weight of the pile-soil plug sys-
tem and hydrostatic uplift should be considered.
In determining the load capacity of a pile, consideration should be given to
the relative deformations between the soil and the pile, as well as the compres-
sibility of the soil-pile system.
Coyle and Reese (1966)
,
Murff (1980)
and
Randolph (1983)
discussed skin
friction and assumed that the maximum skin friction along the pile and the max-
imum end bearing are mobilized simultaneously. However, the ultimate skin
friction increments along the pile are not necessarily directly additive, nor is
the ultimate end bearing necessarily additive with the ultimate skin friction.
In some circumstances, this effect may result in the capacity being less than
that given by
Equation (4.11)
.
In such cases, a more explicit consideration of axial pile performance effects
on pile capacity may be warranted. Pile sizing should be based on what experi-
ence has shown can be installed consistently, practically and economically
under similar conditions with the installation equipment being used. Alterna-
tives for possible remedial action in the event design objectives cannot be
obtained during installation should also be investigated and defined prior to
construction.
For the pile system, the pile-capacity factor of safety is defined in
Table 4.9
according to API RP2A (2007). The allowable skin friction values on the pile
section on the upper surface of the pile should be discounted in computing skin
friction resistance, Q
f
. The end-bearing area of a pilot hole, if drilled, should be
discounted in computing total bearing area.
Search WWH ::
Custom Search