Undrained Load Capacity of Torpedo Anchors in ... - laceo - UFRJ

14000
14000
12000
12000
Load capacity (kN)
10000
8000
6000
4000
2000
0
0.00m
0.15m
0.45m
0.90m
0 10 20 30 40 50 60 70 80 90
Angle (degrees)
Figure 17 – Load capacities for different flukes length
considering a torpedo anchor with 4 flukes and soil B.
Effect of the angle between the load direction and the plane of
the flukes
FE meshes of an anchor with 4 flukes were constructed to
evaluate the effect of the angle between the load and the plane
of the flukes. Two sets of analyses were carried out: in the first
group, called 45° analyses, loads were assumed to be at an
angle of 45° with the plane of the flukes (plane 1, Fig. 11); in
the second group, called 0° analyses, loads were aligned with
the flukes (plane 2, Fig. 11). Again, the anchor is supposed to
be embedded in soil B.
Figure 18 presents the estimated load capacities. From this
figure, it is possible to observe that the load capacities for
inclinations between 45° and 90° are equal, because, as pointed
out before, the failure mechanism is ruled by the vertical
resistance of the anchor. For lower inclinations, the load
capacities estimated for loads aligned with the flukes are
slightly higher than the ones predicted when the loads are
assumed to be between the flukes.
Thus, the load angle with respect to the plane of the flukes
does not alter the load capacity of the anchor. This points to the
conclusion that the lateral projected area of the anchor is not
relevant to the total load capacity of the structure.
Load capacity (kN)
10000
8000
6000
4000
2000
0
0 10 20 30 40 50 60 70 80 90
Angle (degrees)
0°
45°
Figure 18 – Load capacities for different angles between the
plane of the loads and the flukes. Torpedo anchor with 4
flukes and soil B.
CONCLUSIONS
This paper presented a numerical based study on the
undrained load capacity of a typical torpedo anchor embedded
in a purely cohesive isotropic soil using a three-dimensional
nonlinear finite element (FE) model.
In this model, the soil was simulated with solid elements
capable of representing its nonlinear physical behavior and the
large deformations involved. The torpedo anchor was also
modeled with solid elements and its complex geometry was
represented in detail. Moreover, the anchor-soil interaction was
addressed with contact finite elements that allow relative
sliding with friction between the surfaces in contact.
Various analyses were conducted in order to understand the
response of this type of anchor when different soil undrained
shear strengths, load directions and number and width of flukes
are considered.
The obtained results points to two different failure
mechanisms:
1. The first one mobilizes a great amount of soil and is
directly related to its lateral resistance. This
mechanism does not exhibit a clear load limit.
2. The second one mobilizes a small amount of soil and
is related to the vertical resistance of the soil. In this
case, the load capacity is well characterized.
Besides, the total contact area of the anchor and soil seems
to be an important parameter in the determination of its load
capacity and, consequently, the increase of the undrained shear
strength and the number of flukes significantly increases the
load capacity of the torpedo anchor.
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