Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 543

Shear
key

Ss

Grout

Sp

t g

P ile diameter (Dp)

Slee ve diameter (Ds)

FIGURE 7.41 Grouting the annulus between piles and legs.

Filling tubular chord members with a cementitious material will increase
their strength, improve ductility, and increase the radial stiffness of the member
due to grout. The grout restricts local chord wall deformations, reducing
deformation-induced bending stresses and associated stress concentration
factors, so it will improve fatigue life.
Therefore, grout filling of tubular chord elements is used to improve the
static strength of the joint and to extend the fatigue life of the connections made
at the joint. The repair method has the advantage of introducing no additional
wave and current loads on the platform, but local dead loads can be increased.
Only grout-filled joints have been considered. It is therefore assumed that
the material is cementitious and not reinforced. If the joint is simply pumped
full of grout, then a simple grout-filled joint is created. In some instances
there will be a concentric pile within the joint, as is the case with many leg sec-
tions, and the resulting construction is then termed double-skinned. The grout is
assumed to completely fill the available annulus in the joint.
Ring stiffening is sometimes used at the joint to increase the resistance
capacity of the chord wall to applied member forces.
In most cases, grouting the joint takes 3

4 days, because time is needed to
install grout bag seals, to allow seals to set and cure, and then to grout the plug.
Void formation is a potential problem at ring-stiffened joints and at joints
with an expanded can diameter.

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