Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 544

In summary, joint grouting increases the strength and fatigue performance of
a tubular joint. It doesn

'

t increase hydrodynamic load but it does add mass to
the structure. If a large volume of grout is used, excessive heat generated
while setting will need addressing. Consideration of mix design and heat loss
will be required.
The equipment required for a typical grout-filling operation is:

Diving spread ●

Drilling and tapping tools for grout ports ●

Underwater cutting and grinding equipment if temporary seals are to be
placed

●

Grouting spread

●

Monitoring equipment, such as video or still camera ●

Marine growth removal equipment. ●

Grout Filling of Members
Grout filling of a member increases both its cross-sectional strength and its
overall stability. This process provides a relatively easy way of strengthening
tubular members, particularly compression members with or without bending.
The grout filling the compression member increases the axial load capacity
and prevents local buckling.
As a direct effect of grout filling, the additional mass of the member, the
additional earthquake load due to increased inertia and the extra stiffness of
the member and tubular joints along its length need to be considered in design.
This technique is most beneficial to tubes with low L/D ratio and high D/t
ratios.
It is important that the grout completely fill up the tubular member, as small
voids close to the tubular inner wall may reduce the load-carrying capacity of
the strengthened member significantly. Void formation is also a potential
problem for all ring-stiffened tubular members.
If there is no damage to the member but an increase in axial load-carrying
capacity is sought, then a few preliminary calculations will indicate if there is
likely to be sufficient increase in member capacity. If the member is short and
has a low kl/r ratio, then the axial load capacity in compression will be
increased if the element is completely filled and load transference can be
made from the node-capping plate to the grout body. If the element has a
high D/T ratio, then there may be an improvement in load-carrying capacity
due to the prevention of local instability.
A large volume of grout will be used, so the grout design mix should be
done professionally to prevent generation of excess heat during setting.
On the other hand, grout filling has little benefit for tension members. In
addition, full grout filling must be achieved and the increase in mass due to
the filling of a member with grout may result in overstress of the member
under seismic and/or in-place conditions.