Civil Engineering Reference
In-Depth Information
segments), space limitations and water depth at the repair site. Typically,
installation times are 2
-
6 days, depending on size and complexity.
Over the past 20 years there have been numerous applications of stressed
mechanical clamps worldwide. Their use has principally been to repair or to
strengthen jacket components damaged by boat impact, fabrication flaws, fatigue
cracking and corrosion.
Stressed mechanical clamps are one of the quickest clamps to deploy and
have good transfer capacity. They require a detailed survey and good fabrica-
tion tolerances. They are ideal for clamping on intact tubular members to
strengthen, replace or add members.
For diver installation of a stressed mechanical clamp, the following items of
equipment/support are required:
Diving spread and divers
●
Crane for lifting and placing in position
●
Rigging for installation
●
Underwater cutting and grinding equipment, if obstructions have to be
removed
●
Stud-bolt tensioning equipment
●
Monitoring equipment, such as video camera
●
Equipment to remove marine growth and grit blast.
●
Unstressed Grouted Clamp Connections
The grouted sleeve clamp uses short bolts. An unstressed grouted clamp or sleeve
connection comprises sleeves placed around a tubular member or joint with the
annular space filled with grout. The sleeves may be split, as in the case of a clamp,
or continuous, as in a sleeve connection. For split sleeves, short bolts are pro-
vided and are tightened prior to injection of grout into the annulus.
The bond at the grout/steel interface provides the only means of transfer of
load between the tubular member and the clamp. To increase the capacity of the
clamp, its length needs to be increased. Shear keys, usually provided in the form
of weld beads, can increase the clamp capacity, but it should be kept in mind
that the underwater welding option is very expensive.
Unstressed grouted clamps and connections offer a versatile means for
strengthening or repairing tubular joints and members since they require less
accurate offshore survey. Both angular and translation tolerances can be readily
accommodated by the annulus. However, the loading regime and the availabil-
ity of space are dominant in deciding the suitability of an unstressed grouted
connection or clamp.
The installation time for this type of clamp varies depending on the com-
plexity of the clamp and the number of pieces in which the clamp is installed.
The number of bolts that have to be tensioned and the amount of grout will also
influence the installation time. As an example, two X joints strengthened using
unstressed grouted split-sleeve connections were reported to require a total dive
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