Civil Engineering Reference
In-Depth Information
As an example, eight stressed grouted clamps were fully installed on a
platform in the Gulf of Mexico in a total of 18 days. About one-third of this
time was used in removal of obstructions, while cleaning, clamp installation,
grouting and stud-bolt tensioning took an equal amount of time. It is important
to recognize, however, that installation time is very dependent on the complex-
ity of the clamp, access at the repair site, water depth at the repair site and envi-
ronmental conditions that may severely limit dive time and greatly influence
weather downtime.
Stressed grouted clamps can be viewed as representing the strength advan-
tages of stressed mechanical clamps with the tolerance advantages of unstressed
grouted clamps; it is therefore not surprising to note that stressed grouted
clamps are the most popular form of clamp used today.
The disadvantages of stressed grouted clamps include the grout seals, which,
if improperly fitted, often result in leakage of grout and loss of friction. The
advantages of these clamps are good transfer capacity, good tolerance for fit-
up and their ideal potential for clamping on joints and members. They are parti-
cularly good for repair of joints.
The required equipment and tools are the same as for the unstressed grouted
clamps.
Stressed Elastomer-Lined Clamp
Elastomer-lined clamps have not been used for primary structural repairs,
because of concerns that the flexibility of the liner may reduce the efficiency
of the repaired system. Therefore, this type of repair has been limited to second-
ary components where stiffness is not critical to effectiveness. Typically, elas-
tomer-lined clamps are used to seal holes in caissons and for stub connections to
appurtenances.
Installation time for stressed elastomer-lined clamps varies depending on the
complexity of the clamp (for instance, number of clamp segments, space limita-
tions and water depth at the repair site). In general, the times are similar to those
for stressed mechanical clamps.
Stressed elastomer-lined clamps are very similar to stressed mechanical
clamps, except that an elastomer lining is bonded to the inside faces of the
clamp saddle plates. The lining is a solid polychloroprene (Neoprene) sheet.
The strength of the clamp is derived from external bolt loads, which impart
compressive force normal to the interface of the liner and the tubular member.
This type of clamp is not recommended for transfer of forces between structural
components. It is recommended for the attachment of components, such as
guides for appurtenances.
The elastomer lining offers a degree of angular and translation tolerance,
eliminating the need for very accurate offshore surveys, as are required for
stressed mechanical clamps.
The relatively low stiffness of the liner gives rise to significant stud-bolt
load fluctuations due to elastomer relaxation. Fatigue of stud-bolts therefore
Search WWH ::
Custom Search