Civil Engineering Reference
In-Depth Information
The stressed mechanical (friction) clamp uses long stud-bolts to produce a
friction grip on the repaired structural elements.
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The unstressed grouted repair clamp relies upon grout shear strength to
affect load transference, working in a similar way to a grouted pile sleeve
connection.
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The stressed grouted clamp is a hybrid of the above two clamp types, with
load being transferred partly by grout bond but mainly by friction. This type
is popular for its ability to tolerate dimensional variation while achieving
load transfer in a reasonable sleeve length.
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The stressed elastomer-lined clamp is similar to a mechanical clamp except
for the elastomer, which is usually a Neoprene liner that lies between the
member and the clamp. Such clamps are often selected for repairs to cais-
sons and other secondary structural elements.
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The basis of any clamp design must be the establishment of the forces in the
structural elements under operating and storm loading conditions. Normally, the
forces are evaluated for the undamaged condition and then the clamp is designed
so that load transfer is accomplished within the body of the repair clamp.
The technology for clamp installation is highly developed and a number of
specialist companies are now able to provide the necessary equipment and
materials on a contract basis.
Stressed Mechanical (Friction) Clamps
A stressed mechanical clamp is a steel-to-steel friction clamp that is connected
by long tension stud-bolts. The clamp comprises two or more segments of
closely fitting stiffened saddle plates, stressed directly onto a tubular section
by means of long stud-bolts. The strength of the mechanical connection is
obtained from steel-to-steel friction generated by compressive forces normal
to the tubular/clamp saddle interface, applied by the external bolt loads.
Stressed mechanical clamps are generally used for strengthening and repair
of damaged members or for connecting new members. A high degree of toler-
ance is required for close contact between the clamp and the tubular member.
Note that these clamps are unsuitable for repair of tubular joints. Furthermore,
this type of clamp requires full contact between the clamp and member surface
interface, so the clamp offers minimal translation or angular tolerances. Thus,
extremely accurate offshore surveys are needed for its proper construction
and the clamp requires very tight tolerances in fabrication. The connection
between clamp and tubular member is susceptible to crevice corrosion; there-
fore, the clamp needs periodical inspections to confirm bolt tension.
The major advantage of a mechanical clamp is that large forces can be trans-
ferred through friction over a short clamp length, limited only by the hoop resis-
tance of the member.
The time required for installation of stressed mechanical clamps varies
depending on the complexity of the clamp (for instance, number of clamp
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