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C: Design Principles, Tendons [Table of Contents] Sec.4: Design Loads

DNV-OS-C105 Structural Design of TLPS (LRFD method)

[-] Sec.3: Design Principles
[-] C: Design Principles, Tendons
[-] C100: General

Sec.3
C 100   General

Sec.3 C
101   Essential components of the tendon system shall be designed by the principle that, as far as practicable, they are to be capable of being inspected, maintained, repaired and/or replaced.

Sec.3 C
102    Tendon mechanical components shall, as far as practicable, be designed to be "fail safe". Consideration is to be given in the design to possible early detection of failure for essential components, which cannot be designed according to this principle.

Sec.3 C
103   Certain vital tendon components may, due to their specialized functions, and if unproven, require engineering and prototype qualification testing to determine:
—confirmation of anticipated design performance
—fatigue characteristics
—fracture characteristics
—corrosion characteristics
—mechanical characteristics.


Sec.3 C
104   A TLP shall be designed with sufficient safety margin to prevent the potential of tendon rupture. The tendon system and the securing or supporting arrangements shall be designed in such a manner that a possible failure or removal of one tendon is not to cause progressive tendon failure or excessive damage to the securing or supporting arrangement at the platform or at the foundation.

Sec.3 C
105   A fracture control strategy should be adopted to ensure consistency of design, fabrication and in service monitoring assumptions. The objective of such a strategy is to ensure that the largest undetected flaw from fabrication of the tendons will not grow to a size that could induce failure within the design life of the tendon, or within the planned in-service inspection interval, within a reasonable level of reliability. Elements of this strategy include:
—adequate design fatigue life
—adequate fracture toughness
—reliability of inspection during fabrication
—in-service inspection intervals and methods.

See Sec.7 for guidance on fracture control and required fatigue life for tendons.

Sec.3 C
106   Inspection to detect damage due to accidental loads or overloads may be replaced by monitoring the loads and comparing them to the design loads, provided that the events can be measured by the monitoring system. If this method is used the component must be replaced after any overload occurrence or other events exceeding the design scenario.

Sec.3 C
107   All materials liable to corrode shall be protected against corrosion. Special attention should be given to:
—local complex geometries
—areas that are difficult to inspect or repair
—consequences of corrosion damage
—possibilities for electrolytic corrosion
—dissimilar metal.


Sec.3 C
108   All sliding surfaces shall be designed with sufficient additional thickness against wear. Special attention should be given to the following:
—cross-load bearings
—seals
—ball joints.


Sec.3 C
109   Satisfactory considerations shall be given to settlement or subsidence, which may be a significant factor in determining tendon-tension adjustment requirements.

C: Design Principles, Tendons [Table of Contents] Sec.4: Design Loads