scope:

Purpose and Applicability

Part 5C of the ABS Rules for Building and Classing Steel Vessels (Steel Vessel Rules) presents the simplified fatigue assessment criteria for the classification of various types of specialized vessels covered by the Rules. Part 5A and 5B of the ABS Rules for Building and Classing Steel Vessels (Steel Vessel Rules) contains fatigue assessment guidance for vessels subject to the "Common Structural Rules for Bulk Carriers and Oil Tankers". A brief description of the background and objectives of these fatigue criteria is given in Subsection 1/3.

In addition to the simplified fatigue strength criteria required for classification by ABS, the Owner may wish to apply more extensive Spectral-based Fatigue Analysis (SFA) techniques to the vessel's structural systems. It may be an added objective of these Spectral-based Fatigue Analyses to demonstrate a longer design fatigue life than that required for classification.

Spectral-based Fatigue Analysis techniques are used in addition to the SafeHull Fatigue Assessment technique, a Permissible Stress Range method (discussed in Subsection 1/3). The fatigue life of each critical location in the structural system is assessed for adequacy. The critical locations are to be selected using the results of the SafeHull Fatigue Assessment technique which is to be employed in the overall structural design and analysis effort.

The list of critical structural locations which are to be subjected to Spectral-based Fatigue Analysis is to be submitted to ABS for approval.

Provided that Spectral-based Fatigue Analysis is conducted appropriately, ABS will grant the optional classification notation, SFA (years). The SFA (years) notation is granted if the design fatigue life is equal to 20 years or greater. The value in parentheses is the design fatigue life in years specified by the applicant in 5-year increments. The structural system is analyzed to verify that the calculated fatigue life values for the entire system meet or exceed the design fatigue life. The calculated fatigue lives are typically much higher than the design fatigue life. The actual service life of a vessel is dependent on many factors. The SFA (years) notation denotes the design fatigue life of a vessel and is not a guarantee that the vessel or structure will achieve the design fatigue life.

For vessels complying with Part 5A and 5B "Common Structural Rules for Bulk Carriers and Oil Tankers" of the Steel Vessel Rules, the design fatigue life for Spectral-based Fatigue Analysis is equal to 25 years or greater in 5-year increments.