Clasification Society Rulefinder 2020 - Version 9.33 - Fix
Common Structural Rules - Common Structural Rules for Bulk Carriers and Oil Tankers, January 2019 - Part 1 General Hull Requirements - Chapter 4 Loads - Section 1 Introduction - 1 General

1 General

1.1 Application

1.1.1 Scope

This chapter provides the design load for strength and fatigue assessments.

The load combinations are to be derived for the design load scenarios specified in Ch 4, Sec 7. This section uses the concept of design load scenarios to specify consistent design load sets which cover the appropriate operating modes of a bulk carrier or oil tanker.

1.1.2 Equivalent Design Wave EDW

The dynamic loads associated with each dynamic load case are based on the Equivalent Design Wave (EDW) concept. The EDW concept applies a consistent set of dynamic loads to the ship such that specified dominant load response is equivalent to the required long term response value.

1.1.3 Probability level for strength and fatigue assessments

In this chapter, the assessments are to be understood as follows:

  • Strength assessment means the assessment for the strength criteria excluding fatigue, for the loads corresponding to the probability level of 10-8, for the ballast water exchange, for harbour conditions and for flooded conditions.
  • Fatigue assessment means the assessment for the fatigue criteria for the loads corresponding to the probability level of 10-2.

1.1.4 Dynamic load components

All dynamic load components are to be concurrent values calculated for each dynamic load case.

1.1.5 Loads for strength assessment

The strength assessment is to be undertaken for all design load scenarios and the final assessment is to be made on the most onerous strength requirement.

Each design load scenario for strength assessment is composed of a Static (S) load case or a Static + Dynamic (S+D) load case, where the static and dynamic loads are dependent on the loading condition being considered.

The static loads are defined in the following sections:

The EDWs for the strength assessment and the dynamic load combination factors for global loads are listed in Ch 4, Sec 2, [2].

The dynamic load components are defined in the following sections:

1.1.6 Loads for fatigue assessment

Each design load scenario for fatigue assessment is composed of a Static + Dynamic (S+D) load case, where the static and dynamic loads are dependent on the loading condition being considered.

The static loads are defined in the following sections:

The EDWs for the fatigue assessment are listed in Ch 4, Sec 2, [3].

The dynamic load components are defined in the following sections:

1.2 Definitions

1.2.1 Coordinate system

The coordinate system is defined in Ch 1, Sec 4, [3.6.1].

1.2.2 Sign convention for ship motions

The ship motions are defined with respect to the ship’s centre of gravity (COG) as shown in Figure 1, where:

  • Positive surge is translation in the X-axis direction (positive forward).
  • Positive sway is translation in the Y-axis direction (positive towards port side of ship).
  • Positive heave is translation in the Z-axis direction (positive upwards).
  • Positive roll motion is positive rotation about a longitudinal axis through the COG (starboard down and port up).
  • Positive pitch motion is positive rotation about a transverse axis through the COG (bow down and stern up).
  • Positive yaw motion is positive rotation about a vertical axis through the COG (bow moving to port and stern to starboard).

Figure 1 : Definition of positive motions

1.2.3 Sign convention for hull girder loads

The sign conventions of vertical bending moments, vertical shear forces, horizontal bending moments and torsional moments at any ship transverse section are as shown in Figure 2, namely:

  • The vertical bending moments Msw and Mwv are positive when they induce tensile stresses in the strength deck (hogging bending moment) and negative when they induce tensile stresses in the bottom (sagging bending moment).
  • The vertical shear forces Qsw, Qwv are positive in the case of downward resulting forces acting aft of the transverse section and upward resulting forces acting forward of the transverse section under consideration.
  • The horizontal bending moment Mwh is positive when it induces tensile stresses in the starboard side and negative when it induces tensile stresses in the port side.
  • The torsional moment Mwt is positive in the case of resulting moment acting aft of the transverse section following negative rotation around the X-axis, and of resulting moment acting forward of the transverse section following positive rotation around the X-axis.

Figure 2 : Sign conventions for shear forces Qsw, Qwv and bending moments Msw, Mwv, Mwh and Mwt

Parent topic: Section 1 Introduction
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