scope:

Introduction

This Recommended Practice (RP) presents recommendations for the strength analyses of main structures of column-stabilised units.

The design principles, overall requirements, and guidelines for the structural design of column-stabilised units are given in the DNV Offshore Standards:

- DNV-OS-C101 Design of Offshore Steel Structures, General (LRFD method)

- DNV-OS-C103 Structural Design of Column-stabilised Units (LRFD method)

- DNV-OS-C201 Design of Offshore Units (WSD method).

LRFD is use of the load and resistance factor design method. WSD is use of the working stress design method.

Details given in this RP are referring to the LRFD method.

The design principles with use of the LRFD method are described in DNV-OS-C101 Sec.2 with different limit states. A limit state is a condition beyond which a structure or part of a structure exceeds a specified design requirement. Design by the LRFD method is a design method by which the target component safety level is obtained by applying load and resistance factors to characteristic reference values of loads (load effects) and structural resistance.

The general principles described in this RP may also be applied with use of the WSD method. The design principles with use of the WSD method are described in DNV-OS-C201 Sec.2, with design conditions described by different modes of operation (draughts) or phases during the life of the unit. The following design conditions shall normally be considered: installation, operating, survival, transit, accidental, and damaged.