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DNV-OS-C103 Structural Design of Column Stabilised Units (LRFD method) [Table of Contents] Sec.2: Structural Categorisation, Material Selection and Inspection Principles

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

[-] Sec.1: Introduction

SECTION 1
Introduction

Sec.1
A. General

Sec.1
A 100   General

Sec.1 A
101   This offshore standard provides requirements and guidance for the structural design of column-stabilised units, constructed in steel.

Sec.1 A
102   The standard has been written for general world-wide application. Governmental regulations may include requirements in excess of the provisions given by this standard depending on the size, type, location and intended service of an offshore unit or installation.

Sec.1
A 200   Objectives

Sec.1 A
201   The objectives of this standard are to:
—provide an internationally acceptable standard of safety by defining minimum requirements for design of column-stabilised units
—serve as a contractual reference document between suppliers and purchasers
—serve as a guideline for designers, suppliers, purchasers and regulators
—specify procedures and requirements for column-stabilised units subject to DNV verification.

Sec.1
A 300   Assumptions and applications

Sec.1 A
301   The requirements and guidance documented in this standard are generally applicable to all configurations of column-stabilised units, including those with:
—ring pontoons
—twin pontoons.


Sec.1 A
302   A column-stabilised unit is a floating structure that can be relocated. A column-stabilised unit normally consists of a deck box with a number of widely spaced, large diameter, supporting columns that are attached to submerged pontoons.

Sec.1 A
303   Column-stabilised unit may be kept on station by either a passive mooring system, e.g. anchor lines, or an active mooring system, e.g. thrusters, or a combination of these methods.

Sec.1 A
304   Requirements concerning mooring and riser systems are not considered in this standard.

Sec.1 A
305   A column-stabilised unit may be designed to function in a number of modes, e.g. transit, operational and survival. Limiting design criteria modes of operation shall be clearly established and documented. Such limiting design criteria shall include relevant consideration of the following items:
—intact condition, structural strength
—damaged condition, structural strength
—air gap
—watertight integrity and hydrostatic stability.


Sec.1 A
306   For novel designs, or unproved applications of designs where limited or no direct experience exists, relevant analyses and model testing, shall be performed to clearly demonstrate that an acceptable level of safety is obtained.

Sec.1
A 400   Classification

Sec.1 A
401   Classification principles, procedures and applicable class notations related to classification services of offshore units are specified in the DNV Offshore Service Specifications given in Table A1.

Sec.1 A
Table A1 DNV Offshore Service Specifications 
Reference Title 
DNV-OSS-101 Rules for Classification of Drilling and Support Units 
DNV-OSS-102 Rules for Classification of Production and
Storage Units 



Sec.1 A
402   Documentation for classification shall be in accordance with the NPS DocReq (DNV Nauticus Production System for documentation requirements) and DNV-RP-A201.

Sec.1 A
403   Technical requirements given in DNV-OS-C101, section 8, related to Serviceability Limit States, are not mandatory as part of classification.

Sec.1
B. References

Sec.1
B 100   General

Sec.1 B
101   The Offshore Standards, Recommended Practices and Classification Notes given in Table B1 are referred to in this standard.

Sec.1 B
Table B1 DNV Offshore Standards, Classification Notes and Recommended Practices 
Reference Title 
DNV-OS-A101 Safety Principles and Arrangement 
DNV-OS-B101 Metallic Materials 
DNV-OS-C101 Design of Offshore Steel Structures,
General (LRFD method) 
DNV-OS-C301 Stability and Watertight Integrity 
DNV-OS-C401 Fabrication and Testing of Offshore Structures 
DNV-OS-D101 Marine and Machinery Systems and Equipment 
DNV-OS-D301 Fire Protection 
DNV-OS-E301 Position Mooring 
DNV-RP-C103 Column-stabilised Units 
DNV-RP-C201 Buckling of Plated Structures 
DNV-RP-C202 Buckling Strength of Shells 
DNV-RP-C203 Fatigue Strength Analysis 
DNV-RP-C205 Environmental Conditions and Environmental Loads 
Classification Note 30.1 Sec. 2 Buckling Strength Analysis (Bars and Frames) 
Classification Note 30.6 Structural Reliability Analysis of Marine Structures 
 Rules for Planning and Execution of Marine Operations 

Sec.1
C. Definitions

Sec.1
C 100   Verbal forms

Sec.1 C
101   Shall: Indicates a mandatory requirement to be followed for fulfilment or compliance with the present standard. Deviations are not permitted unless formally and rigorously justified, and accepted by all relevant contracting parties.

Sec.1 C
102   Should: Indicates a recommendation that a certain course of action is preferred or particularly suitable. Alternative courses of action are allowable under the standard where agreed between contracting parties but shall be justified and documented.

Sec.1 C
103   May: Indicates a permission, or an option, which is permitted as part of conformance with the standard.

Sec.1
C 200   Terms

Sec.1 C
201   Transit conditions: All unit movements from one geographical location to another.

Sec.1 C
202   Standard terms are given in DNV-OS-C101.

Sec.1
D. Symbols

Sec.1
D 100   Symbols

Sec.1 D
101   Latin characters
raster  = the intercept of the design S-N curve with the log N axis 
ah = horizontal acceleration  
av = vertical acceleration  
g0 = 9.81 m/s2 acceleration due to gravity 
h = Weibull shape parameter 
hop = vertical distance from the load point to the position of maximum filling height 
M = mass of cargo, equipment or other components 
m = the inverse slope of the S-N curve 
n0 = total number of stress fluctuations during the lifetime of the structure 
ni = number of stress fluctuations in i years 
pd = design pressure  
pdyn = pressure head due to flow through pipes 
zb = vertical distance in m from the moulded baseline to the load point 
Cw = reduction factor due to wave particle motion (Smith effect)  
DD = vertical distance from the moulded baseline to the underside of the deck structure 
DFF = Design Fatigue Factor 
PHd = horizontal design force 
PVd = vertical design force 
TE = extreme operational draught measured vertically from the moulded baseline to the assigned load waterline. 



Sec.1 D
102   Greek characters
G = gamma function  
a = angle 
r = density 
gc = contingency factor 
td = nominal design shear stress in the girder adjusted for cut-outs  
gf = partial load factor  
gf,E  = partial load factor for environmental loads 
gf,G,Q = partial load factor for functional and variable loads. 

Sec.1
D 200   Abbreviations

Sec.1 D
201   Abbreviations used in this standard are given in DNV-OS-C101.
DNV-OS-C103 Structural Design of Column Stabilised Units (LRFD method) [Table of Contents] Sec.2: Structural Categorisation, Material Selection and Inspection Principles