DNV Standards

SDC Verifier implemented a bunch of DNV rules and regulations for offshore structures stability. It is possible to perform plate buckling check according to DNV CN30 (DNV Classification Notes no. 30.1. Buckling Strength Analysis, July 1995), plate buckling check and stiffener buckling check according to DNV RP-C201 (Recommended Practice DNV–RP-C201, Buckling Strength of Plated Structures, October 2010), weld strength check according to DNV OS-C101-LRFD (Design of Offshore Steel Structures, General (LRFD Method), April 2011) and DNV OS-C201-WSD (Structural Design of Offshore Units (WSD Method), April 2011), fatigue check according to DNV RP-C203 (Fatigue Design of Offshore Steel Structures April 2016), DNV-CG-0128 – Plate Buckling Standard, supporting both the October 2015 and December 2023 editions.

• Download Plate Buckling Tutorial According to DNV RP-C201.
• Download Weld Strength Check Tutorial based on DNV OS-C101-LRFD and DNV OS-C201-WSD

Buckling Strength Analysis (DNV CN30, July 1995)

Structural stability must be provided for the structure as a whole and for each structural member.

There are basically two ways in which a structure may lose its stability:

• Snap-Through Buckling – it is characterized by a load-deflection curve. The structure collapses when the load is increased beyond the limit point.
• Classical or Bifurcation Buckling. – for relatively small loads, the equilibrium state of the structure is called the pre-buckling state or the fundamental state. When the load is increased, a bifurcation point is reached, at which another solution to the equilibrium equations exists. Beyond the bifurcation point, the pre-buckling path is unstable. The post-buckling behaviour then depends on the characteristics of the secondary path.

Analysis of buckling strength must be based on the most unfavourable buckling mode’s characteristic buckling strength.

Read the help article on implementation of DNV CN30 Plate Buckling in SDC Verifier.

Buckling Strength of Plated Structures (DNV RP-C201, October 2010)

Two different but equally valid approaches are described in the document for evaluating the ultimate strength and buckling of plated structures.

The first technique uses a standard buckling code for stiffened and unstiffened steel panels. The stiffened flat plate section of the earlier DNV Classification Note No. 30.1 “Buckling Strength Analysis” (DNV CN-30) has been updated and developed. For plates, stiffeners, and girders, recommendations are provided.

The second technique uses the PULS (Panel Ultimate Limit State) computerized semi-analytical model. It is founded on a well-known non-linear plate theory, the discretization of deflections by Rayleigh-Ritz, and a numerical method for resolving the equilibrium equations.

Read the help article on implementation of DNV RP-C201 Plate/Stiffener Buckling in SDC Verifier.

Design of Offshore Steel Structures, General (LRFD Method), (DNV OS-C101, April 2011)

DNV-OS-C101 is the general part of the DNV offshore standards for structures. It provides principles, technical requirements and guidance for the structural design of offshore structures and applicable to all types of offshore structures of steel. The standard is primarily intended to be used in design of a structure where a supporting object standard exists, but may also be used as a stand-alone document for objects where no object standard exist.

This regulation is based on the load and resistance factor design method. Structures and structural elements shall be designed to:

• Sustain loads liable to occur during all temporary, operating and damaged conditions, if required
• Maintain acceptable safety for personnel and environment
• Have adequate durability against deterioration during the design life of the structure.

Read the help article on implementation of DNV OS-C101-LRFD Weld Strength in SDC Verifier.

Structural Design of Offshore Units (WSD Method), (DNV OS-C201, April 2011)

This offshore standard provides principles, technical requirements and guidance for the structural design of offshore structures, based on the Working Stress Design (WSD) method.

This regulation has been written for general world-wide application. Statutory regulations may include requirements in excess of the provisions by this standard depending on size, type, location and intended service of the offshore unit or installation.

This section describes design principles and design techniques including:

• Working stress design method
• Design assisted by testing
• Probability based design

Read the help article on implementation of DNV OS-C201-WSD Weld Strength in SDC Verifier.

Fatigue Design of Offshore Steel Structures, (DNV RP-C203, April 2016)

This recommended practice presents recommendations in relation to fatigue analyses based on fatigue tests (S-N data) and fracture mechanics.

The goal of fatigue design is to ensure that the structure has a sufficient fatigue life. Calculated fatigue lives also form the basis for efficient inspection programmes during production and the operational life of the structure.

DNV RP-C203 is valid for carbon manganese steel materials (C-Mn) in air with yield strength less than 960 MPa.

Read the help article on implementation of DNV RP-C203 Fatigue in SDC Verifier.

DNV-CG-0128 – Plate Buckling Standard (October 2015 and December 2023 editions)

SDC Verifier has extended its capabilities to include the DNV-CG-0128 standard, supporting both the October 2015 and December 2023 editions. This standard outlines the criteria for assessing the buckling and ultimate strength limits (ULS) of load-carrying members, with a focus on unstiffened plate buckling. 

Objective
DNV-CG-0128 provides methodologies and principles for the assessment of buckling and ultimate strength limits of structural components, particularly those used in ship hulls and similar plated constructions. The primary objective of these criteria is to ensure robust design and controlled behavior of structures under loading conditions defined by the classification rules for ships and offshore units. 

Scope 
This guideline defines several methodologies for evaluating buckling and ULS, including but not limited to: 

• Closed Form Method (CFM): Section 3 outlines the CFM for assessing the buckling capacity of unstiffened plates, which is the primary method implemented in SDC Verifier. 
• CFM for Struts, Pillars, and Beam-Columns: Guidance for these structural elements is also provided in the standard but is not currently implemented in SDC Verifier. 
• Semi-Analytical Buckling Models (PULS): These models cover both stiffened and unstiffened plates and are discussed in Section 4. 
• Ultimate Hull Girder Capacity: Section 5 addresses the overall buckling capacity of ship hull girders. 
• Non-Linear Finite Element Analysis (FEA): Section 6 includes guidelines for using non-linear FEA to assess structural capacity. 

Application
This guideline applies to the buckling strength assessment of metallic structures in vessels designed in compliance with DNV-RU-SHIP and DNV-RU-OU standards for various offshore unit types. The implemented section focuses on the CFM for unstiffened plates, offering a reliable and efficient means to evaluate the buckling capacity of these structural elements. 

Read the helpful articles on the implementation of DNV CG-0128 Plate Buckling (2015) and DNV CG-0128 Plate Buckling (2023) in the SDC Verifier.

Info on DNV Standards

Det Norske Veritas (DNV) Offshore Codes include Offshore Standards providing technical provisions and acceptance criteria for general use by the offshore industry as well as the technological basis for DNV offshore services.

DNV is an autonomous and independent foundation that undertakes classification, certification, and other verification and consultancy services relating to the quality of ships, offshore units, and installations, and onshore industries worldwide and carries out research about these functions.