IACS adopts new Unified Requirement on Buckling Strength Assessment of Ship Structural Elements (UR S35)


The International Association of Classification Societies (IACS) has developed a standalone Unified Requirement (UR) for buckling strength assessment on different ship types using the net thickness approach. This has resulted in the publication of UR S35 “Buckling Strength Assessment of Ship Structural Elements” which will enter into force on 1 July 2024.

The new harmonised methodology for buckling has been developed applying the toolbox in the Common Structural Rules (CSR) for Bulk Carriers & Oil Tankers which are widely accepted as being technically sound and which have been implemented, maintained and improved over the years with industry’s expertise and experience feeding into the continuous improvement of CSR.

In harmonising the buckling methodology, improvements have been made on the global elastic buckling mode for stiffened panels subject to combined loads (biaxial loads, in-plane shear force and lateral pressure), the torsional buckling mode for stiffeners, buckling strength of U-type stiffeners, plates with opening and also plate panels fitted with sniped stiffeners.

Thorough verification and consequence assessments have been carried out by extensive linear and nonlinear FE analyses, says IACS, with the harmonised requirements showing increased accuracy and effectiveness. The application of the buckling requirements such as scope, loading and permissible utilisation factor will be described in individual UR S series, e.g. in UR S21 on Evaluation of Scantlings of Hatch Covers and Hatch Coamings.

The new UR S35 will serve as an independent buckling toolbox regardless of ship types by collating, as far as possible general requirements on buckling together in one UR. A further benefit arising from the development of UR S35, is to facilitate the merger of the UR S21 and UR S21A (which currently address different ship types) into a single UR S21 Rev.6 also with an entry-into-force date 01 July 2024 to align with that of UR S35.

Commenting on this new UR S35, IACS Secretary General Robert Ashdown (pictured) said: “the adoption of a unified approach to buckling is a significant step in making the rule application check of different ship types easier for Industry but also in enhancing the maintenance of future buckling rule improvements by IACS. Furthermore, it also facilitates the further harmonisation of other relevant IACS that will also be of benefit to the industry.”