SIST EN 1999-1-3:2023/kprA1:2026

SIST EN 1999-1-3:2023/kprA1:2026 is the Slovenian adoption of a CEN draft amendment to Eurocode 9, Part 1-3, on aluminium structures susceptible to fatigue. It updates the rules used by engineers, designers and reviewers for fatigue design of aluminium alloy structures in the ultimate limit state, including safe life design, damage tolerant design and design assisted by testing. This amendment is prepared by CEN/TC 250 and is circulating for enquiry before it becomes part of the standard.

What does SIST EN 1999-1-3:2023/kprA1:2026 specify?

SIST EN 1999-1-3:2023/kprA1:2026 specifies the basis for designing aluminium alloy structures subject to fatigue. It focuses on how to verify fatigue performance, what design approaches may be used, and how this part of Eurocode 9 is meant to be used with the rest of the Eurocodes.

The scope covers:

• safe life design
• damage tolerant design
• design assisted by testing

The document excludes pressurized containment vessels and pipework. It also states that the general assumptions of EN 1990 apply, together with the provisions of EN 1999-1-1 and the other referenced Eurocodes, execution standards and product documents.

In practice, that means a designer must not use this part in isolation. Fatigue design is tied to the broader structural basis in EN 1990-1, the action rules in EN 1991, and the relevant aluminium design and execution standards.

What are the key requirements of SIST EN 1999-1-3:2026?

SIST EN 1999-1-3:2026 is mainly an amendment document, so its technical content is about updating existing design rules and references. The most important changes clarify how fatigue design is linked to the revised Eurocode framework and how reliability is to be achieved in service.

Fatigue design basis

The amended clause 4.2.1 requires fatigue design of aluminium structures to follow the general provisions in EN 1990-1, the loads given in clause 4.3, and the specific aluminium design provisions in the relevant parts of EN 1999. In practice, this ties fatigue checks to the same reliability framework used elsewhere in Eurocode design.

Safe life design (SLD)

The safe life design approach is described as one that should give a suitable level of reliability so that the structure performs for its design service life without routine inspection or monitoring for fatigue cracks. It is intended for cases where a crack in one component could quickly lead to failure. For the reader, this means details, materials and stress levels must be chosen conservatively enough that the structure can remain safe without depending on frequent crack detection.

Damage tolerant design (DTD)

The damage tolerant design approach is updated so that, by the end of each in-service inspection interval, the structure still meets the required reliability level. The amendment highlights three ways this can be achieved: slow crack growth and detectability, multiple load paths, or crack-arresting details. In practice, this is the route to follow when a structure can tolerate a crack for a period, but only if inspection and detail design are planned accordingly.

Fatigue loading and factors

Clause 4.3.1 now points fatigue loading to EN 1991 for loads covered there, and to other relevant European Standards for loads outside EN 1991. Clause 4.4 updates the notes on partial factors for fatigue loads to align with EN 1990-1. This matters because fatigue checks depend on the correct action model and factor format.

Detailed design data

Annex D is updated by replacing Figure D.1 on stress concentration factors for rounded corners in flat plate, and Annex E is updated by deleting wording in a note to 6. This means the amendment also affects detailed fatigue verification data, not only the main design clauses.

What terms does SIST EN 1999-1-3:2026 use?

• Safe life design (SLD) - A design approach that aims for the structure to remain safe for its design life without regular fatigue crack monitoring.
• Damage tolerant design (DTD) - A design approach that accepts the possibility of cracks, provided the structure can tolerate them until detection or arrest.
• Ultimate limit state (ULS) - The safety state used to check that the structure will not fail under the design actions.
• Fatigue loading - Repeated or fluctuating loading that can cause crack initiation and growth over time.
• Stress concentration factor - A factor that describes how local geometry, such as a corner or opening, increases stress.
• In-service inspection interval - The period between planned inspections used to support damage tolerant design.

Who uses SIST EN 1999-1-3:2026?

SIST EN 1999-1-3:2026 is used by structural engineers, detail designers, checking engineers, and organizations responsible for fatigue-sensitive aluminium structures. It is also relevant to fabricators and project teams that must align design, execution and inspection planning.

In practice, these users apply it when they need to:

• choose between safe life and damage tolerant design
• define fatigue loads and partial factors
• assess detail geometry and stress concentrations
• plan inspections where fatigue cracking must be managed
• coordinate design with EN 1990-1, EN 1991 and the relevant execution standards

What changed in SIST EN 1999-1-3:2026 from the previous edition?

This draft amendment modifies EN 1999-1-3:2023. The changes stated in the document include:

• replacement of references to EN 1990 with EN 1990-1
• replacement of references to EN 1999-1-1:2023 with EN 1999-1-1:2023+A1:2026
• replacement of references to EN 1999-1-4:2023 with EN 1999-1-4:2023+A1:2026
• updated Eurocode list in the introduction
• updated statement on direct use of EN 1999 with EN 1990-1 and the other Eurocodes
• updated scope wording in 1.1
• updated normative reference in Clause 2
• revised wording for safe life design and damage tolerant design
• updated source of fatigue loading in 4.3.1
• updated note references for fatigue load partial factors in 4.4
• replacement of Figure D.1
• deletion of note wording in E.2

Which standards are used with SIST EN 1999-1-3:2026?

SIST EN 1999-1-3:2026 is intended to be used with these documents:

• EN 1990-1:2023+A1:2026 - provides the basis of structural and geotechnical design for new structures.
• EN 1991 (all parts) - provides the actions on structures used for fatigue loading.
• Relevant parts of EN 1992 to EN 1999 - provide the companion design rules needed when aluminium design interfaces with other structural materials or Eurocode parts.
• EN 1090-1 - provides execution requirements linked to structural aluminium work.
• EN 1090-3 - provides execution requirements specifically relevant to aluminium structures.
• ENs, EADs and ETAs - provide product-related requirements for construction products used in aluminium structures.

What does the SIST EN 1999-1-3:2026 document contain?

SIST EN 1999-1-3:2026 contains a foreword, a contents list, and 11 modification items that update the parent standard EN 1999-1-3:2023. The amendment revises the introduction to the Eurocodes, the scope, the normative references, the fatigue design clauses, and selected annex material.

It also replaces Figure D.1 in Annex D, so the document includes updated graphical guidance for stress concentration factors in fatigue design. The amendments are meant to keep the document aligned with EN 1990-1 and the current Eurocode structure, while preserving the existing fatigue design framework.