New Eurocodes on design of timber structures now open for comments

The term Eurocodes refers to a set of European standards on load-bearing structures. Currently consisting of 58 parts, the Eurocodes define how these structures must be designed starting from general principles to loads and specific details. When used together with execution and product standards, the Eurocodes form a unified framework for the design and construction of structures. Work on the next generation of Eurocodes is nearly complete. The comment round on the drafts is currently in progress, and new codes should be entering into force sometime between 2025 and 2027.

Read the article in Finnish here.

There are currently four new Eurocode drafts for timber structures:

  • general part EN1995-1-1
  • structural fire design EN1995-1-2
  • bridges EN1995-2
  • execution EN1995-3

To access the drafts, you merely need to join the mirror committee. Committee members can comment on the drafts until the end of 2023 (with the possible exception of part EN1995-1-3). Amendments, simplifications, and error corrections can still be submitted for the drafts, but new content will no longer be accepted.

Eurocode EN1995-1-3 is based on a new technical specification (also called a prestandard), namely TS 19103 Structural design of wood-concrete composite structures. This means that EN1995-1-3 will be submitted for commenting and a final vote roughly a year later than the other parts.

Excerpts from upcoming changes:

The criteria for floor vibrations have been divided into five categories, which can be applied with either an emphasis on floor quality or alternatively on cost efficiency, depending on the site. When compared to currently prevailing practices in Finland, requirements for floor vibration will probably become easier to meet. The opportunity to design low-frequency floors is also new. A committee led by the Finnish Ministry of the Environment will select the national parameters and choices for Finland.

The new draft will affect connection design as it contains plenty of new dimensioning guidelines, new connection types, and carpentry joints. Several experts have contributed to the content, and the verification calculations are still not fully complete.The Eurocodes will include new materials: CLT and LVL (conventional, cross-laminated, and multi-glued). Common material abbreviations are used extensively throughout the Eurocodes.

The calculation of panel bracing in buildings has evolved, as has the calculation of horizontal displacement in cases such as the construction of multi-storey buildings.

Fire design calculations have also advanced considerably: in future, designers can dimension structures and connections for fires lasting more than 60 minutes. CLT is prominent in the guidelines on determining charring rates, with precalculated values based on effective thickness now included to facilitate evaluations. For glued wood products, the fire resistance of the glue is an essential information as it impacts the evaluated charring rates of a building component. The draft includes precalculated values for the typical charring rates of CLT cross-section structures based on the fire duration.

The wooden bridge design draft (EN1995-2) contains several guidelines on structural details, but it remains to be seen how they apply to Finnish conditions. Since the inclusion of guidance on fatigue resistance is new, no one has any previous experience. In addition, there are new definitions on the service life of structures and on the levels of vibration criteria.

The new execution standard draft (EN1995-3) is much like our own national execution standard since Finland’s standard served as one model. However, this draft has a lot of parameters that must be set at a national level, which means that even in Finland it must be reviewed and adjusted to a level suitable for our conditions

While revising the Eurocodes, the following topics were identified as having potential for further development:

  • features specific to the structural design of volumetric element structures need to be evaluated in relation to the Eurocodes
  • the possibility of using AI (Artificial intelligence) in structural design and related usage guidelines
  • FEM (Finite Element Method) calculation practices in Eurocodes compliant calculations and adapting to building information model-based design
  • design guidelines for hybrid structures

The Finnish mirror committee for the timber design Eurocodes will compile the comments received from Finland and formulate statements according to their content. The mirror committee includes experts from universities, research institutes, the wood product industry, and design offices. Anyone can join the mirror committee for free. Membership entitles you to access the necessary documents. Auli Lastunen of the Confederation of Finnish Construction Industries RT is serving as secretary of the Eurocode mirror committees.

CEN (European Organization for Standardisation) will gather the comments from different countries after the formal enquiry round has ended. The CEN technical committee will then process the comments and draw up a proposal for changes to the Eurocodes. In the final vote, each nation has one vote either for or against the Eurocode part. If the result is positive, the Eurocodes can be applied nationally. While member states must determine for themselves what national parameters and conditions, were these are allowed, will be applied in their own country, the Finnish Ministry of the Environment has announced that the recommended values presented in the drafts will be used as widely as possible.

During a transition period which usually lasts for a year, all national design guidelines will need to be updated, as will education materials for structural design. The symbol markings used in the different standards being harmonised as well.

Universities have also begun to prepare comparison calculations and example structural design cases to better visualise the effects of the new Eurocode design methods in comparison to current methods.

ARTICLE AUTHOR Tomi Toratti works as a chief advisor in the woodworking industry in the area of timber structures and standardization. His duties include the development of Eurocodes and standardization of wood products, as well as advocacy for the development of building regulations. Tomi Toratti is the Finnish representative as well as the vice-chairman of the European Timber Structures Eurocode Committee TC250/SC5.

Puuinfo’s YouTube channel has a video of the Eurocode seminar held on 30 May 2023.The presentation materials are on the website of the Federation of the Finnish Woodworking Industries