Flexibility and harmonisation
The EN Eurocodes are the result of a long procedure of bringing together and harmonising the different design traditions in the Member States. In the same time, the Member States keep exclusive competence and responsibility for the levels of safety of works. The differences in the environmental conditions and in the ways of life in the Member States also require flexibility in the National Application of the EN Eurocodes.
Therefore the EN Eurocodes include Nationally Determined Parameters (NDPs) which
- take into account differences in geographical, geological or climatic conditions;
- result from different design cultures and procedures for structural analysis;
- arise from the requirement for safety levels in the relevant Member States.
Member States are encouraged to minimize the number of cases where recommendations for a value or method are not adopted for their NDPs. The principal objectives of further harmonisation are as follows
- the reduction of NDPs in the EN Eurocodes resulting from different design cultures and procedures in structural analysis;
- the reduction of NDPs and their variety through the strict use of recommended values;
- the gradual alignment of safety levels across Member States.
It is important to harmonise not only the values of the NDPs (harmonisation across national borders), but also the methodologies used for their assessment, as well as the design procedures used for different structures (harmonisation across different materials), e.g. reinforced concrete, steel and composite structures.
Further harmonisation of the EN Eurocodes will be achieved through collaboration within CEN/TC250, National Authorities, International Technical Scientific Organisations, Industry and the Commission/JRC.
In the mandates M/466 and M/515 for amending the existing Eurocodes and extending the scope of structural Eurocodes, the European Commission requested CEN to assess all existing Eurocodes concerning the potential to significantly reduce the number of Nationally Determined Parameters. This work should be done in close collaboration with the JRC and be based on the NDPs as defined on National level and uploaded in the specific NDP database.
By choosing the same values and methods, the Member States will boost the free circulation of products and services, while guaranteeing a high level of safety in construction works. In particular, the benefits of using the Eurocodes comprise
- exchange of design and construction services;
- marketing and use of structural components and kits;
- marketing and use of materials and constituent products;
- preparation of common design aids and software;
- increase the competitiveness of the European construction industry.
Harmonisation of NDPs
In all 59 parts of the Eurocodes there are 1 573 Nationally Determined Parameters (NDPs). In a number of cases, an NDP cannot be represented by a single numerical value. In fact, many NDPs take the form of tables, graphs, acceptance of the recommended procedure, choice of calculation approach among given alternatives, introduction of a new procedure, etc.
|1||Values of parameters||397||26.3|
|2||Reference to some set of values – tables||169||11.2|
|3||Acceptance of the recommended procedure, choice of calculation approach, when alternatives are given, or introduction of a new procedure||502||33.3|
|4||Country specific data||18||1.2|
|5||National charts or tables||1||0.1|
|7||References to non-contradictory complementary information||23||1.5|
|8||Decision on the application of informative Annexes||249||16.5|
|9||Provision of further, more detailed information||102||6.8|
|10||Reference to information included in an informative annex||30||2.0|
Among the material Eurocodes, EN 1992: Design of concrete structures and EN 1993: Design of steel structures include the highest amount of NDPs. The objective of further harmonisation for these NDPs, e.g. partial factors for material and product properties, is the adoption of the recommended values.
EN 1991: Actions on structures contains a big number of NDPs, most of them arising from different geographical, geological and climatic conditions. Further harmonisation will be sought with regard to the methodologies used for the assessment of these NDPS.
The database of NDPs is managed by the Safety and Security of Buildings Unit of the DG Joint Research Centre of the European Commission.
By 17 January 2022, the acceptance average of the recommended values (RVs) was 73%. The analysis was based on 72% of the NDPs with RVs that are expected to be uploaded in the Database.