The major concepts developed in the Eurocodes are:
- Fundamental requirements (safety, serviceability, fire and robustness)
- Reliability differentiation
- Design working life
- Quality assurance
The approach of structural reliability within the EN Eurocodes is based on the semi-probabilistic method (limit-state performance design and partial factors method).
The structure and structural members should be designed, executed and maintained in such a way that they meet the following:
- Serviceability requirement - the structure during its intended life will remain fit for the use for which it is required, with the appropriate degrees of reliability and in an economic way.
- Safety requirement - the structure will sustain all actions and influences likely to occur during execution and use.
- Fire requirement - the structural resistance shall be adequate for the required period of time.
- Robustness requirement - the structure will not be damaged by events such as explosion, impact or consequences of human errors, to an extent disproportionate to the original cause.
Different levels of reliability may be adopted for both, structural resistance and serviceability. The choice of the levels of reliability for a particular structure should take account of the relevant factors, including:
- the possible cause and/or mode of attaining a limit state;
- the possible consequences of failure in terms of risk to life, injury and potential economical losses;
- public aversion to failure, and social and environmental conditions in a particular location;
- the expense and procedures necessary to reduce the risk of failure.
The levels of reliability that apply to a particular structure may be specified in one or both of the following ways:
- by classifying the structure as a whole;
- by classifying its components.
Design working life
The design working life is the assumed period for which a structure is to be used for its intended purpose with anticipated maintenance but without major repair being necessary. The notion of design working life is useful for:
- the selection of design actions (e.g. wind, earthquake);
- the consideration of material property deterioration (e.g. fatigue, creep);
- evaluation of the life cycle cost;
- developing maintenance strategies.
The structure should be designed in such a way that deterioration should not impair the durability and performance of the structure having due regard to the anticipated level of maintenance.
The EN Eurocodes assume that appropriate measures are taken in order to provide a structure, which corresponds to the requirements and assumptions made in the design. These measures comprise the definition of the reliability requirements, organisational measures and controls at the stages of design, execution, use and maintenance.