Current Safety Acceptance Criteria in Codes and Standards — A Critical Review

Safety is a major issue in structural engineering. Structures have in general a good record and failures are mainly due to natural disasters or human errors or a combination of both. Safety is a property of the structure that can be achieved or assured and is quantified usually by the probability of failure or the associated reliability index. A more complete parameter to approach safety is risk which is a combination of the likelihood and the consequences of structural failure, viewed in a context. Thereby it is important to distinguish between various types of consequences, i.e. human losses, environmental damage and economic losses. Structural codes traditionally have been concerned foremost with public safety preventing loss of life or injury. The context aspect of risk refers to the environment in which the risk based decision is made and in practice is linked to the decision. Structural codes aim at delivering structures with acceptable risks, i.e. with risks that are acceptable to the public. Procedures and current codified criteria for safety acceptance of new and existing structures are reviewed in this contribution. General approaches for selecting target and acceptable reliability levels such as 1 Human safety approach, 2 Calibration to previous codes, 3 Optimization (cost-benefit) are discussed first. Then the current risk acceptance criteria inherent in the codes and standards are reviewed. Thereby the difference in setting risk acceptance criteria for new and existing structures is highlighted. A "discount" in the safety requirements for existing structures is namely unavoidable due to economical and legal constraints. The need for periodic review of risk acceptance criteria is emphasized. Suggestions for future recommendations regarding the harmonization of safety criteria for new and existing structures are provided.