Economic and human safety reliability levels for existing structures

Abstract

Specifying the target reliability levels is one of the key issues in the assessment of existing structures. For a majority of existing buildings and infrastructures, the design life has been reached or will be reached in the near future. These structures need to be reassessed in order to verify their safety. Eurocodes provide a general basis primarily intended for the design of new structures, but the basic principles can be used for assessing existing buildings, too. Reliability levels are generally based on both economic optimization and criteria for human safety. In this study, both methods are elaborated for existing structures. It appears that the requirement for the same target reliability for existing and new structures is uneconomical. Further, cost optimization seems to yield rather low reliability levels and human safety criteria often become the critical factor. The study concludes with practical guidelines for establishing reliability indices for existing structures linked to Eurocode principles

Human safety criteria for risk-based structural design

“…It is observed that for larger N, the fib bulletin 80 for existing structures requires higher reliability levels than the ISO standard for new structures ('small relative life-saving costs'). This is in contradiction with numerous previous studies advocating lower target levels for existing structures [8,19,[23][24][25] and with the theoretically justified approach to reduce target reliability levels for increasing costs of safety measures. The discrepancy is primarily attributable to the risk-averse value k = 2 adopted in the fib bulletin.…”

“…For railway civil engineering structures, it is assumed that this fraction is commonly low (exceptions may include most exposed workers), individual risk criteria become less important and group risk criteria dominate the derivation of target reliability values [7][8][9]. These criteria include human, economic and environmental criteria and are briefly reviewed in the following sections.…”

“…Essentially, this approach combines economic and human safety aspects. Compared with economic optimization [8,[21][22][23], it should lead to lower target reliability indices, as only the human consequences of structural failure are taken into account, while other losses such as economic and environmental costs are not taken into account. In the LQI approach, the danger to which the people are subjected might vary on an individual basis within the group of people affected, which may be deemed unethical [8].…”

An innovative framework for probabilistic-based structural assessment with an application to existing reinforced concrete structures

“…The safety assessment procedure consists in a comparison between the computed and a target reliability index, β target , given in codes or bibliography [3,33].…”

Requisitos de seguridad estructural basados en los riesgos para las personas

“…Las recomendaciones holandesas relativas a las actividades industriales en general distinguen entre requisitos para los sistemas de nueva construcción y existentes, estableciendo unos límites de aceptación, r IR,adm , de 10 -6 y 10 -5 por año, respectivamente [Vrijling 2005]. Otros autores holandeses adoptan este último valor para la determinación de los índices de fiabilidad requeridos para la evaluación de las estructuras existentes [Steenbergen 2010], alineándose con la citada norma suiza destinada a los mismos fines [SIA 269 2011]. Unos desarrollos similares en la República Checa [Sykora 2013], mientras tanto, están basados en un valor r IR,adm = 10 -6 por año, en concordancia con la norma internacional [ISO 2394[ISO 1998.…”