Reliability-based characteristic values: A stochastic approach to Eurocode 7

In geotechnical engineering, the need for adequate representation of insitu variability has been recognised in recent design codes: in particular, by the European Union's Eurocode 7 (ENV 1997-1 1994), due for release in 2003, which has introduced the concept of characteristic values into the design process. This is a significant shift from traditional design methods based on global factors of safety. It has also caused much controversy, since the Code gives little guidance as to how such values should be determined: hardly surprising, as there is virtually no experience in this subject area. However, it does suggest statistical methods as an appropriate way forward to achieving the ultimate goal of reliability-based characteristic values. This paper describes a numerical (stochastic-based) solution to the above problem. It links random field theory, for generating spatially varying property distributions, with finite elements, for analysing structural response. The stability of a structure is then represented by reliability, the probability that failure will not occur, rather than factor of safety, for which there is no information regarding probability of failure. This enables the derivation of reliability-based characteristic values.