Safety Factors for Assessment of Existing Structures

Abstract

Current structural codes have been developed mainly for new design and are not efficient for assessment because of significant differences between these situations. One of the main differences is the possibility to update information about an existing structure. This paper proposes a way in which updating can be taken into account when developing code safety formats (partial factor and load and resistance factor design). Updating information about individual structural properties such as material strengths by carrying out on-site inspections is discussed. Uncertainties associated with on-site testing including “model” uncertainty are considered and a method for treating these uncertainties in the context of the partial factor format is described. Results indicate that “model” uncertainty may have a significant effect on partial factors. Furthermore, we consider updating information about the resistance of the whole structure by proof load testing or by taking into account the previous safe performance of a structure. Results show that to increase the resistance reduction factor, the level of proof load needs to be high, resulting in a rather high risk of failure during the test. Satisfactory past performance does not have any noticeable effect on resistance factor, but it does have a more significant effect on probability of failure.