Reduced partial factors in UK standards for assessment of bridges and structures

Abstract

Structural engineering design standards are based on a range of input variables for resistance, action and modelling. The distribution type and parameters for each determine the partial factors appropriate to achieve a defined reliability level over a specified reference period. For the assessment of existing bridges and structures, a reduced reliability level may be accepted due to the greater cost of providing reliability through strengthening when compared with the cost of providing it at design. This would allow the use of lower partial factors, although they are still limited by the need to provide a minimum level for human safety. Adoption of this approach for assessment would have significant benefits for an ageing UK infrastructure by reducing the need to carry out costly strengthening and retrofitting schemes while still ensuring appropriate structural reliability levels are maintained. This paper presents a study investigating appropriate reduced partial factors to be applied through UK highway structure assessment standards, the sensitivity of these values to input distribution model assumptions and how they could be implemented in industry.