Target reliability for new road bridges in South Africa

Abstract

Currently, there are no recommendations of target reliability for new-build road bridges tailored to developing countries. Target reliabilities in existing international literature reflect the economic and social circumstances associated with developed countries and may not be economically or societally acceptable for South Africa. This research determines target reliability for new-build road bridges specifically for a South African context. Economic cost optimisation and a societal risk approach are considered. Cost optimisation considers the cost of safety and consequences of failure. The life quality index methodology is used to consider limits on target reliability from a societal risk perspective. Additionally, the effect of structural redundancy on target reliability in bridges is investigated. Target reliabilities from cost optimisation are shown to be slightly higher than those from SANS 10160-1 and correspond with those from ISO 2394:2015. Recommendations of annual target reliability for new-build road bridges in South Africa are proposed - a typical value of β = 4.2 is recommended. Societal limits on target reliability correspond with target reliability from cost optimisation for bridges with minor consequences of failure and do not govern new-build bridges in South Africa. Target reliability reduces with increasing measures of bridge redundancy; a means by which to consider the effect of structural redundancy on target reliability is also proposed.