Determination of a functional index for bridges

Abstract

Bridges are crucial assets forming part of road infrastructure. One of the challenging problems faced by bridge engineers and road asset managers is maintaining these bridges in such a way that they do not only meet optimum condition requirements, but also those requirements that are concerned with the functionality of the bridges. Various indicators, such as the Priority Condition Index, are used to indicate the condition of bridges and to develop a maintenance strategy for bridges, but similar indices for the functionality of bridges are not available. This paper focusses on the need for a functional index for bridges and presents a method to calculate a combined Bridge Functionality Index (BFI) based on traffic volumes accommodated by the bridge and the functional ratings of the detour route that would have to be used should the bridge fail. The proposed BFI was tested on 10 bridges on the Gauteng provincial road network. The study methodology involved identifying the bridges, determining the detour routes and analysing traffic data for the roads over the bridges and for the detour routes. This was followed by the development of the BFI, which is a weighted combination of a Traffic Volume Factor for the road over the bridge and a Functional Index for the detour route. The Functional Index for the detour route is a function of five factors, namely User Risk Factor; Road Capacity Factor; Riding Quality Factor; Road Safety Factor; and Detour Length Factor.