ABSTRACT
Preserving a functional and serviceable civil infrastructure network requires complex methods to devise optimum strategies to schedule expensive preventative and essential maintenance of existing bridge stock (Estes and Frangopol 2001, Frangopol and Liu 2007, Frangopol 2011, Frangopol and Soliman 2016). Quantification of structural safety and redundancy for bridges is an important process in network maintenance management and is strongly dependent on the effects of live loading (Frangopol and Nakib 1991, Nowak et al. 1993). Often times, there has not been sufficient funds for owners of bridge stock to replace, intervene, or even prioritise investment (Ellingwood 2005).
Thus, it is prudent to look into methods of improving the life-cycle safety and cost of newly constructed bridges at the design phase. In practice, the structural capacity is minimised at the ultimate limit state in an effort to reduce material quantities and initial construction costs. Achieving such economy is often accomplished at the expense of structural robustness from a life-cycle perspective. This paper investigates to what extent design traffic loading has on life-cycle safety and cost assessments for bridge structures, using the life-cycle cost model developed by Frangopol et al. (1997). The effects that increased design loading would have on the initial construction cost of a more robust bridge could be balanced by a delayed deterioration to the minimum performance threshold and, consequently, a reduced requirement for financial intervention in the mid to later stages of the bridge’s design-life.
In this paper, a brief summary of the major bridge design and assessment standards used in the UK & Ireland will be presented (Dawe 2003), and the effect of the varying definitions of normative traffic loading, and thus minimum flexural capacity, will be shown on the performance indicators, in this case the reliability index β of a simply supported reinforced concrete slab bridge. An 80 year life-cycle reliability assessment is presented for the five iterations of the bridge design, as well as an associated life-cycle cost assessment that is required to keep the bridge above a minimum acceptable performance threshold, defined as the target reliability index β T. It will be shown how a small relative increase in the flexural capacity at the design stage, and thus initial construction cost, results in a significant offset in the expect cost of failure, and thus the total expected life-cycle cost.
