During the design and construction of a new bridge the level of safety is not explicitly considered. Experience shows that the actual level of safety recommended by design codes is more than sufficient. With new construction, an optimisation of the quantity of material in relation to the margin of safety is not economically justifiable. However, with the evaluation of an existing bridge an optimal intervention in terms of the relation between the cost and adequate reliability must be found. The distinction between a large or small intervention is often clear. Structural interventions can be limited, even avoided, if an evaluation is done using the most advanced methods; the approach proposed in this project.
The goal of this research is to establish a methodology to define the optimal intervention for an existing bridge. The basic idea is to develop an approach that considers the relationship between the cost of bridge maintenance for a given bridge and the benefits of improvement from the point of view of performance (structural safety, serviceability, life expectancy). We consider in this case the target reliability that varies as a function of the particular situation of each structure. The approach, however, must also take into consideration a certain minimal reliability with respect to failure and public safety for all structures.
To attain this goal, the research is focused on three key concepts;
- an integrated approach in which all limit states and all situations of risk are considered in a uniform way,
- the probabilistic modelling of the costs and benefits of the interventions.
- the evolution of the condition state of a structure.
- Indentification of hazard scenarios.
- Definition of the consequences of a given hazard scenario with respect to damage and the economic importance of the bridge.
- Selection of the target safety level as a function of the magnitude of these consequences.
Determined level of safety for the evaluation of existing highway bridges.
Attached final report concludes with a concise practical guide to the selection of target safety level and a number of examples for road bridges.
It has been discovered that 40% of bridge accidents occur during construction, mainly due to human error and there is no need to cover this hazard when evaluating an existing bridge.