The effect of different design lives on the design of bridges and viaducts

European regulations recommend designing new bridges for 100 years. At the same time, renovation or replacement of any bridge affects the performance of the highway network. In addition to traffic hindrance, it has a negative impact on the environment, consumes materials and requires a lot of investments and effort. Therefore, the idea to design new bridges to last longer seems logical and becomes more popular. However, the experience of Rijkswaterstaat (Dutch Ministry of Infrastructure and Water Management) shows that many bridges on a highway network are demolished even before they reach their design life of 100 years, and the major reason for that is the changes in the functional requirements to bridges.
This project considers functional parameters as development of traffic intensity and loads, together with the evolution of the highway network in general in relation to the design life. I have investigated their impact on the design of bridges. Even though the main focus of the project was on the bridge functionality, material degradation was also addressed.
As the way how functional parameters develop in time differs from one bridge to another, this project is aiming to answer if it is possible to find the best design life option for a new bridge to be designed. Another goal is to investigate how the effect of the uncertain parameters can be considered in the design.
In this project, a procedure to compare different designs for bridges to provide a particular crossing was developed. These designs were defined by the assumed design life. The comparison was done in terms of lifecycle costs and lifecycle CO2 equivalent emissions. The tool for probabilistic assessment which have been introduced for this project allows to consider the possible changes in functional parameters and to come up with probabilistic results for different designs. These results can be further compared in order to choose the best design life option.
This procedure suggests an alternative approach to design of bridges. Two main features of this procedure are the focus on the lifecycle of the crossing to be maintained for 200 years, and the tool for probabilistic assessment which allows to account for the uncertainty of functional parameters.
Results of case studies considered in the project reveal that the design life shall be defined based on the unique features of each particular bridge. They also indicate that the developed procedure can help Rijkswaterstaat to make decisions for their task of bridge renovation and replacement.
Although the application of the procedure requires significant design effort, it may result in the better alignment of the assumed design life and the actual technical and functional lives of bridges allowing for more efficient use of the resources and better performance of the highway network.