Longterm Performance of RC & PC Bridges

In recent years steadily increasing budgetary constraints have led to a strengthened awareness regarding the importance of life cycle cost considerations. Although the concept of life cycle costs (LCC) is sound and well formulated from a financial point of view, many uncertainties remain. Especially the prognosis of a structure`s future condition with and without interventions greatly influences LCC. The main processes determining the long term performance of reinforced or pre-stressed concrete structures are apart from loads (which might change over time) and environmental impacts, the time dependent processes creep, shrinkage and relaxation. Furthermore deterioration processes associated with the corrosion of reinforcement, e.g. due to carbonatisation or chloride ingress, as well as fatigue phenomena in concrete and steel influence the LC performance. As a consequence, the prognosis of a structure`s future condition is associated with high uncertainty and can solely be improved by more accurate prognosis models regarding material specific processes such as e.g. creep and relaxation. The relevance of different time dependent processes is mainly influenced by the construction type. Long span reinforced and pre-stressed concrete bridges for instance suffer from excessive deflections due to the long term creep behavior of concrete. In case of statically undetermined structures, such as jointless frame bridges, creep and shrinkage cause a development of constraint loads which might not only endanger serviceability and durability due to the possibility of crack development but also the bearing capacity. As the most influential long term process with respect to concrete bridges apart from corrosion is creep, currently available creep models will be investigated, compared to available monitoring data for real bridges and laboratory specimen (short term and long term), in order to (a) improve knowledge regarding the multi-decade creep properties of concrete, (b) derive an advanced creep model based on the monitoring data, and (c) formulate a general methodology for the identification of long term processes based on monitoring data applicable to all types of processes. Representative of many applications two particularly relevant problems associated with the long-term creep behavior of concrete shall be addressed within the proposed project: Excessive deflections of long span bridges Constraint loads in the design of frame structures/jointless bridges Based on the investigation of the multi-decade creep properties of concrete utilizing available monitoring data, different structural systems will be analyzed with respect to their performances` sensitivity to creep processes. Furthermore performance prediction models and the associated life cycle costs (LCC) related to current code based models and the investigated advanced creep model will be compared.