Structural Monitoring

The condition assessment of aged structures is becoming a more and more important issue for civil infrastructure management systems. The continued use of existing systems is, due to environmental, economical and socio-political assets, of great significance growing larger every year. The performance of many of these in-service structures has decayed over the years of utilization and the inherent level of safety might be inadequate relative to current design documents. Structural integrity has to be guaranteed by the structural safety under ultimate and serviceability conditions in order to ensure the safety of the structure and its users. For the purpose of developing adequate life extension and replacement strategies, issues such as whole-life performance assessment rules, target safety levels and optimum maintenance strategies must be formulated and resolved from a lifetime reliability viewpoint and lifecycle cost perspective. In order to maintain the health of a structure up to a given time into the future, a cost-effective maintenance strategy has to be used. The optimal maintenance strategy will correspond to the minimum expected life-cycle criterion. The optimization problem for existing structures consists of minimizing the total expected cost under the reliability constraints. In front of this background we find the necessity to identify the key parameters and procedures to verify and update the knowledge about the present condition of a structure with respect to a number of aspects. A visual inspection may yield a first qualitative, maybe purely intuitive impression. A better judgment would be based on the evaluation of acquired quantitative information. Recent progress in the development of sensing technologies and material/structure damage characterization combined with current data processing techniques have resulted in a significant interest in diagnostic tools to monitor structural integrity and to detect structural degradation. Adequate monitoring techniques provide qualitative and quantitative knowledge that facilitates more precise condition assessments and resulting maintenance interventions. This includes the observation of mechanical parameters such as loads, strains, displacements and deformations as well as environmentally induced processes such as corrosion. Therefore, the development of monitoring concepts on a continuous time basis for structural components and for the global behavior is fundamental for guaranteeing structural integrity.