ABSTRACT
The deterioration of structural materials may generate complex situations for owners concerned about the security of their infrastructure. The evaluation of the effective safety of these structures and the prediction of its evolution can overcome the scope of numerical modeling and conventional diagnostic tests in the most critical cases. In this context, SHM has demonstrated to be a strategy that can provide reliable and valuable indicators regarding the effective structural condition. Complementing an immediate diagnosis, monitoring results are able to early detect structural changes before their progression to possible collapse scenarios.
This paper presents the SHM carried out on the Foz Dão Bridge. This structure, built in the 1970s, is located in the central region of Portugal and exhibits severe structural deficiencies due to alkali silica expansive reactions (ASR), which gave rise to extensive cracking in the submerged pillars and foundations. A new bridge is under construction at the site, but while the ongoing construction is not concluded, the existing one has to be kept in service and the risk of structural damage at the bottom of the concrete pillars, with unpredictable consequences for the entire structure, justifies a selective structural monitoring strategy.
The implemented SHM system is based on the continuous monitoring of rotations at the top of all the pillars, joint displacements and selected temperatures (Figure 1). The sensor network is connected to a single acquisition device. The recorded results are remotely sent to an external server where the monitoring data is imported, converted, processed and stored in a specific data base. The results can be assessed and visualized, by authorized users, through an interactive web application, in the form of tables or charts. In the paper, the main results achieved during a period of 18 months are briefly presented and discussed. Longitudinal view of the <italic>Foz Dão</italic> Bridge with the location of the observed variables. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig81_1.tif"/>
The effective structural behavior and significant hypothetical damage scenarios were analyzed through a representative numerical modeling. Multiple linear regression models were implemented to isolate the operational and environmental effects allowing the application of alarm states associated with damage limits. For each of the observed deformations, yellow and red thresholds were established. In the paper, the surveillance system and the web-based application that provides remote access to the continuously updated results are also introduced.
