ABSTRACT
As it happens in any structural monitoring system, the main purpose is to identify and measure damage within the structural system, to correctly assess its lifetime behaviour and to perform inspections and repairs in the most optimal cost-effective way (Farrar & Worden, 2007).
Monitoring bridge deformation and the dynamic response to a large variety of external loadings is of great importance for maintaining bridge safety. Generally, it is necessary to detect structural movements at a millimetre level in real time and to all sorts of weather conditions. The comparison of reliable monitoring data with numerical models turns possible an adequate health maintenance of these vital infrastructures.
Traditional (relative) displacements measurement methodologies, such as linear variable differential transformer (LVDT), require a reference point which could constitute a difficulty for their application in large-scale structures. On the other side, absolute acceleration measurements, that don’t require a reference point, are typically used to evaluate the dynamic characteristics of structures. The displacement values are then achieved through double integration of the acceleration data, however the results of this process may not be very good due to a bias in low-frequency contents (Wu, Lijun & Casciati, 2014). In this way noncontact sensors that can obtain direct displacements of the monitored structure are a valuable alternative. Global Navigation Satellite System (GNSS) technology provides continuous and automatic measurements, regardless of the weather conditions and without the need of a ground reference.
Some experiments undertook on a real structure at FEUP campus were made with the goal to obtain structural displacement measurements by GNSS sensors and compare them with values obtained from other traditional sensors.
For this, a static load test was executed using diverse sensors such as accelerometers, tiltmeters, temperature measurement sensors, LVDTs and GNSS antennas. At the same time a numerical model was developed to give further reference values and to compare with the results obtained by the applied sensors. The analyzed footbridge. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig269_1.jpg"/> Comparison of the vertical displacements calculated by GPS and by LVDT1, during loading and unloading of the north span of the footbridge. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig269_2.tif"/>
