Bridges are instrumented with joints to facilitate free thermal expansion of separate structural elements and prevent development of internal stresses due to differential settlements of the supports. In the past, mostly between the years 1960 and 1970, joints were frequently designed as half-joints, which were easy to construct and automatically maintained a level-running surface on the bridge. Additionally, half-joints can be implemented outside of the supports, which minimises the magnitude of the sagging bending moment caused by traffic loads. However, half-joints quickly started displaying signs of degradation, caused by development of a crack in one of the re-entrant corners in combination with water leakage into the joint. This crack, often buried deep inside the joint, is difficult to inspect, causing the exact state of the half-joints to often remain unknown. Another way of assessing the structural integrity of the half-joints of a bridge, is to monitor it using a structural health monitoring (SHM) system.

In this research, the measurement data of the SHM system on the Naardertrekvaart bridge is used to to evaluate its current state and serve as an early warning system for detecting damage. The SHM system, which has been collecting measurement data since 2022, includes inclinometers, displacement sensors, and temperature sensors. The research consists of an extensive data analysis procedure on two datasets of the SHM system. The first dataset contains two years of measurement data, obtained at a low measurement frequency. The second dataset contains one day of high-frequency measurement data. Next, the structural integrity of the half-joints is inferred from the measurement data using multiple custom-built FEM models in combination with manual calculations. Based on the outcome of this research, recommendations are provided on SHM systems on other half-joint bridges and improvements of the SHM system of the Naardertrekvaart bridge are proposed.

Analysis of the deformation of the bridge revealed a distinct dependence on seasonal temperature changes, presumably caused by hindered thermal contraction of the half-joints. Analysis of high-frequency measurement data showed that traffic loads significantly affect bridge deformation, with a substantial portion of rotations occurring from the support platforms' movement. Differences in rotational behaviour can be observed along the width of the bridge and a stiffness parameter is used to identify potential damage. A significant variation in stiffness can be observed at specific support locations, particularly on the east and west sides of support 6. The study highlights difficulties in using the SHM system to determine the bridge's state, suggesting improvements such as understanding traffic load magnitudes, modelling damage effects, and increasing measurement frequency. These adaptations may require cloud storage solutions. Oscillatory measurement approaches on half-joint bridges can reduce thermal influence sensitivity, mitigate the need for development of a digital twin, and enable broader monitoring with fewer sensors.