2.1.1. Steel Bridge

Selected structural members of the bridge were examined. The damage assessment was based on the results of AE signal analysis.

Visual inspection (Figure 1) revealed surface corrosion of the majority of the bridge steel elements (Figure 2), being especially intensified on top surfaces in the area of bottom chords, crossbars, stringers, and lower joints of the truss. Corrosion was also found at the interface between profiles and steel plates of posts, diagonals, and flanges, as well as at the connections between steel angles and web plates, crossbars, and stringers. Due to inadequate drainage of the steel orthotropic plates on the bridge roadway, additional corrosion sites were also detected.

**Figure 1.** Side view of three bridge spans subjected to tests.

**Figure 2.** (**a**) View of the connection between the truss lower chord with the diagonals and the vertical member, with visible advanced surface corrosion. (**b**) View from the inside to the top node, visible surface corrosion of structural elements of the truss, as well as corrosion at the joints at the contact surface of connected profiles. (**c**) View from the inside—the upper node, visible surface and pitting corrosion on the stringers, crossbars, and orthotropic slabs. (**d**) View of the node with signs of pitting and surface corrosion on steel plate and rivets.

The damage was defined as caused by stagnant water. The method of constructing the nodes, the lack of appropriate falls, the counter-falls formed due to bridge deflection, and the lack of openings at the connection of the columns with the lower chord facilitated water accumulation, which, in the absence of a proper protective coating on all steel elements of the bridge, promoted rapid corrosion progression and degradation of the material.

The measurement set included 12 sensors spaced 2–10 m apart. Determining the distance between the sensors in the location involves the measurement of the Hsu–Nielsen signal source. This measurement was also used to determine the speed of wave propagation in the material.
