Bridges in Cephalonia island performed generally adequately during Medicane Ianos. Nonetheless, a critical, simple-supported, multi-span, reinforced concrete bridge founded on steep topography and connecting the village of Agkonas with Myrtos beach and Erissos peninsula collapsed, impacting the transportation network of the island.
The structure, better known to the islanders as the “Chimoniko” bridge, was characterized by a width of ~9 m and a length of ~30 m, and was simply supported on two piers with a height of approximately 10 m (east pier) and 13 m (west pier), respectively. The span length was ~10 m, and the piers were founded on shallow footings on a limestone formation.
During the post-event reconnaissance, on 10/01/2020, detailed UAV-enabled mapping was conducted to better understand the failure mechanism. Orthophotos and DSM were produced (Figures 2 and 3), based on which an initial assessment can be made. A 3D fly-over animation of the failed “Chimoniko” bridge is presented in the following video.
The prevalent failure mode appears to be the scour of the west pier foundation from extensive gully flooding and debris. Such mechanism is consistent with the translational downstream movement of the foundation body, the pier, and the deck beams (Figure 2). Moreover, the failure mode is also supported by the observation that the older (built in 1943), masonry, single-span bridge just upstream of the collapsed structure, did not show any signs of damage.
Contrary to the “Chimoniko” bridge, the older bridge was supported on masonry abutments on both sides of the gully. It can be presumed that the new bridge had a significantly reduced flow capacity, due to the presence of the piers. Particularly the west pier was comparatively more vulnerable since it was located more centrally within the flood/debris flow path. (Figure 3)