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The significant rainfall in October 2018 in northern Iran caused devastating flooding that caused considerable economic losses and claimed at least nine lives. Following the flooding, several bridges have suffered different levels of damage. Immediately after the event, the authors conducted a field investigation to study the performance of RC bridges during the flood. This paper presents the failure modes of flood-affected bridges and provides reasons for every failure case. The results revealed that scour around foundations, pier tilting, flexural failure of piers, and superstructure unseating were the most significant failure modes observed. Pile-supported bridges performed notably better than those with shallow foundations. In addition, observations have revealed that structural integrity plays a crucial role in the general stability of bridges during flooding. Pier ductility is another significant parameter that affects the performance of bridges during flood events. Finally, fragility curves were developed based on the empirical data set provided from the post-flood status of the bridges in the affected region. The river flow velocity (Vs), maximum flow discharge (Qp), and Qp normalized to the 10-year average river discharge (Qm) were considered intensity measures of the fragility analysis. The correlation analyses revealed that despite Vs and Qp/Qm , the flow discharge was not an appropriate intensity measure for generating fragility curves. [ABSTRACT FROM AUTHOR]

Concrete prisms obtained by dividing cubes diagonally have been used successfully in some dam projects in Iran as a flexible and economical erosion protection measure at diversion tunnel outlets ending in a mobile river bed. To establish appropriate design criteria for this new protection measure, systematic hydraulic model tests have been performed. The physical tests allowed us to highlight the performance of the concrete prisms placed at a diversion tunnel outlet compared with an unprotected erodable riverbed. The concrete prisms are placed in such a way that in case of undermining, the protection system is able to deform and limit erosion and scour by always covering most of the river bed at the outlet. Based on the tests results, general applicable design criteria and equations, for estimating the scour hole geometry, its location, and the required size of the prisms as well as the total area to be protected, have been developed. [ABSTRACT FROM AUTHOR]