# Bridge Assessment under Earthquake and Flood-Induced Scour
## 1 Introduction  
Every nation relies on its infrastructure as a cornerstone, with bridges playing vital roles in highway and railway transportation networks. Bridges are critical in supporting first responders during the aftermath of destructive earthquakes and facilitating post-disaster rescue operations, particularly in remote areas. Bridges are susceptible to various natural hazards, including earthquakes, high winds, landslides, floods, and other hazards like explosions and vehicle collisions at bridge bents and abutments. Studying the causes that have led to damage up to the collapse of bridges throughout history, mainly under strong seismic actions and flood-induced scours, has significantly improved design codes and structural health monitoring techniques. Combining two different natural hazards of earthquakes and floods in terms of action on bridge structures may lead a bridge to collapse. Albania is identified as a region with significant seismic activity resulting from the interaction of the Adriatic and Aegean Seas' multiple tectonic plates and complex tectonic processes in the Carpathian region [1]. The damage potential of active seismic faults has been evident in numerous earthquakes, such as the 30 November 1967 earthquake measuring M = 6.6 in Dibra and Librazahl, the 15 April 1979 earthquake measuring M = 6.9 in Montenegro, and the earthquakes on 21 September and 26 November 2019, registering magnitudes of M = 5.8 and M = 6.4, respectively, in Durres, Albania. Floods in Albania happen more frequently, and the sum of the impact of every single one of them may cause a substantial loss. Bridge-flood-induced scour is a significant concern in areas prone to earthquakes and can be compounded by climate change. Hydraulic events are the primary cause of bridge failures globally, with flood-induced scour representing a significant factor in hydraulic-related failures [2]. Scouring results from the erosive force exerted by flowing water, which removes and transports sediment from the streambed and banks and the surrounding areas near the bents and abutments of the bridge [3]. As a result, the restraining conditions of bents at the foundation may be modified. Consequently, the lateral capacity of bents might decrease. This additional flexibility leads to varying dynamic characteristics of the structure, which can exacerbate the detrimental impact of seismic ground motions on structure performance [4]. [PERSON] (2009) [5] meticulously formulated a fragility analysis for road bridges in Turkey built and constructed post-1990s, a crucial step in understanding their vulnerability. These fragility curves address three levels of damage states (DS), primarily influenced by the relative movement of the deck. In 2015, [PERSON] [6] conducted a comprehensive investigation on two actual river-crossing highway bridges and two representative examples, providing invaluable insights into regional multi-hazard scenarios, including earthquakes and floods, across diverse regions in California. These bridges were built at varying points in time, making the study's findings even more significant. The study involved the generation of fragility curves and surfaces in predicting the probability of bridge failures under different levels of earthquakes and floods, a crucial tool for risk assessment. European design codes currently lack guidelines to guarantee adequate bridge foundations that are resistant to scouring and subjected to earthquake lateral loading. This gap in our knowledge and practices is a call to action for all of us, as Eurocedes do not cover the scour and flood effects approach in bridge foundation design. The Italian Code for Construction (NTC 2018, 17 January 2018, 5.1.2.3) for new bridges suggests avoiding, where possible, bents placed in the riverbed. If necessary, the distance between consecutive bents or between a bent and bridge abutment must be at least 40 m measured perpendicular to the mainstream [7].