Bridging Multi-hazard Vulnerability and Sustainability: Approaches and Applications to Nepali Highway Bridges

Highway bridges are the backbone for transportation and economic activities. However, the current global trend portrays that highway bridges are frequently exposed to either independent or cascading natural hazards. The annual drenching precipitation that occurs in Nepal between June through September imposes extreme flooding in the southern plains of Nepal where the strategic East-West Highway (EWH) is located. A similar incident occurred in August 2017 as well. Immediately after the flooding, field reconnaissance was conducted in the central and eastern Nepal. A systematic observation mechanism based on visual inspection, in situ measurement, and judgment were developed and recorded during the field reconnaissance for each bridge. Fifty highway bridges of EWH were inspected. Judgmental fragility functions are developed considering the multi-hazard scenario based on the information collected in situ. This paper also derives the depth-damage curves for typical highway bridges of the EWH. A new methodology was developed to assess the damage of existing bridges in post-flood scenario and damage grading system was designed before the field reconnaissance; finally, the categorical damages are reported. The damages occurred due to the 2017 flash flood are reported and weathering conditions are also depicted as observed in situ.