Stability of substructure Malapedho Bridge in Ngada Regency, East Nusa Tenggara Province

Bridge failure is often caused by problems with the substructure, such as shearing, overturning and foundation subsidence which can cause the bridge structure to tilt and make it unfit for use, and even have the potential to cause the bridge to collapse. Research on the structural stability of the Malapedho Bridge's substructure aims to ensure the strength and stability of the bridge against sliding, overturning, soil bearing capacity and settlement, considering that the bridge had previously collapsed due to flooding. The bridge data used is existing data according to the planning drawings, for bridge loading refers to SNI 1725:2016, and earthquake loading refers to SNI 2833:2016. The safety factor value as a requirement for the strength and stability of the substructure is based on SNI 8460:2017. From the results of the analysis of shear stability, overturning, soil bearing capacity, and settlement of the lower building structure, it was found that the safety factor value exceeds the requirements set by the SNI 8460:2017 standard. Therefore, it can be concluded that the bridge substructure has adequate strength and stability. The research results also indicate that earthquake forces have a significant impact on the shear and overturning stability of the bridge substructure, resulting in a decrease in the strength of the structure.