Assessing structural resilience of masonry chamber-housed substations subject to flood flow and debris impact

Abstract Chamber-housed substations are a common substation type, essential for voltage regulation, load balancing, and fault isolation to ensure power supply grid stability and reliability. As typically ground-based structures, chamber-housed substations are vulnerable to damage from flooding. In the case of chambers constructed from plain masonry, these may be susceptible to structural damage from forces generated by flood flows. Although previous studies have examined substation failures based on flood levels, they often overlook the structural damage caused by moving floodwaters and floating debris, thereby underestimating risks and overestimating substation resilience. The present study introduces an analytical framework that uses computational fluid dynamics (CFD) coupled with finite element (FE) analysis to predict flood forces and structural responses in a level of detail that would hitherto not be possible with existing design code approaches. The CFD-based modelling approach was validated against existing hydraulic experiments and subsequently applied to a case study of a typical masonry chamber-housed substation in Malaysia, a country prone to severe annual flooding. The results reveal that substation walls can withstand flood velocities up to 10 m/s without debris. However, the presence of debris leads to damage at velocities below 2 m/s, highlighting a significant reduction in resilience. Fragility and risk curves, derived from a normalised Weibull function, further reveal that ignoring debris impact underestimates forces on walls by 60% to 83%. These findings highlight the need to update design guidelines to account for debris impact and to develop suitable retrofitting strategies for existing chambers.