Performance-based flood safety-checking for non-engineered masonry structures

• Flood risk assessment for a non-engineered building made of cement blocks.
• Application of the DCFD (Demand and Capacity Factor Design) safety-checking format.
• Introducing Incremental Flood Height Analysis (IFHA).
• Characterization of the uncertainties in material properties and loading.
• Calculating fragilities by using an efficient simulation-based Bayesian procedure.

Demand and Capacity Factor Design (DCFD) is a probability-based safety-checking format for performance-based seismic design and assessment of structures. Inspired from the original DCFD formulation for seismic excitation, this work proposes a similar performance-based safety-checking format for flooding, adopting the flood height as the intensity measure. The proposed DCFD formulation implements the fragility/hazard parameters for flooding. The structural fragility is evaluated by adopting an efficient and simulation-based method yielding the so-called “robust” fragility curve and an associated plus/minus one-standard deviation interval. The structural performance is measured by the (critical) demand to capacity ratio for the weakest element of the weakest wall within the structure, subjected to a combination of hydro-static, hydro-dynamic and accidental debris impact loads. Analogous to the incremental dynamic analysis method proposed for seismic demand assessment, an incremental flood height analysis is used to monitor the structural performance as a function of increasing water height. For each structural modelling configuration, generated based on the characterization of uncertainties in loading and material mechanical properties, the incremental flood height analysis is employed in order to calculate the critical water height corresponding to a demand to capacity ratio of unity. The application of the proposed methodology is demonstrated for both flood fragility/risk assessment and comparative screening of various viable flood mitigation strategies for a non-engineered building made of cement bricks in Dar Es Salaam, Africa.