A reliability-based approach for the impact vulnerability assessment of bridge piers subjected to debris flows

Bridge piers are typically among the most vulnerable structural members subjected to debris flows. This paper proposes a reliability-based approach based on a nonlinear structural analysis to determine the physical vulnerability curves associated with bridge piers given exposure to debris flow impact. Relevant aleatory and epistemic uncertainties in both hazard and structure are incorporated in the method with the inclusion of a fully probabilistic framework. The high- and low-viscosity debris flows are assessed as being representative of two classes of debris flow for their different load patterns. The load effect on a pier column is considered as the combined effect of slurry and boulder impact, which can be characterized, respectively, by Poisson square wave process and Poisson impulse process. A quantitative displacement-based damage index is defined considering the possible failure modes of the pier column. Using a Monte Carlo simulation, a set of vulnerability curves relative to different hazard intensity measures for high- and low-viscosity debris flow is derived and sensitivity studies are conducted to estimate the influences of hazard inputs. The proposed methodology addresses the geographical restrictions of conventional empirical debris flow vulnerability models and provides a general approach for quantitative risk assessment in hazard-prone areas, thereby forming a basis for subsequent engineering design or risk zoning.