Model for the Physical Risk Assessment of Bridges with Unknown Foundation

State highway officials are often put in situations that require them to make difficult decisions, some literally involve life or death. Among these are decisions dealing with bridges that may have structural, scour, or seismic problems. This paper proposes a risk index $\left(R\right)$ that assesses risk and prioritizes bridges with unknown foundations. Primary risk parameters and their factors for bridges with unknown foundations were identified and analyzed, and a model for calculating $R$ was designed. Data were collected for ten bridges from Florida, Indiana, and New York for use in case studies. Two application methods for the model were used to assess $R$ : (1) the abstract model; and (2) the detailed model). Courses of action based on $R$ are discussed for various bridges. The model was validated using a holistic evaluation method, which proved to be robust in risk assessment. Although this paper is written to assist bridge managers in assessing risk and prioritizing activities, the research results shared in this paper are relevant to both researchers and practitioners. The paper provides practitioners with a tool for evaluating and ranking their bridges based on risk and provides researchers with risk parameters and factors, a model to evaluate this risk, and a methodology of quantifying the qualitative effect of subjective factors.