About the research
In recent years, risk-based management of infrastructure assets has gained predominance in infrastructure asset management. The Moving Ahead for Progress in the 21st Century Act (MAP–21), in alignment with this, has required state transportation agencies to incorporate risk-based management into their planning for systematic preventative maintenance, replacement, or rehabilitation for their bridge networks. However, states currently vary in what type of methodology they choose or how they define risk. At present, state agencies are challenged at the network level to identify and quantify these risks and therefore to develop procedures to address these risks. There is an immediate need for research on effective methodologies that will allow state transportation agencies to develop a risk-based approach in managing their bridge networks.
For Iowa bridges, scour risk has been the primary risk to manage, due to increasingly frequent and heavier floods in recent years. Based on scour management history and experience in Iowa, three major modifications to the HYRISK software’s prediction of scour risk and estimate of scour risk costs for the Iowa DOT bridge network are proposed in this study. First, since there have been limited state-owned bridge failures in Iowa, HYRISK’s estimation of bridge failure and user costs was replaced by estimation of the cost of installing scour countermeasures. Second, based on previous studies, soil erodibility was incorporated into HYRISK’s foundation type risk adjustment factor, in addition to a newly developed risk adjustment factor accounting for the presence of scour protections at bridges. Finally, HYRISK’s flow depth distributions were calibrated by using Iowa-specific flood estimation models that resulted in a decreased probability of failure.
The resulting modified HYRISK was then used to estimate Iowa’s annual as well as flood-event-specific cost of scour risk, and this produced arguably more accurate assessment of the Iowa DOT’s scour risk protection needs as well as cost in terms of match to current Iowa DOT scour-related expenditures. This project thus demonstrates HYRISK modifications that can enable improvement for both network- and project-level management of scour risk.
Iowa Department of Transportation ($140,000.00)
Midwest Transportation Center
Contract Number: DTRT13-G-UTC37