DEVELOPMENT OF A DECESION TREE TO REHABILITATE OR REPLACE THE ST. FRANCIS BRIDGE OVER IH-30
Abstract
**Please note that the full text is embargoed until 12/16/2024** ABSTRACT: The ASCE infrastructure report card indicated that about 42% of the nation’s bridges are
over 50 years old, and 7.5% of the bridges are structurally deficient. The 61-year-old St. Francis
bridge over IH-30 is one of the Texas Department of Transportation (TxDOT) bridges that exhibit
significant deterioration in the superstructure, including potholes and delamination in the deck.
The bridge was load posted to 28,000 lb. limit and has substandard vertical and horizontal
clearances to the bottom chord of the beams and supporting piers, respectively, which creates a
high risk for vehicle impact. In 2017, an over-height truck struck the northbound bridge deck and
girder and caused significant damage. In addition, the unprotected piers were unable to withstand
vehicular impact loading. The various deficiencies had to be rectified, either through
reconstruction or retrofitting, to meet current code requirements. The restoration alternatives
included only raising, only retrofitting, and both raising and retrofitting. Eight retrofitting solutions
were then analyzed to enhance the deck, girder, and combined performance. For replacement, the
existing bridge would have to be dismantled, and a new bridge meeting the current code
requirement would be constructed at the footprint of the existing bridge. Pier protection was also
considered to reduce the possibility of pier collision, owing to insufficient horizontal clearance.
It was vital to identify the most effective option among these alternatives before selecting
and implementing the most appropriate one. Accordingly, the current study developed a decision
tree to make an informed decision on whether to retrofit or replace structurally deficient bridges.v
Benefit-Cost Analysis (BCA) was performed, which required the assessment of associated Life
Cycle Cost (LCC) and potential advantages from an improved measure or alternative. The General
Condition Rating (GCR), LCCA, and risk utilities were then independently assessed and merged
into a utility function to calculate the overall benefits. Finally, the Benefit Cost Ratio (BCR) was
calculated by dividing the action costs by the benefits. Moreover, the improved load rating from
diverse retrofitting options and carbon footprint effects for all the alternatives were also taken into
consideration for decision-making purposes. The proposed methodology can be used to make cost-effective decisions for highway bridges with similar deficiencies.