Evaluation and Retrofit of the Austin Congress Avenue Bridge for LRV

A preliminary structural evaluation of the historic Ann W. Richards Congress Avenue Bridge in Austin, Texas was conducted to determine its viability to carry a combination of existing roadway and pedestrian traffic with proposed light rail vehicles (LRV). This article describes the analysis process and findings developed in the preliminary phase of the Austin Urban Rail Advanced Conceptual Engineering Study. The goal of this phase was to perform a high level fatal flaw analysis of the bridge based on information collected from available documentation and considering both center-running and side-running track configurations. The age of the bridge necessitated a historical investigation to recover original drawings, construction records, geotechnical information, etc., and document several modifications made since the bridge's original construction. Additionally, recent inspection reports of the bridge were collected and confirmed with a site visit. Review of a number of Light Rail Transit (LRT) structural design criteria documents developed by several transportation agencies around the U.S. led to development of a set of structural design criteria used for evaluating the bridge structure and retrofit options. Results of simplified analyses of the superstructure and substructure showed that the bridge's box beams would require strengthening in order to accommodate LRV loads in addition to current loads. Substructure analyses indicated that the bent caps seem to have adequate strength while the piers show significant reserve capacity but that the foundation may need to be strengthened. Development of preliminary retrofit schemes was based on analysis results, bearing in mind the presence of a bat colony living in the bridge. Estimated approximate costs established an order-of-magnitude comparative value to help the owner decide if a more detailed study is worth considering.