Modeling and structural health monitoring of a geriatric signature movable bridge

As the infrastructure of the United States age, many bridges are deteriorating into complex, geriatric structural systems. While sensing, imaging and information technology recorded significant advances, routine inspection and traditional load rating approaches by over-idealized analytical models are still serving as common practices available to the owners of geriatric bridges. Further, rehabilitation design and implementation is typically based on "as originally constructed" philosophy. Although in some cases these traditional empirical methods may yield reasonable outcomes due to the application of large safety margins, in the case of deteriorated geriatric systems repair and rehabilitation engineering require a mechanistic approach. Design should be based on fully appreciating the actual global and local behaviors of such systems in their deteriorated state. In addition, with today's economy, limited rehabilitation budgets should be allocated based on greater insight for public safety versus operational demands and based on informed and wise decisions. Structural identification (St-Id) may guide engineers and owners in decision making and budget allocation process by providing them mechanistic and reliable information regarding the probable influences of repairs and retrofits on the behavior and lifetime extension of a bridge. This paper discusses the application of structural identification in the evaluation of rehabilitation design for a deteriorated bridge. A finite element model was developed for simulating the "as-is" condition of the deteriorated bridge and was calibrated using the results from a controlled truck load test performed on the bridge. This finite element model was then used to evaluate and prioritize different rehabilitation plans, and to load rate the bridge for each different rehabilitation scenario. Through these evaluations, it was determined that even though the traditional repair plans may improve the performance of some regions, they may, in fact, adversely impact other members and connections of the system. Based on the analyses results, recommendations to modify the repair plans were submitted to the bridge owner, and a retrofit concept was developed which promised a more economical yet effective solution for providing the desired lifetime extension. In addition, leveraging the FE model, a long-term health monitoring system was designed to capture the most critical responses of the bridge as it further ages in order to alert the owner of any potential hazards which may require immediate intervention.