Bridges, Tunnels and other Transportation Structures
Full Session with Abstracts
Generally, Accelerated Bridge Construction (ABC) employs prefabricated bridge elements or systems moved to the bridge location and installed in place. Accordingly, ABC reduces many uncertainties associated with construction processes and performance during service life. It also improves the life cycle cost by reducing construction time and traffic interruptions, better control over schedule, and normally by higher quality of elements. Nevertheless, prefabricated elements need to be made continuous using cast-in-place joints. These joints, expected to become serviceable quickly, can therefore be viewed as critical elements of the ABC bridges. Instances of defective (leaky) joints have been reported and concerns have been raised about long-term durability of joints. Normally, joints contain reinforcing bars and enclosures of various shapes that in some cases create congestion. To provide shear connectivity, some of these joints are designed with cavities within the precast elements. In all, the specific nature of joint application, in-situ casting; curing; material incompatibility; cold joints; cavities and steel congestion may create potential for defects and anomalies. This, in turn, results in a higher potential for exposure and other detrimental effects with possible degradation in time, therefore reducing the strength and serviceability of the joint and the structure. The long-term deflections and environmental loading will only exacerbate the situation. These may overshadow the many advantages of ABC. Hence, evaluation and health monitoring of ABC critical details, i.e., joints becomes a priority for first assuring a life-cycle performance compatible with the prefabricated elements, and more importantly to address potential problems before damages become excessive. ABC “closure joints” connecting deck elements to each other and to the bridge girders have greater exposure to degrading environmental effects, and often there is more focus on their evaluation. A variety of Non-Destructive Testing (NDT) methods have been utilized in the past for evaluation and structural health monitoring of bridges in general. However, a concerted attempt for categorization of these methods, comparison of capabilities, and selection of methods most applicable to ABC joints is lacking. As a part of the ABC-UTC program at the Florida International University, a comprehensive study is being undertaken to (a) investigate and identify the defects and problems associated with closure joints, (b) review and evaluation of available NDT methods for applicability to closure joints, and (c) finally selection and verification of the most promising methods. This paper summarizes the results of this investigation.