Structural reliability techniques can be employed to evaluate the fatigue performance of fracture-critical members in steel bridges. In this dissertation, two fatigue reliability formulations that can be applied for most details in steel bridges are developed. For details classified according to AASHTO fatigue categories, a limit state function related to the number of stress cycles leading to failure based on Miner’s rule is used; for details not classified according to AASHTO fatigue categories, a limit state function based on linear elastic fracture mechanics and expressed in terms of crack size and growth rate is employed. With the application of fatigue reliability analysis, a procedure for inspection scheduling of steel bridges is developed to yield the optimal (most economical) inspection strategy that meets an acceptable safety level through the planned service life. This inspection scheduling problem is modeled as an optimization problem with an objective function that includes the total expected cost of inspection, repair, and failure formulated using an event tree approach, with appropriate constraints on the interval between inspections, and a specified minimum acceptable (target) safety level. With the help of several illustrations, it is shown that an optimal inspection scheduling plan can thus be developed for any specified fatigue details or fracture-critical sections in steel bridges. A second optimal inspection scheduling procedure is formulated that takes into consideration crack detectability (or quality) of alternative nondestructive inspection techniques. This procedure based on Monte Carlo simulation of crack growth curves yields an optimal inspection technique and associated schedule for a given fracture-critical member in a steel bridge for minimum cost and a target safety level while also taking into account probability of detection (POD) data for candidate nondestructive inspection techniques. Comparisons between the reliability-based procedure and the POD-based procedure for optimal inspection scheduling are discussed. Both scheduling strategies, when contrasted with ad hoc periodic inspection programs for steel bridges, are recommended because they are rational approaches that consider the actual fatigue reliability of the bridge member and account for economy as well as safety. / text

Civil infrastructure throughout the world serves as main arteries for commerce and transportation, commonly forming the backbone of many societies. Bridges have been and remain a crucial part of the success of these civil networks. However, the crucial elements have been built over centuries and have been subject to generations of use. Many current bridges have outlived their intended service life or have been retrofitted to carry additional loads over their original design. A large number of these historic bridges are still in everyday use and their condition needs to be monitored for public safety. Transportation infrastructure authorities have implemented various inspection and management programs throughout the world, mainly visual inspections. However, careful visual inspections can provide valuable information but it has limitations in that it provides no actual stress-strain information to determine structural soundness. Structural Health Monitoring (SHM) has been a growing area of research as officials need to asses and triage the aging infrastructure with methods that provide measurable response information to determine the health of the structure. A rapid improvement in technology has allowed researchers to start using new sensors and algorithms to understand the structural parameters of tested structures due to known and unknown loading scenarios. One of the most promising methods involves the use of wireless sensor nodes to measure structural responses to loads in real time. The structural responses can be processed to help understand the modal parameters, determine the health of the structure, and potentially identify damage. For example, modal parameters of structures are typically used when designing the lateral system of a structure. A better understanding of these parameters can lead to better and more efficient designs. Usually engineers rely on a finite element analysis to identify these parameters. By observing the actual parameters displayed during field testing, the theoretical FE models can be validated for accuracy. This paper will present the field testing of a historic wrought iron truss bridge, in a case study, to establish a repeatable procedure to be used as reference for the testing of other similar structures.