Date of Award
Doctor of Philosophy (PhD)
Over the past few decades, there have been issues of poor fatigue performance (the main failure mechanism) of the welded, tube-to-transverse plate connections within sign support structures. Review of the literature has indicated that a considerable amount of research has been devoted to identifying the structural response characteristics of these signs. Others have tried to identify how these connections may be repaired, retrofitted or simply better designed to sustain longer fatigue lives. However, little attention has been given to using a systematic reliability-based approach to assess the risk of fatigue-induced fracture in these structures.
Using a reliability-based approach to solve structural engineering problems requires a fundamental knowledge of the uncertainty associated with three variables: resistance, demand and modeling error. The present research effort has focused on systematically quantifying this uncertainty. The procedure utilizes statistical parameters determined from probability frequency distributions generated for each of the three variables. Resistance is defined by the fatigue life of the connection, demand is defined by the wind loading (buffeting-type only) and modeling error is evaluated using high-fidelity finite element analysis (FEA) with comparison to measured data from a field monitoring system.
This research effort develops a reliability-based approach for prescribing inspection intervals corresponding to user-specified levels of fatigue-induced fracture risk. The resulting level of risk for a particular structure is dependent upon its geographical location, the type of connection it contains, the orientation of its mast-arm relative to north and the number of years it has been in service. The results of this research effort indicate that implementation of state-of-the-art reliability-based assessment procedures can contribute very valuable procedures for assigning inspection protocols (i.e. inspection intervals) that are based upon probabilities of finding fatigue-induced cracking in these structures. The engineering community can use the results of this research effort to establish inspection intervals based upon risk and thereby better align inspection needs with limited fiscal and human resources.