Application of Compact, Geometrically Complex Shape Memory Alloy Devices for Seismic Enhancement of Highway Bridge Expansion Joints
McCarthy, Emily Ruth
Padgett, Jamie E.
Doctor of Philosophy
Highway bridges are an important part of transportation networks. They provide connectivity across waterways, ravines and other roadways, reducing commuting times and facilitating social community. The disruption of their effective operation caused by earthquake damage has lasting effects based on repair costs, road closure times, traffic rerouting causing extended commute times and additional CO2 emissions, and the potential prevention of emergency responders being able to reach affected regions. Bridge expansion joints have historically been recognized as the most vulnerable component in the bridge system during these seismic events, causing dramatic disruption to bridge functionality because of their location in bridges (points of discontinuity in deck systems). Expansion joint systems are placed in these locations of discontinuity and accommodate bridge movements from thermal effects while facilitating safe driving surfaces across large gaps in the roadway. Commonly installed systems are not designed to survive seismic events, instead failure is assumed and replacement necessary to return the bridge to its functional state. When damaged, the large gaps they span can be un-crossable without external intervention, resulting in non-functioning bridges even when the structural system remains sound. Expensive and complex expansion systems exist, which prevent seismic damage, however they are used mostly in highly seismic regions and limitedly elsewhere. This dissertation provides an expansion joint design that is economical and superior in seismic performance to the commonly installed service level expansion joints so that more bridges in moderate seismic regions can be equipped with expansion systems able to accommodate large longitudinal displacement demands from earthquakes. The use of innovative shape memory alloy (SMA) springs enables a single support bar modular bridge expansion joint (one type of large capacity expansion joint) to accommodate seismic level longitudinal displacements while maintaining existing performance behavior for service level thermal expansion demands. Through limited alteration of the existing configuration, costs are minimized. The resulting design is experimentally and analytically shown to be superior in performance and able to prevent expansion joint system failure during dynamic loading. The use of fragility curves, which are probabilistic statements of demand exceeding capacity, offers a means of measuring performance over a range of earthquake intensities. Convolution with seismic hazard curves for some moderate seismic zones in the US over a range of time intervals provide information on lifetime seismic risk, valuable information for a cost benefit analysis that concludes investment in SMA springs for enhancement of modular bridge expansion joints is worthwhile for the cost reduction they offer over the life of the bridge.