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Exploratory Experimental Studies of Spliced Cam Shape Memory Alloy Bars for Seismic Application
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The exploratory research reported in this document was focused on the behavior of a new generation of superelastic shape memory alloy (SMA) bars and mechanical splices for use in the plastic hinge zone of bridge columns. Superelastic Copper-Aluminum-Manganese (CAM) bars are the new generation and cost-effective SMAs for potential use in earthquake-resistant structures. Large-diameter CAM bars are required for field deployment. However, based on the current technology, CAM bars can be only manufactured in limited lengths, making it necessary to splice several bars in series using mechanical couplers in order to reinforce the entire column plastic hinge zone. The implementation of mechanical couplers in a plastic hinge is not unique, however coupler application has been limited to regions of low seismic hazard due to lack of knowledge about their seismic performance. This study focused on experimental studies of the performance of small and large-diameter CAM bars in a single and multi-splice connection, evaluating both the CAM material as well as the effect of the spliced connection. Three small-diameter and two large-diameter CAM specimens spliced using upset head couplers (also known as headed bar couplers) were studied. Each CAM bar was instrumented with strain gages in the middle and with LVDTs measuring deformation over the entire gage length of the splice. Specimens underwent monotonic tensile loading and static half cyclic loading. Results indicated excellent superelastic behavior and strain recovery of all the spliced CAM bars. It was concluded that splicing multiple CAM bars is a feasible option, however, the heading process for the large-diameter CAM bars should be improved. Additionally, microstructural analysis was performed to investigate the heat affected regions around the upset ends of the small-diameter CAM bars. Results revealed that the heat during the heading process at the upset ends did not adversely affect the superelastic response of the CAM bars.
Report No. CCEER-18-04