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Experimental Studies of Reinforcing Steel and Shape Memory Alloys in Mechanically Spliced Connections for Seismic Application
AuthorJordan, Evan J.
AdvisorSaiidi, M. Saiid
Civil and Environmental Engineering
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The research reported in this document was concerned with the potential application of mechanical reinforcing bar splices for use in the plastic hinge of a bridge column for use in accelerated bridge construction (ABC). The implementation of couplers in a plastic hinge for ABC is not unique, however coupler application has been limited to regions of low seismic hazard due to lack of knowledge about their seismic performance. Recent studies have indicated the feasibility of using some types of couplers in regions of high seismicity. In response to this, preliminary acceptance criteria were developed for couplers to be used in column plastic hinges of bridge columns in seismic regions. In addition to splicing steel reinforcement, splicing superelastic shape memory alloy bars also is necessary in practical implementation in column plastic hinges to eliminate permanent lateral displacement of bridges subjected to earthquakes. Large-diameter Copper-Aluminum-Manganese (CAM) bars are cost-effective SMAs for potential use in earthquake-resistant bridges. However, based on the current technology, CAM bars can be only manufactured in limited lengths, making it necessary to splice several bars in series in order to reinforce the entire column plastic hinge.This study focused on experimental studies of the performance of large diameter CAM bars in a multi-splice connection, evaluating both the CAM material as well as the effect of the spliced connection. Another goal of the study was to evaluate the preliminary acceptance criteria for steel bars by testing 30 specimens spliced using three plausible couplers and provide recommendations for how to modify the procedure.Two CAM specimens each made of two 300-mm long bars with diameter of 30 mm spliced using upset head couplers were studied to address the first objective of the study. Each CAM bar was instrumented with 4 strain gages in the middle and with LVDTs measuring deformation over the entire gage length of the splice. One specimen underwent monotonic tensile loading to failure and the other underwent static cyclic loading with strains ranging from 0.25% to 8% strain.The second objective of the study was addressed by selecting three coupler types sized for #10 bars, each having a different mechanism, and meeting the California Department of Transportation (Caltrans) ultimate splice qualifications. Thirty spliced specimens were subjected to static monotonic tensile loading, static cyclic loading, and dynamic monotonic tensile loading. Strain was measured over the spliced bar region. Material modelling procedures were then performed to determine the magnitude of strain reduction due to the presence of the coupler.From the SMA studies, it was concluded that splicing multiple CAM bars is a feasible option only if the heading process for the CAM bars is improved. Additionally, because there was variability among the CAM samples, additional development is recommended prior to CAM being used as structural reinforcement. From the studies of mechanical splices for steel bars, the acceptance criteria was found to be practical and was able to identify couplers that are not appropriate for seismic application. Several changes in the loading protocols and material model procedures were recommended. It was determined that loading type did not affect the likelihood of fracture within a coupler.