Mechanical bar splices for incorporation in plastic hinge regions of RC members

Abstract

Mechanical devices are incorporated in reinforced concrete (RC) structures in lieu of conventional lap splicing mainly to reduce bar congestion in joints. Mechanical bar splices, which are also referred to as bar couplers, might also be used to connect precast members to accelerate construction. Nevertheless, current codes prohibit the use of bar couplers in plastic hinge regions of RC special moment-resisting frames and RC bridge columns in high seismic zones preventing the use of couplers as precast connections. This may be because of a lack of systematic test data on the coupler performance, limited experimental studies on mechanically spliced RC members, and engineering precautions. All bar couplers available in the U.S. market were evaluated as part of this study and 10 products from six different manufacturers were identified as potential couplers to be used in precast members. New standard test methods for mechanical bar splices were developed and more than 160 bar couplers were tested under uniaxial monotonic and cyclic loading to failure to generate the first-of-its-kind systematic database of the coupler performance. Mechanical properties of these splices were established, and a coupler material model adopted from the literature was found to be viable in producing the splice stress–strain behavior. Furthermore, a parametric study was carried out to investigate the seismic performance of mechanically spliced bridge columns utilizing the verified coupler models. More than 240 pushover analyses were performed. It was found that mechanically spliced bridge columns may exhibit up to 43% lower displacement ductility capacity compared to conventional RC columns and the force capacity of these columns may be up to 10% higher than that for RC columns. Columns spliced with rigid and long couplers will show the lowest displacement capacities. Based on the research findings, a new standard testing method was prepared for seismic couplers and was submitted to the American Association of State Highway Transportation Officials (AASHTO) for possible adoption.