Performance of Reinforcement Bar Mechanical Couplers at Low, Medium, and High Strain-Rates

The Unified Facilities Criteria (UFC) 3-340-02, formerly Army Technical Manual 5-1300/NAVFAC P-397/AFR 88-22 (TM 5-1300), defines the criteria for designing reinforced concrete structures to resist blast effects from accidental explosions. The recent Change 1 to the UFC 3-340-02 included an update to section 4-21.8 “Mechanical Splices of Reinforcement.” This update added the validation test requirements and the acceptance criteria for the use of mechanical couplers in place of lap splicing of steel reinforcing bars in elements at specific locations and under certain conditions. Several types of mechanical couplers have been tested and validated for developing the strength of reinforcing steel for cyclic loading and strain-rates expected during earthquakes. However, no mechanical couplers were shown to meet the longstanding section 4-21.8 requirement that the coupler be capable of developing the ultimate dynamic tensile strength of the reinforcing bar under high strain-rate loading without reducing its ductility. This paper presents the results of tests performed by the U.S. Army Engineer Research and Development Center (ERDC) and documented in ERDC Technical Report TR-09-8, “High Strain-Rate Testing of Mechanical Couplers.” Five different types of mechanical couplers that meet the American Concrete Institute 318 type II requirements were dynamically tested at low, medium, and high strain-rates to obtain their measured performances. The performances of these mechanical couplers were compared to control bars tested at the same strain-rates. The test results were evaluated to determine if requirements of TM 5-1300 and UFC 3-340-02 were achieved. While the evaluation showed that these five mechanical couplers did not consistently meet the section 4-21.8 requirement for unrestricted use, the tests did demonstrate adequate performance for certain couplers at lower response limits. The recent Change 1 of the UFC 3-340-02 is discussed and compared to the previous requirements to provide the industry guidance and a path forward to further testing and validation of mechanical couplers for use in hardened structures.