PSI - Issue 64

5

Author name / Structural Integrity Procedia 00 (2019) 000–000

M. Saiid Saiidi et al. / Procedia Structural Integrity 64 (2024) 2021–2027

2025

Fig. 6. Envelopes of measured moment curvature relationships for RC, SSE, and LSE.

The 75 percent SMA bar length was found to be sufficient. However, as an extra conservatism measure, the SMA bar length in the actual bridge was increased to 80 percent of the column diameter. 3. New generation of NiTi bars incorporating Cobalt The effective “yield” strength of NiTi is 55 to 60 ksi (380 to 420 MPa), which is close to but lower than the actual yield point of Grade 60 mild reinforcing steel, which is specified at 60 ksi (420 MPa) but is expected to be approximately 68 ksi (470 MPa). A new generation of SMA bars has been developed by adding Cobalt to increase the effective yield strength by 50 percent. The behavior of these bars was investigated as part of a larger study to investigate characteristics of different SMA bar types by Gencturk et al. (2024). Fig. 7 shows sample cyclic stress strain diagrams measured in room temperature. The tests were done on dog bone shaped specimens, a sample of which is shown in Fig. 8. The full bar diameter was 18 mm but was reduced to 12.7 mm in the dog bone zone as shown on the left. A sample NiTiCo bar tested to failure under room temperature in also shown in the figure. The fracture occurred within the reduced section zone indicating that the machining to the dog bone shape was effective in preventing failure at the threads. Note the fracture zone does not exhibit local plastic deformation normally seen in mild steel bars tested to failure under tension.

Fig. 7. (left) NiTiCo bar cyclic response; (right) NiTi bar cyclic response.