PSI - Issue 64

M. Saiid Saiidi et al. / Procedia Structural Integrity 64 (2024) 2021–2027 Author name / Structural Integrity Procedia 00 (2019) 000–000

2024

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Upon successful laboratory tests of No. 10 NiTi reinforced bars attached to mild steel reinforcement with HRC couplers, this detail was implemented in the columns of the SR-99 off ramp in downtown Seattle, Washington, as described by Baker et al. (2018). The NiTi bars were used at the top plastic hinges because the columns were extended pile shafts in which the more critical plastic hinge zones are at the top. Fig. 4 shows the SMA reinforcement in one of the column cages and a view of the completed bridge. The length of SMA bars in the plastic hinge zone in the bridge was 80 percent of the column diameter, unlike previous research in which the SMA bar length was at least equal to the column diameter. The reduced length was decided based on further experimental studies to optimize the amount of SMA bars and save cost. Three scaled columns representing the columns of SR-99 were tested, one built with conventional concrete and steel (RC) to serve as a benchmark and two NiTi reinforced ECC columns. The NiTi-ECC columns were designated as SSE and LSE for column with short superelastic and long superelastic bars, respectively. The SMA bar length in SSE and LSE was 75 percent and 100 percent of the column diameter, respectively. All three columns were tested under cyclic loads with increasing drift ratios until failure.

Fig. 4. (left) NiTi bars with HRC couplers in plastic hinge; (right) completed SR-99 bridge.

Fig. 5. (left) RC; (middle) SSE; (right) LSE.

Fig. 5 shows the plastic hinges of the column models at the conclusion of the tests. The drift ratio capacity of RC, SSE, and LSE was 6 percent, 8 percent, and 11 percent, respectively. The figures show the superior performance of the SMA-ECC columns compared to RC. The excellent curvature ductility capacity of SSE and LSE can also be observed in Fig. 6 where the envelopes of the measured moment curvature relationships are compared. The ultimate curvatures in SSE and LSE were approximately 30 percent and 50 percent higher than the RC ultimate curvature. The curvature capacity Furthermore, the SMA-ECC combination reduced the residual drift ratio by over 90 percent in both SMA-ECC columns as shown by Nakashoji and Saiidi (2014). This was true regardless of the SMA bar length.