PSI - Issue 64

M. Esmaelian et al. / Procedia Structural Integrity 64 (2024) 2091–2100 M. Esmaelian/ Structural Integrity Procedia 00 (2024) 000 – 000

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ED capacity. This section studies the effect of ratio of ED to Fe-SMA bars on the cyclic behavior of Fe-SMA prestressed segmental columns. Five specimens with different ED to Fe-SMA ratio are considered and are denoted as S1 to S5 which have a gravity load ratio of 10%, The SMA-PT load ratio has a constant value of 7.5% in all specimens. The number and arrangement of ED bars were kept the same, and the ratio was changed by changing the diameter of the bars in order to eliminate the effect of the ED bar configuration. To obtain ED bar to Fe-SMA ratios of 0.18, 0.45, 0.7, and 0.85, eight mild steel bars with sizes of 10, 16, 20, and 22 mm were used. The bars are fully constrained in the surrounding concrete as described in Section 3.2.2. Figure 7 (a) illustrates that as the ratio of ED/Fe-SMA reinforcement increases from 0.18 to 0.85, there is an increase in residual drift. This is due to the moment induced by the plastic deformation of the ED bars increasing relative to the self-centering moment caused by gravity and the SMA PT forces. A higher ratio of ED bars results in a larger plastic moment and, consequently, larger residual displacements. As shown in Figure 7 (a), when the ED/Fe-SMA reinforcement ratio was increased from 0.18 to 0.85, the residual drifts increased by 2.9 and 4.7 times for drift ratios of +3 and +5%, respectively. The results presented in Figure 7 (b) demonstrate that an increase in the ED to Fe-SMA ratio leads to a corresponding increase in the EVDR. This is because plastic deformation of ED bars and concrete damage both increase energy dissipation capacity. As shown in Figure 7 (b), by increasing the ED/Fe SMA from 0.18 to 0.85, the maximum EVDR increased approximately from 14 to 26%, which is an 87% improvement in EVDR. The EVDR plots of specimen S1 is also included in Figure 7 (b) to further compare the energy dissipation capacity of Fe-SMA prestressed segmental columns without ED devices. Previous experimental studies (Ou et al., 2010) show that a typical segmental column with only prestressing tendons and the same total axial load ratio has a maximum EVDR of around 6% at 5%, whereas the maximum EVDR for S1 is about 10%. This means that Fe-SMA bars are superior to conventional tendons as they provide a higher energy dissipation capacity in addition to self-centering behavior. Therefore, Fe-SMA prestressed segmental columns would require less amount of ED bars to meet the energy dissipation requirements than conventionally prestressed columns. 4.2.2. Influence of bonding condition of Fe-SMA bars This section examines the bond condition of Fe-SMA reinforcements in segmental columns. For this purpose, two specimens denoted as S6 and S7 are considered. Specimen S6 is the proposed segmental column system introduced in section 3.1, which includes unbonded Fe-SMA bars. Specimen S7, on the other hand, includes fully bonded Fe-SMA bars along the height of the column. A gravity load ratio of 12.5% is applied to both specimens, along with an SMA PT ratio of 7.5%, resulting in a total axial load ratio of 20%. Figure 8 (a) shows the residual drifts of specimens S6 and S7. The residual drifts in specimen S7 are significantly larger than those in specimen S6, about 8 and 6 times larger at 3% and 5% drift ratios, respectively. This is because the Fe-SMA bars in specimen S7 are fully bonded to the surrounding concrete and can therefore deform along with the surrounding concrete. This results in stress concentration in the Fe-SMA bars at the segment joints where joint openings occur. The stress concentration causes early loss of prestressing force and more concrete damage, resulting in large residual drifts. In addition, the higher concrete damage and more plastic deformation of the Fe-SMA bars result in higher energy dissipation capacity. According to Figure 8 (b), the maximum EVDR for specimen S7 at 5% drift ratio is 43.1%, while it is only 12.6% for specimen S6. The numerical results are consistent with the findings of previous studies (Roh & Reinhorn, 2010). In conclusion, the application of bonded Fe-SMA rebars as prestressing elements to improve the energy dissipation capacity of segmental columns is not recommended since the self-centering behavior is severely affected.

Figure 8 Effect of bonding condition of Fe-SMA bars on (a) the residual drift (b) the equivalent viscous damping ratio of Fe-SMA prestressed segmental columns