Strain-based analysis of seismically deficient RC bridge piers strengthened with prestressed Fe-SMA plates, CFRP wraps, and CNF-infused UHPFRC jacket

Over the past three decades, research on the seismic strengthening of RC bridge piers has surged due to deficiencies observed in older piers built under outdated seismic codes. In previous studies, the authors developed and tested several hybrid strengthening systems on five 1/3-scale RC bridge piers. These systems used vertical prestressed Fe-SMA plates as the primary flexural strengthening elements, combined with active Fe-SMA confinement, CFRP wraps, or a UHPFRC jacket. While the previous studies assessed the overall structural performance of these strengthened columns, this study focuses on strain analysis to evaluate the strengthening systems’ engagement when the RC strengthened columns are subjected to a quasi-static lateral cyclic loading. In addition, the internal longitudinal strains of the columns are analyzed to provide deeper insights into the effect of the strengthening systems on the columns’ developed internal sectional forces under lateral cyclic loading. Results indicate that the vertical Fe-SMA plates exhibited a linear increase in strain until rupture, with engagement strongly influenced by its anchorage to the RC foundation. Furthermore, high strains were observed in the vertical Fe-SMA plates in columns confined with active and prestressed Fe-SMA jackets. In addition, the analysis showed that the external strengthening elements significantly increased the columns’ internal sectional strains. This is due to the elements’ contribution to increasing the columns’ lateral strength and suppressing their strength degradation as the drift level progressed. Overall, the strain analysis presented in this study provides valuable insights into the effectiveness of the proposed hybrid strengthening systems, thereby contributing to their future refinement.