PSI - Issue 64

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

2092

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1. Introduction Earthquakes pose a significant threat to vertical structural members, such as bridge piers and building columns, causing major damage and residual deformations. Residual deformation is the remaining lateral displacement of a structural member after unloading. Existing monolithic columns dissipate seismic energy by suffering damage in the form of flexural and shear cracking, spalling of the concrete cover, buckling of the reinforcing steel, and fracture. This damage results in large residual drifts during large earthquakes, leading to costly repairs and prolonged downtime. Large residual drifts can have serious effects on the structural integrity and operational functionality of structures. It can cause misalignment, cracking and distortion of structural elements, compromising their load bearing capacity and, more importantly, their serviceability. A conventional solution to reduce residual drift in RC columns is to provide an unbonded post-tensioning (PT) force and a moment-free connection to the foundation, allowing for rocking behavior. This mitigates damage to the plastic hinge region, while the PT force helps the column return to its original position. This ability of a column to recover residual drifts after inelastic deformations is called self-centering. Although RC columns reinforced with unbonded tendons have excellent self-centering behavior, they have low energy dissipation capacity. To solve this problem, bonded steel bars are placed across the column height. However, this method can adversely affect the self centering capacity of the column and requires careful design consideration. Previous studies have used conventional tendons for PT force, which requires a cumbersome post-tensioning process using heavy equipment such as hydraulic jacks, anchor heads, and end anchorages. Iron-based shape memory alloys (Fe-SMAs) could simplify this process due to their shape memory effect (SME), which allows them to recover inelastic deformations upon heating (Raza et al., 2022). The SME of Fe-SMA bars simplifies the prestressing of RC columns through thermal activation, which involves two simple steps: prestraining the bars to a strain limit (up to 4%) and heating them after clamping at both ends of the column. The tendency of the bars to return to their original shape generates a stress up to 300-350 MPa in the bars, called recovery stress (Michels et al., 2018; Shahverdi et al., 2018). RC columns prestressed with Fe-SMA bars exhibit self-centering behavior and higher energy dissipation capacity compared to tendon prestressed columns. This is because the recovery stress of Fe-SMA bars is lower than the stress applied to tendons, thus a larger ratio of Fe-SMA bars is required to achieve the same PT force. In addition, Fe-SMA bars have a lower yield strength and may undergo plastic deformation during seismic loading. Precast construction has recently attracted considerable research interest due to its advantages: accelerated construction speed, minimal traffic disruption, reduced environmental impact, and higher construction quality. Prestressed segmental columns as a form of precast construction have become widely used. Segmental columns, with multiple discrete segments, exhibit controlled rocking behavior under lateral loading without irreversible damage. The presence of PT force enhances their self-centering ability by providing a restoring force to return the column to its original position. Similar to existing RC columns prestressed with conventional strands, segmental columns are traditionally prestressed with steel strands. Despite the cumbersome prestressing process, these columns provide excellent self centering behavior with minimal energy dissipation capacity. However, the behavior of these structures in seismic regions is still under investigation. Researchers have studied various parameters such as size and number of segments, bond condition and configuration of PT element, concrete segment confinement, and various ED devices on the cyclic behavior of prestressed segmental columns (Bu et al., 2016; Li et al., 2017; Nikbakht et al., 2015; Ou et al., 2010; Roh & Reinhorn, 2010; Zhang et al., 2019). Further studies are needed to more comprehensively investigate the behavior of these structures under seismic loading. The purpose of this paper is to investigate the possibility of the use of prestressed Fe-SMA reinforcement for the self-centering of existing and new bridge columns. A simplified retrofitting procedure for prestressing existing RC columns using Fe-SMA bars to achieve self-centering behavior is presented. In addition, a novel self-centering segmental column system is proposed where prestressing is achieved using Fe-SMA bars. Finite element (FE) models in ABAQUS are developed to evaluate the seismic performance of the proposed system. The numerical modeling approach is validated against existing experimental data and the validated model is used to conduct a parametric study to investigate the effect of ED ratio of Fe-SMA bars, bond condition of Fe-SMA bars and concrete confinement on the cyclic behavior of Fe-SMA prestressed segmental columns. The results of the current study are