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    A STUDY ON PULSE CHARACTERISTICS OF 06.02.2023 KAHRAMANMARAS EARTHQUAKES
    (International Association for Earthquake Engineering, 2024) Kocakaplan Sezgin, Sedef; Ahmadi, Ehsan; Georgantzia, Evangelia; Mehdi Kashani, Mohammad Mehdi
    On February 6, 2023, two destructive earthquakes occurred with magnitudes of Mw = 7.7 in Pazarcik (Kahramanmaras, Turkey) and Mw = 7.6 in Elbistan (Kahramanmaras, Turkey), respectively. The earthquakes caused loss of lives and properties (heavy damage and collapse of structures). In the scope of this study, a multi-pulse decomposition method of ground motions is used to investigate the time-position, frequency, amplitude, pulse width, and phase angle of the wave packets. The investigation focuses particularly on time-localization, period, and amplitude of the extracted pulses using two ground motion ensembles: 103 ground motions from the Pazarcık earthquake and 79 ground motions from the Elbistan earthquake. The elastic and inelastic response spectra of the original ground motions and those from the multi-pulse decomposition method were generated for the ground motion ensembles. The distribution of pulse characteristics among the fault ruptures was presented for the Kahramanmaras earthquakes. © 2024, International Association for Earthquake Engineering. All rights reserved.
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    ASSESSING SEISMIC VULNERABILITY OF PRECAST POST-TENSIONED SEGMENTAL PIERS
    (Iop Publishing Ltd, 2024) Kocakaplan, Sedef; Ahmadi, Ehsan; Kashani, Mohammed M.
    Precast post-tensioned segmental (PPS) bridge piers mitigate global and local damages of bridge structures through natural hinges. The application of PPS piers has increased recently in Accelerated Bridge Construction (ABC). Therefore, to increase their use in high-seismicity regions, this paper examines seismic vulnerability assessment of post-tensioned segmental bridge piers with Shape Memory Alloy (SMA) bars through a Finite Element (FE) framework. First, to investigate the energy dissipation capacity of the PPS piers with SMA, an extensive parametric study performed on the key design parameters including, (i) number of segments or aspect ratio, (ii) length, area, and post-tensioning of the SMA bars, and (ii) area and post-tensioning of the tendon. The results are also compared with the piers without SMA bars. Furthermore, an equivalent reinforced concrete (RC) pier to one of the PPS piers is also analysed. Incremental dynamic analysis (IDA) is performed, and fragility curves are generated to evaluate seismic performance of the PPS piers with and without SMA bars using a suite of 44 far-fault ground motions. The IDA results show that, slenderizing the PPS piers tends to change failure criterion from the yielding of the post-tensioning tendon to strength loss of the pier. For squat piers, the yielding of the tendon governs the failure of the pier while for very slender PPS piers, the strength of PPS piers drops due to second-order effects at small drift values prior to the yielding of the post-tensioning tendon. Furthermore, the equivalent RC pier reaches slight and medium damage states in lower intensity measures compared to the PPS piers. Finally, IDA results of PPS piers with SMA bars show that their median IDA curves for drift responses are lower than the ones without SMA bars.
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    Modelling non-linear dynamic behaviour of rocking bridge piers with shape memory alloys
    (Emerald Group Publishing Ltd, 2023) Kocakaplan, Sedef; Ahmadi, Ehsan; Kashani, Mohammad M.
    In recent years, accelerated bridge construction has led to the substantial application of precast post-tensioned segmental (PPS) bridge piers. However, PPS piers are not widely used in high-seismicity regions due to their low energy-dissipation capacity (EDC). To address this deficiency, a series of shape memory alloy (SMA)-concrete composite PPS piers were examined in this work. Non-linear static and dynamic analyses were performed on experimentally validated finite-element models of the SMA-concrete composite piers and the results were compared with those of piers without SMA bars. It was found that the length, area and post-tensioning ratio of the SMA bars affected the EDC of the piers, and an optimal design of the bars is required to reach the highest EDC possible. The effects of SMA bars on the frequency response functions of piers were investigated for the first time in this study and it was found that, unlike the piers without SMA bars, sub-harmonics and super-harmonics were not seen in the responses of the SMA-concrete composite piers, mainly the drift responses. Furthermore, the SMA-concrete composite piers experienced a significant reduction in drift responses compared with piers without SMA bars.
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    Nonlinear seismic fragility analysis of a resilient precast post-tensioned segmental bridge pier
    (Taylor & Francis Ltd, 2022) Ahmadi, Ehsan; Kocakaplan, Sedef; Kashani, Mohammad M.
    The use of precast post-tensioned segmental (PPS) piers is growing in the bridge industry, particularly in Accelerated Bridge Construction (ABC). To increase their use in high-seismicity regions, this study focuses on the seismic performance of the PPS piers under pulse-like near-field earthquakes. Two ensembles of 40 pulse-like near-field ground motions and 44 far-field ground motions along with three bridge piers of various heights are used in a series of incremental dynamic analyses. The piers are analysed under the original pulse-like near-field ground motions, their extracted pulse ground motions, and their corresponding non-pulse ground motions. It is found that the effect of the pulse ground motion is pronounced, when the pulse period is in proximity to the natural period of the pier. It is also seen that pulse-like near-field and far-field ground motions generally have similar effects on the response of PPS piers.
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    Seismic Performance of Precast Post-Tensioned Segmental Bridge Piers with Shape Memory Alloy (SMA) Bars
    (Earthquake Engineering Research Institute, 2022) Kocakaplan Sezgin, Sedef; Ahmadi, Ehsan; Mehdi Kashani, Mohammad Mehdi
    In recent years, accelerated bridge construction (ABC) has led to substantial application of precast posttensioned segmental (PPS) bridge piers in bridge construction. However, PPS piers are not to be used in high-seismicity regions due to their low-energy dissipating capacity. To address this deficiency, this paper examines a segmental bridge pier with unbonded post-tensioned superelastic Shape Memory Alloy (SMA) bars through a Finite Element (FE) framework. The seismic performance of the PPS piers with SMA bars is investigated using far-field ground motions and incremental dynamic analysis (IDA). IDA curves of PPS piers are obtained for top drift and normalized base shear, and results are compared with the ones without SMA bars. It is seen that the PPS piers with SMA bars developed higher normalized base shear responses, which is mainly due to their higher stiffness compared to the ones without SMA. However, the PPS piers with SMA bars reduced the drift responses of the piers. © 2022 12th National Conference on Earthquake Engineering, NCEE 2022 All rights reserved.
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    Seismic performance of resilient self-centering bridge piers equipped with SMA bars
    (Emerald Group Publishing Ltd, 2025) Kocakaplan, Sedef; Ahmadi, Ehsan; Kashani, Mohammad M.
    This study examines the seismic behavior of precast post-tensioned segmental (PPS) bridge piers that are equipped with Shape Memory Alloy (SMA) bars. PPS piers are designed to minimize overall and localized damage to bridges by incorporating natural hinges and rocking mechanisms. The introduction of super-elastic SMA bars has the potential to enhance the use of PPS piers in high-seismic regions. A parametric study is conducted to identify piers with the highest energy dissipation capacity, which are then subjected to dynamic analysis. The aim is to assess the energy dissipation capability of these systems by subjecting the selected piers, both with and without SMA bars, to far-field ground motions using a Finite Element (FE) framework. The seismic performance of the piers is evaluated using Incremental Dynamic Analysis (IDA) curves, which are obtained from analyzing the piers under 44 far-fault ground motions. The IDA results indicate a significant reduction in the drift responses of the piers when SMA bars are utilized.
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    SEISMIC VULNERABILITY ASSESMENT OF PRECAST POST-TENSIONED SEGMENTAL PIERS
    (International Association for Earthquake Engineering, 2024) Sezgin, Sedef Kocakaplan; Ahmadi, Ehsan; Mehdi Kashani, Mohammad Mehdi
    Precast post-tensioned segmental (PPS) bridge piers mitigate global and local damages of bridge structures through natural hinges. The application of PPS piers has increased recently in Accelerated Bridge Construction (ABC). Therefore, to increase their use in high-seismicity regions, this paper examines seismic vulnerability assessment of post-tensioned segmental bridge piers with Shape Memory Alloy (SMA) bars through a Finite Element (FE) framework. First, to investigate the energy dissipation capacity of the PPS piers with SMA, an extensive parametric study performed on the key design parameters including, (i) number of segments or aspect ratio, (ii) length, area, and post-tensioning of the SMA bars, and (ii) area and post-tensioning of the tendon. The results are also compared with the piers without SMA bars. Furthermore, an equivalent reinforced concrete (RC) pier to one of the PPS piers is also analysed. Incremental dynamic analysis (IDA) is performed, and fragility curves are generated to evaluate seismic performance of the PPS piers with and without SMA bars using a suite of 44 far-fault ground motions. The IDA results show that, slenderizing the PPS piers tends to change failure criterion from the yielding of the post-tensioning tendon to strength loss of the pier. For squat piers, the yielding of the tendon governs the failure of the pier while for very slender PPS piers, the strength of PPS piers drops due to second-order effects at small drift values prior to the yielding of the post-tensioning tendon. Furthermore, the equivalent RC pier reaches slight and medium damage states in lower intensity measures compared to the PPS piers. Finally, IDA results of PPS piers with SMA bars show that their median IDA curves for drift responses are lower than the ones without SMA bars. © 2024, International Association for Earthquake Engineering. All rights reserved.
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    Time-domain acceleration-based pulse characterization of 2023 Kahramanmaraş earthquakes
    (Springer, 2024) Sezgin, Sedef Kocakaplan; Ahmadi, Ehsan; Kashani, Mohammad M.
    On February 6, 2023, two significant earthquakes struck the region of Kahramanmara & scedil;, T & uuml;rkiye. The first earthquake, with a magnitude of 7.7 and a depth of 8.6 km, occurred in Pazarc & imath;k, and the second earthquake, with a magnitude 7.6 and a depth of 7.0 km, struck Elbistan. These two devastating events led to the loss of lives and massive destruction of civil infrastructures. In this work, pulse components of the ground motions for both earthquakes are characterized through a multi-pulse decomposition method developed by the authors. The work particularly focuses on cumulative energy, period, and amplitude of dominant pulse components using two extensive ground motion ensembles: (1) 103 ground motions from the Pazarc & imath;k earthquake, and (2) 79 ground motions from the Elbistan earthquake. It is found that, for the Pazarc & imath;k earthquake, pulse cumulative energy is more pronounced for the ground motions in proximity to the rupture lines. However, for the Elbistan earthquake, pulse cumulative energy is not significant for the ground motions in a specific area and is roughly uniformly distributed across all the ground motions and the entire region. It is also seen that dominant pulse periods lie predominantly within the range of 0.5-1.5 s for both earthquakes highlighting the significant damage caused. Finally, the pulse amplitudes exceed 0.5 g for several ground motions of the Pazarc & imath;k earthquake while all the amplitudes fall below 0.5 g for the Elbistan earthquake.