The seismic performances of the Tohma Bridge, equipped with viscous dampers at the expansion joints, and the Adana 15 July Martyrs Bridge, fitted with Shock Transmission Unit (STU) devices at the bearings during the 2023 Kahramanmaraş earthquakes, are examined and assessed in the following sections.
3.2.1. Tohma Bridge
The Tohma Bridge was constructed in 2021 and situated on the Tohma Stream within the boundaries of Malatya province, precisely at coordinates 38.23858° E and 38.50476° N. The superstructure of the bridge was designed as a steel composite continuous beam with reinforced columns. The total length of the bridge with nine spans is 517.50 m. The bridge consists of two edge piers (A1 and A2) and eight central piers (P1–P8). The span lengths are 34.5 m between A1 and P1, 69 m between P2 and P6 (six spans), and 34.5 m between P7–P8 and P8–A2 (two spans). Some views from the bridge are shown in
Figure 14.
The I3000 profile was used as a steel girder, with top and bottom flange widths and thicknesses of 1250 mm and 55 mm. The reinforced concrete slab thickness is 280 mm. The bridge deck concrete class is C45 (fc28 = 45 MPa), while the concrete class for the central and edge piers is C30 (fc28 = 30 MPa). The material grade for the steel girders is S355N (fy = 355 MPa, allowable tensile and compressive strength = 0.55fy). The steel plates on the bridge deck have a maximum thickness of 120 mm. For the reinforced concrete elements of the bridge, S420 steel (fy = 420 MPa) has been selected.
The site soil class was determined as ZC, which has a shear wave velocity ranging from 360 to 760 m/s [
26]. The edge piers are founded on observed conglomerate units from the surface. Since conglomerate units provided sufficient strength and experienced less load compared to the central piers, shallow foundations were used for the edge piers. Due to the central piers resting on alluvial layers, bored piles with a diameter (D) of 120 cm were placed at 3D (360 cm) intervals. Each central pier has 20 piles underneath. The pile lengths in the central piers vary between 14 m and 34 m.
In bridge analyses, considering the ZC soil class, a 5% damped design spectrum was used for the 1000-year return period. The maximum spectral acceleration values for short (SS) and 1.0-s (S1) periods were determined to be 1.117 g and 0.729 g, respectively. The PGA value calculated at the bridge location for the 1000-year earthquake is 0.568 g.
Modular expansion joints, comprising multiple components, were employed on the bridge abutments. There are a total of four fluid viscous dampers, with two each at bridge piers A1 and A2, located at the expansion joints. A fluid viscous damper, which is a Maurer Hydraulic Damper (MHD2500/600), was integrated into the units in the longitudinal viaduct direction. This system allows unrestrained longitudinal movement of the superstructure concerning the substructure, accommodating effects such as creep, shrinkage, and temperature variations. The maximum load capacity of the viscous dampers used on the bridge is 2500 kN, with a longitudinal displacement capacity of ±300 mm, a maximal velocity of 860 mm/s, and a damping coefficient of 2557 kNs/m. Moreover, sliding pot bearings and fixed pot bearings were installed on the top of the piers. The friction coefficient for the sliding pot bearings used on the bridge is 0.06 and the displacement capacity was selected as 300 mm, compatible with the fluid viscous dampers. The load capacity for the fixed pot bearings used on piers P4 and P5 was determined to be 4890 kN.
The fluid viscous dampers and pot bearings were designed to exhibit behavior close to elastic for the 1000-year seismic level. During the 2023 Kahramanmaraş earthquake sequences, the bridge was subjected to strong near-fault pulse-type motions and Tohma Bridge experienced earthquake-induced damage at the hydraulic dampers mounted on the edge piers at the Malatya direction, as well as at the expansion joints and numerous pot bearings. Disconnections and locking have occurred at the connections of the fluid viscous dampers. The pot bearings suffered complete failure with their parts dislocated and ejected from the bearing pedestals.
Figure 15 illustrates the damage to the expansion joint, pot bearings, and dampers on the Tohma Bridge.
The Tohma Bridge was subjected to two mainshocks (M7.7 and M7.6) and numerous aftershock ground motions. To assess the damage behavior of the Tohma Bridge during the M7.7 and M7.6 mainshocks, two strong ground motion stations, TK4406 and TK4412, which are closest to the bridge, were selected. The TK4406 station is located at a distance of 143.07 km from the M7.7 earthquake epicenter and 70.17 km from the M7.6 earthquake epicenter. The TK4412 station is situated at a distance of 176.60 km from the M7.7 earthquake epicenter and 99.89 km from the M7.6 earthquake epicenter. Despite both stations being quite far from the epicenters of the M7.7 and M7.6 earthquakes, they are in proximity to the EAF and its segments.
Figure 16 depicts the position of the Tohma Bridge, the epicenters of the earthquakes (M7.7 and M7.6), fault lines, and the locations of the strong ground motion stations that recorded significant data.
Figure 17 displays recorded accelerations versus time and spectra at the TK4406 station for the horizontal (E-W and N-S) and vertical (U-D) directions during the M7.7 and M7.6 earthquakes. The TK4406 station is situated approximately 29 km to the southwest of the bridge. The shear wave velocity of the ground at the TK4406 station is 815 m/s [
25]. The shear wave velocity of the bridge site ranges from 360 to 760 m/s [
26]. It can be observed from
Figure 17a that the recorded accelerations have significant high-frequency content. This indicates that the accelerations contain rapid fluctuations over short time intervals, which can have considerable implications for the dynamic response of structures subjected to such ground motions. The Peak Ground Accelerations (PGAs) for the M7.7 and M7.6 mainshocks at the TK4406 station are 132.92 cm/s
2 and 382.47 cm/s
2 in the E-W direction and 109.47 cm/s
2 and 444.75 cm/s
2 in the N-S direction, respectively. In the vertical (U-D) direction, the PGAs are 49.71 cm/s
2 and 284.86 cm/s
2, respectively. The PGAs recorded at the TK4406 station for the M7.7 and M7.6 earthquakes are lower than the 1000-year return period earthquake design value of 557.21 cm/s
2. However, during the M7.6 earthquake, the PGAs recorded in the N-S direction are close to the bridge design acceleration values.
The acceleration spectra with 5% damping for the M7.7 and M7.6 earthquakes at the TK4406 station are presented in
Figure 17b for both horizontal directions (E-W and N-S) and the vertical direction (U-D), along with the bridge design curve for a 1000-year return period. When comparing the horizontal acceleration spectra calculated from the M7.7 and M7.6 ground motions recorded at the TK4406 station to the smoothed bridge design acceleration spectrum, it is observed that the spectral accelerations in the E-W, N-S, and U-D directions at TK4406 station for both M7.7 and M7.6 earthquakes are generally lower than the design spectrum accelerations. However, the spectral values of the recorded E-W and N-S components during the M7.6 earthquake exceed the design spectral values in the short period range of 0.1 s and 0.2 s. The maximum spectral accelerations calculated for the M7.6 earthquake in the E-W and N-S directions within the 0.1 s to 0.2 s range are 1496.34 cm/s
2 and 1345.45 cm/s
2, respectively. The design spectrum’s maximum spectral acceleration is 1129.13 cm/s
2. During the M7.6 earthquake, the maximum spectral accelerations recorded in the E-W and N-S directions are 33% and 19% greater than the maximum values of the design spectrum, indicating that the bridge was subjected to high acceleration values within these period ranges. Furthermore, in the vertical direction, the peak spectral acceleration was 985.70 cm/s
2, which is significant because it suggests that the bridge girders lifted off their supports and repeatedly slammed back down, contributing significantly to the observed damage.
Velocity–time histories at the TK4406 station for the M7.7 and M7.6 earthquakes in the horizontal (E-W and N-S) and vertical (U-D) directions are depicted in
Figure 18. The figures clearly show the substantial velocity pulses in the ground velocity components. The Peak Ground Velocities (PGVs) for the M7.7 and M7.6 mainshocks at the TK4406 station are 27.35 cm/s and 35.01 cm/s in the E-W direction and 13.12 cm/s and 21.34 cm/s in the N-S direction, respectively. In the vertical direction, the PGVs for M7.7 and M7.6 mainshocks are 11.70 cm/s and 19.03 cm/s, respectively. When examining the temporal variations in velocities recorded at the TK4406 station during the M7.7 and M7.6 earthquake series, it is observed that velocity values close to the PGVs are repeated numerous times throughout the duration of the earthquake records. The PGVs recorded at the TK4406 station for the M7.7 and M7.6 earthquakes are smaller than the maximum velocity capacity of the viscous dampers installed on the bridge, which is 86 cm/s. However, it can be stated that the fault induced significant directivity and fling effects, resulting in notable velocity pulses and permanent tectonic deformations. These effects caused damage to pot bearings and viscous damper devices.
Displacement time histories at the TK4406 station for the M7.7 and M7.6 earthquakes in the horizontal (E-W and N-S) and vertical (U-D) directions are illustrated in
Figure 19. The figures clearly depict the substantial pulse effects in the displacement records. The Peak Ground Displacements (PGDs) for the M7.7 and M7.6 mainshocks at the TK4406 station are 39.44 cm and 24.19 cm in the E-W direction and 20.15 cm and 20.11 cm in the N-S direction, respectively. In the vertical direction, the PGDs are 10.04 cm and 9.18 cm, respectively. The absolute maximum recorded displacements at the TK4406 station for the M7.7 and M7.6 earthquakes do not exceed the maximum relative displacement capacity of 30 cm for the viscous dampers and pot bearings, except for the maximum ground displacement of 39.44 cm recorded in the E-W direction during the M7.7 earthquake. It can be stated that the substantial movements of the superstructure relative to the substructure during the Kahramanmaraş earthquakes resulted in excessive translation of the bearings and dampers.
Arias intensity graphs for the effective durations of the ground motion records in the E-W, N-S, and U-D directions recorded at the TK4406 station during the M7.7 and M7.6 earthquakes are presented in
Figure 20. Arias Intensity graphs provide valuable insights into the energy content and intensity of ground shaking during an earthquake. It can be generally stated that Arias intensity graphs of the E-W, N-S, and U-D components have similar shapes for each earthquake event. For the M7.7 earthquake, the effective duration in the records falls in the range of 20–70 s, while for the M7.6 earthquake, it is in the range of 15–35 s for E-W, N-S, and U-D directions. The M7.7 earthquake has a longer effective duration than the M7.6 earthquake, meaning that the shaking is more prolonged and more energy is delivered to the structure. The Arias intensity plots of the E-W, N-S, and U-D components are close to each other for each earthquake record.
The second station selected to assess the behavior of the Tohma Bridge during earthquakes is the TK4412 station. The TK4412 station is located to the north of the bridge, approximately 11 km away. The shear wave velocity of the ground at the TK4412 station is 360 m/s. Time histories of acceleration measurements recorded at the TK4412 station during the M7.7 and M7.6 earthquakes are presented in
Figure 21a for the horizontal (E-W and N-S) and vertical (U-D) directions. The PGAs for the M7.7 and M7.6 mainshocks at the TK4412 station are 68.15 cm/s
2 and 126.02 cm/s
2 in the E-W direction and 63.05 cm/s
2 and 157.81 cm/s
2 in the N-S direction, respectively. In the vertical direction, the PGAs for the M7.7 and M7.6 earthquakes are 54.21 cm/s
2 and 79.02 cm/s
2, respectively. The PGAs recorded at the TK4412 station during the M7.7 and M7.6 earthquakes are significantly lower than the 557.21 cm/s
2 value considered for the 1000-year return period earthquake in the bridge design.
Acceleration spectra graphs with 5% damping for the M7.7 and M7.6 earthquakes at the TK4412 station are presented in
Figure 21b for the two horizontal directions (E-W and N-S) and the vertical (U-D) direction, along with the bridge design curve for a 1000-year return period. As can be seen from
Figure 21b, the spectral accelerations recorded in the E-W, N-S, and U-D directions at the TK4406 station for the M7.7 earthquake are significantly lower than the design spectral accelerations. They are below the design spectral values along the period range. However, the spectral accelerations recorded at the TK4412 station have effective values in the range of 0.2 s to 2 s. Considering that the bridge’s periods fall within this range, it can be stated that the M7.7 and M7.6 earthquakes caused significant demands on the bridge.
The velocity–time histories at the TK4412 station for the M7.7 and M7.6 earthquakes in the horizontal (E-W and N-S) and vertical (U-D) directions are depicted in
Figure 22. The figures clearly show the substantial velocity pulses in the ground velocity components at the TK4412 station. The PGVs for the M7.7 and M7.6 mainshocks at the TK4412 station are 47.47 cm/s and 28.63 cm/s in the E-W direction and 26.75 cm/s and 38.83 cm/s in the N-S direction, respectively. In the vertical direction, the PGVs for M7.7 and M7.6 earthquakes are 27.11 cm/s and 29.02 cm/s. The PGVs recorded at the TK4412 station for the M7.7 and M7.6 earthquakes are smaller than the maximum velocity capacity of the viscous damper, which is 86 cm/s. However, an examination of the velocity–time histories recorded at the TK4412 station during the M7.7 and M7.6 earthquake series, as shown in
Figure 22, reveals that velocity values close to the peak ground velocities (PGVs) are repeated numerous times throughout the duration of the earthquake records.
Recorded displacements versus time at the TK4412 station from the M7.7 and M7.6 earthquakes are displayed in
Figure 23 for the horizontal (E-W and N-S) and vertical (U-D) directions. The PGDs for the M7.7 and M7.6 mainshocks at the TK4412 station are 44.63 cm and 16.64 cm in the E-W direction and 28.66 cm and 28.37 cm in the N-S direction, respectively. In the vertical direction, the PGDs for both mainshocks are 24.59 cm and 25.63 cm. The absolute maximum recorded displacements at the TK4412 station for the M7.7 and M7.6 earthquakes exceeded the maximum relative displacement capacity of 30 cm for the viscous damper and pot bearings, particularly in the E-W direction during the M7.7 earthquake. This condition can be attributed to triggering damage in the expansion joint, viscous dampers, and pot bearings.
The Arias intensity graphs for the effective durations of the ground motion records in the E-W, N-S, and U-D directions recorded at the TK4412 station during the M7.7 and M7.6 earthquakes are presented in
Figure 24. For the M7.7 earthquake, the effective duration in the records of E-W and N-S directions falls in the range of 30–80 s, while it is in the range of 30–65 s for the M7.6 earthquake. In the records of the U-D direction, the effective duration for the M7.7 earthquake is in the range of 30–85 s and it falls in the range of 28–80 s for the M7.6 earthquake. The M7.7 earthquake record at the TK4412 station has a longer effective duration than the M7.6 earthquake. The Arias intensity plots for the E-W, N-S, and U-D components differ from each other.
3.2.2. Adana 15th July Martyrs Bridge
The Adana 15 July Martyrs Bridge is a highway and railway bridge located over the Seyhan River in the city of Adana, Turkey. The bridge connects the Seyhan and Yüreğir districts. During the 2023 Kahramanmaraş earthquakes, the construction of the bridge was in its final stages (
Figure 25). The total length of the bridge with 23 spans is 1668.90 m, with 786.90 m consisting of a post-tensioned reinforced concrete box section and 882 m composed of a continuous steel box-section girder system. The bridge, with a total width of 38.85 m, serves as a 6-lane roadway, divided into three lanes for each direction of traffic. Additionally, there is a railway track with one line on the bridge.
In the reinforced concrete section, elastomeric bearings were used. Between the steel superstructure and the piers, there are pot bearings. The movements of both central and edge pier bearings of continuous steel box-section girders were restricted in the transverse direction for both service and seismic loads. The bearings can only move longitudinally. In the steel bridge section, LRN1000X160 pot bearings with a diameter of 1000 mm were utilized at the edge piers and LRN1200X192 pot bearings with a diameter of 1200 mm were used at the central piers. The heights of the pot bearings are 160 mm and 192 mm. The allowable horizontal displacements of the pot bearings at the edge and central piers are 320 mm and 390 mm, respectively. The effective horizontal stiffnesses of the pot bearings at the edge and central piers are 6540 kN/m and 7850 kN/m, respectively. Their maximum vertical load capacities of the edge and central piers are 1610 kN and 2550 kN, respectively. In addition to pot bearings in the steel section, Shock Transmission Unit (STU) devices were used to ensure that all central pier bearings were restrained in the longitudinal direction during seismic events. STU devices allow free longitudinal movement of the superstructure relative to the substructure due to creep, shrinkage, and temperature and lock up under high-speed movement to engage.
The deck, central, and edge piers have a concrete class of C50 (fc28 = 50 MPa). The material grade for the steel elements used to span the openings is S355J2G3 (fy = 355 MPa, allowable tensile and compressive strength = 0.55fy). The steel plates in the bridge have a maximum thickness of 63 mm. The material grade for the steel in the reinforced concrete elements is S420 (fy = 420 MPa). The tensile strength of the prestressing strands in the reinforced concrete elements is 1860 MPa.
The bridge foundation consists of alluvial and conglomerate units. An average shear wave velocity (Vs30) of 1010 m/s was determined for a depth of 30 m and soil class ZB was selected for the analyses (ABP, 2018). Bored piles with a diameter of 120 cm were used at axes P21 and P22. All bridge piles have sockets, with a pile length of 26.0 m at axis P21 and 28.50 m at axis P22.
The seismic design spectrum was defined for horizontal ground motion spectral acceleration values corresponding to return periods of 2475 and 475 years (ABP, 2018). For a 2475-year return period, the maximum spectral acceleration values for short (S
s) and 1.0-second (S
1) periods were determined as 1.064 g and 0.256 g, respectively. In the case of an earthquake with a 475-year return period, the maximum spectral acceleration values for short (S
s) and 1.0-s (S
1) periods were obtained as 0.525 g and 0.13 g, respectively. For the 475-year earthquake, the PGA value at the bridge location is 0.3 g. The dominant periods calculated from the theoretical modal analysis of the bridge model in the longitudinal and transverse directions are 1.318 s and 0.248 s, respectively [
27].
The Adana 15 July Martyrs Bridge experienced the effects of the first and second primary seismic events (M7.7 and M7.6). It can be seen from
Figure 26 that no damage was observed on the Adana 15 July Martyrs Bridge during the inspections following the 2023 Kahramanmaraş earthquake sequences.
To investigate the seismic performance of the Adana 15 July Martyrs Bridge during the 2023 Kahramanmaraş seismic events, the TK0118 station, which is closest to the bridge, was selected. The TK0118 station is located at a distance of 155.36 km from the M7.7 earthquake and 205.81 km from the M7.6 earthquake. The shear wave velocity of the soil at the TK0118 station is 946 m/s [
3].
Figure 27 provides a visual representation of the Adana 15 July Martyrs Bridge’s location, the epicenters of the M7.7, M7.6, and M6.4 earthquakes, and the TK0118 station that recorded significant data.
The TK0118 station is situated approximately 1.0 km northwest of the bridge. The shear wave velocity of the soil beneath the TK0118 station is 946 m/s [
25], while the average shear wave velocity of the bridge foundation soil is 1010 m/s [
27]. The time histories of accelerations recorded at the TK0118 station during the M 7.7 and M 7.6 earthquakes are depicted in
Figure 28a, showing data for both horizontal (E-W and N-S) and vertical (U-D) directions. The PGAs for the M 7.7 and M 7.6 mainshocks at the TK0118 station are 38.01 cm/s
2 and 23.67 cm/s
2 in the E-W direction and 49.24 cm/s
2 and 27.27 cm/s
2 in the N-S direction, respectively. In the vertical direction, the PGAs are 23.21 cm/s
2 and 24.15 cm/s
2, respectively. It is noteworthy that the PGAs recorded at the TK0118 station for the M 7.7 and M 7.6 earthquakes are significantly lower than the PGA, 294.30 cm/s
2, considered in the design of the bridge for a 475-year return period earthquake.
Acceleration spectra with 5% damping for the M 7.7 and M 7.6 earthquakes at the TK0118 station are presented in
Figure 28b, specifically for the two horizontal directions (E-W and N-S) and the vertical (U-D) direction. As can be seen from
Figure 28b, the spectra exhibit significant acceleration within the period range of 0.2 s to 3 s. The theoretical dominant periods of the bridge in the longitudinal and transverse directions are 1.318 s and 0.248 s, respectively, which fall within the 0.2 s to 3 s range in the acceleration spectrums in
Figure 28b. The calculated spectral accelerations at the TK0118 station for the M7.7 and M7.6 earthquakes in the E-W, N-S, and U-D directions are notably lower than the design spectral acceleration values corresponding to 2475-year short and 1-s periods, which are 1043.78 cm/s
2 and 251.14 cm/s
2, respectively. The recorded spectral values are also considerably lower than the design spectral acceleration value of 515.03 cm/s
2 for the short period corresponding to a 475-year earthquake. However, it is worth noting that the recorded spectral values are close to 127.53 cm/s² for the 1-s period corresponding to a 475-year return period earthquake.
The time histories of the velocities at the TK0118 station from the M7.7 and M7.6 earthquakes are plotted in
Figure 29 for the horizontal (E-W and N-S) and vertical (U-D) directions. The large velocity pulses of the components of the velocities can be clearly seen in
Figure 29. PGVs for M7.7 and M7.6 mainshocks at the TK0118 station are 14.51 cm/s and 25.63 cm/s in the E-W direction and 18.76 cm/s and 11.79 cm/s in the N-S direction, respectively. In the vertical direction, the PGVs are 10.88 cm/s and 12.10 cm/s, respectively. Upon examining the temporal changes in the recorded velocities at the TK0118 station during the M7.7 and M7.6 earthquake sequences, it is evident that velocity values closely resembling the PGV values are recurrently observed throughout the duration of the earthquakes.
Recorded displacements versus time at the TK0118 station from the
M 7.7 and M7.6 earthquakes are plotted in
Figure 30 for the horizontal (E-W and N-S) and vertical (U-D) directions. PGDs for M7.7 and M7.6 mainshocks at the TK0118 station are 13.69 cm and 32.12 cm in the E-W direction and 33.63 cm and 9.13 cm in the N-S direction, respectively. In the vertical direction, the PGDs are 10.75 cm and 12.14 cm, respectively. At the TK0118 station, the absolute maximum recorded displacements for the N-S component during the M7.7 earthquake and the E-W component during the M7.6 earthquake exceed the maximum displacement capacity of the pot bearings at the abutment piers, which is 32 cm. However, it is worth noting that the recorded ground displacement values are smaller than the displacement capacity of pot bearings at the central piers, which is 39 cm.
Arias intensity graphs for the effective durations of the recorded ground motion in the E-W, N-S, and U-D directions at the TK0118 station during the M7.7 and M7.6 earthquakes are provided in
Figure 31. For the M7.7 earthquake, the effective duration intervals in the records of E-W, N-S, and U-D directions are 30–100 s, 40–100 s, and 30–100 s, respectively. For the M7.6 earthquake, the effective duration intervals in the records of E-W, N-S, and U-D directions are 35–90 s, 30–90 s, and 20–90 s, respectively. It can be stated that the M7.7 and M7.6 earthquakes recorded at the TK0118 station have similar effective durations. The Arias intensity plots for the E-W, N-S, and U-D components differ from one another.