As an important coastal protective structure, the breakwater is prone to failure due to foundation damage under seismic actions. However, the seismic performance evaluation of breakwaters has received little attention. This study conducts a seismic fragility analysis of composite breakwaters constructed on liquefiable foundations. By adopting a performance-based seismic design (PBSD) approach and considering the record-to-record (RTR) variability of ground motions, the seismic performance of the breakwaters is assessed over their entire lifecycle. Based on the results of the parameter sensitivity analysis, the reinforcement schemes were proposed in terms of delaying foundation liquefaction and limiting the lateral displacement of liquefied soil. The results of the seismic intensity measure (IM) parameter selection indicate that the commonly used peak ground acceleration (PGA) exhibits a weak correlation with the seismic response of the breakwater, whereas the cumulative absolute velocity (CAV) has a strong correlation. The comparison of the reinforcement schemes shows that the Dense Sand Column (DC) scheme provides significant reinforcement effects, while the Concrete Sheet Pile (CSP) scheme is more suitable for reinforcing existing breakwaters. The seismic performance assessment framework can also be applied to other structures where structural damage is closely related to foundation deformation, such as caisson quays and embankments.

Steel and reinforced concrete buildings are popular structural systems. The design of these buildings is regulated by deterministic building codes. In this context, it is established that if building codes are followed, the structure will resist demands without collapsing. However, no regulation is required to control the damage of structures in terms of performance criteria. In this paper, the seismic performance and structural reliability of both steel and reinforced concrete buildings, respectively, are analyzed as a benchmark case of study. Both buildings are designed in an earthquake-prone area for two soil types, respectively. Subsequently, nonlinear dynamic analyzes are conducted and the seismic responses of the models are determined in terms of inter-story drift. To obtain seismic responses, eleven characteristic ground motions of the region are selected corresponding to three performance levels: (1) immediate occupancy, (2) life safety, and (3) collapse prevention, respectively. It was documented that the resulting maximum inter-story drift was much lower than the one obtained from modal analysis. In addition, the risk was computed in terms of reliability index integrating a novel probabilistic approach with performance-based design criteria. According to the results, a small variation in the structural risk among the buildings under consideration is observed. However, buildings designed for rigid soil proved to be more reliable. Additionally, it is observed that the buildings designed with current regulations are too conservative based on the performance criteria limits. Hence, structures located on earthquake-prone areas may be overdesigned when implementing deterministic building codes.

In the seismic design of steel moment-resisting frames (MRFs), the panel zone region can significantly affect overall ductility and energy-dissipation capacity. This study investigates the influence of panel zone flexibility on the seismic response of steel MRFs by comparing two modeling approaches: one with a detailed panel zone representation and the other considering fixed beam-column connections. A total of 30 2D steel MRFs (15 frames incorporating panel zone modeling and 15 frames without panel zone modeling) are subjected to nonlinear time-history analyses using four suites of ground motions compatible with Eurocode 8 (EC8) soil types (A, B, C, and D). Structural performance is evaluated at three distinct performance levels, namely, damage limitation (DL), life safety (LS), and collapse prevention (CP), to capture a wide range of potential damage scenarios. Based on these analyses, the study provides information about the seismic response of these frames. Also, lower-bound, upper-bound, and mean values of behavior factor (q) for each soil type and performance level are displayed, offering insight into how panel zone flexibility can alter a frame's inelastic response under seismic loading. The results indicate that neglecting panel zone action leads to an artificial increase in frame stiffness, resulting in higher base shear estimates and an overestimation of the seismic behavior factor. This unrealistically increased behavior factor can compromise the accuracy of the seismic design, even though it appears conservative. In contrast, including panel zone flexibility provides a more realistic depiction of how forces and deformations develop across the structure. Consequently, proper modeling of the panel zone supports both safety and cost-effectiveness under strong earthquake events.

Vertical irregularity is one of the major causes of the failure of the structure. Buildings with vertical irregularities are widespread and unavoidable during rapid urbanization in almost all countries. The safety of such buildings is most important against vulnerability in an earthquake. The vulnerability of structures is assessed using the damage indices of fragility curves. These fragility curves were developed using the HAZUS method, which is used to find the probability of structural damage due to various seismic excitations. This fragility curve determines the probability of none, slight, moderate, extensive, and complete damage to the structures. These fragility curves help to identify the vulnerability percentage of vertical irregularities compared to the regular building. Research also reveals that the vulnerability of the irregular building is similar to the vulnerability identified in terms of roof displacement, base shear, and drift ratio using the THA method. This research also helps to determine the possibility of damage being observed for the structures carrying stiffness and mass irregularities. It is found that stiffness irregularity is more vulnerable than mass irregularity. An increment in collapse probability is observed in stiffness and mass irregularity on the ground floor. Considerable slight to moderate damage possibility is observed in mass irregularity models, and collapse possibility is observed high in stiffness irregularity models. Also, it is observed that the SSI affects adversely on the structures.

The seismic damage of underground structures has been extensively investigated, and it has been demonstrated that underground structures located at weak interlayer sites are more prone to damage. In this study, a two-story two-span rectangular frame subway station structure is analyzed. A two-dimensional soil-underground structure model is developed using the large-scale finite element analysis software ABAQUS. The equivalent linear soil-underground structure dynamic time-history analysis method is employed to examine the seismic response of underground structures at weak interlayer sites. Variations in the thickness and shear wave velocity of the weak interlayer soil are analyzed. The seismic mitigation effects of split columns and prototype columns in underground structures at weak interlayer sites are systematically compared. The findings indicate that the relative displacement and internal force of key structural components significantly increase when the weak interlayer intersects the underground structure. Furthermore, as the thickness of the interlayer increases, the displacement and internal force also escalate. When the thickness of the weak interlayer remains constant and the shear wave velocity decreases, the relative displacement and internal force of the key structural components gradually intensify. Replacing ordinary columns with split columns substantially reduces the internal force of the middle column, providing an effective seismic mitigation measure for underground structures.

Pile-Supported Wharves (PSW) are critical for maritime operations but are highly vulnerable to seismic events, which can disrupt port activities. Previous seismic events have highlighted that short free length piles in wharf structures are particularly prone to earthquake damage. This paper aims to mitigate damage between the wharf deck and piles connections by adopting the seismic isolation systems. Conventional Wharf (CW) and Isolated Wharf (IW) structures were comprehensively assessed, focusing on Pile-Soil Interaction (PSI), using the finite element software OpenSees for advanced numerical simulations. Non-Linear Time History Analysis (NLTHA) of CW and IW has been conducted to verify the design under Contingency Level Earthquake (CLE) and Maximum Considered Earthquake (MCE) scenarios. The analysis aims to enhance the performance of short free length piles within the IW structure. Comparative analysis of fragility curves between CW and IW structures shows that isolation systems significantly reduce seismic fragility by 49%, 60%, and 67% at the MCE level for minimal damage, control & repairable damage and life safety protection across three performance levels, respectively. These findings indicate that the implementation of isolation measures has significantly enhanced the seismic performance and safety of PSW structures.

In designing earthquake-resistant structures, we traditionally select dynamic loads based on the recurrence period of earthquakes, using individual seismic records or aligning them with the design spectrum. However, these records often represent isolated waveforms lacking continuity, underscoring the need for a deeper understanding of natural seismic phenomena. The Earth's crustal movement, both before and after a significant earthquake, can trigger a series of both minor and major seismic events. These minor earthquakes, which often occur in short time before or after the major seismic events, prompt a critical reassessment of their potential impact on structural design. In this study, we conducted a detailed tunnel response analysis to assess the impact of both single mainshock and multiple earthquake scenarios (including foreshock-mainshock and mainshock- aftershock sequences). Utilizing numerical analysis, we explored how multiple earthquakes affect tunnel deformation. Our findings reveal that sequential seismic events, even those of moderate magnitude, can exert considerable stress on tunnel lining, resulting in heightened bending stress and permanent displacement. This research highlights a significant insight: current seismic design methodologies, which predominantly focus on the largest seismic intensity, may fail to account for the cumulative impact of smaller, yet frequent, seismic events like foreshocks and aftershocks. Our results demonstrate that dynamic analyses considering only a single mainshock are likely to underestimate the potential damage (ie., ovaling deformation, failure lining, permanent displacement etc.) when compared to analyses that incorporate multiple earthquake scenarios.

Architectural aspects of buildings, such as the shape of the plan, play an important role in defining the seismic behavior of the building and the future damages structural and non-structural elements may go through. Several items, like the aesthetic aspects and limitations in the field under construction, make an irregular plan shape to be selected as a desirable option. Correctly understanding the building's behavior on the irregular plan is necessary in this case. With that being said, this research aims to evaluate the seismic performance of buckling restrained braced frames (BRBFs) steel structures having an L-shaped irregular plan. An irregular L-shaped plan amplifies the torsional response of the building and causes stress concentration because of the re-entrant corners. Since the lack of a comprehensive study on the L-shaped plan irregularity in buildings equipped with BRBs and the effect of Soil-structure interaction (SSI) would be felt, three types of buildings, low-, mid-, and high-rise, were considered to study the demands of this system on an L-shaped plan. SSI effects were also considered by the cone method in the frequency domain for a more accurate evaluation of the building's behavior during an earthquake event. Each building is studied having three different base conditions: 1- fixed base, 2- SSI with soil type C, and 3- SSI with soil type D. Structural demands, including base shear, overturning and torsional moment, lateral displacement, inter-story drift, and column capacity were measured for different models with fixed and flexible bases by performing time history analyses. The results signify the significant SSI's impact on the building's demands.