This study analyzed seismic responses of shallow rectangular tunnels within the framework of soil-structure-soil interaction. The idealized soil profile and properties were derived from site-specific investigation reports. Racking curves, typically used in design, were reevaluated to reflect local soil conditions, nonlinear soil behavior, and seismic influences. Results differed significantly from traditional literature findings, emphasizing the importance of localized factors. Finite element methods enabled nonlinear soil parameter modeling and time-history analysis of soil-structure systems. Literature reviews and case studies identified potential damage states with discrete damage levels. The findings quantified probabilities of these damage states and established recurrence relationships for system damages. Fragility curve analyses, widely employed in structural engineering, were used to develop graphical representations of damage probabilities. This study's outcomes provide insights into the seismic behavior of tunnels under localized conditions and enhance reliability in geotechnical and structural engineering designs.

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.

The objective of this investigation is to develop the damage-based energy factor (gamma) for seismic demand evaluation of Reinforced Concrete (RC) and steel structures under probable future ground motions regarding the energy-balance theorem and use in the Performance-Based Plastic Design (PBPD) procedure. Before this, the energy factor was determined considering different ductility levels, where the procedure could be extended at constant specific damage levels in damage-based design theory to consider the influence of the hysteresis energy, frequency content, ground motions amplitude, and duration for design purposes. Hence, the popular Park-Ang damage index was employed as a damage model to obtain energy factor under 400 far-fault ground motion records by investigating the influence of structural and earthquake properties on it, including period of vibration, damage level, ultimate ductility ratio, stiffness hardening, structural deterioration, beta factor, soil class type, magnitude (Mw), and source-to-site distance. Due to the influence of ground motion characteristics by using statistical analysis, the Ap/Vp ratio is employed to determine the energy factor, which depends on soil class type, magnitude, fault mechanism, and source-to-site distance. Also, a simple equation based on nonlinear regression analysis among data is suggested to estimate the energy factor based on influential structural and earthquake characteristics, and its error is demonstrated by the two concepts of bias and standard deviation. Finally, three empirical structures validated by numerical modeling, consisting of a full-scale RC bridge pier, a full-scale fourstory RC building, and the three-story steel frame, are considered to validate the accuracy of the proposed method and equation. Statistical results illustrate that the difference between estimated displacements and obtained ones from direct time history analysis is not higher than 20 %, especially compared to the existing damage-based coefficient method.

Recent research has shown that full mobilization of foundation bearing capacity may be beneficial in terms of structural integrity-especially in the case of seismic motions that exceed the design limits. Full mobilization of foundation bearing capacity may serve as seismic isolation because it limits the inertia loading transmitted to the superstructure. Although most research has focused on rocking shallow or embedded foundations, a rocking pile group has attracted much less attention. A potential reason is the probability of structural damage below the ground level (at the piles), which may be difficult to repair or even detect. To shed more light on the problem, the present study investigates the seismic performance of a rocking pile group in clay, aiming to assess its efficiency as a seismic isolation alternative. Employing the finite-element (FE) method, an idealized yet realistic example of a single bridge pier supported by a pile group foundation is analyzed. A carefully calibrated and thoroughly validated kinematic hardening constitutive model is employed for the soil, and the concrete damage plasticity model is applied for the structural members. Using a suite of records as seismic excitation, the response of an intentionally underdesigned rocking pile group is compared with that of a conventionally (capacity) designed system. Similarly to what has been shown for shallow foundations, the comparison reveals that the rocking pile group can be beneficial for the seismic performance of the bridge, reducing the flexural demand on the pier at the expense of increased settlement. Interestingly, the rocking pile group exhibits a genuinely ductile response, such that none of the studied ground motions could lead to full mobilization of the bending moment capacity of the piles. Thus, pile structural damage is avoided. The findings of the present study reveal the advantages of exploiting nonlinear soil-foundation response and indicate that there is a great potential to optimize the contemporary seismic foundation design, which conventionally culminates in massive pile group foundations. The rocking pile group concept may be of particular interest for the retrofit of existing bridges that do not meet the requirements of the current seismic design provision because it can reduce or even completely avoid strengthening the foundation. Ultimately the presented findings call for a shift toward performance-based design, with due consideration of geotechnical failure modes.