George A. Papagiannopoulos

This study investigates the three-dimensional seismic response of plan-irregular reinforced concrete (RC) frame structures subjected to near-fault pulse-like ground motions. The primary scientific contribution lies in evaluating how perimeter-distributed, short-stroke displacement-activated hysteretic dampers interact with complex structural torsional modes under the coupled influence of soil–structure interaction (SSI). Through unscaled nonlinear time–history analyses, this research exposes a critical vulnerability: foundation flexibility elongates the structural period, moving the system into close resonance with near-fault pulse content and more than doubling peak inter-storey drift demands. Concurrently, we demonstrate that the supplemental hysteretic system provides immediate elastic stiffness that successfully counteracts this SSI-induced period elongation, restricting peak drift amplifications to under 0.21% while actively mitigating torsional twisting. These findings provide a quantitative framework for the dual management of foundation flexibility and torsional irregularity using short-stroke metallic yielding devices.

The seismic behavior of an above-ground steel liquid storage tank supported on steel columns and retrofitted with a compact lever-arm amplification mechanism combined with a steel slit damper (SSD) is investigated in this study. The lever-arm mechanism amplifies the relative displacements transmitted to the SSD, enabling efficient energy dissipation through a compact device. Both the conventional and the retrofitted tank are subjected to nonlinear time history analyses (NLTHA), with soil–structure interaction (SSI) explicitly incorporated into the numerical models. The comparison between the two configurations reveals that the retrofitted tank achieves notable reductions in column drift and hydrodynamic wall pressures. The conventional tank is found to be particularly susceptible under soft-soil conditions, while the lever-arm/SSD system demonstrates consistent mitigation performance across all examined soil profiles. The numerical results indicate that the proposed system not only minimizes structural damage but also achieves an average quantitative reduction of 26% in fluid sloshing wave heights compared to the conventional bare frame. These outcomes establish the proposed passive control scheme as a viable and effective retrofit strategy for the seismic upgrading of elevated steel liquid storage tanks at sites with diverse geotechnical characteristics.

The present work focuses on the nonlinear seismic response of transmission tower systems when subjected to successive earthquake ground motions. To this end, nonlinear time-history analyses were carried out by applying multiple ground motion records in sequence, thereby replicating realistic scenarios in which structures endure repeated seismic loading during and following major earthquakes. The structural behavior was examined through two distinct modeling frameworks: a pinned configuration, where tower members are considered to resist axial forces only, and an SSI-based model, which captures the interaction between the structure and the supporting soil. Both frameworks were assessed in terms of several critical response quantities, namely peak displacements, permanent displacements following each seismic event, acceleration demands, and base shear forces developed at the foundation level. The comparative evaluation of the two models brought to light considerable discrepancies in the computed response, confirming that the dynamic characteristics of the soil and its coupling with the structure have a pronounced effect on the overall seismic performance of transmission towers. In addition, it was shown that the cumulative effect of successive seismic excitations drives a gradual buildup of deformations, yielding displacement demands that far exceed those obtained from conventional single-earthquake analyses. These outcomes point to the necessity of incorporating SSI and multi-sequence seismic loading into both the design and the seismic assessment of transmission infrastructure, as approaches relying solely on single-event excitation are likely to significantly underestimate the true seismic demand imposed on such structures.

Damping modeling significantly influences the numerical seismic response of buildings, something that, despite being repeatedly emphasized in earthquake engineering research, is still overlooked even by seismic codes. It is a fact that, for simplification and ease of application, modern seismic design provisions assume damping for buildings entirely composed of a single material, e.g., reinforced concrete or structural steel. The current codes offer no guidance on damping assumptions for so-called mixed buildings comprising a lower part (stories) of reinforced concrete and an upper part (stories) of structural steel. Despite the growing use of mixed reinforced concrete-structural steel buildings, damping modeling of their seismic response remains almost unexplored. This study aims to contribute to this field by investigating the effect of different damping models on the elastic and inelastic seismic response of realistic three-dimensional mixed buildings. Modal response spectrum and time-history analyses served for this purpose. Key seismic response parameters, including interstory drift ratios, floor accelerations, and base shear demands, are extracted and systematically compared for the examined damping models. The results highlight the sensitivity of computed seismic demands to the assumed damping model. Guidance on selecting a damping model for the seismic analysis of mixed reinforced concrete-structural steel buildings is provided.

This research examined the phenomenon of pounding between neighboring steel structures, both with and without tension-only braces, utilizing an extensive nonlinear time-history analysis. The evaluation of the structural response was conducted using essential engineering demand parameters such as inter-story drift ratio (IDR), residual inter-story drift ratio (RIDR), peak floor acceleration (PFA), base shear, and base moment. The findings indicated that the addition of tension-only braces plays a crucial role in diminishing the structural response during seismic activities. The tension-only brace effectively alleviates the negative impacts of structural pounding by offering supplementary restraint and energy dissipation mechanisms, which enhances the overall seismic performance of the steel frame structures. These results highlight the potential advantages of adopting tension-only braces as a passive control method to mitigate pounding-related structural damage in closely situated buildings.

This article examines the seismic assessment and strengthening of a traditional load-bearing masonry structure subjected to strong motion data, with particular emphasis on the effects of soil–structure interaction (SSI). The case study is the Archaeological Museum of Lemnos (AML)—a three-storey building with a composite load-bearing system of timber-framed stone masonry. Over time, the structure has undergone irreversible modifications, primarily involving reinforced concrete (RC) interventions. The building’s seismic performance was evaluated using two finite element models developed in the SAP2000 software (v. 25.3.00). The first model simulates the original structure, strengthened by grout injections, while the second represents the current condition of the structural system following RC additions. Soil–structure interaction was also investigated, given that the local soil is classified as Category D according to Eurocode 8 (EC8). Each model was analyzed under two different support conditions: fixed-base and SSI-inclusive. A suite of appropriate accelerograms was applied to both models, in compliance with Eurocode 8 using the SeismoMatch software, and linear time-history analyses were conducted. The results underscore the significant impact of SSI on the increase of peak tensile stress and interstorey drift ratios (IDRs), and highlight the influence of different strengthening techniques on the seismic response of historic load-bearing masonry structures.

This review article provides an in-depth exploration of the recent advancements in the seismic analysis and design of steel–concrete composite structures, as reflected in the literature from the last ten years. It investigates key factors, such as material behavior, connection detailing, analytical modeling techniques, and design methodologies. The article highlights the synergistic benefits derived from the combination of steel and concrete components to improve seismic performance. Various composite systems, including composite beams, beam-columns, frames, shear walls, foundations, and beam–column joints, are analyzed through experimental studies to assess their dynamic response characteristics under extreme earthquake conditions. The article evaluates advanced numerical modeling methods, including finite element analysis and fiber-based models, for their capability to predict the nonlinear behavior of composite buildings and bridges. A comparative analysis of modern seismic isolation and energy dissipation techniques is also included. Furthermore, the optimization of composite structures in seismically active regions is discussed. The article concludes by identifying areas where additional research is necessary to enhance the seismic resilience of steel–concrete composite structures.

The objective of this study was to examine the seismic behavior of steel buildings equipped with linear and nonlinear viscous dampers that may exhibit variable capacity. More specifically, nonlinear time history analyses were conducted on two three-dimensional steel buildings utilizing a number of recorded seismic motions. Initially, it was assumed that the distribution of viscous dampers was uniform along the height of the building and, thus, the damping coefficients used to size the viscous dampers were derived. Subsequently, nonlinear time history analyses were performed assuming either linear or nonlinear viscous dampers, which may operate at 80%, 100%, and 120% of their capacity. The response parameters extracted by these analyses included the base shear (structural and inertial), the inter-story drift ratio (IDR), the residual inter-story drift ratio (RIDR), the absolute floor accelerations, the formation of plastic hinges, and the forces experienced by the dampers. On the basis of these response parameters, the most appropriate type of viscous dampers was indicated.

This review article presents a detailed investigation into the seismic behavior of structures employing supplementary dampers or additional damping mechanisms over the past decade. The study covers a range of damping systems, including viscous, viscoelastic, and friction dampers, as well as tuned mass dampers and other approaches. A systematic analysis of more than 160 publications in the current literature is undertaken, providing a clear overview of structures equipped with supplementary damping devices and the challenges they face. The theoretical principles that underpin these technologies are examined, along with their practical applications and effectiveness in alleviating seismic effects. Additionally, the article highlights recent developments in the design of damping devices, the challenges related to their implementation, and prospective directions for future research. By synthesizing results from experimental studies, numerical simulations, and real-world applications, this review offers valuable insights for researchers and engineers involved in the design of earthquake-resistant structures.

This paper presents a comprehensive method for analyzing prestressed concrete bridges subjected to multiple concurrent dynamic loads, incorporating soil–structure interaction (SSI) and seismic wave propagation effects. The study develops a comprehensive numerical framework that simultaneously accounts for traveling seismic waves, train-induced vibrations, and soil–foundation dynamics. Three-dimensional finite element modeling captures the complex interaction between the bridge structure, foundation system, and surrounding soil medium. The investigation considers the spatial variability of ground motion and its influence on the bridge’s dynamic response, particularly examining how different wave velocities and coherency patterns affect structural behavior. Advanced material constitutive models based on damage mechanics theory are implemented to represent both linear and non-linear structure responses under dynamic loading conditions. The analysis reveals that traditional simplified approaches, which neglect SSI, train, and seismic loading combinations, and traveling wave effects may significantly misestimate the structural demands. The results demonstrate how wave passage effects can either amplify or attenuate the combined response depending on the relationship between seismic wave velocity, the frequency content of the ground motion recordings, and the local soil conditions. These findings could contribute to the development of more reliable design methodologies for prestressed bridges in seismically active regions with significant railway traffic.