Structural Seismic Design and Evaluation

1. Introduction

Significant damage to structures, induced by the occurrence of strong earthquakes, has been observed in recent decades. This has led researchers worldwide to address several issues concerning structural seismic design and evaluation (SSDE) for different types of structures, including steel and concrete buildings. In fact, the scope of the term SSDE is extremely extensive, meaning that the following discussion will cover only a small part of this large issue. Topics of interest include (a) the evaluation of the reliability of concrete and steel structures with energy-dissipating devices, (b) seismic performance and risk analyses of structures, (c) deterministic and probabilistic methods of dynamic analysis in structural engineering, (d) the seismic behavior and modeling of nonstructural elements, and (e) the seismic performance of new structural systems.

During the last four decades, based on the results of investigations, important steps have been taken within the field of SSDE, including the emergence of new analysis and design procedures. A change associated with this is the considerable shift from traditional elastic to inelastic analyses in the profession. There is no doubt that the most accurate analysis method is the step-by-step nonlinear seismic procedure, provided that the dynamic characteristics of the structure, as well as the loading, unloading, and reloading processes onto the structural members, are adequately represented.

Among the many important efforts relating to the analysis and seismic design of structures, we can mention new smart materials, innovative connections and structural members, energy dissipation devices, and structural systems. The aim of the remainder of this paper is to discuss the results of specific investigations focusing on the improvement of SSDE.

2. Recent Advancements in SSED

The use of innovative structural systems to improve the seismic performance of buildings is one of the topics that have been addressed recently. Various studies have evaluated the advantages of incorporating different devices into structures, such as buckling-restrained braces (BRBs), viscous dampers, and base isolators. For instance, Della Corte et al. [1] analyzed experimental and theoretical advancements in BRB design, highlighting their energy dissipation capacity and greater ductility compared with traditional systems. The study addressed key aspects such as deformation capacity, connection design, and the effects of non-adherent material layers. It also compared different design approaches and examined the performance of BRBs using real-world tests and numerical models. The authors concluded that BRBs offer an efficient and cost-effective solution for seismic design, although challenges such as residual displacements remain. Bai and Ou [2] developed a performance-based plastic design method for dual systems of reinforced concrete frames with BRBs. The method was validated through static and dynamic analyses on 5- and 10-story structures, demonstrating that they meet the desired seismic performance levels. This method can be applied to other structural systems with braces to enhance their seismic resistance.

Some studies have evaluated the economic benefits of incorporating innovative structural systems to improve the seismic resilience of communities. For example, Hu et al. [3] compared the seismic performance of mid-rise steel buildings with three lateral force-resisting systems: moment-resisting frames (MRF), buckling-restrained braced frames, and re-centering non-buckling braced frames. Using incremental dynamic analyses (IDA), vulnerability functions were derived, and economic loss performance pyramids were established. The results highlighted the advantages and limitations of each system in reducing economic losses due to seismic events. Laguardia et al. [4] analyzed 12,016 reinforced concrete buildings to develop vulnerability, fragility, and loss curves, along with an Expected Annual Loss (EAL) assessment. Using data from damage observations from the 2009 L’Aquila earthquake, the methodology incorporated undamaged and non-surveyed buildings based on typological distributions in reference municipalities. The results showed that the completed database improves the reliability of seismic risk assessments, although EAL assessments are minimally affected by the choice of reference municipality. Important contributions in the same area can be found in other studies [5,6,7].

Another current topic of great interest is the use of alternative methodologies for seismic design. One such relatively recent approach is performance-based seismic design (PBSD), which has been the focus of numerous recent studies and incorporated into several building codes around the world. A significant number of studies have focused on the implementation of this methodology in the seismic design and evaluation of various types of structures, highlighting the advantages of these alternative seismic design approaches [8,9]. Steneker et al. [10] proposed a framework to optimize seismic upgrade strategies for buildings, considering both structural and nonstructural components. It introduces the Median Shift Probability method, a modified version of the Performance-Based Earthquake Engineering (PBEE) methodology, to quickly assess the impact of structural upgrades on nonstructural components by analyzing how structural changes affect floor-level hazards. This approach allows for the disaggregation of expected losses and identifies combined upgrade strategies that are tailored to a building’s specific conditions, optimizing the use of resources in the early design stages.

Bakhshivand et al. [11] assessed the seismic performance of buildings with dual lateral force-resisting systems combining special moment frames and special concentrically braced frames (SMF-SCBF) using the FEMA P695 methodology. Six building archetypes (2, 4, 8, 12, 16, and 20 stories) were designed according to ASCE 7–16 and AISC 341–16 and analyzed using nonlinear models in OpenSees. The buildings were evaluated through nonlinear static and dynamic analyses under 44 far-field ground motions, examining peak and residual drift ratios, hysteresis behavior, collapse fragility curves, and seismic performance factors (R, Ω, and C_d). The results revealed that long-period dual SMF-SCBF systems (16 stories or higher) that were compliant with current codes performed poorly and were prone to severe damage during strong earthquakes. Ciurlanti et al. [12] highlighted the gap between societal expectations and the seismic performance of modern buildings in the aftermath of an earthquake. They claimed that current life safety codes are insufficient for new structures, necessitating higher performance standards to minimize business disruption and economic losses. This study explored strategies to achieve (a) advanced design methods, (b) improved seismic design performance, and (c) low-damage technologies. A parametric cost–benefit analysis compared reinforced concrete buildings that are designed for varying seismic intensities using traditional vs. advanced approaches (force-based vs. displacement-based) and technologies. The results, enhanced by machine learning, showed that displacement-based designs and low-damage technologies significantly improve performance, reducing economic losses by over 50%, with only a 5–10% increase in initial costs.

Many other studies have also been conducted with different specific objectives regarding the evaluation of the seismic behavior of structures in terms of risk assessment, the effects of irregularity, and response modification factors. For example, Parizat et al. [13] aimed to develop equations for moment-resisting reinforced concrete frames to estimate the total floor acceleration based on the fact that failures in nonstructural components (NSCs) due to earthquakes can result in casualties, significant economic losses, disabled critical infrastructures, and loss of building functionality, as well as the fact that planning under the peak floor response or peak floor acceleration is receiving significantly less attention. The data used were obtained from the results of 984 inelastic response simulations and processed to create an idealized equation based on the earthquake characteristics. The proposed equation offers engineers a quantitative approach to understanding the inertial forces that are applied to NSCs in buildings during earthquakes, allowing them to assess the potential risks. Blasi et al. [14] analyzed the seismic response of regular and irregular reinforced concrete frames. Their main results showed an important influence of irregularity, especially on floor accelerations and displacements caused by the change in mass and stiffness over height. Hussain et al. [15] aimed to overcome the limitation that recommended seismic design coefficients in design codes are based on previous research by conducting a study, focusing primarily on regular low- to medium-rise building configurations and using two-dimensional analysis, to validate overstrength factors, as well as amplification and response modification coefficients, using three-dimensional (3D) dynamic response simulation and bidirectional earthquake records for high-rise buildings with different structural systems and irregularities. They suggested increasing the response modification coefficients by 5% and 10% for the structural systems studied. Ricci et al. [16] evaluated the behavior and failure probabilities for reinforced concrete MRF using nonlinear static analysis. Based on their results, they proposed a simplified equation to evaluate the behavioral factors.

In another study, Yousefabadi and Kazemi [17] investigated the performance of a structural system based on a reinforced concrete column and steel beam (RCS) system, with a focus on evaluating the seismic design coefficients using the FEMA-P695 methodology. The RCS system offers a more efficient and cost-effective solution compared with conventional steel and RC moment-resisting frames, with higher damping and lateral stiffness of RC columns and a greater energy dissipation capacity of the steel beams. To reach their objectives, 32 archetypes were designed with varying building heights, span lengths, concrete strengths, gravity load levels, seismic load levels, and column–beam strength ratios. Nonlinear analytical models were developed for the selected archetypes, and the modeling assumptions were validated through five distinct experimental tests. The authors concluded that the design requirements of the RCS system are efficient, providing a high safety margin. However, the level of conservatism was found to be excessively high. Thus, it is possible to use a larger R-factor in the design process or implement some relaxations in the design requirements relating to this structural system. Nanclares et al. [18] presented the results of a nonlinear dynamic analysis of a highway bridge, idealized as a 3D finite element model according to the design codes from different periods. Based on the observed results, they proposed to provide higher shear strength, higher ductility, and buckling restraint to structures that are designed based on outdated requirements.

3. Contribution of This Special Issue

The central objective of this Special Issue was to provide a publishing platform for the global community of researchers in traditional and emerging subdisciplines of the field relating to the seismic behavior of structures and structural design in order to present and discuss recent advancements in this broad field. Although several topics were considered in the Special Issue, most of the papers published fall within the following categories: (a) evaluations of the reliability of concrete and steel structures with energy-dissipating devices, (b) seismic performance and risk analyses of structures, (c) experimental and computational simulations of dynamic effects on structures, (d) the seismic behavior and modeling of nonstructural elements, and (e) quantification of earthquake demands and structural capacity. The contributions of a few of the included papers are presented below.

The protection of existing structures against strong earthquakes has been the subject of some interest. For example, Di Egidio et al. [19] studied the effectiveness of intermediate discontinuities for the seismic protection of new and existing framed structures under the action of harmonic and seismic excitations. The intermediate elasto-plastic discontinuity used in the study was described using the Bouc–Wen model, which in turn was represented with a 3-DOF reduced model. This technique has received an increasing amount of interest, because it is cheaper and technically easier to implement than base isolation. In another study, Chonratana and Chatpattananan [20] proposed a damage index to assess the seismic-resistant design of masonry wall buildings that are reinforced with double x-bracing concrete frames. This damage index was calculated by using the analytic results obtained from four-story concrete structures with masonry walls under cyclical lateral forces, along with the Park–Ang model. The damage index can be used in the seismic-resistant design of masonry walls that are reinforced with x-bracing concrete frames. Kuria and Kegyes-Brassai [21] analyzed the evolution, utilization, and challenges of typical pushover analyses, such as the capacity spectrum and displacement coefficient methods, for evaluating the seismic performance of structures. These methods, along with the advanced versions (multi-mode, modal, adaptive, and energy-based pushover analysis) help determine seismic demands with great accuracy. The authors stated that such advanced versions improved accuracy by considering major vibration modes; however, it sometimes failed to address specific aspects, such as bidirectional responses and torsional effects. The paper highlighted the continuing refinement of the pushover methods, reflecting the sustained attention that they receive from both industry practitioners and researchers.

The above discussion and that presented in Section 2 of the paper clearly illustrate the considerable advancements in the field of SSDE in recent years. However, as discussed in the Conclusion, it is also clear that much more research is needed to make structures more resilient to the action of strong earthquakes.

4. Conclusions

The considerable damage to structures after the occurrence of strong earthquakes in recent decades has led researchers worldwide to address several issues concerning structural seismic design and evaluation (SSDE). It is worth mentioning that the term SSDE covers an extremely broad field, so in this paper, only a few aspects of this large issue are covered.

During the last four decades, based on the results of a number of investigations, important steps have been taken within the field of SSDE, including the emergence of new analysis and design procedures. Among these important efforts, we can mention new smart materials, innovative connections and structural members, energy dissipation devices, and structural systems. In this paper, a few contributions to the field were briefly mentioned. Nevertheless, it is important to emphasize that further research is needed to make structures more resilient to the action of strong earthquakes.

In general, the limitations of the investigations presented in Chapters 2 and 3 can be described in one or more of the following ways: (a) In the case of buildings, the structural models are based on framed members. In addition, the effects of connections are neglected. (b) When experimental investigations are considered, structural subassemblies are used, thus ignoring important parts of the structure. (c) Cyclic loads are assumed, neglecting the effects of the dynamic characteristics of the structures. (d) The concentrated plasticity model is considered. (e) The Rayleigh model is adopted to simulate viscous damping, (f) In some countries, the adoption of emerging seismic response control systems has been slower compared with some developed nations, mainly due to the lack of experimental studies and the absence of local regulations that would enable large-scale implementation. (g) The estimation of economic losses is limited in many studies to the use of international databases, such as FEMA P-58. To achieve a more accurate estimation when applied to other regions, a database reflecting local construction costs and practices should be developed. (h) Seismic loss analyses have been limited to only a few specific cases. Regional studies should be conducted to estimate losses and enhance community resilience against this phenomenon.