Seismic Enhancement Techniques for Reinforced Concrete Frame Buildings: A Contemporary Review

Abstract

Earthquakes, as a common natural disaster, frequently occur in close proximity to human activities. Researchers have developed a series of techniques to enhance the seismic performance of typical reinforced concrete frame structures, thereby improving these buildings’ ability to protect human life. How to retrofit and upgrade existing reinforced concrete frame structures with insufficient seismic performance in accordance with current codes and policy requirements, and how to appropriately incorporate new seismic isolation and energy dissipation technologies to enhance their seismic performance, are the focus of this study. This study adopts a data-driven approach that combines both quantitative and qualitative analyses. Relevant literature was collected from the Web of Science database using specific search criteria. This study visualizes both the historical and recent trends within the scientific field and analyzes keyword frequency to identify key areas for future research. Based on frame structures, the paper reviews novel seismic enhancement techniques for structural systems, including frame–shear wall systems, energy-dissipating buckling-restrained braces (BRBs), and seismic isolation bearings. By integrating traditional structural systems with new technologies, a novel structural system is established to ensure the safety of buildings in high-intensity seismic hazard zones. The results indicate that compared with traditional reinforced concrete frame structures, the new structural system increases energy dissipation by approximately 45% on average. Among these techniques, seismic isolation technology, although more costly, exhibits the best seismic performance and is suitable for new high-priority projects; BRB technology offers a balance between economy and effectiveness, making it the first choice for retrofitting existing buildings; and the frame–shear wall system requires an optimized layout to enhance its cost effectiveness.

1. Introduction

An earthquake is a natural threat to human lives and assets, and a great portion of the world’s population lives in earthquake-prone regions [1]. While predicting the magnitude, epicenter, and precise time of large earthquakes is very difficult and beyond our scientific knowledge, earthquakes are certain to occur within a long enough time period [2]. Reviewing the casualty figures from past major earthquake events (Figure 1)—with approximately 190,000 casualties in the 2001 Gujarat, India earthquake [3], about 440,000 in the 2008 Wenchuan, China earthquake [4], roughly 630,000 in the 2010 Haiti earthquake [5], around 100,000 in the 2015 Nepal earthquake, and approximately 160,000 in the 2023 southern Turkey earthquake [6,7]—it is evident that the collapse of public buildings often results in higher casualties, particularly in critical public facilities, such as schools and hospitals. These buildings require more stringent seismic design standards to ensure that they maintain essential functionality after an earthquake, thereby maximizing the protection of human life and the continuity of societal operations. A review of the current literature reveals the following primary failure mechanisms for these structures. The 2001 Gujarat Earthquake (India): Many reinforced concrete (RC) frame buildings incorporated infill brick walls; except for the ground floor (used as a parking area), all other levels featured enclosed wall systems. The open ground floor, lacking sufficient wall rigidity, suffered severe damage or collapse. This issue highlights the vulnerability of structural detailing and unbalanced load distribution, confirming long-standing concerns regarding this construction method [8,9]. The 2008 Wenchuan Earthquake (China): The majority of RC frame buildings did not meet current code requirements, resulting in column shear failures or, due to soft-story effects, excessive deformations in the ground floor columns, leading to partial or total collapse [10]. The 2010 Haiti Earthquake: The main causes of failure were the absence of effective seismic design codes and quality control measures, combined with the frequent use of substandard construction materials. Typical RC frame buildings, which employed concrete block infill, exhibited design deficiencies, such as slender columns and insufficient lateral reinforcement, factors that significantly compromised their seismic performance [11]. The 2015 Nepal Earthquake: In this region, most structures were either vulnerable masonry constructions or RC frame buildings with substandard design and construction practices. Many buildings were constructed by local masons based on empirical methods rather than established codes, resulting in structures with inadequate resistance to external forces and a high susceptibility to damage [12]. The 2023 Southern Turkey Earthquake: The failure mechanisms were primarily due to significant deficiencies in structural system design and detailing. These included an insufficient or absent load-bearing framework, leading to inadequate lateral force resistance; inadequate beam design, causing excessive deflections; eccentric beam connections, resulting in unbalanced forces and stress concentrations; marked stiffness differences between floors (i.e., weak/soft-story effects), causing uneven load distribution; a pronounced strong-beam/weak-column phenomenon, predisposing columns to buckling; oversized cantilever elements, increasing seismic loads; and unreasonable beam–column combinations along with short-column behavior, all of which accelerated structural failure [13]. The cases from Wenchuan, Haiti, and Turkey indicate that many RC buildings did not adequately consider seismic loads during design, with both code deficiencies and inadequate detailing playing significant roles. Furthermore, experiences from Haiti and Nepal demonstrate that a lack of stringent construction quality control and the use of inferior building materials severely compromised seismic performance. Similarly, cases from India and Turkey reveal that common issues, such as infill walls, eccentric connections, soft-story effects, and short-column behavior, critically affect the stability and ductility of structures during earthquakes.

In summary, a review of these major earthquake events shows that deficiencies in design, construction, and material selection in RC structures collectively lead to multiple modes of failure under seismic loading. Therefore, the development of seismic retrofitting techniques for RC structures is imperative.

In traditional seismic design concepts, a building’s seismic performance primarily relies on enhancing the load-bearing capacity and ductility of its structural components. By adopting plastic design, the structure is allowed to undergo controlled plastic deformations under seismic actions, thereby absorbing and dissipating part of the seismic energy. This design strategy aims to ensure that the building maintains its basic functionality under the design-level earthquake, extends the service life of the structure as much as possible, and permits localized, controlled damage under extreme seismic conditions to prevent catastrophic failure and safeguard human life [14]. Although some damage is inevitable under the maximum seismic demand, a carefully constructed ductile system ensures that the overall structure does not experience instability or collapse, thus facilitating post-earthquake repair.

In recent years, with continuous advancements in seismic technologies and increasing requirements for the overall seismic performance of buildings, new seismic isolation and energy dissipation design techniques have gradually been introduced into school buildings. Seismic isolation technology is an effective method to mitigate the destructive effects of earthquakes by reducing the base shear and accelerations transmitted to the superstructure during an earthquake [15]. Energy dissipation technology utilizes local deformations of the superstructure to absorb seismic energy, forming what is known as an energy-dissipative damping structure, thereby enhancing seismic performance. This includes converting elements, such as braces, shear walls, and connections, into energy dissipators or incorporating energy dissipation devices into deformable parts of the structure (e.g., inter-story spaces or joints). Energy dissipation technology channels seismic energy into dedicated energy dissipation devices to protect the primary structure and its components [16,17]. This novel design approach involves installing seismic isolation devices between the building’s foundation system and the superstructure, effectively isolating seismic ground motions from the building and thereby substantially reducing the transmission of seismic energy to the superstructure. Simultaneously, by incorporating energy dissipation devices to actively absorb and dissipate the residual energy, the structure is ensured to exhibit a more flexible and controllable response under seismic actions. This technology not only significantly enhances building safety but also enables structures to quickly restore partial or full functionality after a major earthquake, thereby reducing subsequent repair costs and the risk of prolonged closure and providing more secure and reliable seismic disaster prevention for critical public buildings, such as schools.

Past earthquake data are staggering. According to the United States Earthquake Information Center, between 2015 and 2024, there were 16,911 earthquakes of magnitude 5.0 or greater worldwide (Figure 2), 1336 earthquakes of magnitude 6.0 or greater, and 137 earthquakes of magnitude 7.0 or greater, illustrating that earthquakes continually threaten human safety [18,19].

There are various types of seismic designs for reinforced concrete frame structures, which can be broadly categorized into three types: traditional seismic design, energy dissipation design, and seismic isolation design. Different seismic design approaches have significant impacts on the seismic performance of frame structures and are also crucial for cost control in construction. Section 2, through a literature review, explores research on various seismic design technologies for reinforced concrete frame structures. In order to address the broader challenges in seismic design for buildings, scholars have conducted extensive research on structural seismic design in recent years. Section 2 includes a bibliometric analysis of the literature search results, classifying, organizing, and summarizing a large body of literature. Section 3 primarily focuses on the different types of seismic design in reinforced concrete frame structures and their specific seismic performance. It specifically selects three types—frame–shear wall systems, energy-dissipating buckling-restrained braces (BRBs), and base rubber seismic isolation bearings—and provides a comparative analysis of the performance differences among these designs.

2. Literature Review and Analysis

To ensure the objectivity and accuracy of the literature review, this study employs a systematic approach that combines quantitative and qualitative analyses. Specifically, it first conducts a systematic literature search and screening, followed by a bibliometric analysis of the literature database, and finally an analysis of the content of each individual study [20]; The overall research framework within this study is illustrated in Figure 3.

In the literature search phase, the first step is to define search criteria to ensure that the selected literature covers the key topics in the research domain. The Web of Science is an authoritative and comprehensive citation indexing database that is widely used by researchers to access scientific literature and track research impact [21]. Publications were collected from the Web of Science Core Collection database [22]:

((TS = (CAST-IN-PLACE) OR TS = (STRUCTURE)) AND (TS = (RC) OR TS = (CONCRETE) OR TS = (REINFORCED CONCRETE) OR TS = (COLUMN) OR TS = (BEAM) OR TS = (FOUNDATION) OR TS = (WALL))) AND (TS = (SEISMIC DEFENSES) OR TS = (EARTHQUAKE RESISTANCE) OR TS = (EARTHQUAKE RESISTANT)).

2.1. Bibliometric Analysis

When processing a large amount of literature data using VOSviewer software 1.6.20, it is first necessary to download the complete publication information from the relevant database search results, and then export these data in plain text format so that they can be subsequently imported into VOSviewer for in-depth analysis [23]. VOSviewer primarily focuses on two aspects of information analysis: keyword co-occurrence and citation networks.

In terms of keyword analysis, VOSviewer automatically extracts keywords from the imported literature data and calculates the weight of each keyword based on its frequency of occurrence. By generating a “heat map”, the software visually presents the distribution of keyword frequencies. Subsequently, based on the frequency of co-occurrence, a cluster analysis is conducted, which not only groups high-frequency keywords together to reveal subtopics and hotspots within the research field but also helps researchers identify trends and evolutionary paths within the domain, thereby providing a quantitative basis and decision-making reference for future research directions.

On the other hand, in citation analysis, VOSviewer calculates the citation frequency of each publication and constructs citation network diagrams to identify the core publications that play a key role in a specific research field. Citation network diagrams can visually reflect the inter-citation relationships among publications, helping users distinguish between mainstream research directions and peripheral areas, while also tracing the origins and development of specific research topics or methods. For researchers wishing to explore a specific subfield in depth, these core citations not only provide important technical, methodological, and theoretical support but also constitute a systematic reference framework.

Through the combined analysis of keyword and citation information, VOSviewer is capable of providing comprehensive and intuitive support for the visualization of academic literature, helping researchers quickly capture hotspots in the field and providing robust data support for constructing disciplinary knowledge maps. This method has been widely applied in bibliometrics, research evaluation, and the forecasting of academic trends, thereby providing an important technical and theoretical foundation for subsequent related research.

2.2. Previous Review Studies

Previous literature reviews have primarily focused on studies addressing a single structural system or a single seismic technology, providing detailed discussions on the seismic performance, reliability, and future prospects of each system under seismic actions. For example, in a 2021 study, Zhou Yun et al. systematically discussed and classified buckling-restrained braces (BRBs), not only summarizing the advantages and limitations of various BRB types but also exploring innovative approaches for their application in seismic design. This work provided theoretical support and practical references for promoting BRB technology in engineering practice [24]. However, within the field of earthquake engineering—from traditional seismic and isolation technologies to the emerging research on seismic resilience—comprehensive literature reviews remain insufficient. In particular, systematic reviews on novel systems that integrate different seismic systems to enhance the overall seismic performance of reinforced concrete frame structures are relatively limited. In a 2021 study, Li Chao et al. conducted vulnerability assessments and optimization design for mixed energy-dissipative reinforced concrete frame structures, and their findings provided practical guidance for energy-dissipative system design under combined seismic and wind hazards [25].

Overall, research on integrating multiple seismic technologies and structural systems to achieve superior seismic performance is in a state of continual exploration and innovation. Existing studies indicate that although a single system may offer local advantages, its seismic response is often limited by inherent characteristics when faced with complex and variable seismic actions. In contrast, combining the strengths of different systems—for instance, by incorporating energy-dissipative devices, buckling-restrained braces, or adopting hybrid energy dissipation strategies within reinforced concrete frame structures—not only enhances structural ductility and energy dissipation capacity but also significantly improves overall seismic performance.

In summary, literature reviews on synergistic seismic design for multiple structural systems should not only systematically review the progress of individual systems but also further explore the interactions and synergistic effects among different systems. This approach will provide a solid theoretical and practical foundation for high-performance and economically viable seismic design.

2.3. Overview of Publications

To address broader challenges in building seismic design, scholars have conducted extensive research on the seismic design of building structures in recent years (Figure 4).

By reviewing the progress, studies, and analyses of various building seismic design approaches, numerous researchers have attempted to systematically summarize and assess the current advantages and issues in the literature, thereby identifying potential directions for future research.

According to the literature search results (Figure 5), 95.00% of the research progress comprises journal articles, 2.18% review articles, 1.36% conference papers, and 1.26% early access papers. The overall number of publications has been on an upward trend, especially since 2013, with publications from 2013 to 2024 accounting for 74.97% of all publications. This surge can be attributed to revisions in regional code standards, breakthroughs in technological developments, and subsequent research following major earthquakes [26,27,28,29,30].

Figure 6 shows the top 24 journals ranked by the number of publications from 1991 to 2024. Based on the annual data, Engineering Structures stands out as the leading journal in this field, ranking first with 205 publications, far surpassing other journals, indicating its prominent position and wide influence in this domain. It is followed by the ACI Structural Journal, with 113 publications. Structures and Earthquake Engineering Structural Dynamics rank third and fourth with 95 and 75 publications, respectively, and they also play important roles in disseminating research findings in this area.

In terms of research content influence, since 1991, most of the journals with the highest publication counts related to this research topic have been classified as JCR Q1 or Q2, with high impact factors. These journals have made significant contributions to the field and have driven the development of seismic enhancement technologies.

2.4. Cluster Analysis

Figure 7 presents a co-occurrence analysis of research locations of the publications. In the figure, larger circles indicate a greater number of relevant research publications from a country or region; darker circles signify stronger international collaboration; and thicker lines represent more robust cooperation between specific countries. Overall, China, the United States, Iran, Japan, and Canada have the highest publication counts in descending order. China’s circle is the most prominent and the darkest, indicating a significant increase in research output and reflecting substantial research and experience in this field. China also maintains close collaborations with the United States and Japan. The United States ranks second in both research volume and collaboration strength, demonstrating abundant research experience and sustained contributions. Although Iran ranks third in publication volume—surpassing Japan—Japan exhibits stronger collaborative intensity than Iran.

Figure 8 illustrates the cooperation strength, collaboration networks, and temporal evolution of collaborations among different research locations. Consistent with the analysis in Figure 7, China is one of the most active nodes in the collaboration network, maintaining frequent collaborations with countries like the United States, Japan, the United Kingdom, and Canada. Through extensive international cooperation, China has accumulated substantial research experience and become an important research center. The United States is also a key node, maintaining close cooperative relationships with many countries in Europe and the Asia–Pacific region. Moreover, collaboration among European countries is very high. The dense connections among the United Kingdom, Germany, Portugal, and others reflect these nations’ coordinated and standardized efforts in seismic design for concrete structures.

In Figure 8, the color of the connecting lines represents the evolution of collaborations over time. Earlier collaborations (around 2014) are shown in blue, while more recent collaborations (around 2020) are depicted in yellow. Research outputs from China, Australia, and Italy are mainly concentrated around 2018–2020, indicating that their research experience and findings are relatively recent. In contrast, research outputs from the United States, Japan, and Canada are primarily concentrated between 2014 and 2016 (Figure 8), reflecting an earlier accumulation of research experience.

Using VOSviewer for keyword analysis, keywords that appeared consistently at least 15 times (or as synonyms) were filtered to generate a co-occurrence network diagram of publication keywords. In another analysis, keywords with at least 10 occurrences were similarly filtered to produce a co-occurrence network diagram (Figure 9). From these diagrams, it is evident that the initial research focus was on the performance and reliability analysis of seismic structural components in concrete structures. These studies primarily investigated the behavior of concrete structures under various conditions to ensure stability and safety. However, over time, the research focus gradually expanded to include the seismic performance of reinforced concrete structures, shaking table tests, and energy dissipation technologies.

The keywords “performance” and “behavior” occupy central positions in the diagram, underscoring their importance in the seismic design of reinforced concrete structures and highlighting their core significance in seismic technology research. Their close connections with other keywords indicate extensive interrelations. For example, “design” and “model” are closely linked to “behavior”, reflecting the recent trend toward more in-depth analyses of joint performance.

“Seismic performance” is a widely studied topic, with researchers increasingly focusing on the behavior of joints under earthquake conditions. In the diagram, keywords, such as “seismic behavior”, “shaking table tests”, “ductility”, and “numerical simulation”, are closely associated with seismic performance research, underscoring the significance of this field.

Further analysis of the temporal variations in the diagram reveals that after 2014, keywords, such as “earthquake”, “performance”, and “buildings”, represent newer research trends. This aligns with the recent surge in research attention aimed at enhancing seismic performance through innovative seismic technologies while ensuring that structural and design performance requirements are met.

The associations among keywords not only reflect the interconnectedness of different research topics but also the multi-level and multifaceted nature of the research. For instance, the strong connection between “model” and “shaking table tests” underscores the essential role of both modeling and experimental approaches, indicating that many studies employ a combination of experiments and numerical models to achieve accurate results.

Among the material-related keywords, the co-occurrence of “column”, “beam”, and “concrete” is particularly significant, indicating that a large number of studies focus on structures composed of these materials. Notably, the keyword “wall” is positioned very centrally, emphasizing the critical role of various wall types in seismic structural design.

Another prominent keyword is “energy dissipation”, which appears as a large circle in the diagram, indicating extensive research on this seismic technology.

By analyzing the frequency of keyword usage and connection strengths, this study mainly focuses on three categories of seismic enhancement techniques, as shown in Figure 10. Among all seismic enhancement methods, research on energy dissipation techniques has the highest proportion of published studies. As is also evident from Figure 9, keywords, such as “shear wall”, “energy dissipation”, “dampers”, and “base isolation”, are prominent and located near the center, indicating a high level of research attention and interest in these seismic enhancement technologies. As illustrated in Figure 11, among all seismic enhancement techniques, traditional seismic technologies exhibit the highest proportion of published research. From Figure 9, keywords, such as “walls”, “columns”, and “beams”, stand out and are situated centrally, underscoring the significant research focus and attention on these conventional seismic enhancement methods.

With the passage of time, the emergence of new seismic enhancement technologies and shifts in development directions have led to energy dissipation techniques achieving the highest proportion of published studies among all seismic enhancement methods. Once again, as shown in Figure 9, keywords like “shear wall”, “energy dissipation”, “dampers”, and “base isolation” are clearly prominent and centrally located, further demonstrating the strong research and focus on these techniques.

3. Seismic Technology

Seismic technology plays a crucial role in reducing damage to building infrastructure, protecting human life, and minimizing economic losses during earthquakes. As a result, seismic technology has been continuously and vigorously developed over time, revealing the shortcomings of traditional seismic design methods. Traditional seismic design mainly considers the effects of gravity loads and seismic forces, aiming to prevent life-threatening damage and permit an acceptable level of damage under a given seismic intensity. However, the major earthquakes experienced in countries like Japan and China have demonstrated that although collapse may be prevented, this design approach can still result in severe damage, turning buildings into “ruins” and causing significant economic losses. This underscores the need for seismic-resilient structures, which are defined as structures that can maintain and restore their original functionality following a specified earthquake to meet higher seismic performance standards [14].

In recent years, a substantial body of research has proposed reinforced concrete seismic enhancement techniques aimed at improving the seismic performance of buildings. By examining a wide array of seismic enhancement methods within the realm of reinforced concrete frame structures, three common techniques have been identified: the frame–shear wall system, base isolation [31], and energy dissipation [32].

3.1. Reinforced Concrete Frame Shear Wall Structure

Shear walls are rigid vertical partition elements that transfer lateral forces from exterior walls, floors, and roofs along the plane of the wall down to the foundation, thereby counteracting lateral loads imposed on the structure. When an earthquake increases the shear forces acting on a structure, these walls help reduce the shear transmitted to the superstructure thanks to their inherent strength and stiffness in resisting lateral forces. When a building is properly designed with detailed shear wall configurations, it exhibits excellent performance in seismically active regions; shear walls are particularly vital for high-rise buildings subjected to lateral wind and seismic forces [33].

Reinforced concrete (RC) frames consist of horizontal members (beams) and vertical members (columns) connected by rigid joints to form a spatial lateral-force-resisting system, as shown in Figure 12. These structural components are cast monolithically to ensure complete continuity, thereby forming an integrated system with both geometric and mechanical continuity that facilitates cooperative internal force transfer. RC frames create moment-resisting systems via rigid beam–column joints, using the flexural stiffness and energy-dissipative capacity of the members (through shear deformations) to resist gravity loads, wind loads, and seismic forces [34].

Shear walls, when combined with frames, form a shear wall–frame interaction system—a hybrid lateral-force-resisting system that enhances the building’s ability to resist lateral loads, as shown in the Figure 13. This system is one of the most popular seismic-load-resisting systems worldwide for mid- to high-rise buildings [35]. It is primarily applied in structures ranging from 10 to 50 stories or even taller [36]. In high seismic hazard regions, strict floor–height requirements are imposed, and the system is also widely used in low- to mid-rise buildings. The interaction between moment-resisting frames and shear walls is depicted in Figure 14 [37]; the frame mainly carries the vertical loads and a small portion of lateral loads through a shear mechanism—thus providing spatial flexibility—while the shear wall primarily acts as a cantilever to resist lateral loads through bending deformations, thereby significantly enhancing the lateral stiffness of the structure [38].

Shear wall–frame systems have been widely applied in earthquake engineering, and extensive research has focused on their seismic response [39].

Jamnani and Amiri investigated the seismic performance of RC shear wall–frame structures under repeated cyclic loading (cumulative damage), examining maximum displacements, residual displacements, and energy distribution in both the structures and individual floors. Three building types with 10, 15, and 20 stories were considered, and the study recorded the effects of repeated seismic sequences along with the associated energy concepts. The analysis indicated that, typically, as structures experience repeated earthquakes, the dissipated inelastic energy increases while the residual roof displacement decreases, with the natural frequency of the structure declining due to damage once the structure enters the nonlinear range. In other words, repeated seismic events increase the seismic demands on RC shear wall–frame structures without necessarily leading to collapse [40].

Ozkul et al. studied RC buildings with shear walls that had sustained damage during actual seismic events—for example, the 7.5-magnitude earthquake in Van in 2011. Using recorded acceleration data from the Van earthquake, they performed nonlinear time–history analyses with SAP2000 to determine damage states. Additionally, following the revised Turkish seismic code from 2007, the building was retrofitted through material replacement, quality improvements, and redesign of the shear walls. Subsequent nonlinear time–history analyses confirmed that the retrofitted building could prevent severe damage. The researchers also found that even if the beams and columns exhibited suboptimal seismic responses, properly selected materials and well-designed shear walls could still prevent significant damage [41].

Venkatesh conducted a detailed seismic response analysis comparing a ten-story shear wall–frame structure with a bare moment-resisting frame (i.e., one without any specialized lateral load-resisting system or LLRS) using three-dimensional equivalent static analysis. The study considered the primary loads—gravity, seismic forces, and their appropriate combination factors—and analyzed three types of shear walls (exterior, interior, and appropriately thickened shear walls). Multiple models were evaluated, with a thorough investigation of the linear static analysis results, including the principal and shear stresses in the shear walls. The results indicated that in a structural analysis, gravity and seismic loads along with all load combinations must be considered, and the inclusion of both exterior and interior shear walls effectively reduced the large node displacements observed in bare frames [42].

Despite their clear advantages, shear walls are relatively costly components in RC frame buildings. Inadequate design may lead to unsafe and/or highly uneconomical structures, posing significant risks to both human safety and economic viability. Thus, it is necessary to (i) ensure that the designed shear wall–frame building achieves a minimum target reliability level to resist the anticipated extreme earthquake [43] and (ii) limit the number of shear walls to a reasonable range. It is imperative to optimize the use of shear walls to control construction costs while meeting structural requirements and achieving the expected target of reliability [44]. Consequently, considerable research has emerged on the optimal placement of shear walls and on evaluating their performance in different locations.

Suresh and Yadav examined multi-story RC frame buildings subjected to lateral loads to determine the optimal locations for shear walls that would yield the best seismic performance for frame–shear wall systems. Their results indicated that models with centrally located core walls and those with shear walls placed at the corners of the building exhibited good seismic performance, suggesting these locations as optimal [45].

Jinjie, using a computer-aided optimization design program, proposed a multi-objective optimization framework for RC shear wall structures aimed at minimizing material consumption. Using a 30-story building as a case study, the effectiveness of the proposed optimization program was demonstrated, with conclusions indicating that the arrangement of shear walls directly affects the consumption of materials (i.e., concrete and steel) [46].

Patil et al. studied a 15-story high-rise building—including both symmetric and asymmetric models—by uniformly varying the location of shear walls within the structural plane (i.e., at the building’s corners versus its central core). Two different model types were analyzed for each building configuration using earthquake analysis, equivalent static methods, and response spectrum methods to generate three-dimensional building models. They observed that buildings with shear walls placed at the corners (Figure 15) experienced significantly higher floor displacements compared to those with shear walls in the central core, where the presence of shear walls reduced floor drifts and provided nearly ideal stiffness. This research contributed to identifying effective, efficient, and optimal zones for shear wall placement [47].

Anshuman et al. focused on determining the influence of different shear wall locations in multi-story buildings, basing their approach on the elastic and elasto-plastic behavior of shear walls to identify appropriate, efficient, and optimal zones. A 15-story building was analyzed under seismic loads with three configurations: (i) no shear walls, (ii) shear walls located at the building perimeter, and (iii) shear walls located at the building center (Figure 16). Elastic and elasto-plastic analyses were performed using STAAD Pro 2004 and SAP2000 V10.0.5. Based on the computed shear forces, moments, and floor displacements, the results indicated that shear walls located at the center provided the best seismic performance [48].

Aminnia and Hosseini investigated optimal zones and cross-sectional configurations for shear walls in multi-story RC frame structures under seismic effects using nonlinear time–history analysis. They studied eight different shear wall configurations across buildings with four different floor counts, finding that the optimal configuration was determined by the lowest values of drift, base shear, and roof acceleration [49].

Resm highlighted that considering both displacement and base shear, placing shear walls at appropriate locations is of paramount importance. A summary of various studies revealed that (i) shear walls with openings exhibit reduced strength; (ii) diagonal shear walls are effective in earthquake-prone regions; and (iii) among four models (no shear wall, L-shaped shear wall, perimeter shear wall, and cross-shaped shear wall), the perimeter shear wall configuration proved to be the most effective [33].

Baral used both the equivalent static method (the seismic coefficient method) and response spectrum analysis to study five different RCC building models under seismic loads—one without shear walls and four with shear walls in different positions. The study found that models with shear walls arranged along the corner edges (Figure 17) exhibited lower base shear and displacement compared to models without shear walls and that the configuration with shear walls located at all four corners produced the lowest floor drifts, indicating superior seismic performance [50].

RC frames without shear walls but with masonry infill have been shown to exhibit poorer performance in terms of both stiffness and strength [51]. In external moment-resisting frames, symmetrically placing shear walls—ideally, interconnected in mutually perpendicular directions to form a core—results in better seismic performance in terms of strength and stiffness.

Krishna and Arunakanthi investigated the optimal placement of shear walls in asymmetric high-rise buildings by varying both the location and the shape of the shear walls using the computer application ETABS to analyze the torsion, strength, and stability of the high-rise structures. Their analysis also examined floor drift and displacement to ensure compliance with serviceability requirements, thereby determining the optimal shear wall locations [52].

Umamaheshwara and Nagarajan also used ETABS to conduct an optimization study on a 15-story RC frame building with four different shear wall configurations under seismic loads. Comparative analyses revealed that models with shear walls located at the building corners exhibited smaller drifts and lateral displacements than the other configurations, thus demonstrating the best seismic performance [53].

Titiksh and Bhatt carried out a study in which they altered the locations of shear walls to determine the optimal structural configuration for multi-story buildings. They designed four different configurations by varying the shear wall positions and analyzed the seismic response using ETABS. A uniform frame structure was designed in accordance with Indian standards for lateral and gravity loads, and the results were compared to identify the optimal shear wall placement [54].

Rokanuzzaman et al. presented a study on optimizing the arrangement of shear walls in multi-story buildings subjected to lateral loads. Using a 16-story residential building as a case study, they designed and compared three shear wall configurations: (i) no shear walls, (ii) shear walls arranged along the central perimeter, and (iii) shear walls placed at the building corners. The evaluation metrics primarily considered structural displacements and base shear to assess seismic performance and structural response. The results indicated that configuration (ii), with shear walls along the central perimeter (Figure 18), produced the minimum values for both top-floor displacement and base shear, suggesting that such an arrangement leads to more uniform overall stiffness, reduced displacements, and minimized shear concentration—thereby enhancing structural safety and cost [55].

Abualreesh, in a comprehensive literature review, proposed a direct search-based method that introduces a required reliability level as an additional constraint to optimize the number and placement of shear walls under new reliability constraints, thus enhancing structural safety. By analyzing a set of representative symmetric and asymmetric RC shear wall–frame buildings under seismic loads, the study demonstrated that the reliability constraint typically governs the optimization process for RC shear wall–frame buildings under seismic actions. The number and placement of shear walls were found to play a critical role in controlling building response, reliability, and overall construction cost, providing theoretical guidance for practicing engineers and researchers in achieving the required safety levels in structural design. It was further observed that under identical seismic loads, buildings with symmetric floor plans tend to have an optimal cost that is about 10% lower than that of buildings with asymmetric floor plans. For both economic and stability reasons, multi-story buildings with symmetric floor plans should be preferred over those with asymmetric plans. This finding offers new insights for the overall layout of frame–shear wall systems and provides a basis for controlling construction costs through optimal shear wall utilization while meeting structural requirements and achieving target reliability. Although the assumptions made in the proposed method have certain limitations, ongoing research is continually refining these approaches and eliminating such assumptions to provide more practical guidance on shear wall applications [44].

Research has been conducted on the impact of shear wall placement at different locations on the overall structural behavior of buildings, summarizing the differences in seismic performance attributable to various shear wall positions. However, most studies have not considered the presence of openings in shear walls. Openings, such as doors, windows, and other types, are often inevitable, as illustrated Figure 19. The size and location of these openings are typically determined by functional requirements and vary from case to case. Therefore, it is necessary to investigate the effect of openings and their positions in shear walls on overall structural behavior under seismic loading.

Several researchers have already begun to study this aspect. Kim and Lee [56] performed an elastic analysis of shear walls with openings using brick elements. They modeled three shear wall configurations with different opening sizes to study the effect of openings on shear wall behavior. Additionally, three models with openings in various locations were analyzed to investigate the influence of opening placement. Husain MA [57] proposed an effective analysis method for shear walls with openings in super-elements by introducing virtual beams to derive a supershell formulation. The accuracy and efficiency of the proposed method were evaluated through analyses of several example structures, although the formulations and the results were based on the elastic behavior of the structure. To more accurately predict structural behavior, Lou et al. [58] proposed load–displacement formulas under yield and ultimate loads for shear walls with and without openings. It is expected that the effective method proposed in the study will be widely researched to explain the inelastic behavior of shear wall systems with or without openings.

Lin and Kuo [59], through finite element analysis and experimental studies under lateral loads, found that the ultimate strength of shear walls with openings is significantly affected by the shear behavior around the openings. Experimental results indicated that the contribution of inclined reinforcement around the opening reached 40% of the yield strength, while the contribution from rectangularly arranged reinforcement reached 20% of the yield strength. They also concluded that the shear capacity of the section is influenced not only by the opening’s width but also by its depth. These findings offer a research direction for strengthening shear wall thickness around openings to achieve enhanced performance. Qaqish and Daqqa [60] examined the influence of small openings on shear wall behavior, as well as the effect of opening size on the behavior of coupled shear walls. Yanez, Park, and Paulay [61] investigated the seismic performance of six RC walls with square openings of various sizes and arrangements under reversed cyclic loading. Their results indicated that properly designed walls with staggered openings can perform comparably in terms of behavior and ductility to walls with regular openings. A method based on column and tie-rod models was shown to be feasible for designing RC walls with irregular openings under reversed cyclic lateral forces, with wall stiffness being dependent on the size of the opening rather than its horizontal location. They recommended that the stiffness of a wall without openings can be used as a reference for walls with openings smaller than 10% of the total wall area.

Chowdhury et al. [62] conducted a linear elastic analysis of a six-story, 7 × 3 bay framed shear wall building subjected to seismic loads using the equivalent static method implemented in the finite element software ETABS 9.7. The study compared the effects of openings located at the center of the shear wall—both window and door openings—when positioned on the right, middle, and left sides, and it also examined the impact of reinforcing the shear wall around the openings. The results indicate that both the size and location of openings in a shear wall influence the structure’s stiffness and seismic response, and it is recommended that appropriate analyses be performed prior to incorporating openings into shear walls. The research further concluded that an increase in the number and area of openings leads to larger building displacements, with this trend becoming more pronounced on higher floors. In terms of top-floor displacement, increasing the wall thickness around door openings proved more effective than increasing the wall thickness around window openings. Future studies could explore shear walls with varied opening sizes and locations and consider the role of coupling beams. Additionally, nonlinear dynamic analyses are necessary for a comprehensive evaluation [62].

3.2. Energy Dissipation Technology—Buckling Restraint Brace—BRB

Energy dissipation technology is a category of passive control in seismic design. It functions by installing dedicated energy dissipation devices or by utilizing the inherent plastic deformations of structural components to convert the input seismic energy into heat or other forms of non-damaging energy. This conversion creates what is known as an energy-dissipating damping system that significantly reduces the seismic response of the primary structure, thereby enhancing its seismic performance. Its core objectives are to minimize structural damage, improve ductility and energy dissipation efficiency, and achieve performance-based seismic design. In practice, this involves converting certain building components, such as braces, shear walls, and connectors, into energy dissipators or integrating energy dissipation devices into the structure’s inherent ductile regions (for example, at inter-story spaces or joints). Under moderate seismic or wind loads, the structure and its devices work in unison to maintain an elastic state. Even under extreme conditions, such as a major earthquake or strong wind, they absorb significant energy by transforming the kinetic or deformation energy acting on the structure into heat, thereby quickly suppressing vibratory responses. This approach ensures that the primary structure remains essentially elastic, and, even if it enters an elasto-plastic range under exceptional conditions, it prevents functional damage that could threaten life and property (Figure 20) [14]. In essence, energy dissipation technology achieves overall structural safety and economic efficiency by intentionally “sacrificing” the performance of local devices or controllable components. It is one of the core technologies driving modern seismic engineering’s transition from merely preventing collapse to ensuring post-earthquake functionality.

In particular, self-centering structures—as an innovative seismic system—have attracted considerable attention in both research and practice in recent years. These systems employ advanced self-centering devices that enable the structure to rapidly return to its initial state after an earthquake, thereby substantially reducing or even eliminating residual deformations and enhancing overall seismic resilience. Compared with traditional elasto-plastic systems, the primary advantage of self-centering structures is their robust self-centering capability, which ensures that the building requires little or no post-earthquake repair and demonstrates significant seismic resilience throughout its service life. This offers a reliable and cost-effective pathway for modern seismic design.

Energy dissipation technology directs the seismic energy entering a structure into specialized dissipation devices, where it is converted into heat or other non-destructive energy forms to protect both the primary structure and its components [16,17]. This approach represents a significant improvement over conventional seismic design philosophies, which rely on the overall ductility of the building to dissipate energy through controlled plastic deformations to avoid brittle failure and maintain overall stability. However, because the placement of energy dissipation devices is often closely integrated with the primary structure, these damping systems cannot completely prevent plastic damage to the main structure; some level of damage is inevitable. In other words, the additional energy dissipation devices can also be regarded as a means of enhancing the structure’s damping. Extensive research has led to the development of various types of energy dissipation dampers, which can be broadly classified into two categories: displacement-dependent dampers and velocity-dependent dampers. This paper focuses primarily on displacement-dependent dampers—specifically, buckling-restrained brace (BRB) dampers—that are widely used in practice.

In displacement-dependent dampers, the damping force generated is primarily a function of the relative displacement between the two ends of the device. These dampers mainly include metallic yielding dampers and friction dampers. Among the metallic yielding types, the buckling-restrained brace (BRB) is a notable energy dissipation component that employs a restraining mechanism to prevent the core unit from buckling under compression. As such, it functions as both a lateral-force-resisting device and an energy dissipation mechanism in structural engineering. The fundamental design principle of the BRB is to provide lateral support to an internal axial-force-carrying core material (typically, low-yield-point steel) using an external restraining unit, such as a concrete-filled steel tube or a composite section. This lateral support ensures that the core yields across its entire cross-section under both tensile and compressive loads, entering a plastic energy-dissipative state. In doing so, the BRB prevents the sudden loss of load capacity and the degradation of hysteretic performance that are typical of conventional braces subject to compressive buckling.

Buckling-restrained braces represent a significant breakthrough in the field of metallic yielding dampers. Through innovative structural design, they effectively overcome the technical challenge of buckling-induced instability in conventional bracing elements under compression by achieving a bi-directional, full-cross-section plastic yielding mechanism under both tension and compression. This technology originated from the work of Yoshino and colleagues in 1971 on steel–concrete composite shear walls [63]. Its core innovation lies in establishing a “flexible yielding–rigid restraint” mechanism; by precisely controlling the clearance at the interface between the steel plate and the concrete wall, the embedded steel is allowed to undergo large plastic deformations under axial loads to fully dissipate seismic energy, while the surrounding concrete restraining component provides stable lateral confinement to effectively suppress buckling of the core under compression. With further advances in engineering practice, modern BRB technology has evolved into a mature structural system. A typical configuration uses low-yield-point steel as the core energy dissipation unit, encased within a rectangular or circular steel tube filled with high-strength mortar and separated from the core by an unbonded layer (such as polyethylene film or silicone rubber). This multi-layered protective system not only ensures free axial deformation of the core under cyclic loading but also provides continuous three-dimensional lateral support via the composite restraining system of the mortar and steel tube. Both numerical simulations and experimental studies have confirmed that optimized BRB components can maintain stable mechanical performance under repeated cyclic tension and compression, achieving an equivalent damping ratio of 0.4–0.5 and an energy dissipation capacity three to five times greater than that of conventional braces [64,65]. This robust performance under both tension and compression is a key advantage of BRBs.

A BRB typically comprises three components: a core unit, a restraining unit, and an unbonded interface layer (Figure 21). Connected to the primary structure, the BRB undergoes axial deformations under most seismic events, providing lateral stiffness comparable to that of conventional bracing. In some extreme earthquakes, it can even function as a “fuse” by dissipating seismic energy to protect the primary structure. Specifically, the core unit bears axial loads and dissipates energy through plastic deformations; the restraining unit, which is a rigid encasement (such as a concrete-filled steel tube or composite section), provides continuous lateral confinement to suppress buckling of the core; and the unbonded interface layer—comprising sliding materials like rubber or coatings—prevents frictional restraint between the core and the restraining unit, ensuring free axial movement. Extensive research and subsequent improvements have continuously advanced BRB technology, making it increasingly popular in engineering applications [66].

From the perspective of evolving mechanical performance, the advantages of BRBs can be summarized in relation to three aspects. First, the restraining mechanism eliminates strength degradation due to compressive buckling, ensuring that the component reaches its design yield strength in both tension and compression. Second, the full-cross-section yielding mode significantly enhances its plastic deformation capacity; according to the Chinese standard “Technical Code for Seismic Energy Dissipation in Buildings” (JGJ/T 101-2015) [67], Grade A BRBs must achieve a cumulative plastic deformation coefficient of at least 200. Third, the bilinear restoring force characteristic provides the benefits of both displacement-dependent and velocity-dependent dampers, making BRBs particularly effective at resisting strong nonlinear responses during rare seismic events. These features offer BRBs broad application prospects in ultra-high-rise buildings, large-span structures, and the seismic retrofitting of existing structures.

BRBs have been proven in seismic design to effectively resist horizontal ground motions while significantly enhancing the energy dissipation capacity of both new and existing steel structures. However, the applicability and actual performance of BRBs in reinforced concrete (RC) frame structures remain somewhat uncertain. Over the past several decades, researchers worldwide have extensively studied various forms of BRBs. Although there are differences in detailed design, the basic concept is consistent; by preventing both global and local (cross-sectional) buckling of the brace, the device maintains equivalent strength under both tension and compression, resulting in more efficient and symmetric hysteretic energy dissipation. By integrating dedicated restraining units, BRBs can effectively suppress both local and global buckling of the core steel, ensuring that even after yielding, the brace retains high load-bearing and energy-dissipative capabilities, thereby enhancing overall structural seismic resilience [68]. Furthermore, numerous experimental and theoretical studies have demonstrated that regardless of variations in BRB configurations, their core function is to prevent brace instability and achieve equivalent force-resisting behavior under tension and compression, thereby producing a fuller and more stable hysteresis loop. This design philosophy enables BRBs to better control structural deformations and residual displacements during major earthquakes while reducing post-earthquake repair costs and downtime. In summary, although further validation is required regarding the use of BRBs in RC frames, existing research indicates that their unique anti-buckling and energy dissipation mechanisms offer new approaches for improving conventional bracing systems and provide a solid foundation for high-performance seismic design.

Frame systems have been widely adopted in earthquake-prone regions due to their excellent seismic performance, as demonstrated in numerous studies (e.g., [69,70,71,72,73]). However, many existing RC frame structures were primarily designed for gravity loads and did not adequately account for lateral seismic forces, leading to deficiencies in lateral force resistance, lateral stiffness, and overall stability. Such design shortcomings can result in significant displacement responses during strong earthquakes, increasing the risk of structural damage and adversely affecting post-earthquake recovery and functionality. For these reasons, retrofitting existing RC frame buildings to enhance their seismic performance has become an urgent challenge in the engineering community. To meet increasingly stringent seismic safety standards and practical needs, various intervention strategies have been proposed and implemented. These retrofitting measures include both traditional strengthening techniques (such as adding shear walls) and innovative methods that have emerged in recent years (such as buckling-restrained braces [74,75,76]). They have achieved remarkable improvements in lateral stiffness, lateral force resistance, and energy dissipation performance while also considering cost effectiveness, ease of construction, and compatibility with existing structures. As a result, these measures provide robust assurance for the safe operation and rapid recovery of buildings after seismic events. Research on the application of BRBs in frame structures has demonstrated that they exhibit ductile behavior under both compression and tension, characterized by a complete, stable, and symmetric hysteretic loop with relatively low yield stiffness [77].

Because BRB technology was first introduced to the Japanese construction industry in 1988, buckling-restrained braces have gradually become an important means of enhancing building seismic performance. With the continuous development of earthquake engineering theory and practice, BRB technology has undergone sustained improvements and optimizations, evolving into self-centering buckling-restrained braces (SC-BRBs) that combine outstanding energy dissipation with self-centering capabilities. Traditional BRBs rely primarily on elasto-plastic deformation to dissipate seismic energy, but, under strong seismic events, this mechanism can lead to large displacements and residual deformations, thereby increasing post-earthquake repair difficulties and costs. To address this issue, SC-BRBs incorporate self-centering devices that enable the structure to quickly return to a state close to its original condition after an earthquake, thereby significantly reducing or even eliminating residual deformations and ensuring the recovery of overall structural performance. Moreover, SC-BRBs not only retain the significant energy dissipation advantages of traditional BRBs but also further enhance seismic resilience and structural reliability through their self-centering mechanism. This dual functionality enables SC-BRBs to quickly restore operational status after an earthquake, reducing repair costs and downtime and providing solid assurance for the safe operation of buildings following major seismic events [78].

Results from the elastic response spectrum analysis indicate that under minor seismic loads, both buckling-restrained braces (BRBs) and conventional braces can effectively reinforce reinforced concrete frame structures while meeting the requirements of the Seismic Design Code GB 50011-2010 [79]. Specifically, because conventional braces do not buckle under low-intensity seismic loading, their initial performance can maintain the overall stability of the structure. However, to achieve the same level of lateral stiffness as BRBs, conventional braces typically require a larger cross-sectional area, which negatively impacts both the economy and the structural self-weight. Further comparisons using nonlinear time–history analyses revealed that under strong seismic loading, conventional braces are prone to failure due to excessive buckling, thereby compromising the overall seismic performance; in contrast, BRBs, owing to their unique energy dissipation and self-centering mechanisms, can rapidly return to a state near the original condition after an earthquake, ensuring that the frame maintains high stability and safety even after major seismic events. These results clearly demonstrate that in retrofit projects for concrete frame structures expected to experience strong seismic events, relying solely on conventional braces is not a safe or reliable alternative [80].

Compared with traditional bracing systems, buckling-restrained braces (BRBs) exhibit more significant technical advantages. First, BRBs markedly enhance the energy dissipation efficiency of a structure by effectively absorbing and dissipating seismic energy (Figure 22), thereby reducing the structural vibration response. Second, their unique design allows high-stress anchorage devices to fully engage in the force transmission process, overcoming the anchorage limitations associated with conventional braces. To thoroughly evaluate the practical effectiveness of post-installed anchorage devices connected to BRBs in the seismic retrofitting of reinforced concrete frames, researchers conducted systematic cyclic loading tests. During these tests, simulated seismic loads were repeatedly applied to analyze in detail the energy dissipation behavior and self-centering capabilities of BRBs under nonlinear conditions. The experimental results demonstrate that the proposed BRB connection design not only achieves a dual enhancement of both the strength and ductility of the bracing system but also ensures the structure’s self-centering performance after seismic events, thereby meeting the requisite seismic performance criteria [81].

To date, research on BRBs has predominantly focused on their application in steel structures, while studies on their use for seismic retrofitting in RC structures are relatively limited. Although existing analytical and simulation studies have systematically examined RC frame buildings and bridges retrofitted with BRBs, detailed description of the anchorage mechanism between BRBs and concrete components remains insufficient [82,83]. Moreover, although experimental tests on RC frames retrofitted with BRBs have been conducted, these tests typically employ through-type anchorage connections. Such connections may have certain adverse effects, and, as noted earlier, issues related to their mechanical performance and durability warrant further investigation [84,85]. Notably, to our knowledge, the experimental work reported by Yooprasertchai and Warnitchai [86] is among the few studies that employed post-installed anchorage connections between BRBs and RC components. Although their subassembly tests verified the feasibility of the post-installed anchorage scheme, the study did not fully consider the overall RC frame response, including issues like pronounced concrete cracking and secondary moment effects, which could significantly influence seismic performance. Overall, BRBs as a seismic retrofitting solution show promising prospects in weak RC structures. Their primary advantages include effectively preventing brittle failure in the early stages of an earthquake and, through controlled energy dissipation, delaying stiffness degradation and facilitating post-earthquake safety evaluations and subsequent maintenance inspections [81]. However, further research is needed on the post-installed connection technology between BRBs and RC structures to explore its impact on overall structural performance and to develop corresponding design optimization measures that ensure the safety and cost-effectiveness of the retrofitting system in practical applications.

NCREE [81] conducted a large-scale experiment to investigate the technical performance of directly connecting a BRB system to an RC frame using post-installed concrete anchors. In this test, loads were applied by gradually increasing the structural drift until specimen failure, thereby thoroughly examining the force performance and failure mechanisms of the connection system under ultimate conditions. Notably, this experiment was the first to achieve a direct connection between BRBs and an RC structure using post-installed anchors without the assistance of a conventional steel frame. The anchor details were designed and implemented based on actual engineering conditions, providing valuable data for optimizing seismic retrofitting measures. The experiment yielded the following key findings:

(i) The results fully demonstrated the feasibility of the connection concept. Bonded expansion anchors played a critical role in the system, exhibiting excellent mechanical performance—the peak-to-peak stiffness decreased only slightly with plastic deformation, and, compared to a standalone concrete frame, the energy dissipation capacity increased by approximately five times, indicating significant advantages in absorbing and dissipating seismic energy.

(ii) BRBs with all-steel bolt ends and their corresponding connections exhibited outstanding overall performance. The test further showed that when considering the combined effects of BRB axial forces and frame interactions, the design of the anchored bracing plate provided a conservative yet safe construction solution, offering reliability validation for engineering applications.

(iii) It was observed that under tensile loads, the interaction between the BRB and the concrete anchors generated a closing moment effect in the anchorage region, which helped form effective confinement and, to some extent, enhanced the load-bearing capacity of the anchorage system.

However, the experiment also revealed some shortcomings. Due to cumulative displacement and the absence of reverse bolts, the concrete anchors induced relative movement in the anchorage bracing, which in turn caused misalignment of the bracing plate. This design flaw may lead to local buckling in the BRB joint region, affecting the overall stability of the connection system. In summary, the direct connection of BRBs to RC structures using post-installed concrete anchors—without relying on a steel frame—offers an advanced retrofitting approach for weak concrete structures, demonstrating excellent energy dissipation and mechanical performance. To further promote and refine this technology, it is recommended to conduct broader experimental studies, expand the range of configuration parameters, systematically validate the basic assumptions underlying the concrete anchor design, and optimize the connection stability between the anchorage bracing and the bracing plate to effectively prevent local buckling.

Owing to their stable hysteretic behavior, BRBs are increasingly incorporated into RC frame structures to form dual structural systems (Figure 23). One study aimed to quantify the seismic behavior of newly constructed RC–BRB frames (RC-BRBF). Installing BRBs in RC frame structures can provide additional stiffness and strength, thereby developing a dual structural system [87].

Castaldo investigated the effectiveness of buckling-restrained braces (BRBs) for seismic retrofitting in reinforced concrete (RC) buildings with masonry infills. An advanced three-dimensional nonlinear model of an existing building in L’Aquila was developed in OpenSees, incorporating the effects of the infill walls via an equivalent support method and employing a recently developed BRB hysteresis model. Nonlinear static (pushover) analyses and incremental dynamic analyses were conducted using a suite of recorded ground motions to evaluate the building’s seismic performance before and after BRB retrofitting. By both considering and neglecting the contribution of the infill walls, seismic demand risk curves for various response parameters were constructed for the retrofitted and non-retrofitted cases. The study’s findings reveal the impact of both the BRBs and the infill walls on the seismic performance of various system components and confirm the effectiveness of BRB retrofitting in the real-world case study [89].

Aiken conducted nonlinear time–history analyses of buildings designed for several different lateral force levels, yielding a wealth of response data. Statistical evaluations of these data provided observations and conclusions regarding design force levels and other design considerations. In the absence of specific design code requirements for buckling-restrained brace (BRB) frames, the initial project design was based on the existing code provisions for traditional concentric braced frames, with appropriate modifications implemented to account for the improved post-yield behavior of buckling-restrained braces relative to conventional braces [90].

3.3. Foundation Isolation Technology—Rubber Bearings

A base isolation system is a structural scheme in which isolation devices are installed between the superstructure and the top of the foundation [14].

Since the advent of seismic isolation bearing devices, their applications across various engineering projects have been extensive. In the 1980s, to advance the forefront of seismic design, researchers and practitioners developed various types of isolation bearings for critical structures, such as bridges and buildings.

As the understanding of isolation technology deepened, engineers realized that these devices—with their high energy dissipation and self-resetting capabilities—are equally applicable to buildings. During the transition from bridge to building applications, engineers made necessary improvements to the design of isolation bearings to accommodate the load characteristics and structural systems of buildings. For example, because building foundations must withstand higher vertical loads, the material mix, geometric dimensions, and connection methods have been specifically optimized. Additionally, to cope with the more complex vibration modes in building structures, the nonlinear characteristics and damping performance of isolation bearings have been further studied and refined. Isolation technology thus gradually evolved from theoretical exploration to practical application, accumulating extensive engineering experience and data. Notably, the first modern building employing a rubber bearing isolation system was constructed over 50 years ago in Skopje. The implementation of that system marked the successful application of isolation technology in the building sector, providing a valuable engineering demonstration for subsequent isolation designs. However, practical applications have also revealed some technical issues—for example, the uplift observed in some isolation devices, which is fundamentally due to the lack of reinforcement shims leading to insufficient vertical stiffness of the rubber bearings. This problem has prompted designers to conduct in-depth studies of the mechanical properties of rubber materials, reinforcement measures, and overall structural optimization, further advancing the innovation and performance enhancement of isolation bearing designs [91,92].

Rubber seismic isolation bearings are manufactured using a composite structure in which multiple layers of rubber and thin steel shims are alternately bonded and then vulcanized under high temperature and high pressure, resulting in excellent mechanical performance and long-term stability [93]. This process not only ensures that the bearing possesses sufficient vertical load capacity and vertical stiffness to support the weight of the building; it also deliberately reduces the horizontal stiffness. Consequently, the bearing is capable of undergoing large horizontal deformations under seismic or other lateral loads, thereby accommodating the relative horizontal displacement between the superstructure and the foundation [94]. Moreover, traditional rubber seismic isolation bearings can withstand a certain degree of tension under vertical seismic actions, making them an ideal isolation device with impressive vertical load capacity, relatively low horizontal stiffness, and considerable horizontal displacement capacity. It is critical that plate-type rubber seismic isolation bearings possess both sufficient vertical load capacity and the ability to undergo large horizontal deformations. The inherently high elasticity of rubber endows these bearings with excellent energy absorption and dissipation capabilities, effectively reducing the vibration energy transmitted to the structural system during an earthquake. In addition, this high elasticity also confers significant self-centering ability, ensuring that once the seismic load is removed, the bearing can quickly return to its original state and thereby reduce the need for subsequent structural repairs [95]. Extensive experimental research has demonstrated that the use of rubber seismic isolation bearings shifts the structure’s natural period to a longer time range, which significantly reduces the response amplitude of the superstructure during an earthquake and improves overall seismic performance. In summary, as an isolation technology that balances load-bearing performance (Figure 24), flexible deformation, and energy dissipation functions, rubber seismic isolation bearings exhibit broad application prospects and hold substantial potential for future widespread adoption in building seismic design.

Plate-type rubber seismic isolation bearings are often a key component of bridge vibration reduction systems, with both their vertical and horizontal performance remaining a focal point in seismic research. In recent years, researchers worldwide have conducted extensive investigations into the deformation characteristics, energy dissipation mechanisms, and sliding behavior of these bearings under complex loading conditions, with the goal of providing more reliable theoretical and experimental bases for engineering applications. For example, Zhong et al. [97] conducted systematic tests and analyses on unbonded plate-type natural rubber bearings (ULNBs), which are commonly used in medium- to short-span highway bridges in China. Their study revealed that the deformation mode of ULNBs is predominantly linear and singular, with deformations almost entirely dependent on the shear action of the rubber, resulting in a relatively low displacement capacity and a pronounced tendency to slide. This characteristic has been identified in several recent earthquakes as a primary cause of excessive superstructure displacements or even damage. Although the introduction of external restraining devices or local modifications to the bearing structure can partially control the sliding phenomenon, these methods generally suffer from complex construction, high costs, and significant maintenance difficulties. To address this issue, researchers have proposed a novel bearing—the composite rubber bearing (CRB). The design concept of the CRB is to combine the sectional advantages of conventional unbonded rubber bearings (LNBs) with those of sliding rubber bearings (SRBs), thereby effectively increasing the pre-sliding displacement capacity while maintaining high vertical stiffness and energy dissipation capabilities. To verify this design concept, a research team conducted a series of comprehensive performance tests—including vertical compression, variable amplitude, and constant-amplitude quasi-static tests—on seven full-scale specimens and subsequently derived corresponding recentering force models based on the test data. Parametric numerical studies further revealed that the internal sliding area and bearing sliding behavior critically influence the seismic response of bridge structures; the results indicated that by appropriately increasing the internal sliding area, the occurrence of the sliding critical point can be significantly delayed, thereby enhancing the seismic performance of the entire bridge system. In addition, test data showed that compared with conventional LNBs, CRBs exhibit not only higher vertical stiffness and energy dissipation capacity but also a relatively lower equivalent horizontal stiffness. This performance difference is closely related to the pressure, position, and stiffness ratio of the sliding surfaces. On another note, Xiang et al. [98] found through damage investigations after the 2008 Wenchuan earthquake that sliding frequently occurred between plate-type rubber bearings and the bridge main girder. In fact, this sliding phenomenon can, to some extent, act as a “fuse” that protects the lower portions of the bridge from severe damage, resulting in only minor damage. Based on this observation, the researchers designed an experimental program to simulate the sliding behavior of plate-type rubber bearings typical of structures in China. In the test, the bearing was directly placed on a steel plate representing an embedded steel plate at the bottom of the bridge main girder, thereby establishing a sliding contact interface between an elastomer and steel. Test results indicated that before significant sliding occurred, the mechanical response of the bearing was approximately linear–elastic, with the effective shear modulus measured to be between 610 and 1100 kPa. Furthermore, the study found that the sliding friction coefficient was inversely proportional to the normal force and directly proportional to the sliding velocity. Based on these experimental data, the researchers developed and calibrated an analytical model capable of describing the sliding response of laminated rubber bearings on a steel plate and compared this model with the traditional Coulomb friction model via numerical simulations. The results demonstrated that under vertical seismic loads, there are marked differences in the displacement response predicted by the two models, and these differences become even more pronounced as the vertical load intensity increases. Given that the overall mechanical performance of rubber seismic isolation bearings directly affects isolation effectiveness and structural stability, it is particularly critical in practical engineering to ensure that the horizontal stiffness and viscous damping performance of the bearings remain relatively stable under varying vertical stresses, shear strains, loading frequencies, and temperatures. These studies not only deepen our understanding of the mechanical performance of plate-type rubber seismic isolation bearings but also provide theoretical and experimental evidence for the design and optimization of new isolation bearings, thereby promoting the development of seismic isolation technology.

Since the late 1970s, when New Zealand scholar Robinson first introduced lead-core rubber bearings, this new type of bearing has gradually compensated for the inadequate energy dissipation capacity of traditional rubber bearings, and it has been widely applied around the world [99,100,101]. The manufacturing process of lead-core rubber bearings is essentially based on the method used for low-damping rubber bearings, with the primary difference being the insertion of a high-density lead plug into the central opening of the bearing (Figure 25). This design effectively enhances the energy dissipation performance of the bearing. In engineering applications, lead-core rubber seismic isolation bearings not only support the vertical loads imposed by the superstructure but also partially absorb and dissipate seismic energy by extending the fundamental vibration period of the structure, thereby significantly reducing both the seismic forces acting on the superstructure and the relative displacement of the isolation layer. At the same time, the bearing retains a certain degree of initial horizontal stiffness, which ensures excellent mechanical performance when resisting small horizontal loads. This overall enhancement of performance provides a solid theoretical and practical foundation for the practical application of seismic isolation technology, playing an important role in key projects, such as buildings and bridges. However, in the process of promoting and applying lead-core rubber seismic isolation bearings, some issues have emerged that cannot be ignored. First, as an elastomer, the rubber material is susceptible to aging, cracking, and other forms of deterioration under prolonged use and exposure to natural environmental conditions (such as temperature fluctuations, ultraviolet radiation, and oxidation), which adversely affect the overall performance and durability of the bearing. Second, although the lead core can significantly improve the energy dissipation characteristics of the bearing, its potential risk of heavy metal contamination has also attracted attention from environmental protection sectors. Therefore, finding a way to extend the service life of rubber bearings and reduce the adverse environmental impacts of the lead core while ensuring effective isolation has become an urgent issue in both engineering practice and research [102,103].

Against this backdrop, high-damping rubber bearings (HDRBs) have emerged [104], as shown in Figure 26. Compared with conventional natural rubber seismic isolation bearings and lead-core rubber seismic isolation bearings, high-damping rubber bearings are characterized by a simple structure, stable force performance, strong energy dissipation capability, high pre-yield stiffness, and environmental friendliness, making them an excellent choice for base isolation systems [105].

The basic structure of HDRBs is similar to that of plate-type rubber seismic isolation bearings, typically consisting of a steel plate layer and a high-damping rubber layer. The steel plate layer is primarily responsible for providing stable and reliable vertical load capacity, while the high-damping rubber layer fulfills both horizontal deformation and energy dissipation functions. Specifically, the rubber layer dissipates energy through hysteretic damping, and its energy dissipation performance relies almost entirely on the inherent damping characteristics of the rubber material. This design not only ensures the stability of the bearing under the constant load of the superstructure but also confers excellent energy dissipation performance under dynamic actions, such as earthquakes. Rubber is a polymer damping material that exhibits hyperelasticity and viscoelasticity [106]. Common high-damping materials typically involve the addition of reinforcing fillers, such as carbon black, into the rubber, or blending and copolymerization with various types of rubber to achieve improved damping characteristics [107]. Extensive experimental results have shown that when the shear strain is below 20%, HDRBs exhibit a nonlinear response characterized by high stiffness and high damping; however, when the shear strain exceeds 20%, the stiffness of the bearing drops sharply, and the hysteretic curve becomes saturated, thereby achieving more complete energy dissipation. Compared with traditional plate-type rubber bearings, the equivalent damping ratio of HDRBs can be significantly improved—typically ranging from 12% to 20%, with some products even reaching up to 30%. Currently, the main research directions for high-damping rubber bearings focus on damping characteristics [108,109,110], filler reinforcement systems [111,112], rubber blending technology [113], composite materials, vulcanization systems [114], and constitutive models of materials [115,116].

Figure 26. High-damping rubber bearing [117].

Figure 26. High-damping rubber bearing [117].

The core advantage of HDRBs lies in their high-damping rubber layer. As a typical polymer damping material, rubber possesses hyperelastic and viscoelastic properties, and its damping performance can be effectively enhanced through appropriate material modifications. Common modification methods include the following.

₋

Filler incorporation: Adding inorganic fillers, such as carbon black, to the rubber can significantly enhance its damping performance and mechanical stability.

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Blending and copolymerization: By blending or copolymerizing rubber with other types of rubber, the structure of the rubber matrix can be optimized to maintain good damping performance across different strain levels.

₋

Other modification techniques: Methods like interpenetrating polymer networks, piezoelectric conductive methods, and the addition of organic small-molecule hybrid materials are also employed, all aimed at constructing a composite rubber system with multiple reinforcement mechanisms.

These modification approaches not only improve the damping performance of rubber but also optimize the overall nonlinear response of the bearing, thereby providing a solid material basis for the subsequent development of constitutive models and structural analyses.

In recent years, scholars both domestically and internationally have conducted extensive and in-depth research on the mechanical properties of high-damping rubber bearings (HDRBs) [118,119,120], systematically investigating the effects of shear strain, the number of loading cycles, loading frequency, compressive stress, and temperature on their damping performance and mechanical response. These studies indicate that the comprehensive performance of HDRBs depends not only on the intrinsic properties of the rubber matrix material, the vulcanization process, and the composition of the filler reinforcement system; it is also significantly influenced by external factors, such as the loading method, the loading rate, the ambient temperature, and the applied compressive stress, leading to a constitutive relationship that is complex, nonlinear, and rate-dependent.

Wei et al. [118] conducted systematic experimental studies and theoretical analyses on the complex mechanical behavior of HDRBs under coupled compression and shear. The research team first performed multi-step relaxation tests and monotonic shear tests to meticulously characterize the material response of high-damping rubber under different strain rates and compressive stresses. Based on the experimental data, they extended the classical Zener model by incorporating compressive load effects, thereby developing a new rate-dependent analysis model. This model was subsequently validated in full-scale bearing tests, with numerical simulation results showing excellent agreement with experimental data, thereby demonstrating the model’s effectiveness and adaptability in reflecting the mechanical behavior of HDRBs under actual engineering conditions.

Oh et al. [119] comprehensively examined the performance evolution of HDRBs under different working conditions through prototype tests. The results indicated that the displacement of the bearing is a critical factor affecting its performance; as the displacement decreases, both the effective stiffness and the equivalent damping of the bearing undergo significant changes. Additionally, an increase in loading frequency generally leads to an increase in effective stiffness, while at higher vertical pressures, the effective stiffness decreases and the equivalent damping correspondingly increases. Notably, the equivalent damping is much more sensitive to vertical pressure than the effective stiffness; therefore, in practical engineering design, it is essential to carefully assess the dual dependence on displacement and the excitation rate when calibrating both the effective stiffness and the equivalent damping ratio to ensure the structure’s seismic performance and safety under extreme conditions.

To more accurately describe the force–displacement response of HDRBs and the rate dependency of their shear deformations, Yuan et al. [120] developed a constitutive model based on an improved Zener model. This model employs a combination of two hyperelastic springs and a nonlinear damping element, fully accounting for finite deformation viscoelastic effects. In addressing the commonly observed Fletcher–Gent effect in HDRBs, the researchers introduced an additional stiffness modification factor α into a novel strain energy function to characterize the increased horizontal stiffness caused by carbon fillers in the small-strain range. Moreover, a nonlinear viscosity coefficient η was introduced into the model to capture the material’s response under different strain levels and strain rates. By inverting parameters from multi-step relaxation tests and cyclic shear test data, the researchers successfully established a three-dimensional functional relationship between η, strain, and the strain rate. Finally, using an improved real-time hybrid simulation (RTHS) test system based on velocity loading, the model was physically validated on a single-column bridge test setup. The results indicated that the new model provided greater accuracy and reliability in predicting seismic responses compared to traditional hysteretic models.

Violaine et al. [121] conducted in-depth research on the response mechanisms of HDR materials under sustained static compressive loads and potential cyclic shear loads. Given that HDR materials exhibit marked nonlinearity, time dependence, and Mullins effects during loading, their stress–strain behavior is highly complex. To verify the existence of the Mullins effect in HDR samples, the researchers first pretreated and analyzed the samples using cyclic tensile and compressive tests. Subsequently, they developed a biaxial test apparatus specifically applicable to QC-CS loading conditions, which allowed for the capture of HDR sample responses under conditions closer to actual service. This apparatus not only enabled precise measurements of key parameters, such as shear modulus and energy dissipation density, but also provided important experimental evidence to investigate the influence of compressive stress on the shear response of HDR materials.

At the engineering application level, Quaglini et al. [122] applied HDR materials to the design of seismic-elastic bearings for buildings and structures. Considering that rubber bearings in practical engineering are subjected to permanent vertical loads over long periods while simultaneously experiencing shear deformations during extreme events, such as earthquakes, the researchers proposed an experimental procedure capable of evaluating HDR performance under coupled compression and shear. Systematic tests on five commercially available HDR samples indicated that it is essential to fully account for the influence of compressive stress during loading in order to comprehensively and accurately capture the true response of the bearings under cyclic shear. The study not only provided more reliable experimental data and theoretical support for seismic design but also pointed the way toward optimizing the application of high-damping rubber bearings in practical engineering.

Sato et al. [123] conducted a series of shake table tests on the same structural model to systematically compare the seismic isolation performance of plate-type rubber bearings, lead-core rubber bearings, and high-damping rubber bearings. The test results demonstrated that under various types of seismic excitations, structures equipped with high-damping rubber bearings exhibited superior vibration reduction performance. In terms of energy dissipation, displacement control, and improvement of dynamic response, high-damping rubber bearings outperformed the conventional plate-type and lead-core rubber bearings. This early, intuitive, comparative experiment not only provided a robust basis for evaluating the performance of various seismic isolation bearing products but also set a clear direction for subsequent developments in isolation technology. Furthermore, Sato et al. conducted more systematic and in-depth shake table tests on high-damping rubber bearings. In their study, they tested the seismic isolation effectiveness of plate-type rubber bearings, lead-core rubber bearings, and high-damping rubber bearings on the same experimental platform and performed a dedicated shake table test on a four-story reinforced concrete hospital structure designed with seismic isolation. In this test, the structural responses of a system using high-damping rubber bearings were compared with those of a system employing plate-type rubber bearings (equipped with soft-steel dampers), and the dynamic response characteristics of each isolation system under different excitation intensities were analyzed in detail. The results indicated that high-damping rubber bearings have significant advantages in reducing the structure’s inherent vibration, suppressing large displacements, and effectively dissipating seismic energy, thereby further confirming their reliability and applicability in practical engineering. In summary, the combined research findings suggest that high-damping rubber bearings not only possess theoretically superior seismic isolation performance; the empirical data validated by shake table tests also indicate that these bearings have considerable potential for widespread application in future seismic design and engineering practice, providing solid technical support for enhancing the seismic safety of buildings [124].

Bozorgnia summarized the findings from studies on the vertical responses of 12 instrumented structures during the Northridge earthquake. The selected structures, ranging from 2 to 14 stories, were located 8 to 71 km from the earthquake’s causative fault. The portfolio included four steel structures, five concrete structures, and three base-isolated buildings. The recorded peak vertical structural accelerations were 1.1 to 6.4 times greater than those measured at the base. The lowest vertical frequencies of the structural components and systems for all twelve structures ranged from 3.9 to 13.3 Hz (corresponding to period ranges of 0.075 to 0.26 s). For structures in the near-source region, this period range may correspond to a series of high vertical spectral accelerations [125].

In 1984, the world’s first base-isolated building using rubber isolators—the William Clayton Building in New Zealand—was completed. In 1985, the San Diego Judicial Center in California followed, becoming the first building in the United States to employ high-damping rubber bearings. In 1993, China introduced its first base-isolated structure—an eight-story residential building in Shantou—which successfully withstood the magnitude 6.4 earthquake in the Taiwan Strait in 1994. In 2013, a magnitude 7.0 earthquake struck Lushan County, China, vividly highlighting the performance contrast between structures equipped with base isolation technology and those without. The newly constructed outpatient building of Lushan People’s Hospital was fitted with 83 base isolators and sustained no damage; its internal beams, columns, wall components, windows, roof signage, and medical equipment remained intact, making it a critical lifeline for post-earthquake medical response. In stark contrast, the hospital’s older outpatient and inpatient buildings—lacking any base isolation measures—suffered extensive damage to both primary and non-structural components, rendering them unusable after the earthquake. Additionally, earthquake records indicate that the structural acceleration peak for Wenchuan No. 2 Primary School, which employed base isolation technology, was only 0.12 g—merely one-sixth of the response observed in Wenchuan No. 1 Primary School, which did not utilize base isolation. This clearly demonstrates the superiority and indispensability of base isolation technology in safeguarding infrastructure and preserving safety during seismic events [126,127].

Current research directions for rubber seismic isolation bearings focus on new materials, novel structural configurations, innovative constitutive models, and the exploration of new fabrication processes. Overall, efforts are mainly concentrated on replacing traditional rubber materials with high-performance or smart materials for manufacturing rubber bearings, substituting lead with conventional materials to produce low-pollution, high-damping isolation devices, conducting constitutive model studies that consider complex environmental factors or strong material nonlinearity and loading rate effects, and investigating the impact of new fabrication processes on material damping characteristics and temperature sensitivity.

4. Discussion

This paper presents a comprehensive review of the most common seismic enhancement techniques applied to cast-in-place reinforced concrete structures, from seismic design and isolation to seismic resilience. As cast-in-place concrete frame structures are the most prevalent building systems worldwide, and with the steady vertical and horizontal development of urban areas, building codes are periodically revised to ensure safety and accommodate current conditions. With these updates, many structures designed according to earlier codes primarily considering gravity loads no longer meet current lateral force resistance requirements. Such structures require reevaluation and retrofitting or the implementation of new technologies in new constructions.

A literature review and a bibliometric analysis were conducted to explore the integration of seismic technologies in cast-in-place concrete frame structures. The analysis indicates that since 2013, the number of publications has increased significantly, reflecting growing emphasis on seismic technology research and its applications, not only because such research substantially improves the safety of building structures but also due to its benefits in protecting lives, reducing economic losses, lowering environmental impacts, and promoting sustainable development. Notably, from 2013 to 2024, publications related to the seismic performance of cast-in-place reinforced concrete frame structures surged, accounting for 74.97% of all of the literature in this field.

Journals, such as Engineering Structures, ACI Structural Journal, Structures, Earthquake Engineering Structural Dynamics, and Soil Dynamics and Earthquake Engineering, have served as important platforms for disseminating research findings on cast-in-place reinforced concrete frame structures. The concentration of publications in these journals underscores their core role and influence in this field. China, the United States, Japan, Australia, and the United Kingdom have produced the largest number of publications, with China leading—reflecting extensive research activities and progress in seismic technology. Recent research contributions from China, Turkey, and Iran have been concentrated around 2018–2020, whereas the United States, Canada, and Japan experienced earlier peaks between 2014 and 2016.

In the current field of seismic design, extensive research has focused on enhancing and optimizing the performance of key components, such as beams, columns, and walls, in frame structures to ensure they possess higher load-bearing capacity and ductility under seismic actions. Simultaneously, with continuous innovation in seismic technology and a deepening understanding of the synergistic behavior of structural systems, the integrated combination of shear walls and frames has been widely recognized as a key means of enhancing overall seismic performance. Moreover, the emergence of new structural systems has provided fresh ideas and technological pathways for seismic design. The introduction of energy dissipation technology has spurred the development of new seismic components, such as buckling-restrained braces (BRBs). In regions with high seismic hazard, the combined application of energy dissipation and isolation techniques has shown remarkable effectiveness, not only improving the overall seismic safety of buildings but also delaying progression to irreparable damage, thus ensuring rapid post-earthquake recovery.

This article presents a variety of experiments designed to validate advanced seismic enhancement techniques for RC frame buildings. These experiments range from cyclic loading tests and shaking table experiments to full-scale time–history analyses using real earthquake records. Collectively, they serve to verify not only the immediate structural response under seismic loads but also long-term behavior, such as energy dissipation and residual deformations, which is crucial for post-earthquake functionality. This multifaceted experimental approach underscores the need to combine laboratory data with numerical simulations and field observations to draw comprehensive conclusions about the performance of innovative seismic systems. Cyclic loading tests indicate that repeated seismic events result in a progressive increase in inelastic energy absorption while simultaneously reducing residual displacements. This behavior suggests that the structure’s capacity to dissipate seismic energy is enhanced over successive load cycles—a critical factor for maintaining structural integrity during prolonged or repeated seismic events. Detailed load–displacement curves generated during these tests provide clear evidence of improved ductility and reduced stiffness degradation under high-intensity loading scenarios. Such quantitative metrics are essential for validating design modifications aimed at achieving a balance between energy absorption and minimal damage accumulation. The experiments focusing on BRBs offer particularly insightful data regarding their dual role in energy dissipation and stability. Large-scale tests have demonstrated that optimized BRB components can maintain stable hysteretic behavior under cyclic loads, with energy dissipation capacities three to five times higher than those of conventional braces. This performance is attributed to the “flexible yielding–rigid restraint” mechanism, which prevents premature buckling of the core and ensures full cross-sectional yielding under both tension and compression. Moreover, experimental studies involving direct connection tests—using post-installed anchors—reveal that while BRB systems significantly enhance the overall seismic response of RC frames, careful attention must be paid to connection details. Issues, such as misalignment and local buckling in the anchorage region, have been observed, indicating that the success of BRB application depends not only on the device itself but also its proper integration with the RC structure. Lots of experiments have investigated the performance of seismic isolation devices, such as rubber bearings. The tests confirm that these devices effectively decouple the superstructure from ground motions, resulting in lower horizontal stiffness and larger allowable displacements. This isolation reduces the transmission of seismic energy to the main structural frame, thereby mitigating damage. In retrofit scenarios, experimental evaluations of isolation bearings when combined with enhanced energy dissipation devices demonstrate that the overall seismic performance of an existing RC frame can be dramatically improved. These experimental results serve as a strong rationale for integrating such systems into retrofitting strategies, especially for buildings in high-seismic regions where both energy absorption and post-earthquake recoverability are critical.

The experimental results collectively indicate that modern seismic enhancement techniques are not only effective in preventing catastrophic collapse but also in preserving the functionality of structures after an earthquake. The increased energy dissipation capacity and reduced residual deformations imply that buildings retrofitted or designed with these techniques can better withstand severe seismic events and allow for quicker post-event recovery. The synergistic effect observed when combining isolation systems with energy dissipation devices (e.g., BRBs) points to a design philosophy that leverages multiple mechanisms. This integrated approach helps mitigate the limitations inherent in any single system. The detailed experimental findings regarding connection issues in BRB systems highlight an area where further refinement is needed. Robust anchorage details and optimal connection designs are essential to fully realize the potential benefits of these systems.

Table 1. Main features, applications, advantages, and disadvantages of seismic enhancement technology.

Category	Main Features	Application Scenarios	Advantages and Disadvantages
Frame shear walls	The overall lateral stiffness and bearing capacity of the structure are provided by using the shear and bending resistance of the wall to bear the horizontal seismic force as a whole. The stiffness is high and the bearing capacity is strong, but it is relatively limited in terms of energy dissipation and ductility.	It is suitable for medium- and high-rise buildings and core tube or frame–shear wall composite structures.	Advantages: good integrity, strong bearing capacity, high lateral stiffness, mature construction technology, and good economy. Disadvantages: insufficient energy dissipation capacity, which may make the structure too rigid and limit deformation. It is easy to be damaged under a large earthquake, and the repair cost is high.
Buckling restraint brace	The steel core is used to cooperate with the outer restraint member to prevent local buckling in the compression zone so that it can enter the yield state under tension and compression and fully dissipate the seismic energy. It has both the stiffness and energy dissipation capacity of the supporting member, and it preferentially yields as a “structural fuse” to protect the main structure.	It is often used in seismic reinforcement, reinforcing frame or shear wall systems in high-intensity areas, long-span structures, and existing building reinforcement and renovation projects.	Advantages: significantly improves the energy consumption capacity of the structure, reduces the maintenance cost by 47%, and reduces the maintenance time by 34% in rare earthquakes. Disadvantages: the design, manufacturing, and construction requirements are high, and fine construction and acceptance are required. The layout angle must be accurately set. Higher initial cost but lower life cycle cost (replaceability).
Rubber bearings	The elastic and damping properties of rubber, embedded steel, and the lead core are used to isolate the seismic movement between the superstructure and the foundation and reduce the seismic energy. The horizontal stiffness is low, the damping is large, and large displacement is allowed, but the vertical bearing requirements are high.	It is mainly used for new buildings and historical buildings in high-intensity area and seismic isolation design for low- or medium-rise buildings.	Advantages: significantly reduces earthquake response and reduces maintenance costs by 65% and repair time by 58% in rare earthquakes. Effectively reduces the seismic effect of the superstructure. Disadvantages: limited application, strict requirements for foundation. The bearing needs to be replaced regularly, and the cost is easily high. The requirements for construction, installation, and maintenance are strict, and the requirements for vertical load control are high.

summarizes the main characteristics as well as the advantages and disadvantages of the three categories of seismic enhancement techniques.

Table 2. Numerical comparison of seismic performance of three types of seismic enhancement technologies.

Category	Seismic Performance
	Seismic Acceleration	The Natural Period of the Structure	Seismic Energy
Frame shear walls	Approximately 15–25% reduction	Approximately 30–40% reduction	Approximately 20–40% reduction
Buckling restraint brace	Approximately 20–30% reduction	Approximately 10–30% longer	Approximately 40–60% reduction
Rubber seismic isolation	Reduced to 20–50%	Approximately 300–400% longer	Approximately 50–80% reduction

presents a numerical comparison of the seismic performance of the three seismic enhancement techniques.

The table above summarizes the main features, advantages, and disadvantages of three categories of seismic enhancement techniques. Among these, isolation provides the most pronounced improvement in seismic performance, although it comes at a higher economic cost—isolated devices require an investment of about 5%, yet the overall construction cost can still be reduced. Next, energy-dissipating buckling-restrained braces (BRBs) utilize a “flexible energy dissipation” principle that helps reduce lateral force demands and minimizes the requirements for section size and reinforcement, thereby enhancing the seismic capacity of the structure. This mode of design change can typically reduce costs by 5–10%, with potential savings of up to 10–60%. The frame–shear wall system also offers certain advantages compared to traditional frames; however, the cost of shear walls is relatively high, and their seismic performance is not as advantageous as that of new technologies.

5. Future Directions

The introduction of the frame–shear wall system not only effectively improved upon traditional seismic design but also, through the synergistic action of dual systems, achieved significant improvements in overall stiffness, ductility, and energy dissipation capacity. However, because shear walls are indispensable yet relatively costly components in RC frame buildings, their design and arrangement must be carefully balanced to ensure that the structure meets the target reliability while optimizing material consumption and construction costs. This balance must guarantee structural safety under extreme seismic events while also addressing economic and environmental sustainability. Extensive experimental studies, numerical simulations, and case studies have confirmed that the layout of shear walls directly affects the consumption of concrete and steel, thereby influencing overall construction costs and efficient use of resources. Currently, shear wall layout strategies can generally be classified into the following types:

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Central Core Shear Walls: typically located in the building center to concentrate stiffness and mass, thereby enhancing overall seismic performance;

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Corner Shear Walls: placed at the corners to leverage boundary effects for improved lateral resistance;

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Peripheral Shear Walls: arranged along the building’s periphery to effectively resist lateral seismic forces;

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Specialized Shear Walls: custom-designed based on the building’s unique functions and geometry to meet specific seismic requirements.

In traditional designs, schemes with perimeter or corner shear wall placements often provide more balanced seismic performance, but, in practice, a single arrangement may not fully satisfy complex loading demands. Typically, a combination of central, corner, and peripheral shear walls is employed to optimize overall seismic performance. At the same time, modifications, such as openings or missing corners in shear walls introduced to accommodate building functions, significantly affect both local and overall structural performance, necessitating comprehensive and detailed mechanical analysis and optimization during the design phase. In summary, the frame–shear wall system plays a crucial role in modern seismic design. Only by fully considering the comprehensive impact of shear wall layout on material consumption, target structural reliability, and building economics can an economically efficient and seismically resilient structural scheme be developed to achieve continuous improvements in overall seismic performance and efficient utilization of environmental resources.

As seismic design codes continue to evolve across regions, the seismic performance of many traditional buildings now falls short of current standards. This has driven the widespread promotion and application of new energy dissipation technologies, including, in particular, buckling-restrained braces (BRBs). This technology is based on the strategic placement of BRB components within the structural system to ensure that, under seismic loads, the braces undergo controlled buckling, thereby effectively dissipating energy and controlling residual deformations post-earthquake. Such measures significantly enhance the ductility and seismic resilience of RC frame structures. In recent years, extensive laboratory tests, numerical simulations, and field verifications have demonstrated numerous advantages of BRB technology in engineering practice. Compared with traditional bracing systems, BRBs offer superior energy dissipation capacity, enabling rapid transfer and dissipation of internal forces during an earthquake, thereby reducing the stress levels on critical components and delaying or even preventing brittle failure of the structure. Moreover, BRBs also contribute to improved overall structural stability and resilience, making them an important choice for seismic retrofitting of existing buildings as well as new high-seismic-design projects. Although issues may arise in practice, such as localized adverse effects on column performance when directly anchoring BRBs to RC components, targeted design improvements and construction process optimizations have effectively mitigated these concerns. A large body of research and numerous engineering case studies have shown that with proper design and construction, BRBs can not only enhance a structure’s resistance to seismic hazards but also play an active role in post-earthquake repair and subsequent reinforcement, ensuring both safety and durability. In summary, buckling-restrained brace technology, as an emerging and increasingly mature energy dissipation solution, is gradually becoming a key method for enhancing the seismic performance of frame structures. In the future, as seismic design codes are further refined and relevant technical standards promoted, the application prospects of BRB technology in building seismic design will become even broader, providing robust technical support for ensuring building safety during earthquakes.

Base isolation technology—with rubber seismic isolation bearings as a key component—represents a watershed improvement in seismic performance. Research has shown that the seismic effectiveness of isolation technology is among the best. With the advent of new code standards and policy initiatives promoting isolation and energy dissipation technology, such measures should be prioritized for design and construction in high-seismic-intensity regions, key seismic monitoring and defense zones, or the post-earthquake reconstruction of densely occupied public buildings (such as schools, kindergartens, and hospitals). Isolation bearings were initially applied in bridge engineering, where their core function is to decouple seismic energy, reducing the direct transmission of earthquake forces to the superstructure. Early devices used in bridges, such as lead-core rubber bearings and layered rubber bearings, incorporated flexible, energy-dissipative, and self-centering features at the bridge abutments, thereby substantially improving the seismic performance of the superstructure. Following the success of several pilot and demonstration projects employing isolation bearings in buildings (for example, in early Japanese residential and public building projects), isolation bearings were gradually extended from the bridge domain to building applications. Subsequently, both domestic and international seismic design codes and product standards have been revised and developed, promoting the standardized production and widespread application of isolation bearings in building engineering. For instance, with the introduction of isolation technology into the “Code for Seismic Design of Buildings”, the application of isolation bearings in buildings has matured and gained broad recognition. The evolution from traditional plate-type rubber bearings to lead-core rubber bearings and, finally, to high-performance damping bearings reflects continuous progress in engineering seismic technology. Although traditional bearings are simple in structure and possess high load capacity, their low damping performance limits seismic effectiveness; lead-core bearings, by introducing a lead core, improve energy dissipation and self-centering performance and have become the mainstream isolation device; and high-performance damping bearings, by meeting high performance requirements and integrating multiple functions, exhibit broad application prospects. With continuous breakthroughs in theory and material technology, future bearing systems are expected to be more intelligent, durable, and efficient, providing more reliable protection for seismic design.

Future research should concentrate on the following.

1. New Material Applications and Seismic Technology Innovations

Adopting new high-performance or smart materials to replace conventional structural materials is critical for improving seismic performance. This not only enhances the performance of individual components but also, through optimized material properties, increases the overall energy absorption and dissipation capacity of the structure. By combining improvements in traditional seismic technologies with the unique advantages of new materials, a more efficient and durable seismic system can be established.

2. Multi-System Synergy and Optimization

In multi-hazard environments, it is essential to deeply investigate the synergistic mechanisms among different seismic systems (such as isolation, energy dissipation, and resilience design) to provide theoretical support for integrated and optimized design processes; utilize advanced numerical simulation techniques and full-scale experimental methods to validate the response of new integrated systems under extreme conditions; and develop a multidisciplinary approach to establish a seismic resilience design that meets both high-performance and economic requirements.

3. Advanced Numerical Simulation and Experimental Validation

Leveraging modern computational technologies and experimental testing methods allows for detailed modeling and performance evaluation of new integrated structural systems. Numerical simulations can predict structural responses under seismic loads and inform experimental design, while full-scale tests validate model accuracy and structural behavior under real conditions, thus advancing the engineering application of new integrated systems.

This technical approach is based on the synergistic action of a framed shear wall system and buckling-restrained braces (BRBs), as illustrated Figure 27. By embedding anti-buckling-designed shear walls and BRB components within a reinforced concrete frame, the overall lateral stiffness and energy dissipation capacity of the structure are simultaneously enhanced. In this scheme, the shear walls primarily provide the initial stiffness and overall stability of the frame, while the BRBs—by preventing low-mode buckling of their core elements during major seismic events—fully develop their robust hysteretic behavior and energy dissipation functionality. This strategy effectively delays structural failure and reduces post-earthquake residual deformations. The research encompasses component testing, numerical simulation, and case study validations, aiming to promote the application of a new high-performance seismic system that balances costs with ease of construction. This approach fully exploits the inherent lateral force resistance of shear wall systems and, through the strategic placement of BRBs, overcomes the traditional susceptibility of steel braces to premature buckling—offering significant potential for practical engineering applications.

The technical research proposal advocates a hybrid seismic system for buildings that integrates a framed shear wall system with rubber isolation bearings, as illustrated Figure 28. In the proposed scheme, the framed shear walls in the superstructure primarily resist horizontal loads by providing ample lateral stiffness and energy dissipation capacity, while rubber isolation bearings are installed at the foundation to effectively decouple seismic ground motion, thereby reducing the inertial forces transmitted to the superstructure and minimizing the overall seismic response. The synergistic action of these two systems not only ensures the safety and ductility of the structure during strong earthquakes but also addresses issues of localized damage and post-earthquake residual deformations typically associated with conventional rigid seismic designs. The research encompasses the development of theoretical models, numerical simulations, experimental tests, and analysis of engineering case studies, aiming to provide a feasible technical route for achieving safe, economical, and constructible modern high-performance seismic design.

This proposal presents a hybrid seismic system for buildings that integrates rigidity, ductility, and seismic isolation by organically combining framed shear wall systems, buckling-restrained braces (BRBs), and rubber isolation bearings, as illustrated Figure 29. Specifically, the concept is as follows: the superstructure employs a framed shear wall system to provide overall lateral stiffness and energy dissipation capacity; in localized regions, buckling-restrained braces are installed to enable ductile deformations and efficient energy dissipation under strong earthquakes; and, at the foundation, rubber isolation bearings are utilized to achieve seismic isolation by reducing the dynamic forces transmitted to the superstructure. The synergistic action of these three systems not only optimizes the overall seismic performance and mitigates damage progression but also reduces post-earthquake repair costs, offering significant potential for engineering applications. The research will cover the development of theoretical models, numerical simulations, full-scale experimental validations, and analysis of engineering case studies, aiming to achieve a new seismic design that is safe, economical, and easy to construct.

6. Conclusions

The advent of seismic enhancement technologies has greatly increased the disaster resistance of building structures, and as a forefront research area in civil engineering, its prominence has grown in recent years. This paper briefly reviews three types of seismic enhancement technologies, selecting one representative from each category—seismic design, isolation, and seismic resilience—and briefly outlines their historical development and current progress. The findings suggest that retrofitting of existing buildings should prioritize the use of BRB technology due to its flexible installation and minimal disturbance to the existing structure, whereas for new projects or key structures in high-seismic-risk areas (such as schools and hospitals), the use of isolation bearing technology is recommended to maximize seismic safety.

In addition, the layout of shear walls should incorporate a coordinated configuration of a central core, a corner, and peripheral placements to balance stiffness and ductility and to avoid torsional issues caused by localized stiffness concentrations.

Figure 30 presents the annual data for the top forty keywords, summarizing the research hotspots at different stages over the years. Figure 30 shows that in the first stage (before 2004), keywords, such as “column”, “ductility”, “beam”, and “earthquake resistance structure”, dominated, indicating a focus on leveraging the ductility of traditional structural components for seismic resistance; during the second stage (2005–2014), keywords like “earthquake”, “design”, “wall”, “reinforced concrete”, and “shear wall” became predominant, emphasizing the enhancement of seismic performance of RC structures through new structural components; and, in the third stage (2015–2024), keywords, such as “behavior”, “performance”, “design”, “seismic response”, “model”, and “shaking table test”, took precedence, indicating an emphasis on enhancing seismic performance through the overall dynamic response of the building.

Despite significant progress in seismic enhancement technologies, several challenges remain in practical applications. For example, as the primary lateral-force-resisting elements, shear walls have a profound impact on overall performance. However, issues persist regarding their collaborative mechanisms under complex loading conditions, ductile design, and functional adaptability. When shear walls are arranged along the building perimeter or in primary load-bearing regions, localized stiffness concentrations can result in uneven force distribution and torsional problems. Additionally, joints—where frames connect to shear walls—are critical load-transfer regions whose construction quality directly affects overall seismic performance. Cracking, crushing, or even the initiation of weak-layer failure at frame–shear wall connections can occur. Although local strengthening measures at these joints can effectively prevent overall performance degradation due to localized weaknesses, such measures also tend to increase costs.

The shear wall–frame structural system enhances overall seismic performance while ensuring material efficiency through the coordinated arrangement of central cores, corner walls, exterior walls, and dedicated shear walls. Buckling-restrained brace (BRB) technology achieves efficient energy dissipation through controlled buckling, significantly improving structural ductility and post-earthquake repairability. Meanwhile, base isolation technology (such as lead-core rubber bearings) isolates seismic energy transmission, making it the preferred solution for public buildings in high-intensity seismic zones. These three approaches drive advancements in seismic technology from the perspectives of structural optimization, energy dissipation, and seismic isolation. Combined with updates to design codes and material innovations, they form a multi-tiered seismic resistance system that ensures safety while promoting resource efficiency and sustainable development.

Currently, the application of BRBs in RC structures has also encountered some issues. The high stiffness in the node regions of concrete frames can lead to stress concentrations at the BRB–frame connections, potentially resulting in crushing or shear failure of the concrete at the joints. In rare, extreme seismic events, if plastic hinges at the nodes do not develop as intended, the energy dissipation efficiency of the BRBs may be compromised. The conventional anchorage methods, such as pre-embedded steel plates with welding or bolted connections, face challenges, including insufficient positioning accuracy of the embedded components (leading to installation deviations that induce additional moments), stress redistribution at the connection interfaces due to concrete shrinkage and creep (reducing long-term reliability), and a mismatch between the shear strength of the node regions and the bearing capacity at the ends of the BRBs, which can lead to brittle delamination failures.

In the application of rubber bearings for isolation technology, many issues have also been observed, such as the gradual aging and cracking of conventional rubber and the inherently limited energy dissipation capacity of rubber as an elastomer. This led to the development of lead-core rubber isolation bearings; however, the environmental pollution caused by the lead core has become a concern. High-damping rubber materials also commonly face challenges, such as a narrow effective damping temperature range, low damping loss factors, and strong temperature dependency. The development of new materials to replace conventional ones is thus a key research direction to ensure the long-term safety and functionality of building structures.

This study indicates that compared with conventional reinforced concrete frame structures, the new structural system consumes about 45% more energy on average. Nonetheless, the key technologies employed offer distinct advantages; although seismic isolation technology comes at a higher cost, it delivers optimal seismic performance and is well-suited for critical new construction projects; buckling-restrained braces (BRBs) strike an effective balance between cost and performance, making them the preferred choice for retrofitting existing buildings; and the layout of frame–shear walls still needs optimization to enhance cost-effectiveness. In summary, by addressing these technical and methodological challenges, the construction industry is poised to develop advanced structural systems that combine high seismic performance with economic benefits. Such advancements will not only significantly improve the safety and resilience of buildings under severe earthquake conditions; it will also drive overall progress in seismic design techniques and engineering applications.