Accurate prediction of the fundamental period is essential to the seismic design and safety assessment of buildings. However, existing empirical formulas in building codes are typically calibrated using low- to mediumrise building datasets and often neglect critical design parameters such as seismic design level (SDL). To address these limitations, this study conducted ambient vibration tests on 356 tall buildings in China with different structural systems and SDLs to obtain the two main translational fundamental periods. In addition, 414 records from the China Academy of Building Research were collected, which resulted in a relatively homogeneous database of 770 tall buildings. Using building height, structural system, and SDL as input features, prediction models were developed and compared based on nine established machine learning methods. Among these, the Extreme Gradient Boosting (XGBoost) model exhibited the best performance, achieving an R2 of 0.9429 and a MAPE of 12.46%. Notably, for buildings with fundamental periods greater than 2 s, the XGBoost model significantly outperformed existing empirical code-based formulas, addressing the research gaps identified in previous studies. Furthermore, SHAP analysis identified building height as the dominant predictor and indicated that SDL provides additional predictive information within the proposed model. Model-based sensitivity analysis showed that increasing the SDL from seismic intensity 7-8 is associated with an approximately 10% - 15% reduction in the predicted fundamental period. These results suggest that SDL may be a useful variable for future refinement of empirical period-estimation formulas. For the 356 newly tested buildings, the ratio between the two measured horizontal periods was mainly distributed between 1.0 and 1.5, with a mean value of 1.254, providing a supplementary reference for the dynamic characteristics of similar tall buildings.

Corridor-type school buildings, as critical public infrastructure within educational facilities, are of paramount concern regarding their seismic performance. However, seismic damage investigations consistently reveal the susceptibility of this structural type to severe damage and disproportionate collapse. To tackle this critical issue, this study adopted a synergistic methodology integrating component-level quasi-static testing with in-situ structural monitoring. The seismic response characteristics and collapse mechanisms of representative corridor-type school buildings located in high-seismicity regions were investigated. Comparative analyses of mechanical behaviors and failure modes of bare frame components (BF) and infill-frame composite components (IF) were performed through scaled quasi-static tests. Furthermore, a reliable shear force estimation approach was established based on monitored strain and acceleration data, elucidating the intrinsic mechanisms of differential damage among same-story components and the global structural response patterns. The results demonstrate significant disparities in "strong brittle" and "weak-ductile" performance among vertical load-bearing components. Specifically, high-stiffness IF components attract a disproportionate share of seismic shear but possess limited deformation capacity, leading to premature failure under seismic loading and initiating a collapse chain characterized by "performance divergence-shear force concentration-component failure." Consequently, the global ultimate displacement capacity of the structure was governed by these low-deformation-capacity units. This inherent stiffness-deformation incompatibility is identified as a primary driver of the severe structural damage and collapse observed. These findings provide a theoretical foundation and technical reference for the seismic design optimization of corridor type school buildings.

The aging effect represents a critical factor in seismic research for jacket platforms. This study investigated the seismic performance of aged jacket platforms with consideration of the soil-pile-structure interaction (SPSI). Shaking table tests with a 1/20 scaled model that incorporates the corrosion effects of jacket platforms with service lives of 0, 20, and 30 years were conducted to compare the dynamic characteristics and structural responses of these models under onshore and offshore earthquake excitations. To complement the experimental study, three corresponding finite element (FE) models considering SPSI effects were developed to enable detailed seismic fragility analyses for aged jacket platforms. The results suggest that jacket platforms exhibit significantly higher collapse transcendence probability under offshore earthquake, with 2-3 times larger responses than those under onshore events. Furthermore, after 20 years of service life, the collapse transcendence probability of these platforms increases substantially-by about 20 %-40 % compared to jacket platforms with 0 years of service life-primarily due to extensive corrosion. The experimental and numerical results obtained through this study serve as a valuable basis for risk assessment and seismic design of aged offshore jacket platforms.

Recent earthquakes have highlighted the vulnerability of reinforced concrete (RC) school buildings with cantilevered outdoor corridors due to the lack of consideration for infill walls in seismic design. In particular, the confining effect of the infill walls causes significant differences in the constitutive behaviour of the various load-bearing components on the same floor of the building, which is often overlooked in current seismic design practices. Based on this motivation, this paper aims to study the efficacy of enhancing seismic performance in buildings by modifying the stiffness ratio between bare columns and captive columns through the widening of bare columns. Using Xuankou middle school as a case study, dynamic time-history analyses were performed on buildings with stiffness ratios ranging from 3.41 to 1. Inter-story drift ratio, performance achievement ratio, and the applicability of the recommended stiffness ratio across different building heights were investigated. The results indicate that infill walls significantly influence column behavior, with captive columns playing a dominant role in the building's seismic resistance. While infill walls enhance performance under low-intensity seismic events, there may be potential overestimations in designs that ignore local infill-frame interactions during rare earthquakes. Although reducing the stiffness ratio from 3.41 to 2.85 yields limited performance improvements, a stiffness ratio of 1.31 ensures compliance with performance-based requirements and is recommended as the optimal value. Buildings with this ratio have good seismic performance across various common heights, with advantages that grow as building height increases. Additionally, excessive stiffness ratios may lead to the redistribution of soft story to other floors. This simplified seismic approach offers valuable insights for optimizing the seismic design and strengthening strategies in reinforced concrete school buildings and similar structures with central-opening.

Destructive earthquakes frequently inflict considerable damage on multistory buildings, with reinforced concrete (RC) frame structures being particularly susceptible. Although the "strong column-weak beam" principle is a common design approach, post-earthquake investigations reveal that failures rarely follow this mode, with damage often concentrated in vertical load-bearing components like wall-column systems instead of beams. This discrepancy raises concerns about the adequacy of current design approaches and highlights the complex interactions between columns, walls, and other structural elements during seismic events. This study aims to investigate the seismic response and collapse mechanisms of soft-story RC frames, emphasizing column behavior, axial compression ratios, and the performance of buildings with soft stories. To achieve this, a shaking table test was conducted on scaled-down RC frame columns, and numerical simulations were developed to analyze displacement responses under varying axial compression ratios and seismic accelerations. Experimental results indicate that bare columns demonstrate considerable deformation capacity, characterized by pronounced shifts in natural frequency during seismic loading. Numerical simulations show that buildings with open first stories exhibit low axial compression ratios, which result in minimal second-order gravity effects and substantial displacement margins. These characteristics reduce the risk of collapse even under high seismic accelerations. The findings suggest that soft-story RC frames, designed based on the story-yield mechanism, exhibit greater collapse resistance than anticipated. For the majority of multi-story buildings, the axial load ratio generally remains below 0.3 when calculated using realistic loading conditions and material strengths. Under these circumstances, the collapse drift ratio can reach values as high as 1/16 or greater. In contrast, the maximum drift ratio observed under a seismic input of 1.0 g is significantly lower, reaching only 1/36. Moreover, building collapse typically involves complex component failure modes with varying structural characteristics, deviating from uniform patterns predicted by traditional design theories. This study provides new insights into the seismic performance and failure mechanisms of multistory frames with soft stories, offering valuable guidance for improving seismic design codes and enhancing the resilience of these structures under earthquake loading.

Seismic damage to buildings reveals significant stiffness effects caused by infill walls, with improper arrangement potentially leading to severe local damage or structural collapse. This study proposes a structural seismic design concept aimed at balancing seismic shear force distribution among RC columns affected by infill walls. Quasistatic tests on two RC frame specimens (a bare frame and a frame with half-height infill walls) and vulnerability assessments of six RC school buildings were conducted. Results indicate that infill walls under windows transform RC columns from bending-dominated to shear-dominated deformation modes, increasing lateral capacity by 77 % but reducing ductility by 42 %. In structures combining bare and captive columns, the seismic shear demand on captive columns is 1.74 times higher than on bare columns, with the lower ductility of captive columns governing the overall seismic response. Structures designed for concept of balanced seismic shear force distribution show surprisingly good performance in fragility analyses. While infill walls mitigate overall structural damage during frequent and precautionary seismic events, structures with more uniform shear distribution exhibit reduced damage susceptibility in rare and extremely rare earthquakes. When the PGA reaches 0.8 g, the addition of infill walls increases the structure's collapse probability by 35 %, while structures using the balanced design concept approach the collapse probability of bare frame structures. These findings highlight the importance of balanced seismic shear force distribution in future structural designs. Additionally, due to the confining effect of infill walls on column deformation, the nominal inter-storey drift ratio (IDRn) was proposed to serve as a new structural damage index. The results using IDRn show higher damage probability estimates than those using IDR, highlighting a potential risk in current seismic design practices that warrants further investigation.

Semi-enclosed buildings, characterized by frame columns only on the street-facing fa & ccedil;ade and masonry walls on the rear and lateral sides, exhibit a distinct "U-shaped open" plan configuration. This building typology is prevalent in multi-story urban structures but exhibits significant seismic vulnerability, prone to severe earthquake damage. This study conducted shaking table tests to investigate the dynamic response characteristics of such structures, aiming to elucidate their collapse mechanisms under seismic excitations. The experimental program was designed based on first-floor damage patterns observed in semi-enclosed buildings stuck by the Luding earthquake in 2022. Testing protocols captured macroscopic phenomena, including motion patterns, component damage states, and strain data at critical locations, under varying peak ground acceleration levels. Microscopic analyses of strain data were performed to evaluate shear force distribution among characteristic components and coaxial elements, as well as the lateral deformation characteristics of structural members. The test results revealed that longitudinal motion dominated the model's dynamic behavior. Seismic shear forces concentrated significantly along the perforated wall axis. This concentration induced early failure initiation at these critical locations. Following the failure of perforated wall axis members, the structural system experienced rapid load-bearing capacity degradation, leading to sequential failure of remaining components and ultimate longitudinal collapse of the test model. The observed failure modes exhibited striking consistency with real-world earthquake damage patterns, validating the experimental model's representativeness and creditability. This research not only identifies the seismic vulnerability mechanisms inherent in semi-enclosed buildings but also provides critical insights for enhancing their collapse-resistant design strategies.

Frame–masonry hybrid structures, though economically practical and widespread in rural China, face significant collapse risks during earthquakes due to shear imbalances from a component mismatch. A severe case was No. 7, Group 1, Detuo Town, after the 2022 Luding earthquake, where damage was concentrated on the ground floor. Numerical modeling revealed that the axis Ⓒ perforated wall, bearing 78% of the seismic shear due to its stiffness, suffered shear failure from geometric and structural factors, triggering a shear concentration–brittle failure chain reaction, pushing the building to near collapse. Meanwhile, the axis Ⓐ frame column, only sustaining 12% shear, sustained minor damage. Based on this typical seismic damage, this study proposes a collapse-resistant design using the deformation saturation theory to achieve balanced shear distribution by adjusting frame column sections. The results showed that compared to the prototype model, the collapse-resistant model (RE) under PGA = 0.4 g saw maximum displacement drop from 16.66 mm to 5.42 mm, which was reduced by 67.5%, the shear share of axis Ⓐ rose from 18% to 45%, the shear force of axis Ⓒ decreased from 70% to 46%, the shear ratio changed from 1:4 to 1:1, and maximum component damage was at 75% of the performance point, indicating significantly enhanced collapse resistance. These findings highlight the importance of balanced seismic shear distribution in preventing shear concentration and brittle failure, validate the deformation saturation theory, and offer a theoretical basis and design reference for the seismic reinforcement of similar hybrid structures.

Multi-story buildings in seismic regions are susceptible to earthquake-induced damage; however, the direct correlation between observed damage patterns and underlying failure mechanisms remains insufficiently understood. The Ms6.8 Luding earthquake, which struck Luding County, Sichuan Province, China, in September 2022, offers a unique opportunity to investigate this relationship, as it affected a concentrated area with diverse building types and preserved a wide range of damage states. This study leverages the distinctive conditions of the Luding earthquake to elucidate the influence of wall element distribution on structural failure modes under seismic loading. To elucidate the underlying mechanisms, three representative buildings were analyzed using a one-dimensional numerical model. The simulations yielded shear force distributions, shear ratios, and displacement ratios across structural components, enabling a detailed assessment of failure modes. The results indicate that torsion-dominated structures are susceptible to premature failure of low-stiffness components due to excessive displacement, whereas high-stiffness components generally remain intact owing to their ductility. In contrast, translation-dominated structures fail when high-stiffness components fracture at small displacements, resulting in global collapse without substantial ductility or load-bearing contribution from other elements. Structures that remained undamaged exhibited a relatively uniform stiffness distribution, enabling them to resist seismic forces primarily through overall capacity rather than ductility. The numerical results closely reproduced the observed damage patterns, thus validating the proposed mechanisms for the three structural categories. These findings contribute to a deeper understanding of seismic damage processes and provide a basis for enhancing seismic design and retrofitting strategies for both new and existing structures.

Hybrid reinforced frame-masonry (HFM) building structures are widely used in China and East Asia. However, they have been observed to sustain significant damage during recent earthquakes, where the confined masonry elements incur severe failures while the frame elements remain largely intact. This failure phenomenon results from the simplification of HFM structures as frame-only systems in seismic design, which neglects the actual behavior and failure mechanisms of these structures. To address this issue, a 1/4 scale specimen representing a typical HFM structure was tested on shaking table to analyze its seismic behavior. The experimental results indicate that, when subjected to seismic events, the confined masonry components fail in shear at relatively small displacements, which leads to a substantial reduction in the lateral stiffness of the structure. Subsequently, damage is observed in the frame columns and transverse infill walls, ultimately culminating in collapse once the transverse walls incur severe damage. At a 0.2 g ground acceleration, the seismic shear force in the confined masonry grid was found to be 63 times greater than that in the frame grid. At 0.5 g ground acceleration, the frame and masonry grids exhibited similar lateral displacement phases. This indicates that, despite misalignment between the center of stiffness and center of mass, the torsional effects were greatly constrained by the transverse walls. Based on these findings, it is recommended that the lateral load-resisting components of HFM structures be defined by their damage states, rather than by column grid divisions alone. These results provide valuable insights into the seismic vulnerability and failure mechanisms of HFM structures, highlighting the need for improved seismic assessment and design methods.

Frequent seismic events have demonstrated that building collapse is primarily caused by the loss of load-bearing capacity in vertical structural members. In response to this risk, various national design codes have been established. This study conducted field investigations at an earthquake site in Luding County, Sichuan Province, which was struck at a magnitude of 6.8 on 5 September 2022. In this case, the lower x-direction load-bearing wall of the Tianyi Hotel suffered severe shear damage, and the building was on the verge of collapse. However, no obvious damage was seen in the elementary school dormitory. Numerical simulation analysis revealed that during the earthquake, the buildings primarily experienced y-direction displacement in the x-direction, with significant differences in the stress state among different axes. In the model of Tianyi Hotel, the x-direction load-bearing walls suffered shear damage, while the frame columns were still in the elastic stage. At this point, the shear force of the walls was 6–9 times that of the frame columns. Comparing the damage characteristics of the two buildings during the earthquake, it was found that different structural forms lead to different internal force distributions. This phenomenon is further interpreted through the principle of “deformation saturation”, with core structural components being modeled and tested using quasi-static experiments. The results indicated substantial differences in material properties among different structural forms, including variations in lateral stiffness, ultimate load-bearing capacity, and maximum displacement. Moreover, at the same floor level, components with smaller ultimate displacements are decisive of the overall structural stability. To ensure seismic resilience and stability, it is essential to consider not only the load-bearing capacity but also the rational arrangement and cooperative interactions between different components to achieve a balanced distribution of overall stiffness. This approach significantly enhances the building’s resistance to collapse.

Recent earthquakes have highlighted the vulnerability of infilled reinforced concrete structures due to the insufficient consideration of infill masonry walls' contribution to strength and stiffness. This study presents a novel refractory straw block (RSB) designed to address these challenges and improve the seismic performance of reinforced concrete (RC) frames. Unlike traditional infills, RSB is characterized by low-elastic-modulus, lowdensity, and high-ductility. Quasi-static tests were performed on three types of frames: unfilled, infilled hollow grouted bricks (HGB), and infilled RSBs. Failure model, stiffness, and load-displacement response of three specimens were investigated and analyzed. The results indicate that RSBs as infill material does not alter the failure mode and constitutive relationship of bare frame, while HGBs leads to shear failure. The peak load for the specimen IF-HGB was 69.3 kN at 1.1 % drift, compared to 38.8 kN at 2.4 % drift for the specimen IF-RSB, and 36.4 kN at 2.0 % drift for the specimen BF. The strengths of specimens IF-HGB and IF-RSB were 1.90 and 1.07 times that of specimen BF, respectively. The stiffness of specimen IF-HGB was 3.7 times that of the other specimens, but its allowable displacement was only 61 % of theirs. Dynamic time-history analyses were also performed on structures with no longitudinal infill (BF), with RSBs (SBF), and with fired bricks (FBF). At the design level of rare events (magnitude 8, PGA 400 gal), severe damage occurred, but collapse was limited. When the PGA increased further, the collapse probability of model FBF rose rapidly, whereas the collapse probabilities of models SBF and BF remained low and similar. Accounting for the confining effect of walls, model FBF showed a higher probability of severe damage than models SBF and BF, particularly under minor earthquakes. The maximum inter-storey drift ratio of the model SBF and FBF were respectively 1.2 times and 1.7 times that of the model BF, which shows that straw blocks as infill can greatly avoid the effect of infill on the seismic behavior of the structure. The study also emphasized the often-overlooked confining effect of masonry on columns, which can lead to unrealistic damage assessments and seismic shear force distributions.

Offshore platforms located in seismically active areas may be subjected to different seismic effects during service. The seismic performance of offshore platforms under different earthquakes was studied using shaking table tests and finite element analysis (FEA). The dynamic properties, acceleration, displacement and strain responses of the scale model under near-field, far-field and offshore earthquakes were studied. On this basis, more consideration was given to soil-pile-structure interactions (SPSIs), and this finite element (FE) model was analyzed for seismic fragility using incremental dynamic analysis (IDA). By combining the results of the tests and FEA, it was found that the dynamic response of the platform was significantly larger under offshore earthquakes than under onshore earthquakes. The collapse resistance of offshore platform under offshore earthquakes was inferior to that under onshore earthquakes. Therefore, seismic performance assessment of long-period offshore platforms based on onshore earthquakes may overestimate its seismic capacity and pose potential risks to platforms in service.

Historically, earthquakes have caused extensive damage to multi-story buildings, often leading to partial or total collapses. Nevertheless, these severely damaged structures rarely exhibit the "strong column–weak beam" failure pattern, and the performance of their vertical load-bearing components varies notably. Our study reveals that the uneven distribution of infill walls leads to divergent mechanical behaviors in columns located at different positions within the frame structure. To address this issue, an acceleration–strain coupled testing system was developed and implemented in a typical reinforced concrete (RC) frame structure of a veranda-style teaching building. This system, utilizing strong-motion seismographs for trigger acquisition, collected synchronized strain data from both columns adjacent to the veranda and those partially constrained by infill walls. Two sets of records were obtained, preliminarily confirming the internal force concentration due to the infill walls' constraints. Furthermore, the varied mechanical behaviors of components along two axes emerge as the primary factors causing significant structural damage and collapse. Based on these characteristic behaviors, quasi-static tests were conducted on frame columns, both unrestricted and partially restricted by infill walls. Results indicate that the constraining effect of the partial infill walls intensifies with deformation, markedly affecting column behavior. Notably, the load-bearing capacity, ductility, and ultimate displacement exhibited substantial differences between the two column types. The coexistence of these mechanically diverse components within the same structure leads to a sequence of failures, thereby altering the mechanisms of structural damage and collapse.

为准确测量砌体墙初始刚度和抗剪强度,提出基于逐级偏压加载平衡拉应力的试验方法,设计并制作 6 组不同砖块类型和不同构造措施的砌体墙片模型,并在精密测试条件下进行拟静力试验.试验结果表明:基于逐级偏压加载的方法能够较好地模拟实际工程墙体剪切破坏模式.烧结普通砖砌筑的墙片抗剪强度高于蒸压粉煤灰砖砌筑的墙片.带构造柱的墙体具有更高的变形能力和延性.本文的研究结果可为准确测量砌体墙的力学参数提供一种可靠的试验方法.

为研究不同砌筑材料对钢筋混凝土框架(RC框架)抗震性能的影响,采用有限元分别建立纯框架、加气混凝土砌块和秸秆草砖 3 种不同类型的填充墙框架有限元模型,考察不同材料、不同砌筑高度对RC框架抗震性能的影响.数值模拟结果表明,不同砌筑高度的加气混凝土砌块对RC框架受力性能影响较大,由于填充墙的存在,柱变为短柱,最大承载力下降约为 42％,而秸秆草砖填充墙框架耗能变化率只有3.43％,与纯框架的受力、变形基本相同.与加气混凝土砌块相比,采用秸秆草砖作为砌块,其对RC框架的受力影响较小,秸秆草砖作为填充墙原料优于加气混凝土砌块,建议工程采用秸秆草砖作为砌筑材料.

为研究地震作用下钢筋混凝土框架结构倒塌机理,验证基于内力分配得到的抗倒塌措施的合理性,设计2组缩尺比例为1:4的框架结构模型并开展振动台对比试验,单次双向输入地震动峰值加速度为1.0g,分析地震作用下填充墙-框架结构变形模式和破坏特点,对比分析有、无落地剪力墙框架结构柱间内力分配规律.研究结果表明,填充墙影响框架结构整体变形及柱破坏模式,横向满砌填充墙约束结构扭转变形,即使在双向地震作用下,偏心结构也未发生扭转;由于窗下半高连续填充墙的约束作用,窗间柱抗侧刚度变大,在地震作用下承担的地震剪力是不受半高连续填充墙约束柱的6～8倍;设置落地剪力墙可优化底层柱间地震剪力分配,使框架柱地震剪力分配趋于均匀,避免结构因"凝震聚力"而发生倒塌,实现"大震不倒".

2022年9月5日,四川省泸定县发生6.8级地震,对当地建筑造成了严重的损坏.对极震区砌体结构、框架结构、底框架结构以及框架-砌体混杂式结构进行了详细调查,分析了破坏原因.结果表明:缺乏合理约束的砌体结构都发生了不同程度的破坏,圈梁和构造柱完善、刚度均衡的砌体结构基本完好.框架结构中填充墙的破坏较严重,填充墙和框架柱有显著的相互作用.混杂式结构抗侧刚度平面分布严重失衡,破坏严重,墙体平面分布对结构的破坏模式起决定性作用.

结构地震倒塌机理是一个关键而又艰难的课题.通过震害分析和逻辑推论否定了目前支配世界各国抗震设计规范的"弱柱强梁"倒塌理论.基于震害调查、模型实验和理论分析,提出了替代"弱柱强梁"的"变形饱和"理论.对于常见的多层建筑,同一楼层中如果抗侧刚度差异很大的构件"混搭",地震作用下,刚度大的构件将出现内力凝聚现象,即使侧移很小其分担的剪力也容易达到其承载力极限并发生脆性破坏,即"变形饱和",从而触发结构整体倒塌.通过合理的结构布置,避免内力凝聚,使结构具有超强的抗震能力.基于变形饱和理论,对泸定地震中4栋典型结构的震害现象进行了详细分析和解释,既回答了震损建筑为什么破坏,也回答了样板建筑为什么不破坏,进而为设计具有超强抗震能力的建筑结构提供参考.相关方法还可用于韧性城乡建设中既有建筑的地震风险排查和评定.