Bulletin of Earthquake Engineering最新文献

This study introduces three types of multivariable fragility surfaces, integrating effective structural features to improve damage assessment. The incorporation of additional information such as building occupancies, structural responses, and underlying soil types enhances the accuracy of conventional fragility curve predictions. Additionally, three modification factors are proposed to further refine conventional fragility curves and provide more precise predictions. The multivariable fragility surfaces are developed for eccentric brace frames modeled in Opensees software which is validated by experimental results and subjected to incremental dynamic analysis with 44 far-field ground motions. The influence of soil flexibilities on structural responses is incorporated through Winkler springs, representing soil-structure interaction. Diverse occupancies, such as hospitals, museums, and residential structures, are assessed using various peak floor acceleration thresholds and story drift ratios, employing multidimensional limit state functions to consider both structural and nonstructural losses. To account for uncertainties in structural responses and a single intensity measurement, a damage-sensitive feature derived from roof acceleration response, obtained through signal processing and system identification techniques, is introduced. The results for the proposed multivariable fragility surfaces indicate that the spectral acceleration corresponding to a 50% probability of exceedance could vary between 10.2 and 89%, in comparison to the corresponding conventional fragility curves. Finally, to evaluate the application of the enhanced fragility surface and modification factors, two instrumented EBF buildings, a 4-story EBF building, and a real 5-story hospital EBF, are selected as case studies. With additional details on soil types, occupancies, and structural responses, the process of employing modification factors resulting in enhanced fragility curves is demonstrated.

Following the seismic events that shook Albania in November 2019, more than 14,000 buildings were impacted, resulting in 51 fatalities, over 3000 injuries, and displacing around fourteen thousand residents from their homes. The majority of these affected individuals were concentrated in highly populated Tirana and Durres. This result was expected because of the predominant building type in the region, which is characterized by unreinforced masonry structures that have not been subjected to recent assessments or rehabilitation initiatives. The study outlines observed issues and challenges, leading to an analytical investigation into the seismic capacity of various masonry building types observed during post-earthquake reconnaissance. Nineteen masonry structures, ranging from 2 to 6 stories, were selected to correspond to frequently used typified projects in construction. Based on the laboratory test results assessing the characteristics of structural wall parts, analytical models for each building were created. Nonlinear static analysis was employed to estimate the seismic displacement capacities of each building. To further explore the importance of the findings, the nonlinear behavior of a group of representative buildings was analyzed in relation to the seismic sequences that occurred during the 2019 Albania earthquakes. The outcomes of this study are believed to be generalizable to various similar buildings and applicable to a wide range of masonry structures.

A correct Intensity Measure (IM) selection is essential for Performance-Based Earthquake Engineering (PBEE) applications, as any probabilistic seismic demand model (PSDM) depends significantly on the IM. If a single IM can describe the complexity of the corresponding ground motion record, it can be defined as sufficient in an absolute sense. However, this is unlikely because a single number should be able to inform on the frequency content, the amplitude, the duration, the energy content, etc. For this reason, literature studies have defined sufficiency in a relative sense to investigate whether one IM is more sufficient (i.e., more informative) than another in predicting the structural response. This work explores the relative sufficiency of eight scalar IMs through Nonlinear Response History Analyses (NRHAs) using two sets of 20 pairs of ground motion records. Both sets are spectrum-compatible and consist of unscaled natural and spectral-matched records. Also, both Cloud and Incremental Dynamic Analysis procedures are used. This study demonstrates that Cloud analysis cannot be used in its conventional form to study sufficiency when spectral-matched accelerograms are used. When natural accelerograms are employed, the results clearly indicate the existence of a sufficient IM among those selected. Conversely, it is more difficult to define the relative sufficiency of the IMs for spectral-matched records because the operation of record adjusting leads to similar structural demands. This result could question either the validity of using spectral-matched accelerograms for PBEE due to the lack of aleatory variability in the structural demand or the necessity of having a sufficient IM when a PSDM is fitted in a PBEE analysis using spectral-matched accelerograms.

A novel and efficient method based on shear models considering hysteretic characteristics is proposed for predicting structural seismic responses. This method simplifies an actual building by representing it as a lumped mass shear model, with a set of tunable parameters allocated to the interstory restoring force model of each floor. The shear model is calibrated by matching the cyclic interstory pushover curves between the equivalent inelastic spring of each floor and the refined beam–column element model using a metaheuristic optimization algorithm. The novelty of the proposed method lies in its consideration of both cyclic envelopes and hysteretic characteristics (stiffness and strength deterioration and pinching behavior) and its automatic parameter calibration. Validation of the parameter calibration procedure is performed by comparing it with empirical methods via the application on three lateral load tests of reinforced concrete (RC) columns that exhibit varying degrees of hysteretic degradation. The efficiency and accuracy of the proposed method are confirmed through four illustrative examples, including the seismic response predictions of a bare RC frame, two steel frames, and an infilled wall RC frame. Despite the relatively large errors in the acceleration response predictions, the results demonstrate that the proposed method can accurately and efficiently predict the displacement and velocity responses.

This research explores the impact of earthquake directionality and orientation on the seismic performance of reinforced concrete (RC) frame structures, an area previously overlooked in seismic design. The multi-directional component of ground motion was not taken into consideration during the seismic performance design of the majority of RC frame structures. Focusing on a case study in Padang City, Indonesia, a region known for moderate seismic activity, this study assesses the behavior of an eight-story ordinary moment resisting frame (OMRF) under various directional components and orientation angles of ground motions. Through Nonlinear Dynamic Analysis (NL-DA) using Nonlinear Time History Analyses (NL-THA), the study incorporates 14 ground motions across East–West and North–South directions, varying from 0° to 60° in 15-degree increments. Incremental Dynamic Analysis (IDA) evaluates the building's response, employing capacity curves, fragility curves, and CMR scores to understand damage probabilities and structural behaviors under different earthquake directions. The objectives include (1) assessing the building's seismic resilience through IDA capacity curves in line with FEMA 356 performance-based design standards, (2) developing fragility curves and the CMR to predict the potential of damages and structural response in various ground motion directions, and (3) formulating a generic relationship between intensity measure (IM), structural behavior (S_B), and incidence angle (θ) via regression analysis. Results highlight the crucial role of θ in influencing structural response, with deterioration in structural behavior noted as the angle of incidence increases. This pattern underscores the varying stress distributions and deformation patterns in response to directional ground movements. The study's findings emphasize incorporating directionality in seismic risk assessments and structural designs, offering valuable insights for improving resilience against future seismic events. Eventually, the link between θ, IM, and S_B is crucial for assessing and mitigating seismic risk, since it indicates that θ is a major element impacting how buildings respond to seismic occurrences.

Seismic-resistant self-centering concentrically braced frames (SC-CBFs) are susceptible to the concentration of inter-story drifts during earthquakes owing to the relatively low energy dissipation ability of braces. To address this limitation, this study proposed a novel solution by designing a strong backup (SB) system to mitigate inter-story deformation concentration in “weak” stories. The proposed SB system consisting of truss members can be attached to the existing SC-CBF through pin connections, forming a system, termed strong backup SC-CBF (SC-CBF-SB), to promote a more uniform distribution of inter-story drifts along the height of the frame and mitigate the weak story behavior. A six-story chevron-braced frame is adopted to investigate the seismic performance of SC-CBF and SC-CBF-SB. Finite element models of SC-CBF and SC-CBF-SB are built. The mechanical characteristics and dynamic responses of the SC-CBF-SB are examined. To comprehensively evaluate the performance of both SC-CBF and SC-CBF-SB, static pushover analyses and nonlinear time-history analyses are conducted. Additionally, incremental dynamic analysis (IDA) is performed to evaluate the responses (particularly drift concentration) of both frame types subjected to increasing seismic intensity levels. Numerical results show that the maximum value of the drift concentration factor (DCF) is around 1.3 and 1.8 for SC-CBF-SB and SC-CBF, respectively, indicating that SC-CBF-SB can effectively mitigate inter-story drift concentration of SC-CBF. Meanwhile, the proposed SB system has a minimal negative impact on the favorable SC ability of the frame.

The latest earthquakes (Morrocco, Nepal, Sichuan – China, etc.) have highlighted the critical importance of local-site parameters on the vulnerability of existing building stock. The paper performs the clustering method based on the sub-surface parameters for structural damage prediction. The data set includes the damage status for 44 locations after the 2023 Kahramanmaraş earthquake sequence and local site parameters: Vs₃₀, predominant frequency (f₀), horizontal to vertical spectral ratio value (A₀), and engineering bedrock depth (VsD₇₆₀). The Fuzzy C-Means (FCM) and Spectral Clustering (SC) algorithms are carried out on the pre-processed data set, including the sub-surface parameters for each location and the data set clustered into two-clusters within each method. Then, the estimated clusters are compared with the post-earthquake two clusters representing the cluster of damage and no-damage state for considered locations that composed through official damage assessment reports The FCM algorithm yielded a 90% accuracy compared to actual clusters, while the results of the SC algorithm indicated an 86% accuracy. Among the parameters, the VsD₇₆₀ and f₀ demonstrate the ability to establish a discernible demarcation by manifesting distinguishable clustering patterns. Notably, the Area Under the Curve of the Receiver Operating Characteristic (AUC-ROC) value is calculated at 97% and 85% for FCM and SC algorithms, respectively. The outcomes of this study offer the potential to predict the structural damage status of a location under a crucial seismic hazard in the pre-earthquake condition. This enables the development earthquake-resistant cities prior to earthquakes or implement necessary precautions to mitigate seismic risk in the afterward.

Seismic retrofitting solutions for reinforced concrete (RC) school building types in high-seismic regions are extensively reported in the state-of-the-art. Conversely, limited studies have focused on the extent of retrofitting needed for RC school buildings in low- to moderate-seismic regions. To explore this aspect, seismic retrofitting options for RC school buildings in Sri Lanka are investigated. Three retrofitting options are examined: (1) adding/altering masonry infill walls (MI walls) to reduce irregularity in buildings, (2) RC jacketing of columns and (3) a combination of adding/altering MI walls and RC jacketing. These retrofit options are applied to a common typology of Sri Lankan MI-RC school buildings, considering two and three storey height variations. A simplified numerical modelling approach that accounts for the contribution of MIs, the shear failure of RC column and torsional effects is adopted to analyse the performance of the school buildings with and without retrofit. Based on the analyses, three damage states are defined: damage limitation (DL), significant damage (SD) and near collapse (NC). Finally, a multi-criteria decision making (MCDM) method is used to determine the optimal retrofitting option for the considered school building typology, considering engineering and economic parameters. The optimal retrofit solution for the three-storey MI-RC school building is found to be jacketing of ground floor columns. Conversely, for the two-storey MI-RC school building, alteration of infill walls (MI walls) is deemed optimal. Finally, a sensitivity analysis is carried out on the MCDM method.

Earthquake-prone regions have seen the resilience of traditional timber-framed masonry construction systems through previous seismic events. The post-earthquake studies show that these building systems have exceptional resilience to seismic activity and can endure multiple seismic events throughout their lifespan. This performance stands out from many contemporary constructions. Although there is a significant amount of evidence regarding the distinct behavior of these structures during earthquakes, there is a limited amount of meaningful quantitative experimental data on their seismic performance. This study showcases the findings of a series of half-scale shake table experiments carried out on a single-room; single-story timber frame filled with dry bond brick masonry. Two half-scale models were created and tested on a shaking table to investigate the seismic performance of timber framed masonry structural systems. One model was left without infill, while the other was infilled with dry bond brick masonry. To analyze the dynamic behavior, both models were exposed to random base excitation. Additionally, the models were tested with gradually increasing ground motion to study their response to seismic activity, following a method known as single ground motion record incremental dynamic analysis. The evaluation focused on the dynamic characteristics, including the assessment of natural frequencies, damping, mode shapes, and stiffness degradation. The stiffness decreased to 43% of the undamaged stiffness in the model with bricks and 62% of the undamaged stiffness in the model without infill. An assessment and evaluation were conducted on the peak acceleration and displacement responses, as well as the global hysteresis response. The acceleration response was significantly higher for the model with brick infill, with an amplification of 300%. In contrast, the model without infill had a lower amplification value of 150%. According to the findings of the study, it is evident that the timber framed structure exhibits a significant level of flexibility and deformability. Additionally, the structure's ability to dissipate energy increased as the peak ground acceleration of the input ground motion increased.