Bulletin of Earthquake Engineering最新文献

Under earthquake loads, reinforced concrete chimneys with openings are prone to stress concentration and damage around these openings, possibly leading to structural collapse. In this paper, the stress concentration factor was proposed to quantitatively analyse the range of stress concentrations around openings under various parameters and identify the most significant coefficients affecting the stress concentration range. 9 Groups of numerical analysis models for chimneys with different parameterized openings were established, and more than 200 pushover analyses were conducted. The effects of the chimney wall thickness, wall diameter, opening size, and spacing between openings on the stress around the openings were investigated. Recommendations for limiting opening sizes were given, and a method for designing reinforcement steel bars for strengthening was proposed. The numerical results indicated that the central angle of a single opening cross-section should be less than 70°, and the total central angle of multiple openings should be less than 140°; the spacing between openings should not be less than 0.5 times the width of the opening; the range of the steel reinforcement range should be 4.5 times the wall thickness for circular openings; and for rectangular openings, it should be 3.5 times the wall thickness. The added reinforcement steel should have a reinforcement ratio for strengthening of 1.3 times that of the original reinforcement ratio. Finally, through dynamic analysis, it was verified that the opening reinforcement design method proposed in this paper can effectively reduce the stress concentration around openings.

This special issue focuses on the seismic performance of adjacent interacting masonry structures, particularly in historical European city centers. The AIMS project provided unique data on interacting masonry structures through large-scale shake table tests on two adjacent half-scale stone masonry buildings. The experimental campaign was accomapgnied by a blind prediction study where participants modeled the aggregate’s seismic response. Findings highlight challenges in accurately predicting displacement demands and failure modes, providing critical insights for improving future modeling techniques for masonry buildings.

The existing Reinforced Concrete (RC) buildings stock is often characterized by a significant seismic vulnerability, due to the absence of capacity design principles, even in regions with high seismic hazard, such as Italy. Approximately 67% of existing RC buildings in Italy have been designed without considering seismic actions (GLD), resulting in very low transverse reinforcement amount in beams and, particularly, in columns. Additionally, beam-column joints typically totally lack stirrups. Consequently, shear failures under seismic actions are very likely for this pre-code building typology, often limiting their seismic capacity. However, the assessment of shear failures in beams/columns or joints varies significantly from code to code worldwide. The main goal of this work is to quantify the impact of different code-based brittle capacity models on the seismic capacity assessment and retrofit, focusing on GLD Italian pre-1970 RC buildings. This comparative analysis is carried out by first considering three current codes, emphasizing their, even significant, differences: European (EN 1998-3-1. 2005), Italian (D.M. 2018), and American (ASCE SEI/41 2017) standards. Then, shear capacity models prescribed by the current drafts of the next generation of Eurocodes are implemented and compared to the current models. The assessment includes: (i) a parametric comparison among models; (ii) the evaluation of case-study buildings capacity in their as-built condition and after shear strengthening interventions. The latter is performed on 3D “bare” models, due to the lack of practical guidance in most codes on modelling masonry infills.

Liquefaction can significantly alter the ground response. However, no existing design spectrum accounts for the severity of soil liquefaction. This work aims to develop correction factors that can be used to adjust code-based design spectra to reflect the specific liquefaction susceptibility of a site. The correction factor is derived as the ratio of response spectra calculated by two types of 1D nonlinear site response analyses: effective stress analysis, which can model porewater pressure (PWP) generation, and total stress analysis. We considered seven real profiles and 200 motions in our analysis. Four combinations of soil nonlinear models and PWP generation models are also utilized to account for epistemic uncertainties. Results show that the response spectral ratio for liquefied sites typically falls below one for periods less than 1–2 s and rises above one for longer periods. Meanwhile, the response spectral ratio reflects the overall liquefaction susceptibility influenced by PWP, factor of safety, and liquefiable layer depth, while the liquefaction potential index (LPI) captures their complex interplay. Accordingly, we propose four LPI-dependent factors: three correction factors for peak ground acceleration, 0.2 s spectral acceleration (Sa), and 1.0 s Sa, and a long-period adjustment factor applicable for periods exceeding 1 s. The correction factors linearly decrease with increasing LPI, while the adjustment factor exhibits the opposite trend. A design spectrum for a liquefiable site can be readily constructed by adjusting the code-based design spectrum using the proposed correction factor, as illustrated in the example. This approach is applicable as long as LPI is available from a simplified liquefaction analysis or a liquefaction hazard map.

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.