Bulletin of Earthquake Engineering最新文献

Buckling-restrained braced frames (BRBFs) often experience excessive drift demand, leading to increased structural and non-structural damage. Short-core buckling-restrained braced frames (SBRBFs), which utilize braces with reduced or short yielding core lengths (SBRBs), exhibit enhanced lateral stiffness, resulting in reduced seismic-induced drift responses and associated losses; however, this comes at the cost of increased ductility demand on the braces. This study evaluates the seismic vulnerability of SBRBFs in comparison to BRBFs using nonlinear time history analysis (NLTHA) under both far-fault (FF) and near-fault (NF) ground motion records. In addition to the conventional engineering demand parameters (EDPs), namely residual drift ratio (RDR), inter-storey drift ratio (IDR), maximum ductility (µ_max), and cumulative ductility (µ_cum), the residual ductility (µ_res) is also introduced. The median capacity values of all considered ductility-based EDPs are presented using a correlation model with the frame drift responses. Furthermore, a Probabilistic Seismic Demand Model (PSDM) is developed, and fragility curves are constructed for different damage states (DSs) corresponding to all the considered EDPs. Analysis outputs indicate that, compared to BRBFs, SBRBFs significantly reduce the RDR and IDR responses, leading to improved seismic performance, particularly in low-rise structures. However, SBRBFs experience higher ductility demand, but remain well within the experimentally validated capacity limits of SBRBs. Correlations among EDPs show a shift toward higher ductility median capacity values for the DSs in SBRBFs. Finally, though the SBRBFs improve the seismic response positively, their effectiveness tends to diminish with increasing building height.

Selection of accelerometric time histories is a fundamental step in seismic microzonation studies as well as in structural and ground response analyses. In this study we apply the procedure of Mascandola et al. (2020) for record selection in vast areas to the Lazio region (Central Italy). Unlike the original approach, we apply a different unsupervised clustering algorithm to divide the study area into mesozones, defined as zones that are homogeneous in terms of seismic hazard. Moreover, we apply the conditional spectrum ((CS)) method for the selection of ground motion time histories. Concerning the zoning of the study area, two clustering algorithms are compared: K-means and Spectral clustering. We found that the latter provides a zonation that is more consistent with the spatial distribution of the seismic hazard as well as of hazard disaggregation and is therefore suggested for record selection in vast areas. For each mesozone, two conditional spectra (computed for two conditioning oscillator periods) are then defined and adopted as reference for the selection of real accelerometric records. The latter are selected from a large sample of accelerograms that include earthquakes having magnitude and distance consistent with the seismic scenarios controlling the hazard. The article ends with a comparison of different techniques for the selection of real acceleration time histories. We analyze the impact of different sets of accelerograms on the ground response of two soil profiles resonating at the same periods used for conditioning the spectra (i.e., 0.2s and 1.0s). The results confirm that the conditional spectrum approach is targeted at oscillatory systems with a well-specific vibration period, for which the conditional spectrum might provide more conservative ground motions than the standard uniform hazard spectrum approach. Conversely, the latter approach is preferable for dynamic analyses of systems where more than one response period is relevant. Furthermore, our findings show that dividing the area into mesozones and selecting accelerograms using a single reference spectrum for each mesozone produces results comparable to those obtained through conventional methods based on site-specific record selection. Therefore, our approach can significantly streamline the selection of accelerometric time histories, especially in the case of vast areas.

During earthquakes, the axial force at the top of central columns in subway stations undergoes significant fluctuations, exacerbating column damage and causing noticeable variations in hysteresis curves. Currently, there is a lack of mechanical models for central columns subjected to vertical variable axial forces. This study conducted a theoretical analysis of Engineering Cementitious Composites (ECC) jacketing to enhance the seismic resilience of central columns. Using test and numerical analysis data from previous column tests under vertical variable axial force, a predictive formula for bearing capacity was developed through exponential fitting of stiffness changes and strength degradation, considering axial force amplitude and frequency variations. Additionally, by integrating the plane section assumption, elasticity theory, and the time-dependent variation of vertical axial force, a hysteresis rule was proposed. This enabled the establishment of calculation formulas for key feature points in the hysteresis curve and the development of a restoring force model for central columns. The study also systematically analyzed the sequence of failure points in column specimens. Test verification confirmed the high accuracy of the proposed mechanical models. Furthermore, a strength model for ECC jacketed composite columns was formulated, demonstrating that ECC jacket can increase the bearing capacity of specimens by over 50%. Increasing the thickness of the ECC jacket proved more effective than embedding wire mesh in ordinary concrete. This study provides a novel mechanical model and practical insights, offering significant guidance for future engineering research and seismic design of subway stations.

Forming the failure mechanism of “strong column and weak beam” in prestressed concrete (PC) frame structures designed with a response modification factor (R ≈ 3.0) as implied in China’s current seismic design code poses a challenge. Due to the absence of a scientifically standardized method for calculating the values of R, the values of R stipulated in various regional codes are typically determined based on engineering experience, resulting in notable discrepancies. This study employs static pushover analysis and nonlinear time history analysis methods to investigate the seismic performance of PC frame with varying floor configurations and prestressing ratios. Based on the analytical results, the R-values of PC frame structures are evaluated using the capacity-demand ratios method. The results reveal that the occurrence of plastic hinges in PC frame columns is delayed, while in PC frame beams, it is advanced as the prestressing ratio increases. The maximum inter-story drift of PC frame structures complies with the specification limit with the increase of prestressing ratio. The capacity (critical collapse state) and demand (rare earthquakes) value of R is distributed in 16.1–34.9 and 5.3–7.8, respectively. The value is exceeding China’s standard requirements by more than double. The values of capacity-demand ratios are distributed between 1.8 and 4.4, indicating ample safety reserves within PC structures. The limit value of prestressing ratios is recommended to increase to 0.85.

Most seismic building codes worldwide allow the definition of the seismic action (horizontal component of ground motion) using a simplified approach based on modifying the ordinates of an elastic acceleration or displacement response spectrum expected on outcropping bedrock through appropriate soil factors. The procedure is only suitable for geotechnically stable soil sites (i.e. non-liquefiable). The details of the method may differ from code to code but, all share the same idea of classifying soil deposits into a restricted number of categories based on the geotechnical characteristics of the soil deposit and the weighted average of the shear wave velocity of the top 30 m (i.e., V_S30) or a surrogate parameter such as the site’s fundamental period. Finally, specific soil factors are associated with each soil category to scale the ordinates of the elastic response spectrum defined on outcropping bedrock and flat topographic surface. Being a method specifically developed for design, the search for a balance between simplicity and accuracy increases the uncertainty of the results. Recent studies based on analyzing recorded strong motion data and numerical simulations have raised doubts about the reliability of this approach, given the tendency of the current soil factors to either underestimate or overestimate the horizontal acceleration at the free surface of the soil deposit. If, onto one hand, the underestimation of the seismic action is related to the level of safety, on the other hand, the overestimation of the seismic action may lead to overdesign with an increase in construction costs. In 2018 the authors of this paper have published an article on this journal on assessing the reliability of current Eurocode 8 and the Italian building code (NTC18) soil factors using the results of a large number of numerical simulations. In this paper the same authors update their 2018 study by including strong motion data from real recordings. Updated hazard-dependent soil factors for Eurocode 8 and the Italian building code (NTC18) are defined by complementing numerical and real ground motion data. The role of epistemic uncertainty in specifying soil amplification factors is highlighted also through a comparison with soil factors calculated from other international building codes (e.g. 2021 IBC and ASCE 7–16) and recent publications.

Current seismic codes predominantly focus on isolated structures, despite the widespread presence of building aggregates in urban environments. This issue is particularly relevant in Costa Rica, where partially grouted reinforced concrete block masonry (PG-RCM) buildings are routinely constructed directly adjacent to each other with no separation, forming aggregates through contact between independent walls rather than shared structural elements. These modern aggregate configurations, frequently built on varying ground elevations, represent a common construction practice whose complex seismic interactions are not explicitly addressed in typical design provisions. This study investigates the seismic behaviour of contemporary PG-RCM aggregates through advanced numerical modelling. The research employs non-linear dynamic analysis with bidirectional seismic excitation, using multilayered shell elements with integrated reinforcement and a damage-based material model for masonry components. The numerical model was validated against experimental data from cyclic pseudostatic loading test on individual PG-RCM wall panel. Subsequent analyses examined both isolated and aggregate configurations, with compression-only contact interactions between adjacent units modelled through zero-length elements. A five-unit aggregate model proved sufficient to capture the effects of structural interactions. The results reveal that in level-ground arrangements, damage concentrates in one end unit of the aggregate, which acts as an energy dissipator through contact-based load transfer, thereby reducing damage in adjacent units. When units are built at different elevations, a critical height difference threshold was identified, above which the highest unit consistently experiences the most severe damage, regardless of its position in the aggregate. These findings demonstrate how contact interaction between adjacent structures significantly alters their seismic response, particularly when combined with elevation differences, emphasising that these complex interactions warrant further investigation to inform the potential future development of targeted seismic design guidance.

Past earthquakes have shown that reinforced concrete (RC) wall buildings are vulnerable to seismic damage. Identifying vulnerable buildings before future events enable the implementation of prevention strategies, such as retrofitting vulnerable structures. Assessing the seismic vulnerability of a large building stock is complex, and a rapid and effective evaluation is necessary to identify vulnerable buildings. Different methods have been proposed to evaluate the seismic vulnerability of buildings, ranging from complex analytical methods to simplified empirical methods that rely on the statistical treatment of observed damage after past earthquakes to calculate seismic indices. However, limited studies have been conducted to relate seismic indices to observed damage for Chilean buildings. The main objective of this research is to evaluate seismic indices to assess the seismic vulnerability of RC wall buildings using empirical data from the 2010 Maule earthquake. A database of 158 undamaged buildings and 30 damaged buildings following the 2010 Maule earthquake is considered. For each building, three capacity-based indices, two demand-based indices, and six demand-to-capacity indices are calculated. The demand-based indices are calculated using both the actual seismic demand and the seismic design demand. The ability of each seismic index to identify undamaged and damaged buildings is quantified using Receiver Operating Characteristic (ROC) analysis. Results suggest that capacity-based indices alone are not adequate to identify damaged buildings, while demand-based and demand-to-capacity based indices are more accurate at identifying damaged buildings. Although demand-based indices using seismic design demand are less accurate than those using the actual seismic demand, they remain practical when detailed seismic data is unavailable.

The present study aims to identify the optimal criteria for the Normalization Measure (NM) and Intensity Measure (IM) in the two-criteria scaling process of earthquake Ground Motions (GMs) to reduce uncertainty in the development of Probabilistic Seismic Demand Models (PSDMs) for more reliable seismic risk assessment. For this purpose, five 2-, 4-, 8-, 12-, and 20-story steel buildings with a seismic force-resisting system consisting of perimeter Special Moment-resisting Frames (SMFs) located in Los Angeles, California, are selected as the case study. Four sets of GMs including 160 real GMs with mid to large magnitudes at near to moderate distances are selected from Baker’s GM database. The maximum values of transient and residual inter-story drift ratios and peak floor accelerations are considered as Engineering Demand Parameters (EDPs). A total of 85 potential candidates for selecting suitable NM and IM are investigated, categorized into four groups: (I) acceleration-related, (II) velocity-related, (III) displacement-related, and (IV) hybrid criteria. Accordingly, each set of GMs is normalized and scaled with 85 × 85 different combinations for NM and IM. Then, PSDMs for each investigated building are developed using Incremental Dynamic Analysis (IDA) on 2D nonlinear frame models under the scaled GM sets. The developed PSDMs with different NMs are employed for probabilistic seismic risk analysis and the estimation of seismic demand hazard curves. The optimal criteria for developing PSDMs are identified based on efficiency, practicality, proficiency, sufficiency, and reliable seismic risk assessment. The obtained results reveal the high sensitivity of the optimal NM to the building vibration period, the selected set of GMs, and the EDP under study. For instance, while Peak Ground Acceleration (PGA) is the optimal NM for estimating the risk of the acceleration response parameter, a unique criterion cannot be proposed for the transient and residual drift response parameters that would perform optimally under most conditions; however, I_Np is the best NM for most short-period (2-story) SMFs, and Sv_avg and MVSI are the two superior NMs for most long-period (4- to 20-story) ones. This study provides valuable insights into the impact of the mentioned factors on the selection of the optimal criteria.

Sustainable structures or structural components as one of the frontiers in civil engineering can solve the problem of construction and demolition waste and also enhance the reuse of structural components at the end of their service life or after damage. In terms of sustainable assessment, steel-concrete composite beams with or without novel demountable shear connectors were performed in this work. Structural configuration and mechanical properties of proposed sustainable steel-concrete composite beams were firstly presented and then the nonlinear analysis of this composite beams using the Abaqus software was validated. Three specimens with different types of shear connectors were designed and tested under two-point loading to investigate the flexural behavior and deconstructability. Results from this research showed that these composite beams exhibited a flexure-shear or flexural behavior, presenting the typical failure modes of yielding of steel beam, slab concrete split or concrete crushing of plug. Compared to that of traditional composite beam with embedded welded bolts, specimens with demountable shear bolts and demountable shear connections experienced reduced initial flexural stiffness (about 29.8% and 37.2%), yield strength (by about 18.3% and 32.1%) and ultimate strength (about 12.9% and 24.9%) due to the relative slip between the steel beam and precast concrete slab, respectively. Whereas these of composite beams developed a better deformation capacity and ductility coefficient. Additionally, sustainable steel-concrete composite beam with demountable shear connections could easily allow for easy installment and disassemble to achieve the recycle of these structural members and also replacement with new plugs to permit a quick seismic rehabilitation after earthquake. Finally, some suggestions of this sustainable composite beam and demountable shear connections were proposed to provide references for the design in practice.

Reinforced concrete (RC) wall buildings are multi-storey structures comprising several modes of response that contribute to both the displacement-based and force-based demands acting on them during seismic shaking. This research investigates how code-specified methods for selecting ground motion records affect this response, with particular attention to higher-mode contributions. The study contrasts two target spectra: the uniform hazard spectrum (UHS) and the conditional spectrum (CS), both now permitted in the upcoming Eurocode 8 revision. It examines the influence of their choice for several shear wall buildings designed using Eurocode 8 (EC8). By assessing record selection strategies, including UHS alone and different CS with conditional periods beyond the primary mode, T₁, impacts on engineering demand parameters (EDPs) such as peak-storey drift, wall shear demand, and overturning moment are quantified. The findings indicate that the UHS approach generally leads a more conservative higher structural demand estimate across all EDPs, which is not always very cost-effective. Not surprisingly, using the more advanced CS approach tends to yield much lower demands, but is found to be heavily dependent on the conditioning criteria used. While drift demands can be well-represented when conditioning to the first mode period, CS(Sa(T₁)), EDPs such as shear forces and bending moments can be severely underestimated. More critically, when other conditional selection strategies are used (e.g., CS(Sa(T₂)), CS(Sa(T₃)), etc.), these EDPs increase notably, which could lead to uncon servative designs. This study emphasises the importance of understanding the trade-offs between the presumed increase in accuracy when using the CS versus the UHS for RC wall buildings. It is also an important clarification for the next generation of Eurocode 8 that engineers must be aware of.