Bulletin of Earthquake Engineering最新文献

Offshore wind energy is increasingly recognised as a vital source of renewable energy worldwide, with offshore wind farms currently being operated and developed in regions of moderate to high seismic activity. However, there is still limited data on how large-scale offshore wind turbines perform during earthquakes, highlighting the need for further research. This study focuses on the assessment of the seismic performance of large-scale jacket-supported offshore turbines, which have received less attention compared to monopile-supported turbines, and can offer a more attractive solution in seismic regions. Using a risk-based approach, this study investigates the seismic acceleration demands at the rotor-nacelle assembly (RNA) level for a four-legged, X-braced reference steel jacket structure supporting a 10-MW turbine, acting as a representative example of existing and future large-scale jacket-supported offshore wind turbines. The structure is assumed to be located in a reference site in a highly seismically active region, where the hazard is driven by different source types. Particular focus is given to the associated hazard-consistent ground-motion selection methodology considering combined horizontal and vertical ground-motion excitation at different seismic intensity levels that is required for the proper evaluation of the structural system response. 300 nonlinear response history analyses are conducted where the performance is evaluated against a representative range of RNA acceleration limits for which conditional fragility curves are developed. Moreover, to aid in further damage and loss assessments of such structures, a demand curve showing the annual rate of exceeding different demand values is reported. In addition, the contribution of higher-mode response including vertical system excitation is discussed. Finally, in order to relate the acceleration demands to potential structural damage levels, buckling strength evaluations for the support tower are presented and discussed.

Seismic performance assessment of a RC frame building was conducted for original and strengthened states to investigate the effectiveness of strengthening technique of infill walls by carbon fiber reinforced polymer (CFRP). Structural model representing CFRP strengthened infill wall was based on the previous experimental work of the author. In the first part of this paper, the experimental work was explained briefly, details of strengthening technique and proposed structural model were given. In the second part, nonlinear time history analyses of a RC frame building were performed for original and strengthened states. Maximum interstory drift ratios obtained from nonlinear time history analysis were used to derive cumulative density functions and a comparison was made in terms of probability of exceedance curves of original and strengthened buildings. It was concluded that strengthening of selected infill walls by CFRP as proposed in this study clearly improved seismic behavior of the structure and that improvement was quantified with cumulative density functions.

The evaluation of repairability for column specimens is a critical component in assessing seismic toughness and can guide post-earthquake repairs. Under the effect of vertical variable axial force, the residual deformation limit specified in FEMA P-58 may be overly high. Existing studies generally suffer from limitations such as insufficient sample numbers, large errors, and incomplete evaluation processes. In this study, the change mode of axial compression ratio at the top of the central column was analyzed, and systematically evaluated the influence of vertical variable axial force and structural parameters on the bearing capacity and residual deformation of columns. The bearing capacity prediction model and residual deformation prediction model of column specimens considering multi-factor changes were established respectively. Based on damage index, the residual deformation limit of the repair interval of column specimens was divided, and the repairability probability model of column specimens was established. Finally, a complete set of columns repairability evaluation procedures was established. The results indicated that the residual deformation limit within the repair interval of column specimens was significantly lower than that proposed by FEMAP-58 and previous research when vertical variable axial force was applied. Specifically, when the change frequency was 3, the residual deformation limits for the “no repair required” and “can be repaired” intervals were less than half of those proposed by FEMAP-58, with the latter decreasing to 0.14% as the amplitude increases. Additionally, the interval limits provided by FEMAP-58 remained applicable when the change frequency of vertical variable axial force was 2 and the amplitude was small; but these limits decreased significantly with increasing amplitude. Ultimately, a comprehensive column reparability assessment system was established, providing critical decision-making basis for the functional recovery of subway station columns after earthquakes.

Performance-based seismic design of post-installed fasteners is an open question since the current state-of-the-art fastener seismic qualification methods (EOTA TR 049 and ACI 355) do not provide fastener capacity information that may be used for performance-based design. The published fastener seismic capacities are not related to actual earthquakes in seismic design scenarios. The seismic qualification and assessment framework of fasteners is conceptually incorrect since its first publication in ACI 355.2–00. This framework was adopted in EOTA documents and referred in EN 1992–4:2018 and EN 1998–1–1:2024 too. To promote the development of performance-based seismic design and a related appropriate fastener qualification framework, a holistic approach is proposed that can provide transparency and opportunities for future improvements. The approach hypothesizes that seismic design scenarios of connections with post-installed fasteners may be characterised by one single simplified parameter. An energy based term, the accumulated damage potential (ADP) has been adopted for this purpose, which has been proposed in the literature for the estimation of fastener displacements in crack cycling tests. The ADP seems to be able to reflect the response of structural members at the location of connections under any earthquake action in any type of building, considering any type of non-structural component and any type of post-installed fastener. Major future work is anticipated in multiple fields to develop the new framework. This paper explores the specifics of such a development, provides a comprehensive assessment of the current status quo, and based on a gap analysis sets the direction for future research. Currently, there are no simplified methods available for designers to determine the ADP in design. Fastener capacity information is very limited in the current assessment documents and does not allow designers to perceive the real seismic capacity of fasteners or their sensitivity to different crack widths. This paper provides an outlook for future developments in seismic design and qualification, which are suitable to account for the fastener response in the relevant range of ADP and the relevant range of maximum crack widths considered in actual seismic design scenarios.

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.