Bulletin of Earthquake Engineering最新文献

A hybrid frame with resilient members and energy dissipation devices is proposed as a solution to address the issues of the safety and post-earthquake repairability of concrete structures in earthquake-prone zones. This paper experimentally investigates the seismic performance of concrete-filled square steel tube (CFT) columns reinforced with low-bond ultrahigh-strength steel (LBUHSS) bars, which are proposed for the hybrid frames. 8 large-scale specimens with different types of LBUHSS bars, axial load ratios, and shear span ratios were tested. The results show that the use of LBUHSS bars significantly improved the seismic behavior of the CFT columns, including improving the deformation capacity and bearing capacity of the columns and controlling their post-earthquake residual displacements, especially at the large deformation stages of the columns. The cumulative damage and plastic deformation of the specimens decreased with the introduction of the steel bars. The shear-span ratio and axial loads both have a significant influence on the seismic behavior of columns. A simplified finite element analysis model was proposed and applied for a parametrical analysis. Based on the study, two simplified calculation models were proposed to predicate the peak and ultimate deformation of the reinforced CFT columns.

This paper compares two methods for retrofitting an existing hospital concrete structure to improve its seismic performance: internal and external retrofitting. Internal retrofitting involves adding chevron braces, reinforcing shear walls with Fibre-reinforced plastic coating, and wrapping the walls, columns, and beams using steel jackets. External retrofitting uses two braced exterior steel frames connected to the concrete building using dampers. The paper also proposes a new design objective for hospital structures that ensures immediate occupancy performance level under earthquake hazard level-1 and prevents collapse under higher ground motion intensity. The paper evaluates the base structure, the two retrofitting schemes, and the proposed design method using pushover and nonlinear dynamic analyses under 20 selected earthquake records. The paper then compares the probabilistic seismic risk models using fragility curves. The results show that external retrofitting is more effective and economical than internal retrofitting and that the proposed design objective can significantly reduce the seismic risk of hospital structures.

It is widely acknowledged that seismic duration has significant impacts on structural responses for traditional concrete frames. However, it still has not been comprehensively investigated towards self-centering systems, given the unique nonlinear behaviors and performance. This study investigates the influence of seismic duration on deformation responses, energy demands, damage progress and collapse capacity for self-centering concrete frames (SCCF). Six SCCFs with varying heights and structural features are designed and examined through nonlinear time history analyses utilizing two spectrally equivalent record sets with distinct durations. The results show a negligible correlation between seismic duration and peak deformations, yet earthquakes with shorter durations tend to enlarge residual deformations in SCCFs. Long-duration earthquakes impose significantly higher energy demands, negatively impacting damage development in SCCFs, while the energy distribution within structures remains consistent across the two record sets. Furthermore, SCCFs are observed to experience increased risks of collapse under earthquakes with longer durations, with the impact being more pronounced in SCCFs with larger self-centering parameters. Additionally, the duration-blind record set suggested in FEMA P695 is found to be inadequate for assessing collapse capacity for systems subjected to long-duration earthquakes. Consequently, it underscores the necessity of explicitly considering the duration effect in seismic designs and performance evaluations for SCCFs.

The proposed research work presents a comprehensive approach to assessing the seismic vulnerability of archaeological sites. This approach aims to be a quick and easy-to-use investigation procedure that enables accurate and large-scale evaluations. While the methods employed are well-established in the literature and have been widely applied to buildings, this study contributes by proposing a structured framework that integrates different assessment procedures at different levels of analysis, specifically tailored to archaeological sites. The analysis is divided into three stages within the conceptual framework: (i) the application of the Masonry Quality Index; (ii) seismic vulnerability assessment and prediction of expected damage; and (iii) analysis of individual walls’ structural response through strength domain, capacity and fragility curves. Specifically, the study explores and adapts four Vulnerability Index methods, i.e. GNDT, Formisano, Vicente and Ferreira methods, to suit the specific characteristics of archaeological sites. To this end, a simplified procedure is proposed to estimate the conventional strength in the methods’ forms. The comparison of the index-based methods is then crucial for critically evaluating the reliability of vulnerability estimations. The paper illustrates the application of this framework through a detailed case study, i.e. the archaeological site of Wupatki Pueblo in Arizona (US), demonstrating its effectiveness in evaluating the seismic risk and defining the vulnerability distribution of the site. Consequently, this approach facilitates the identification of the most sensitive areas, which necessitate further investigation, providing useful outcomes for the decision-making process concerning the conservation and protection of archaeological sites.

In the general practice of performance-based seismic assessment and dynamic analysis of building structures, the recorded ground motions from past earthquake events are selected and modified according to the site conditions and hazard level of the project’s site. For this purpose, only the mainshock earthquake event is considered for the analysis while neglecting the foreshocks and aftershocks. However, in several real cases, especially for existing RC buildings with non-seismic detailing, low- to moderate-magnitude foreshocks and aftershocks may also affect the seismic performance. Several studies have shown that the application of repeated earthquake events may lead to damage accumulation and significant seismic losses, even if the structure is at a life safety performance level. This study examines the seismic performance of mid-rise RC frame structures in Pakistan under repeated earthquakes. For this purpose, a representative case study building has been selected for the detailed analysis after surveying typical existing RC buildings in Pakistan. The detailed nonlinear finite element model is constructed and subjected to several cases of repeated earthquakes with different intensity levels. The seismic performance in terms of key demand parameters is evaluated for single earthquake scenarios (mainshock only) and seismic sequences (foreshock, mainshock, and aftershock). The results showed the application of seismic sequences has a negligible effect on the peak seismic force and displacement demands of the buildings compared to the single mainshock event. However, an increase in seismic performance indicators, including residual displacements and inelastic hysteretic energy, is observed. Resultantly, an increase in structural damage (quantified in terms of material cracking, yielding, crushing, etc.) is also observed for ground motion sequences compared to the single ground motion.

South Korea was considered a stable continental region (SCR) until the recent seismic events, specifically the 5.5- and 5.4- magnitude earthquakes in Gyeongju and Pohang, respectively, highlighting the need for reliable ground-motion models (GMMs), which are key to seismic hazard assessment analysis. Although it is appropriate to employ GMMs that are tailored to regional characteristics, irrespective of whether they are developed based on a stochastic method or actual data, a model that is similar to the tailored GMM can also be used. Recently, several earthquakes with magnitudes greater than 5 have occurred in South Korea, enabling us to assess whether the GMMs previously developed in Korea or those applied for South Korea's disaster management system are suitable for use throughout the country. Therefore, this study conducted an evaluation to assess the suitability of GMMs tailored to domestic characteristics. GMMs developed for various regions including active crustal regions, SCRs, and South Korea, were employed. Amplification functions were applied to several GMMs developed for hard rock sites. A total of 48 GMMs, considering site effects, were compared using the Korean earthquake ground motion data. The suitability of GMMs for Korea was assessed through statistical techniques such as log-likelihood method, multivariate logarithmic score, Euclidean distance-based ranking, Euclidean metric distance, deviance information criterion, and cumulative-distribution-based area metric method. Ensemble GMMs were also developed based on the rank results and analyzed using statistical methods. Un-normalized weight was used to calculate the outcomes of the above mentioned six ranking methods, and weighted GMMs were judged to be optimal for South Korea.

Reinforced concrete (RC) rigid-frame bridges with tall hollow piers were widely constructed in Southwestern China, an earthquake-prone area. For such bridges, the seismic damages may be underestimated if multiple bends of tall piers are overlooked using a conventional damage measure such as the drift ratio. Moreover, the seismic damage assessment can be inaccurate if tall piers’ shear damages are ignored using the sectional curvature as a damage measure. Along these lines, this paper proposes a novel seismic damage measure, the piecewise drift ratio (PDR), involving both shear effects and multiple-bend deformations; it has been validated by hybrid tests and analyzed employing fragility curves. Damage state limits represented by the PDR are estimated through statistical analysis of the 40 existing tests of hollow piers. To validate the PDR, a finite element model of an RC rigid-frame bridge with two tall piers was established and adequately calibrated based on model-updating hybrid simulations. To comprehensively evaluate the PDR, ground motions were selected and grouped into four categories by identifying their first two-class nature frequency and their amplitude ratio; to determine fragility curves, both the spectral acceleration at the fundamental period with 5% damping, S_a(T₁, 5%), and the peak ground acceleration have been adopted as intensity measures. Results show the effectiveness of the proposed PDR, provide a more severe ground motion for assessment, and reveal the high exceedance probability of the complete damage state of tall piers under some potential seismic scenarios.

Examining the reliquefaction resistance of sand deposits is more challenging due to the complex interplay of several factors that may increase or decrease the resistance. This resulted in severe limitations in understanding the reliquefaction mechanism of sand deposits subjected to repeated shaking events. The present study attempted to overcome this limitation by examining the reliquefaction resistance using 1-g shaking table experiments. A total of 65 shakings were performed on saturated Solani sand with varying acceleration amplitude, dynamic frequency, shaking duration, and relative density of the sand specimen. All the above factors were experimented with three different shaking patterns (incremental, uniform and decremental) and independent events. For each shaking event, generation and dissipation of excess pore pressure, soil subsidence, and relative density variations were presented. The beneficial effect of seismic preshaking were applicable in partially liquefied soils that were subjected to incremental shaking pattern. On the other hand, contrary results were reported for uniform and decremental shaking patterns, where the later found to be more damaging. The state of the soil (partially or completely liquefied) governs the reliquefaction resistance, as the beneficial effect of preshaking was applicable only in partially liquefied soils, irrespective of the shaking pattern. Whereas complete liquefaction disturbs the structure of existing sand specimens and results in reduced reliquefaction resistance for future seismic events.

Exposure models for regional seismic risk assessment often place assets at the centroids of administrative units for which data are available. At best, a top-down approach is followed, where such data are spatially disaggregated over a denser spatial grid, using proxy datasets such as the distribution of population or the density of night-time lights. The resolution of the spatial grid is either dictated by the resolution of the proxy dataset, or by constraints in computational resources. On the other hand, if a building-by-building database is available, it often needs to be aggregated and brought to a resolution that ensures acceptable calculation runtimes and memory demands. Several studies have now investigated the impact of exposure aggregation on loss estimates. Herein, unlike previous attempts, we can leverage upon an extensive building-by-building database for the Swiss territory, which we can use as ground truth. We firstly proceed to assess the aggregation-induced errors of standard risk metrics at different spatial scales. Then a new strategy for performing said aggregation is proposed, relying on a K-means clustering of site parameters and a reduction of the loss ratio uncertainty for aggregated assets. These interventions are designed with the objective of minimizing errors, while keeping the computational cost manageable.

Three concrete buildings with six storeys above ground and two basements have been designed in detail according to the first generation of Eurocodes 2 (including structural fire design) and 8, as well as the official drafts of their second generation counterparts as of the end of 2023. In one horizontal direction the buildings have a wall-, frame-equivalent-dual- or frame-lateral-load-resisting system; in the other, the first two buildings have a wall-system and the third a wall-equivalent-dual. The design seismic action is in all cases according to the current generation Eurocode 8, scaled to a peak ground acceleration on rock of 0.2 or 0.3 g. Seismic design is for ductility class (DC) Medium (M) of the current generation or DC 3 of the new one, which have the same behaviour factors, q, in all structural systems considered; so, in each building seismic action effects from the analysis are the same for the two Eurocode generations. All designs are assessed through nonlinear response history analysis (NLRHA), carried out according to the pertinent Eurocode 8 rules. Designs according to the second generation meet the performance goals of Eurocode 8 much better and transparently than with the first generation, but use markedly larger steel quantities and indeed often unnecessarily so, especially for confining reinforcement—which sometimes comes out in quantities that cannot be placed. Proposals are made for a more rational linkage of local ductility demands with the q-factor and implemented in alternative second generation designs. Minor changes to the new generation’s design/detailing rules for ductile walls are also proposed and implemented in these alternative designs; they prove only partially effective in resolving certain deadlocks originating from poorly justified detailing rules that produce unnecessary and counterproductive wall flexural overstrengths. The new generation Eurocode 8 lacks design rules for the free height of ductile walls within rigid basements, which is a weak link, very likely to fail under the high shear force which balances the wall’s moment resistance at the top of the rigid basement. NLRHA confirms that the alternative provisions proposed for second generation Eurocode 8 give more cost-effective designs than the first generation, with better overall performance at about the same or even lower cost.