Bulletin of Earthquake Engineering最新文献

The regional seismic risk assessment of reinforced concrete (RC) building portfolios is a critical issue in earthquake engineering due to their high vulnerability and widespread distribution in seismic prone areas. A pertinent aspect in regional seismic risk applications is the ability to accurately quantify the exceedance of any damage state, generally via fragility functions. To this end, this study derives analytical fragility functions for large-scale seismic risk applications of non-ductile RC buildings with masonry infills characteristic of the Italian peninsula and Southern Europe in general. These were derived using a large database of archetype buildings developed to represent the temporal evolution in construction practice in Italy based on an extensive literature review and interviews with practising engineers and architects. Fragility functions for several infilled RC taxonomy classes were derived for multiple damage states using state-of-the-art analysis on detailed numerical models. Average spectral acceleration was adopted as the intensity measure throughout, since it has been shown to notably reduce dispersion and bias in quantifying the response, and subsequently refine the seismic risk estimates, for these typologies. The fragility functions are compared against empirical data collected following past earthquakes in Italy, namely L’Aquila 2009 and Umbria-Marche 1997. The development of empirical fragility functions was carried out using a novel derivation of average spectral acceleration-based ground-motion fields considering spatial and cross-period correlation models, which is a key component and development in this study. This paper shows how recent advances in analytical fragility function development can be integrated with past empirical observations to give more accurate and representative damage estimates for regional assessment.

This paper analyzed the strong motion characteristics based on 86 three-component strong motion records of the M_W 6.6 Luding earthquake. Additionally, the factors that influence the variation in ground motion for three earthquakes with similar magnitude in Sichuan Province were investigated. The analysis result indicates a strong correlation between the observed ground motion parameters and the distribution of published Modified Mercalli Intensity. The residual analysis reveals that the spectral accelerations at periods 0.1–10.0 s are amplified to 0.0798–0.3057 times the mean level in the rupture forward direction and weakened to 0.0738–0.2831 times the mean level in the rupture backward direction. The maximum pulse direction recorded by the 51LDJ station is N6°E, aligning with the vertical fault direction. The velocity pulses has distinct bidirectional pulses in the waveforms, with a PGV of 37.0 cm/s. The source effect of the strike-slip M_W 6.6 Luding and M_W 6.5 Jiuzhaigou earthquakes on ground motion is relatively less significant compared to the average level of mainshocks in southwest China. However, the thrust-fault M_W 6.7 Lushan earthquake exhibits a stronger source effect on ground motion during short and medium periods, but a weaker source effect during long periods when compared to the average level. The anelastic attenuation of the Longmenshan, Xianshuihe, and Huya fault zones in Sichuan exhibits significant regional variation and periodic correlation. This phenomenon is closely linked to the regional tectonic background variations and the heterogeneity of crustal structure within the area.

Masonry-infilled reinforced concrete (MI-RC) buildings are one of the abundant building inventories and are commonly seen because of their relatively cheaper construction materials, and easier workmanship. However, often due to the negligence of the design guidelines or disregard of the contribution of masonry infills in structural weight and stiffness, these buildings become seismically vulnerable. Generally, the design involves uncertain parameters related to material and geometric properties, a slight change of which may lead to large variation in the structural response. More specifically, the masonry infill wall parameters can result in huge structural response variation. The issue of variation in structural response becomes more critical considering the large uncertainty involved in the quantification of earthquakes and the ground motion parameters while conducting time history analysis. Usually, peak ground acceleration (PGA) is considered as the ground motion intensity measure (IM) to define the ground shaking. However, several other IMs, such as arias intensity, specific energy density, the ratio of peak ground velocity to peak ground acceleration, dominant frequency, and the strong motion duration can also influence and determine the severity of seismic damage caused to the buildings, explicitly in case of infilled RC frames. The present study is an effort to quantify the effect of several such ground motion parameters, on the response of masonry-infilled reinforced concrete frame. An attempt has also been made for modification of the established demand–capacity relationship, also known as IM versus EDP (engineering demand parameter) based on the relative frequency characteristics of the building and the ground motion. It is suggested that relating the EDP with multiple ground motion parameters considering the frequency characteristics of the building and the ground motion can give a more realistic picture of the effect of seismic vibration of such buildings.

In a recent work, we evidenced some empirical discrepancies between the macroseismic intensity estimates in Italy in the last decade with respect to those made previously. A possible reason might be the progressive adoption by Italian researchers of the European Macroseismic Scale (EMS) in place of the Mercalli Cancani Sieberg (MCS) scale mostly used up to 2009. In theory, in modern settlements where reinforced concrete (RC) buildings are increasingly replacing those in masonry, EMS should overestimate MCS because the former accounts for the lower vulnerability of RC whereas the latter does not because RC buildings were not considered at all by the MCS scale since they were almost absent at the time (1912–1932) when it was compiled by Sieberg. However, such theoretical inference is contradicted by the empirical evidence that, on average, MCS intensities really estimated in Italy over the past decade slightly overestimate EMS and not vice versa as it should be. A possible explanation is that the EMS scale had not been well calibrated to reproduce the MCS, as its authors intended to do. Another possible reason for the discrepancies between the last decade and the previous ones might be that the MCS scale applied today is not the same as that defined by Sieberg at the beginning of the twentieth century. In order to better understand the possible causes of such discrepancies, we present here a formal comparison between the definitions of the different degrees of such macroseismic scales. After such analysis, we might argue that another possible reason for the observed discrepancy may come from the inaccurate assessment of building vulnerability when assessing the EMS intensity.

Structures in earthquake-prone areas may suffer from accumulative damages caused by sequential shocks, including the mainshock and aftershock of an earthquake or several strong motions throughout their service lifespan. Sequential shocks lead to a decrease in the capacity of structures. Nevertheless, seismic fragility curves and their applications do not often consider the sequential effect. This study investigates the impact of sequential seismic events on seismic fragility curves of 3-, 6-, and 9-story reinforced concrete buildings constructed before and after 1982 in Japan. The research proposes analytical fragility curves based on dynamic nonlinear multi-degree-of-freedom analyses under the influence of single shock and sequential shock of recorded motions of six destructive earthquakes in Japan. The results demonstrate that the seismic sequence increases the probability of damage ratio. This increase in the fragility curve follows the Gaussian function. The study presents a regression model that can be used for other seismic areas to estimate the effect of seismic sequences on single shock seismic fragility curves.

The probabilistic seismic hazard assessment contains two ingredients: (1) the seismic source model with earthquake rates and rupture parameters for specification of the statistical distribution of earthquakes in time and space and (2) the ground motion model, for estimation of ground shaking level at a site for each earthquake rupture. The selection of these models significantly impacts the resulting hazard maps, and it can be challenging, particularly in seismotectonic regions where overlapping structures, sited at different depths, coexist. Eastern Central Italy is a well-known active compressional environment of the central Mediterranean with a complex tectonic structure with a lithospheric double shear zone. In this study, we propose a seismic hazard assessment to analyze the contribution of these two shear zones as overlapping multi-depth seismogenic volumes to ground motion at a given hazard level. We specifically focus on selecting relevant and applicable parameters for earthquake rate modeling, emphasizing the importance of defining rate computation and rupture-depth parametrization in hazard analysis. To achieve this, we utilized a seismotectonic- and catalog-based 3D adaptive smoothed seismicity approach following the methodology given by (Pandolfi et al. in Seismol Res Lett 95: 1–11, 2023). Finally, we demonstrated how this innovative 3D approach can identify with high resolution the individual sources' contribution with particular attention to the depth location of structures that strongly influence the ground motion. Moreover, combining seismotectonic data with seismicity avoids the challenges associated with structures with scarce geologic, geodetic, or paleoseismological data. Our result provides detailed insights into the seismic hazard within the Adriatic Thrust Zone.

This article presents models to predict median horizontal elastic response spectral accelerations for 5% damping from earthquakes with moment magnitudes ranging from 3.5 to 7.25 occurring in the United Kingdom. This model was derived using the hybrid stochastic-empirical method based on an existing ground-motion model for California and a stochastic model for the UK that was developed specifically for this purpose. The model is presented in two consistent formats, both for two distance metrics, with different target end-users. Firstly, we provide a complete logic tree with 162 branches, and associated weights, capturing epistemic uncertainties in the depth to the top of rupture, geometric spreading, anelastic path attenuation, site attenuation and stress drop, which is more likely to be used for research. The weights for these branches were derived using Bayesian updating of a priori weights from expert judgment. Secondly, we provide a backbone model with three and five branches corresponding to different percentiles, with corresponding weights, capturing the overall epistemic uncertainty, which is tailored for engineering applications. The derived models are compared with ground-motion observations, both instrumental and macroseismic, from the UK and surrounding region (northern France, Belgium, the Netherlands, western Germany and western Scandinavia). These comparisons show that the model is well-centred (low overall bias and no obvious trends with magnitude or distance) and that the branches capture the body and range of the technically defensible interpretations. In addition, comparisons with ground-motion models that have been previously used within seismic hazard assessments for the UK show that ground-motion predictions from the proposed model match those from previous models quite closely for most magnitudes and distances. The models are available as computer subroutines for ease of use.

Building code implementation in developing countries is a serious concern due to poorly regulated construction practices. Deficiencies in terms of material strength and structural detailing are found the most in reinforced concrete frames in Pakistan. This paper presents the results of quasi-static cyclic tests performed on reduced-scale RC frames with and without beam-column joint detailing and considering normal and low-strength concrete respectively. Fragility functions and loss curves for the standard/sub-standard frames were derived using an experimentally validated numerical model. Furthermore, the existing RC frames building stock was rehabilitated with various configurations of steel bracing i.e. one way diagonal, one way eccentric, two way diagonal, two way eccentric and concentric. The developed fragility and loss curves for the rehabilitated frames confirmed that the two way diagonal steel bracing system outclasses the other types. Moreover, inter-story drift limits for as-built and rehabilitated frames were proposed under design base earthquakes and maximum considered earthquakes. Maximum considered earthquakes pushed the ductile as-built frame further than the moderate damage state, thus rehabilitation after such an event will be required for the structure. The presented results will help in seismic risk assessment, decision-making and public awareness.

In this paper, closed-form expressions to calculate both the mean annual failure rate and the confidence factor are proposed. Reliability indicators are estimated assuming a normalization between capacity and demand called (I_{DC})_. Simplified closed-form expressions are obtained in accordance with the probability seismic demand analysis used in SAC/FEMA. Uncertainties associated to mechanical, geometrical, and epistemic properties are taken into account, as well as uncertainties related to the occurrence of earthquakes. A comparison of both the mean annual failure rate and the confidence factor with (I_{DC}) and the expressions proposed by Cornell and collaborators is performed. The numerical approach for the mean annual failure rate is obtained to verify the approximation of the closed-form solutions. Reliability indicators are obtained using six continuous reinforced concrete bridges designed to comply with three drift thresholds (0.002, 0.003 and 0.004). The bridge systems are situated in transition soil of Mexico City. Maximum differences of 4.1% and 10.6% are obtained between the proposed expression and the numerical solution for the mean annual rate of failure, estimated for two limit states: serviceability and collapse. The confidence factor presents differences of 5.2% between the present study and the original formulation.