Bulletin of Earthquake Engineering最新文献

The devastating (:{M}_{W}) 7.8 Pazarcık earthquake on February 6, 2023, profoundly impacted a large region in south-central Türkiye and northwestern Syria, resulting in over 50,000 casualties and widespread damage. To better understand source properties and wave-propagation effects of this event, we analyze the strong ground-motion data recorded at ~ 230 stations. We determine the regional distance-dependent attenuation using the horizontal RotD50 Fourier acceleration amplitude spectrum (FAS) in the frequency range of 0.1–20 Hz. We find an apparent near-source saturation effect which needs to incorporate an additional finite-fault factor for the distance scaling. Uncertainty and sensitivity analyses are considered by variable decay rates in the geometric spreading model. For each decay rate, we derive a corresponding (:Qleft(fright)) model to account for the frequency-dependent anelastic attention. Significant duration of ground motions is modelled for two different measurements based on Arias intensity ((:{I}_{A})). For site amplification, we construct a model containing both (:{V}_{S30})-scaling and peak ground acceleration (PGA)-scaling. Source parameters are then determined using a reference Fourier source spectrum at 1.0 km. Specifically, we estimate the mean corner-frequency as (:{f}_{0})= 0.036 Hz, Brune stress drop as Δσ = 4.79 MPa and the reference rock site κ₀ = 0.051 s. By analyzing near-source pulse-like waveforms, we demonstrate that the mismatch of peak ground velocity (PGV) between our model and close-distance observations is due to the rupture directivity effect. Finally, we compare ground motions of the 2023 (:{M}_{W}) 7.8 event to those of the 2023 (:{M}_{W}) 7.6 Elbistan and the 2020 (:{M}_{W}) 6.7 Sivrice earthquakes. Attenuation effects estimated for the three events are found to be identical between ~ 0.2 and 6.0 Hz, with slight differences in site responses above ~ 5.0 Hz. Source spectra comparisons indicate that the source properties are complicated for all three events. Our comprehensive ground-motion analyses contribute to understanding and modeling regional properties of attenuation, site response, and event-based source characteristics that are important for future region-specific seismic hazard assessment.

The seismic resilience of steel bridge piers can be weakened due to the ageing effect that occurs throughout their entire life-cycle stage. Seismic strengthening is a practical approach to enhance the seismic performance of ageing piers. Nevertheless, the conventional strengthening methods often result in a higher stiffness of bridge piers. This can potentially intensify the local seismic responses of the strengthened bridge pier and change the failure mode during seismic events. Hence, this study extends a strengthening technique, the Contact Stiffener Strengthening Method (CSSM), which aims to enhance the ductility of ageing steel bridge piers without causing an excessive increase in stiffness. This method uses the contact effect to increase the seismic performance of aging piers by ingeniously designed stiffeners. The static and dynamic approaches are employed to compare the effects of CSSM and traditional strengthening methods on seismic performance enhancement. Finally, this study proposes the prediction methods for the ultimate strength and displacement of the strengthened piers. The analysis results reveal that the occurrence of the contact phenomenon and buckling at the free-end plate indicate the initiation and ultimate states of the contact stiffeners. The strengthening efficiency in retrofitted piers is greatly influenced by the parameters of the free-end plate. The strengthening efficiency of bridge piers can be significantly affected by varying parameters of corrosion when using the same contact stiffener. The errors in the proposed prediction methods for the ultimate displacement and ultimate strength of the strengthened piers can be controlled within 15% and 10%, respectively.

Following the 2010/2011 Canterbury, New Zealand earthquake sequence, Auckland Council actively identified and assessed commercial buildings within the Auckland region to establish whether they were earthquake prone. Masonry infill buildings are one class of building type that was considered to be potentially earthquake-prone, with this building type constituting a significant proportion (9%) of all commercial buildings in the Auckland region. Despite the Auckland region being categorised as a low seismicity region in the current New Zealand seismic loadings standard, rupture of the Wairoa North fault located within the Auckland region could potentially generate significant earthquake shaking in the future. The reported study was undertaken to forecast the damage distribution for low-rise and mid-rise masonry infill buildings when subjected to ground motions from the Wairoa North fault that incorporated a combined mainshock-aftershock earthquake sequence. The results showed that mid-rise masonry infill buildings were forecast to exhibit significant damage when compared to low-rise masonry infill buildings. In addition, the seismic risk associated with mid-rise masonry infill buildings was forecast to significantly increase when aftershock earthquake scenarios were applied. It is noted that the increased seismic risk of mid-rise masonry infill buildings (when compared to their low-rise equivalent) was unsurprising because post-earthquake observation following the Canterbury earthquake sequence showed that mid-rise masonry infill buildings sustained higher levels of damage in comparison to low-rise masonry infill buildings.

Two new structure-specific scalar intensity measures for plane reinforced concrete moment resisting frames under far-fault ground motions are proposed. These intensity measures, of the spectral acceleration and spectral displacement type, are characterized as multi-modal and multi-level. They encompass the effects of the first four natural periods and are defined for four performance levels, including considerations of inelasticity up to the collapse prevention level. This is achieved with the aid of equivalent linear modal damping ratios previously developed by the authors for performance-based seismic design purposes. These modal damping ratios, dependent on period, soil type, and deformation, are associated with the transformation of the original multi-degree-of-freedom (MDOF) nonlinear structure into an equivalent MDOF linear one. The proposed intensity measures are conceptualized to be simple and elegant, incorporating all the aforementioned features rationally, without the artificial combination of terms, definition of period ranges, or addition of coefficients determined by optimization procedures. This approach sets it apart from existing measures that attempt to account for multiple modes and inelasticity. A comparison of the proposed intensity measures against ten of the most popular existing ones in the literature, focusing on efficiency, practicality, proficiency, scaling robustness and sufficiency, demonstrate their advantages.

Significant damages to precast wall-slab-wall (WSW) systems due to past earthquakes in near-field zones has been reported in the literature. This led to research on the seismic behavior of precast structures. Most of them concentrated on precast framed structures. Comparatively, fewer studies have been conducted on WSW systems, especially in exploring their performance in near-field earthquakes. This study focuses on the analysis of a 5-story precast WSW structure and the corresponding monolithic WSW structures under near-field (NF) and far-field (FF) earthquakes. The normalized backbone curves (M-θ curves) for precast and monolithic wall-slab connections were modeled using link elements at the slab-wall interface. A default plastic hinge is assigned at a distance of 0.1 L from the slab-wall interface. Three types of earthquakes were considered: far-field (FF), near-field forward directivity (NFD), and near-field fling step effect (NFFE). Nonlinear time history analysis (NLTHA) is performed in the computer program SAP2000 using an ensemble of 7 different earthquake records for each type. The earthquake records are normalized for three levels of peak ground acceleration (PGA): 0.4 g, 0.6 g, and 0.8 g. The responses of interest include top story displacement (TSD), maximum inter-story drift ratio (MIDR), base shear (BS), and maximum acceleration (MA). Comparative studies utilized the ensemble average of responses. The findings reveal that the theoretical analysis of precast frames shows greater vulnerability compared to conventional monolithic frames (as commonly practiced without specifying M-θ curves at the slab-wall interface). Moreover, NFFE led to increased top story displacement and MIDR responses in all types of precast and monolithic WSW structures under study.

This study investigates the seismic behaviour of a special mixed reinforced concrete-steel structure that supports an oil refinery reactor. The structure is 64.90 m tall and consists of three parts: (a) a reinforced concrete frame basement; (b) a steel braced frame that supports the oil reactor and (c) the steel reactor itself. A three-dimensional model of the structure is created to perform static non-linear (pushover) analyses in order to obtain the capacity curves and understand the overall inelastic behavior of the structure. The results of the pushover analyses reveal that the structure exhibits similar inelastic behavior in both horizontal directions and satisfies the capacity design principles. The structure exhibits limited ductility considering the fact that has been designed with a behavior factor of q = 1.5 and primary damages are expected mainly in concrete members. Subsequently, dynamic non-linear time-history (NLTH) analyses are performed utilizing the three translational components of three seismic motions recorded during past earthquakes. These results involve: (i) the maximum values for displacements, accelerations and base shears; (ii) the maximum stresses at critical points of the oil refining reactor and (iii) the formation of plastic hinges at columns, beams and braces of the structure. Contrary to pushover analyses, NLTH analyses revealed the development of plastic hinges, hence seismic damage, that do not follow the desirable formation pattern. Moreover, the accelerations and displacements observed are expected to cause failure of the piping and mechanical equipment, while local failure of the high-stress areas of the shell of the reactor may be possible. Localized strengthening might be necessary to avoid repair works and downtime after such seismic event.

The Italian seismic code provides a simplified approach to account for the effect of local seismostratigraphical configuration on the expected ground motion. This approach, common with other seismic codes, provides specific ‘soil factors’ as a function of a set of reference subsoil conditions (soil classes): these factors are considered in 1D subsoil configurations to modify the uniform probability hazard spectrum deduced from probabilistic seismic hazard at reference soil conditions. It is inferred that, to provide a coherent management of uncertainty affecting the response spectrum to be used for the design, the contribution of uncertainty affecting soil factors must be carefully considered to avoid biases in the hazard evaluation. In the present study, variability of soil factors representative of each soil class has been explored by numerical simulation relative to many seismostratigraphical configurations inferred from seismic microzonation studies available in Italy relative to 1689 municipalities. This analysis shows that variability of soil factors is of the same order of magnitude of variability affecting reference response spectra, which implies that the former cannot be neglected as presently happens in the common practice. It is also shown that neglecting this contribution can lead to underestimate the impact of subsoil configuration on the regularized response spectrum provided by the norm, in particular, in the short period range.

Many design codes, such as ACI 318−19, ACI 352.1R-11 and ASCE 41−17, offer deterministic inter-storey drift limit functions of the gravity shear ratios for flat slab floor systems acting as the primary lateral load-resisting system. However, such deterministic limits are not capable of capturing the inherent aleatory uncertainty in the damage capacities of slab-column connections, inducing unknown failure risks during seismic events. To address this, seismic fragility analysis is conducted to generate fragility curves relating the probability of a connection exceeding a performance level or damage state to the inter-story drift ratio and gravity shear ratio. The developed fragility curves are based on an updated experimental database of 221 interior reinforced concrete and post-tensioned slab-column connections without and with shear reinforcement under combined gravity and lateral loadings. Two damage states are introduced, yielding and failure due to punching shear or flexure. The developed fragility curves are used as basis for generating reliability-based formulations and charts to aid designers in determining the drift limits as a function of the design gravity shear ratio as well as a chosen reliability index. The analysis showed that connections with continuous bottom reinforcement, shear reinforcement, or prestressing have enhanced drift capacities and reliability. Also, higher gravity shear ratios significantly lower the limit drift ratio of both reinforced concrete and post-tensioned slab-column connections without shear reinforcement at a given reliability index value. Comparing the proposed reliability-based drift limits to the deterministic limits in ACI 318−19, ACI 352.1R-11 and ASCE 41−17 revealed that the code limits tend to correspond to a reliability index ranging from about 0 to 2.5 for connections without shear reinforcement; and 3 to 8 for connections with shear reinforcement. The existing design limits for slab-column connections without shear reinforcement are least reliable at high gravity shear ratios with reliability index generally below 1.25. These results signify that the proposed reliability-based limits can prompt more informed risk-based designs, especially for connections without shear reinforcement.

In past seismic events, earthquakes have often caused significant damage to buildings. It is noteworthy that most of the existing buildings are reinforced concrete structures. Therefore, in order to mitigate the damage caused by earthquakes, it is important to conduct damage assessment of reinforced concrete structures. Considering that damage at the material level is the fundamental cause of component and structural performance degradation, indices based on material damage often have advantages in reflecting and evaluating component and structural damage. This paper proposes a damage constitutive model for concrete based on existing research results. Then, aiming at the shortcomings of current research on steel bar damage constitutive models, a steel bar damage constitutive model under cyclic loading is proposed, reflecting various failure modes of steel bars under seismic actions. Based on this, a multi-level damage index system from materials to components to structures is established. Through multi-level experimental simulations and finite element analysis, the accuracy of the proposed damage indices is validated, and performance indices for components and structures are provided. These indices can effectively reflect the damaged state of components and entire structures and can be used to guide seismic design, damage assessment, and strengthening design.

In previous earthquakes, a significant number of adjacent buildings in a series have been damaged due to collisions. Pounding between adjacent structures in a series causes them to inflict multiple blows on one another, which is a complex type of collision. Previous studies have produced inconsistent or conflicting research conclusions due to various parameters of buildings and excitation. It is challenging to determine a universal law of collision reactions between adjacent buildings in a row. To address the complexity of these parameters, the dimensional analysis method is used. This work establishes a mathematical model for the dimensionless collision response of adjacent structures in a row. The layout of the structures is considered through three different configurations, and the effects of unilateral and bilateral collisions are compared. The analysis also considers the impacts of the frequency ratio, mass ratio and gap size of the oscillators. According to the impact of pounding, the displacement and velocity responses of the outer structures with low mass and stiffness can be divided into multiple spectral regions based on the frequency ratio of the structure and excitation. The effects of the mass ratio and frequency ratio on the responses of the outer flexible structures are correlated with the spectral regions. The results indicate that placing a structure with a small mass and stiffness outside is dangerous, since it causes a much larger pounding force and displacement of the outer structure. Compared with the unilateral impact response, the bilateral impact response induces a smaller displacement of the middle structure with a slight mass and stiffness.