Earthquake Engineering & Structural Dynamics最新文献

Hospital functionality relies not only on the building's structural robustness but also on the seismic performance of its Nonstructural elements, Systems, and Contents (NSC). The objective of this study is to characterize the earthquake-induced damage to the medical equipment deployed in the full-scale, five-story concrete building tested at the University of California, San Diego (UCSD) in 2012 when subjected to Design (DE) and Maximum Considered Earthquake (MCE) levels of demand with Fixed-to-the-Base (FB) support condition. The experimental equipment displacement responses are extracted using the Camera Projection Technique (CPT). Then, sophisticated rolling and sliding models, including instantaneous motion tracking and impact detection are developed to reproduce the equipment behavior obtained from CPT. It was found that CPT was capable of extracting the observed responses and identifying impacts despite the severity of the shaking as long as no significant uplift of the equipment occurred. In addition, both numerical models were capable of reproducing the equipment's displacement trajectories, rotations about the vertical axis (yaw), and impacts as long as no interlocking of the equipment's parts occurred. Moreover, a case study of a partially equipped Emergency Room (ER) was set up to demonstrate that even for low-intensity motions, the damage to equipment may be significant. Finally, the impact acceleration ($�{\vec{a}}_{�i�m�p�}$) is proposed as a proxy indicator of damage to medical equipment; however, more functionality tests accompanied by detailed pre- and post-inspections are needed to define robust damage limit states and performance objectives for medical equipment.

Vibration isolation metamaterial barrier has been extensively studied in mitigating the damage induced by vibration, while a deeper understanding of the vibration isolation characteristics based on laboratory experiments is still lacking. In this work, a locally resonant metamaterial barrier is proposed, and a large-scale laboratory experiment was first designed to investigate the isolation mechanism of the proposed metamaterial barrier. The metamaterial vibration isolation barrier is assembled by arraying 5 × 5 resonators. To better explain the observations in experiments and unveil the underlying isolation mechanism, COMSOL Multiphysics was also employed to simulate the laboratory experiment. Subsequently, the vibration isolation effect is quantitatively analyzed by analyzing the acceleration amplitude reduction spectrum (ARS) of the ground surface. The vibration isolation mechanism is discussed by monitoring the acceleration field around the metamaterial barrier. The results indicate that two significant locally resonant attenuation domains are observed, which are induced by the first-order and second-order vertical resonance frequencies of the metamaterial. Another experimental scheme that simultaneously monitored the acceleration of the mass block and the bottom of resonators was implemented to investigate vibration in the resonator. The vibration energy distribution on the mass block and the bottom of the resonator is found to depend significantly on the vibration frequency. When the frequency is lower than a certain frequency, the locally resonant is dominant. Otherwise, the geometric scattering is dominant. The vibration isolation mechanism of the locally resonance metamaterial was investigated by laboratory experiments and provided an effective solving path for isolating the low-frequency vibration.

Identification of damaged structures after natural disasters, such as earthquakes, is crucial for ensuring public safety and facilitating timely repairs. Recently, machine learning-based models have shown promise in this direction. Traditional machine-learning approaches require a significant amount of labeled data for training. However, obtaining labeled data for damage identification can be challenging because it is time-consuming and expensive. To resolve this issue, this study proposes a generalized zero-shot learning (GZSL) methodology to identify the degree of structural damage in images. The proposed methodology was used for assessing the failure mode of reinforced concrete shear walls involving pixel images on a scale of 0–1. The GZSL model with ResNet18 as its backbone demonstrated good performance, achieving 100% and 86.7% accuracies on training and test sets, respectively. This methodology was also utilized for assessing building damage using wavelet images with a broader color spectrum; the ResNet50-based GZSL model demonstrated excellent performance, achieving an accuracy of 68%, even with a smaller number of samples that included both seen and unseen classes.

Many methods for seismic risk assessment rely on the selection of a seismic intensity measure (IM) and the development of models of the seismic demand conditional on the IM. The individual importance of these two features to accurately assess seismic performance is well known. In contrast, this study aims to evaluate the impact that the combined selection of IM and the demand model has on risk estimates. Using a hypothetical seismic source model and a non-stationary stochastic ground-motion model, we present risk estimates for a mid-rise steel structure for 15 different IMs and five demand models derived by cloud analysis (four based on regression and a fifth based on an empirical binning approach). The impact of these choices is investigated through a novel method of model performance evaluation using a benchmark solution obtained via the unconditional approach (i.e., directly estimating demand exceedance frequencies from simulated ground motion time histories). The obtained results are also compared against traditional IM performance metrics, for example, efficiency and sufficiency. Finally, we demonstrate how risk estimate inaccuracies are propagated by performing a damage assessment on two example components. The results show that, for the scenario under investigation, Arias intensity combined with the binned demand model provides the best risk estimates, if sufficient samples are available, whilst ground displacement and duration-based IMs ranked worst, irrespective of the demand model. The findings highlight the importance and interconnectedness of the selection of the IM and the demand model when using cloud analysis and present a clear method of determining the most accurate combination for risk assessments.

Early earthquake design codes used peak ground accelerations (PGAs) as intensity measures (IMs) to characterize the demands of ground motions on structures, but have since shifted towards using spectral accelerations because they provide a better indication of demand. The design of acceleration-sensitive nonstructural components has followed a similar approach, with modern codes being based on an estimate of the spectral acceleration at the period of the nonstructural component. However, most fragility curves for loss assessment of acceleration-sensitive nonstructural components, including the existing FEMA P58 library, continue to be based on peak floor accelerations (PFAs). Similar to PGAs as an IM for buildings, a limitation of PFA as an engineering demand parameter (EDP) for nonstructural components is its lack of dependence on the period of those components. In this study, fifteen alternative EDPs suggested in the literature are evaluated as potential candidates for developing seismic damage fragility curves. Acceleration-sensitive nonstructural components are simulated by single-degree-of-freedom (SDOF) components with elastic perfectly plastic behavior, with a period range of 0.01 to 1 s, and varying strength levels. Nonlinear response history analyses are conducted for the SDOFs, using floor motions obtained from both the first floor and the roof of buildings designed with four distinct seismic force-resisting systems. Ductility demands for each SDOF are taken as an indicator of damage and are predicted using a linear regression model developed for each specific EDP. The suitability of candidate EDPs is evaluated based on their efficiency and relative sufficiency. Furthermore, a comparison is made between the expected annual loss calculated using fragility curves derived from the selected EDPs to quantify how the EDP used for a fragility curve can affect the seismic loss assessment. The results reveal that the PFA is a suitable EDP only for nonstructural components with very short periods (i.e., less than 0.1 s). Moreover, although the spectral acceleration at the period of the SDOF nonstructural component is a suitable EDP for components that are nearly elastic and are located on the roof of buildings, the peaks that develop in the floor spectra can grossly overstate the demands on nonstructural components that experience significant nonlinearity in their response. In such situations, an average of the spectral accelerations in a range of periods near the period of the SDOF nonstructural component is more appropriate.

Inerters (ID) and Clutched Inerter Devices (CID) are a novel technology with demonstrated seismic control potential. However, the inherent nonlinearity and discontinuity of the clutching phenomena in CIDs can pose significant challenges for their accurate numerical modeling. In general, conventional existing methods either oversimplify the physics involved or are sensitive to the step size and thus are inherently unstable, demanding excessive numerical resources. Most relevant studies to date have focused on small-scale systems with a limited number of inerters and have used simplified models due to the lack of analysis tools. At the same time, the Mixed Lagrangian Formulation (MLF), has proven to be a powerful tool for simulating non-smooth dynamics phenomena. This paper presents an alternative way of modeling the behavior of CIDs in both MLF and conventional finite element method. We put forward an original formulation of the inerter element, clutching behavior, and the inerter-related dissipation model, as well as their associated computational scheme in MLF and the equivalent construction in FEM. The newly proposed CID element in MLF is then implemented and validated through three examples, including a single degree of freedom system, a multi 10-storey moment resisting frame (MRF), and a 10-storey self-centering concentrically braced frame (SC-CBF) with multiple rocking sections. The results are compared to those from existing models used for clutching inerter and to the proposed FE model. Finally, the advantages of using the MLF framework and salient characteristics of the structures equipped with clutched inerters are discussed. The modeling strategy proposed in this work empowers researchers to simulate structures with a larger number of degrees of freedom, equipped with a considerable amount of inerter-based devices, with reduced effort and improved computational performance.

During strong earthquakes, the footing of a rockable bridge can temporarily and partially separate from the support. This rocking motion can activate rigid-like motions, reducing the deformation along the height of bridge piers and leading to smaller bending moments. As a result, rockable footing has been considered as a possibility for low-damage seismic design of structures. For bridges, the seismic-induced interaction between girders and adjacent abutments can change the structural dynamics due to the impeded girder movements. Although bridges with rockable footing, for example, the South Rangitikei viaduct, have been constructed, research on rockable bridges mainly focused on a single-segment case. Physical experiments on rockable bridges considering pounding are very limited. In this work, large-scale shake table experiments were performed on a two-segment bridge model with abutments. The cases without pounding and with girder-girder pounding alone were considered as references to help interpret the results. To investigate the consequence of footing rocking, the results of the rockable bridge on a rigid base were compared to that of the fixed-base bridge. The study reveals that compared to a fixed-base segment, the girder of a rockable segment is easier to move laterally. This change in dynamics due to rocking leads to less maximum pounding forces and thus reduces the damage potential to girders and abutments.

Seismic vehicle-bridge interaction (SVBI) is the study of vehicle-bridge interaction (VBI) in the presence of earthquake excitation. SVBI is an interdisciplinary problem of increasing importance to the design and safety of railways. This study deploys a consistent methodology to decouple the vehicle-bridge system and solve independently the bridge and vehicle subsystems, bypassing multiple challenges the seismic response analysis of a coupled vehicle-bridge system entails. The proposed approach builds upon the previously established Extended Modified Bridge System (EMBS) method for decoupling vehicle-bridge systems (in the absence of earthquake excitation). Its premise is to first characterize and then assess the relative importance of the VBI effect on the bridge and vehicle responses and replicate it by modifying the pertinent uncoupled equations of motion (EOMs). The formulation deployed accommodates multi-degree of freedom models for both the vehicle and bridge and can thus tackle complex systems. The analysis examines the ability of the proposed decoupling approach to predict the response of a realistic system vehicle-bridge system under a suit of historical earthquake records. The decoupled results are in excellent agreement with the coupled solutions for all earthquake records and scenarios (i.e., earthquake excitation solely in the transverse direction of the bridge, as well as in both the transverse and vertical directions simultaneously).

This paper presents a new uniaxial constitutive material formulation with softening for simulating the inelastic behavior of steel rectangular tubes in concrete-filled steel tube (CFST) members. The primary behavioral characteristics of the steel tube in CFST members are isolated and pronounced through a carefully designed experimental campaign with CFST specimens subjected to uniaxial strain-based loading protocols. The model is expressed in an effective stress–strain domain, where the effective uniaxial strain is defined as the uniaxial displacement within a dissipative zone over a predefined length. In the pre-peak state, the proposed model can effectively capture the combined kinematic/isotropic hardening and Bauschinger effect—characteristic of mild structural steels—within the framework of rate-independent plasticity. In the post-peak state, the proposed model traces strength deterioration due to outward local buckling, which is a characteristic nonlinear geometric instability in CFST members due to the presence of the filled concrete in the steel tube. The proposed constitutive formulation incorporates a softening branch that exponentially decays to trace the stabilization of the outward buckling wave within the buckling region in successive inelastic loading cycles. Cyclic deterioration of the effective stress is explicitly considered via an energy-based rule. The proposed model is calibrated to a CFST dataset. Regression equations are proposed for predicting the input model parameters. These equations cover a wide range of geometric parameters and structural steel materials in CFST members. Comparisons with prior tests on actual CFST beam-columns under planar symmetric cyclic loading suggest that conventional 2-dimensional displacement-based beam-column elements can predict the full-range of the hysteretic behavior of the CFST members with the proposed constitutive formulation including cases where the post-peak response of CFST members exhibits negative stiffness.