Earthquake Engineering & Structural Dynamics最新文献

This paper proposes a hybrid data-driven and physics-based simulation technique for seismic response evaluation of steel Buckling-Restrained Braced Frames (BRBFs) considering brace fracture. Buckling-Restrained Brace (BRB) fracture is represented by cumulative plastic deformation capacity. A dataset, consisting of 95 past BRB laboratory tests and 120 simulated BRB responses generated using the finite element method, is first developed. An Artificial Neural Network-based (ANN) predictive model is then trained using the training dataset to estimate the cumulative plastic deformation of BRBs. The prediction capability of the ANN-based predictive model is validated using the training dataset and an existing regression-based predictive model. In the second part of the paper, an hybrid simulation technique combining the data-driven model and physics-based numerical modeling is presented to conduct the nonlinear time history analysis, followed by 1) validation against a full-scale BRBF testing and 2) demonstration of the proposed simulation technique using a six-story BRBF. The results confirm that the proposed predictive model can predict the BRB fracture with sufficient accuracy. Furthermore, the hybrid data-driven physics-based simulation technique can be used as a powerful tool for dynamic analysis of BRBFs considering BRB fracture.

Calibrating parametric fragility curves via empirical damage data is one of the standard approaches to derive seismic structural vulnerability models. Fragilities based on empirical data require the characterization of the ground motion (GM) intensity at the building sites in the area affected by the earthquake producing the observed damages. This is commonly conducted via ShakeMap, that is, a map of the expected values of a Gaussian random field (GRF) of the logarithms of a GM intensity measure conditional to magnitude, location, and possibly a set of recordings of the earthquake. Once that intensity and damage data at the same sites are available, the typical approach calibrates a two-parameter fragility model. However, ShakeMap estimates are affected by uncertainty deriving from that of the GM model used to characterize it. Furthermore, such an uncertainty can be reduced by building damage data, which provide information on the shaking intensity at the sites where damage is observed. It is shown herein that if this uncertainty is not addressed, also considering the shaking information provided by damage, the estimates of the fragility parameters obtained using a median ShakeMap only can be biased, and a recommended maximum likelihood estimation procedure – which exploits the expectation maximization algorithm – is provided. These arguments are illustrated via an application considering damage data from the 2009 L'Aquila earthquake in central Italy.

This study presents the Flexible Rocking Model on Concentrated Springs (FRMCS), developed to investigate 2D laterally flexible oscillators rocking and sliding on deformable support media during ground excitations. In this model, concentrated vertical springs and viscous dampers simulate the contact forces from support medium at the corners of the body; the tensionless vertical contact element is linear in compression. Horizontal concentrated springs and linear viscous dampers simulate the frictional behaviour at the corners; the constitutive law for the springs models elastic deformations and sliding (according to Coulomb's friction law). With these elements, FRMCS can model the response of a rocking body which can experience sliding and free-flight phases of motion. The consideration of the flexibility of the support medium enables the evaluation of the forces exerted by the support medium on the structure during an impact. In this study, the FRMCS response is first compared to a previous model where the support medium deformability and the effects of sliding and free-flight are ignored. Then, the responses of four configurations, which feature either stiff or soft lateral springs and stiff or soft high-grip support media, are examined under the influence of pulse excitations. Finally, to understand the potential influence of sliding, a configuration with a low-grip support medium is explored. The comparative influence of lateral flexibility and support medium deformability and sliding is quantified with stability diagrams and various response spectra, describing structural force and moment demands.

Most traditional passive friction dampers are limited to the design of single activated energy dissipation mechanism; therefore, when the seismic intensity is not strong enough to activate the mechanism, traditional friction dampers can only increase stiffness of the structure just like braces; only when the mechanism is activated will the energy dissipation elements perform energy absorption and assist the structure to absorb received seismic energy. The objective of this study is to improve this defect of traditional friction dampers, developing a Multi–Level Friction Damper (MFD) with a two-stage energy dissipation mechanism, helping building structures (e.g., hospitals, high-tech plants) reduce the acceleration responses of the superstructure. MFDs are proven to provide more comprehensive protection and have higher energy dissipation benefits than traditional friction dampers by the validation of numerical analysis and shaking table test. The study in turn performed parameter fitting with the results of the numerical simulation analysis and shaking table test, and the experimental results turned out to be satisfactory, validating the accuracy of the theoretical formulas.

To passively achieve an inertial device with unidirectional force transmission similar to Bang Bang control, this study introduces a novel energy dissipation device known as the resettable-inertia damper (RID). The ingenious motion principles of the RID, encompassing a rack-and-pinion, bevel gear commutation system, speed transmission, and eddy current damping, are elucidated in detail. In particular, a unidirectional rotational flywheel within the device selectively engages when the primary structure reciprocates. The physical mass of the flywheel undergoes conversion into an amplified inertia through the rack-and-pinion mechanism, which enables the enhancement of damping effects coupling the flywheel rotation and eddy current configuration. A coupled multibody dynamic model, combining the clutching effect, the flywheel inertia, and the rotational damping, is formulated to analyze the system with RID (RIDS). Currently, an analysis of the hysteretic behaviors of RID is carried out. To facilitate the design and evaluation of the performance of RIDS, an equivalent linearization method is proposed for RIDS. The feasibility of this simplified method is validated under harmonic excitation. Additionally, the study examines the performance of equivalent linear systems (ELSs) and RIDS under natural ground motions and stochastic stationary excitation in peak and variance responses levels, respectively. Comparison of RID with traditional inerter shows that RID can achieve a more pronounced control with less force transferred to the structure and with the potential to recover vibration energy, highlighting its unique advantages.

This paper presents a methodology to minimally modify a ground motion time history to induce collapse in nonlinear single-degree-of-freedom systems (SDOF). The metric used to characterize the modification is the Arias intensity. The proposed procedure is a heuristic extension of a closed-form solution derived to achieve a target maximum response in linear systems. The methodology is presented as a potential alternative to incremental dynamic analysis (IDA) widely used in earthquake engineering.

Unbonded fiber-reinforced elastomeric isolators (FREIs) are a cost-effective seismic isolation technology that uses lightweight fiber-fabric reinforcement and forgoes the attachment plates connecting the isolators to the supports. These devices exhibit a complex nonlinear mechanical behavior under lateral deformation, which has typically been represented by uniaxial phenomenological models. In this paper, a new model, called Pivot Bouc–Wen model, is proposed to address the shortcomings of existing numerical models and obtain a better prediction of the response over the whole range of motion. The model has been formulated with the objective of providing (a) improved interpretability of the model parameters, (b) adequate energy dissipation prediction at multiple deformation levels, and (c) stable response at large deformations. The model combines a nonlinear elastic spring and a Bouc–Wen element with a modified pivot hysteresis rule to capture the lateral response of the isolators at different deformation amplitudes. Initial values for the model parameters are recommended based on existing analytical formulations of the quasi-static lateral response of FREIs and data corresponding to 36 cyclic tests from 12 different experimental programs. The proposed and existing models are compared in their ability to predict the lateral cyclic test results from a previous experimental study. The models are further compared via response history analyses of idealized one, two, three and four-story base-isolated shear buildings subjected to 30 ground motions at different intensity levels. The results highlight the importance of capturing the hysteretic response of the isolators at multiple deformation levels and not only at the maximum expected displacement.

The derailment of a high-speed train is a complex and uncertain dynamic process, especially under running conditions where the derailment index lacks comprehensive experimental validation. This research focuses on elucidating the mechanism of an earthquake-induced train derailment and validating the structural response-based spectrum intensity derailment index. To achieve this, a multi-array shaking table system was utilized to test the safety of a running train and to physically replicate train derailment process under severe earthquake impact. We investigated the vibration characteristics and derailment progression of trains operating at different speeds, exposed to earthquakes of varying frequencies and intensities. In stationary derailments, significant wheelset lift was observed due to lateral rolling vibrations. However, in running test cases, there was no separation between the wheels and rails. Instead, the wheels underwent a long period of climbing and descending on the rails, similar to damped single-degree-of-freedom oscillations. As the wheel climbed the rail and reached a critical potential energy point, the wheel flange of the wheel could potentially fall due to gravity or come off the rail due to external disturbances. The critical potential energy could be represented by the spectrum intensity threshold, and the prediction results aligned well with the derailment test results for both stationary and running trains. Furthermore, the method of determining train derailment based on structural responses was consistent with the test results. The spectrum intensity index shows strong positive correlations with other wheel-force-related indicators, albeit adopting a conservative perspective, reinforcing its efficacy in assessing train safety.

This study investigates the idea of adding an extra magnetic restoring force to a rocking block to improve its overall dynamic performance. The proposed concept ensues by introducing a pair of identical magnets to the rocking block. Both magnets are considered lumped on their respective volume centers and are embedded within the rocking block and the supporting base. When properly magnetized, this pair of magnets provides the rocking block with an extra magnetic restoring force which, although it takes on its maximum value when the two magnets are in contact, decreases as the distance between the two magnets increases. The proposed concept, subjected to pulse-type base excitations, reveals the inherent problem of magnetic restoring forces. From the overturning spectra of the rocking block, it is found that there are cases where the block fails (overturning) in the presence of magnets, while the same free-of-magnets block rocks safely (no overturning) when its own weight acts as the only restoring force. This interesting finding appears to be counterintuitive. Is it possible that by providing additional restoring force the block is “driven” to overturn? This study shows that when the rocking block returns toward the vertical position, the angular velocity, in the presence of magnets, is higher than the angular velocity, in the absence of them. This increase in the angular velocity is a direct outcome of the nature of the magnetic restoring forces, and it is mainly the reason that causes the overturning of the rigid block during its free vibration regime. To mitigate the shortcomings of using magnetic restoring forces, the idea of a semi-active control of the pair of magnets is introduced and explained in detail. This paper concludes with the advantages and potential disadvantages of the overall performance of rigid blocks in the presence of magnetic restoring forces.

Laboratory tests on nominally identical reinforced concrete (RC) components have demonstrated the existence of failure mode variability and its significant impact on the strength and deformation capacity of RC components. In comparison with record-to-record and modeling uncertainties, the impact of failure mode uncertainty on the seismic fragility of RC structural systems has received less attention. This study presents a methodology for propagating failure mode variability in the probabilistic seismic assessment of RC structural systems. In the proposed methodology, strength hierarchy calculations are used to identify the structural system's susceptibility to failure mode variability. Subsequently, a number of segregate models corresponding to the number of failure mode combinations are developed. Nonlinear response history analyses of the segregates are used to quantify each segregate's seismic fragility and risk. Finally, the total probability theorem is used to derive the combined seismic fragility of the structure. The proposed methodology is demonstrated using an older-type (pre-1970s) four-story RC frame building archetype with ground floor columns susceptible to failure mode switch between flexure- and flexure-shear mechanisms. The results show that the seismic fragility and collapse risk of the RC buildings with failure mode variability significantly changes when failure mode variability is propagated. In the example, accounting for component-level failure mode variability can shift the median collapse fragility by more than 20%. Furthermore, the collapse risk (i.e., probability of collapse in 50 years) of the archetype changed by at least 30%. Similar changes may be observed in other types of structures with significant failure mode uncertainty, not limited to RC structures.