Earthquake Engineering & Structural Dynamics最新文献

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.

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.

Structural response prediction under earthquakes is crucial for evaluating the structural performance and subsequent functional restoration. Deep learning provides the potential to rapidly obtain the responses by skipping the time-consuming nonlinear finite element analysis. However, a single deep learning network may only predict the time history responses of one specific structure, resulting in redundancy and resource waste when building multiple networks for modeling different structures. Thus, this study proposes a Structure Temporal Fusion Network (STFN) that can predict responses of various homogeneous structures using a single network. The key concept is that the seismic waves and the structural characteristics, such as story numbers, are fused together to predict diverse time history responses. Two numeric experiments are conducted, including predicting responses of ideal single-degree-of-freedom (SDOF) structures and regular multistory reinforced concrete frames. Furthermore, a series of ablation analyses are carried out to validate the network architecture. The results indicate that STFN can predict nonlinear time history responses of different structures with mean square errors in the magnitude of $�{10}^{�-�4�}$ and $�{10}^{�-�5�}$ for two experiments, respectively. The solutions also highlight the importance of fusing static characteristics for the modeling of various structures with only one network. The STFN presents a promising solution for time history response prediction across multiple structures in regions.

The recently upgraded six Degree-of-Freedom Shaking Table, LHPOST6, at UC San Diego, underwent a series of forced vibration tests to evaluate the post-upgrade dynamic response of the foundation-soil system. The resulting data were instrumental in obtaining frequency response curves of the system, which were used to determine its low-strain natural frequencies, effective viscous damping ratios, and reaction mass displacements. The extensive experimental data motivated the creation of a detailed Soil-Structure-Interaction model of the reaction mass-soil system. The structure and soil were modeled using 3D Finite Elements in STKO-OpenSees and calibrated with the acquired data via a parametric study. The 3D continuum FE model and the calibration procedure based on a single soil parameter (shear wave velocity profile) proved to be an effective tool to reproduce the experimental results accurately. This paper describes the Finite Element model, its calibration, and validation. In addition, the paper provides suggestions to simplify continuum models and promote their use in professional practice. The objectives of this campaign, alongside the growing accessibility of high-performance computing, may serve as a step toward using SSI continuum models in the industry.

A rigid block model with elasto-plastic softening interfaces is developed for nonlinear static analysis of masonry structures subject to monotonic loading. Cracking, crushing, and shear failures are taken into account at interfaces, following a simple micro-modeling approach. An optimization-based formulation is used for the solution of the equation systems governing the behavior of the rigid block assemblage. A simple incremental solution procedure is implemented to take into account the material softening behavior and the effects of large displacements on equilibrium conditions. The interface models are validated against tension and shear tests on bi-block prisms from the literature. Applications to numerical and experimental out-of-plane loaded masonry walls as well as to circular arches with mortar joints are presented to evaluate the effects of tensile strength and the accuracy of the developed model against responses involving P-Δ effects. Comparisons with experimental tests on shear walls also involving cracking of the units in the failure mechanisms are finally reported to discuss the potentialities and limitations of the proposed modeling approach.

The ultra-high toughness cementitious composite (UHTCC) has the tensile strain-hardening characteristic and an excellent ability to prevent tensile cracking. To enhance the seismic and durability performance of the conventional buckling-restrained steel plate shear wall (BRSPSW), UHTCC-enhanced BRSPSW (UBRSPSW) was proposed in this paper as a new type of lateral bearing system. The buckling of the inner steel plate is restrained by UHTCC-normal concrete (NC) functionally graded panels, where the panels are composed of UHTCC and NC layers. In this study, experimental and numerical research was carried out on the UBRSPSWs. Six specimens were tested to investigate the seismic behavior of the UBRSPSW. Parameters including the number of stiffeners, the thickness of UHTCC-NC functionally graded panels, the material of restraining panels, and the gap between the inner steel plate and restraining panels were considered in the test design. Mechanical response and failure modes of the structures under cyclic loads were analyzed. The obtained hysteretic curves and corresponding skeleton curves indicated that the proposed design had excellent seismic performance. Compared to the steel plate shear wall (SPSW), the load-bearing capacity of UBRSPSW was improved by 13%, respectively. The appearance of macrocracks was delayed by a drift angle of 1.2%. In addition, a refined finite element (FE) model was developed and validated by the results obtained from experiments. The development and distribution of bending moments in the restraining panels were extracted based on the FE method. Then, the loading capacity design method of restraining panels and a theoretical model for controlling the crack width of restraining panels were proposed. The research results of this paper can provide useful suggestions for the seismic design of UBRSPSWs.

To predict the seismic response of column-supported silos (CSSs), the granular–structure interaction (GSI) analysis method is proposed with considering the combined effect of the friction between the particles–particles and the particles–silo wall. Using free-body dynamic equilibrium equations, we reconstruct the mutual interactions between different grain portions and between the grains and the silo wall to develop the ideal calculation model of the CSS structure. Based on the analysis model, additional dynamic overpressure and the effective mass caused by the stored content interacting with the silo wall is obtained with different slenderness ratios and peak accelerations. The additional bending moment caused by the friction between the particles and silo wall is further quantified. To verify the reliability of the proposed method, we discuss some applicative examples by comparing the GSI method with other theories, Eurocode 8, and experimental results. Moreover, the along-the-height acceleration profiles of the silo wall and the ensiled content are analyzed according to the shaking-table tests. The results show that the GSI method can match Janssen's theory well in the case of static pressure at slenderness ratios exceeding 1.0. The overpressure profiles along the height of the silo wall follow a nonlinear distribution, different from Eurocode 8. The bending moment obtained by predictive formulas agrees well with the experimental results for the CSS, indicating that the GSI method is reasonable. Some design and construction recommendations, including the maximum overpressure position, the reference range of the dynamic overpressure coefficient, and the reduction factors of the ensiled content mass, are proposed to facilitate the engineering applications of CSSs, considering different slenderness ratios.

Nonstructural damage, usually predominates in buildings subjected to low to moderate seismic intensities and contributes significantly to business interruption and economic losses. It promotes a rapidly growing need for experimental research and qualification of various types of nonstructural elements in buildings in the recent decades. To provide a novel option of experimentally simulating the realistic boundary conditions for various nonstructural elements in labs, we developed the Nonstructural Element Simulator on Shake Table (NEST), a passively controlled three-layer substructural testbed driven by existing shake tables. This paper presents the first experimental implementation of NEST on a challenging 42-story archetype tall building. The dynamic properties of the substructure were tuned to adapt the archetype building and the required shake table motions were solved as a reverse problem by an open-loop control algorithm. The test results proved the capability of NEST to replicate the history responses of the target floors in the archetype building under either recorded earthquake ground motion or artificial loading protocols for qualification purposes. In all cases, the synthetic relative error in the floor accelerations and the inter-story drift within the frequency range of interest was less than 5% in the numerical domain and less than 30% in the physical realization. The seismic responses of a variety of nonstructural elements to the substructural motions show that, in the mid-story of the archetype tall building, the ceiling sustained minimum damage because of the small floor acceleration while the indoor contents slid significantly and even overturned.