Earthquake Engineering & Structural Dynamics最新文献

Seismic design tools are based on surrogate models of the designed structure and the responses of those surrogates to earthquake ground motions. To design symmetric flexible rocking structures, a surrogate model that includes rocking and flexure is needed. In this paper, we derive the equation of motion of a flexible multi-degree-of-freedom (MDOF) structure rocking on its base in modal coordinates. Then, we introduce a set of two-degree-of-freedom (2DOF) surrogate models that accounts only for the first elastic vibration mode of the multimass structure and its rotation about the base pivot points. We investigate the surrogates' ability to represent the dynamics of an elastic MDOF structure that uplifts and rocks and the interaction between rocking and flexure. Therein, we detail the simplifications for the equations of motion of the 2DOF surrogate models and the adopted rocking impact model, and develop and check the sliding initiation condition. We show that the simplified 2DOF surrogate model responses compare well to experimental results. Then we assess the 2DOF surrogate model accuracy in representing the earthquake response of the MDOF model using Cloud Analysis and the coefficient of determination $�R^2$ approach. We find that simplified 2DOF surrogate of the MDOF model is quite accurate ($��R^2��=��0.99�$) in estimating its maximum relative top displacement and acceptably accurate ($��R^2��=��0.90�$) in estimating its maximum base rotation based on a thousand randomly generated flexible rocking structure earthquake response analyses. Lastly, we discuss using the simplified 2DOF surrogate model of symmetric flexible rocking structures in preliminary seismic design, and give examples featuring a continuous elastic hollow semi-conical chimney and an inelastic flexible MDOF structure, both with a base that may uplift.

To overcome the deficiencies of large particle radius, strict vibration conditions, and low kinetic energy exchange rate of traditional particle dampers, it is proposed to organically combine the rack and pinion inerter device with a stacked single particle damper (SSPD) to form a novel stacked single particle-inerter damping system (SSPIS). Based on a detailed analysis of the force state of particles at various stages, the vibration damping mechanism of SSPIS is analyzed, and a mechanical model of a single-degree-of-freedom (SDOF) structure equipped with an SSPIS is established. The numerical simulation and analysis process of SSPIS is provided, and a parametric design method of inerter device based on the structural performance requirements is proposed. The accuracy of the theoretical mechanical model and numerical simulation analysis process of SSPIS is verified through shaking table tests of a single-story steel frame, and the actual damping control effect of SSPIS on the controlled structure is investigated. Both test and theoretical results show that the numerical simulation analysis process of SSPIS is clear and accurate, and the mechanical model of the SSPIS-SDOF structural system is highly accurate. The inerter device in SSPIS can significantly improve the momentum exchange efficiency between particles and structures, and SSPIS could adaptively adjust the particle radius size on demand compared with the traditional particle dampers, with a high damping frequency band, and can realize good damping control effect under the earthquake with various types of sites, which has expansive engineering application scenarios.

This study proposes a novel velocity divergence-generalized adaptive probability density evolution method (VD-GAPDEM) for calculating the probability density function of the stochastic response process of stochastic structures under stochastic dynamic loads. First, based on the principle of probability conservation, the velocity divergence-generalized adaptive probability density evolution equation (VD-GAPDEE) is derived for a stochastic system that can effectively consider the shape and location changes of the joint transitional probability density of representative points (RPs) in the stochastic response process. Second, a novel VD-GAPDEM is proposed to solve the VD-GAPDEE directly using the point selection technique based on the generalized F discrepancy and the second-order Runge–Kutta method with a smoothing kernel method (Runge–Kutta-SKFAM). Furthermore, the differences and connections between VD-GAPDEM and the existing probability density evolution method are analyzed. Additionally, the high computational efficiency and accuracy of the proposed VD-GAPDEM are demonstrated through three typical examples of stochastic response analysis, involving stochastic systems subjected to stochastic dynamic loads.

This paper introduces a novel pocket-type dissipative rocking connection for self-centering tubular steel bridge piers. Unlike typical self-centering systems, this connection does not utilize post-tensioned tendons and relies solely on gravity load for re-centering, but it employs a redundant mechanism to prevent geometrical instability and collapse. The connection consists of several components, including an embedded sleeve component and a ring plate bearing against the column and frictionally connected to the embedded component. During rocking, the ring plate provides two-level energy dissipation through friction and material yielding. In this connection, any residual drift could be easily recovered by untightening bolts in the frictional connection of the ring plate. A finite element model with contact elements at surface interfaces between different components was developed to simulate the response of the connection under vertical and lateral loading. Finite element analyses and quasi-static cyclic tests of a quarter-scale specimen demonstrated that the connection could provide adequate lateral resistance and a flag-shaped hysteresis response with marginal or recoverable residual displacements. Test results confirmed that the connection can sustain large lateral drifts (up to 7.6%) without structural damage. Test results also indicated that the hysteresis characteristics of the connection are highly influenced by the type and configuration of the washers in the bolt assembly of the frictional connection. The lateral strength and energy dissipation properties of the connection were greatly improved when conical spring washers were added to the bolt assembly.

Lateral spreading has historically caused extensive pile failure in liquefaction-prone areas during strong earthquakes. A critical design scenario involves piles embedded in lateral spreading ground composed of a nonliquefied soil crust overlying a liquefied layer; it is critical because both layers can exert loads on the piles. Different thicknesses of the liquefied soil and the upper nonliquefied crust may engender different pile response patterns. Accordingly, to investigate factors influencing the lateral responses of a single pile embedded in liquefied ground with a nonliquefied crust, we conduct parametric analyses. The effects of liquefied and nonliquefied soil thicknesses are analyzed first, followed by those of pile-head rotational restraint, pile diameter, and lateral spreading displacement. We observe two main pile response patterns for various liquefied soil thicknesses. The ground can be categorized into thin or thick liquefied ground depending on whether its liquefied soil thickness is less or greater than a critical value, namely, critical liquefied soil thickness; this critical thickness is dependent on the pile-head rotational restraint, pile diameter, and lateral spreading displacement. The difference in the patterns stems from the varying roles of the upper nonliquefied soil layer during lateral spreading. For the thin liquefied ground, the nonliquefied layer contributes to adding lateral spreading force; therefore, the displacement, moment, and shear force responses of the pile increase with the nonliquefied soil thickness. However, for the thick liquefied ground, the nonliquefied layer provides resistance to lateral spreading; therefore, the maximum displacement, moment, and shear force of the pile initially decreases and then gradually increases with the nonliquefied soil thickness.

Fast and accurate identification of structural modal parameters after an earthquake is crucial for assessing structural conditions and facilitating repair. With the development of modern earthquake observation techniques, the recorded ground motion can be leveraged as extra input information for modal identification, enabling the experimental modal analysis applicable. This study develops a Bayesian modal identification algorithm that aims at estimating the most probable value (MPV) of modal parameters and their identification uncertainty. Incorporating the recorded seismic input, the algorithm utilizes with the structural equation of motion in the frequency domain to formulate the likelihood function and adopts a constrained Laplace method for Bayesian posterior approximation of modal parameters. With the aid of complex matrix calculus, an iterative scheme is developed, allowing a fast search of the MPV of modal parameters and an analytical evaluation of the posterior covariance matrix. The performance of the proposed algorithm is validated by examples with synthetic, laboratory and field data, respectively. In addition, its effectiveness on predicting structural responses under a future earthquake is illustrated, showing its potential for various downstream applications in seismic structural health monitoring.

This paper investigates a steel moment resisting frame (MRF) with a novel type of self-centering (SC) base isolators, wherein superelastic shape memory alloy (SMA) U-shaped dampers (SMAUDs) work as core components. A two-story steel MRF model equipped with two SMAUD-based isolators was designed and built in the laboratory, and a series of shake table tests were conducted to examine the dynamic behavior and seismic performance of the frame. Throughout all the tests, no interventions, such as repair or replacement of frame or isolator members, were done. Shake table test results demonstrated that the SMAUD-based isolators could withstand multiple strong earthquakes with stable SC behavior. The utilization of SMAUD-based isolators provided effective protection for the frame, enabling it to restore its original position with minimal structural damage. A numerical model of the tested steel MRF with SMAUD-based isolators was also built. The results obtained from the numerical analyses agreed with those of the shake table tests satisfactorily. A comparative study of the seismic performance between the MRF with SMAUD-based isolators and the MRF with traditional steel U-shaped damper-based isolators was also conducted in the shake table tests. The results showed that SMAUD-based isolators not only inherit the isolation function of conventional isolators to protect the frame but also possess an SC ability to eliminate residual isolator deformation effectively. Moreover, SMAUD-based isolators demonstrate remarkable resilience to withstand multiple strong seismic events without any need for repair or replacement.

Current seismic design codes for bridge structures do not account for the influence of aftershock sequences, which, to some extent, overestimate the seismic performance for bridges subjected to mainshock-aftershock (MS-AS) scenarios. To address the great need for ground motion sequences tailored to specific research sites for fragility analysis, this study proposes a method for generating artificial MS-AS ground motion sequences based on the evolutional bimodal Kanai–Tajimi model and the Epidemic–Type Aftershock Sequence model. We establish a framework for MS-AS fragility analysis using an input–output Hidden Markov Model (IOHMM), where the damage states (DS) of bridge piers are considered unobservable and are inferred statistically through damage indices in an unsupervised manner. Model parameters are trained using intensity measure (IM) sequences and damage index (DI) sequences. Fragility curves for both the mainshock and state-dependent aftershocks considering multiple aftershocks are formulated based on the initial state probability and state transition probabilities of the proposed IOHMM. The fragility analysis results reveal that as the initial seismic damage level increases, the probability of aftershocks causing higher damage levels in the structure also increases, highlighting the significant impact of aftershocks on structural damage increments. Furthermore, we extend the proposed model to a bivariate seismic intensity measure and develop fragility surfaces. The proposed framework provides a novel approach and insights for tackling seismic fragility under multiple aftershocks.

This paper presents the shake table testing and finite element (FE) modeling of a modular prefabricated concrete bridge-like specimen. The specimen comprised four equal-height cylindrical reinforced concrete (RC) columns capped with an RC slab. The structural connections were non-monolithic. Hence, controlled relative motion of the members, including rocking (uplift) of the piers, was allowed. The columns were connected to the slab with stiff tendons that provided positive post-uplift stiffness. The specimen was subjected to 184 triaxial shake table tests, so that a statistical validation of numerical models can be performed. Subsequently, a detailed three-dimensional FE model of the bridge was developed. The objectives of the present study were to: i) investigate the shake table response of a modular bridge with positive post-uplift stiffness under multiple ground motions, ii) develop an FE model of the proposed structural system, iii) investigate the influence of geometrical imperfections on rocking bridges, and iv) evaluate the efficiency of using additional dissipative rebars. After being subjected to 184 shake table tests, the specimen showed zero damage, moderate displacements and tendon forces (TFs), low slab torsion, and zero residual displacements. The shake table tests were practically repeatable. The proposed FE model accurately captured the experimental results. Geometrical imperfections heavily affect the response of negative stiffness systems. However, they have a marginal influence on positive stiffness systems. When comparing systems with equivalent uplift resistance and post-uplift stiffness, the use of additional dissipative rebars results in lower slab torsion and TFs, provided that the rebars do not fracture.

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.