Earthquake Engineering & Structural Dynamics最新文献

Structures allowing their bases to uplift and rock during an earthquake event usually experience less damage; thus, they are more resilient to seismic hazards. Accurate simulation is critical to design and seismic performance evaluation of these flexible rocking structures. Motivated from this, this article presents a new rigid-flexible coupled rocking model for numerical evaluation of flexible rocking structures under both cyclic and dynamic loadings. The key idea in the model formulation is that the total motion of flexible rocking structure can be decomposed into a rigid-body motion and an associated flexible deformation. The flexible deformation of the rocking body is described using displacement field of classical Timoshenko beam. Using this approach and appropriate degrees-of-freedom (DOFs), the governing equations-of-motion for flexible rocking structures are formulated using the variational principle. Multiple springs with appropriate constitutive model are distributed along rocking base to represent the inelastic behavior of rocking body. Potential post-tensioned tendons are also considered in this model. In addition, nonlinear stress distribution along the rocking base, which cannot be considered in existing flexible rocking model, is also incorporated in the developed model. The proposed model is subsequently validated against published experimental data through quasi-static and shake table tests, showing good accuracy when the rocking structure is relatively stockier. Finally, a parametric investigation on the effect of flexibility, nonlinear stress distribution and yield stress of rocking body on the rocking response is performed. This preliminary investigation shows that influence of flexibility and yield stress is significant while impact of nonlinear stress distribution is minor.

Targeting the great demand for adding non-structural elevators to old residential buildings, this article proposes an updated configuration of tuned mass damper inerter (U-TMDI) applied in external non-structural elevators. An analog 2-DOF system is established to describe the residential building controlled by an inerter elevator. Then, three closed-form optimal solutions for designing the U-TMDI are derived via the fixed-point method, equal modal damping criterion, and the infinity damping assumption. Subsequently, these optimal solutions are compared and discussed involving the expressions of tuning frequency ratio and the optimal damping parameters, root locus diagram and supplemental damping ratios, transfer function, and robustness to frequency variation, respectively. Finally, a residential building example is adopted to validate the feasibility of the proposed retrofitting strategy and the closed-form optimal design solutions. It is demonstrated that the optimal tuning frequency ratios derived by the fixed-point method and equal modal damping criterion are different for U-TMDI due to the influence of elevator stiffness ratio $�\eta$, while its degradation forms for tuned mass damper (TMD) are identical, recognizing the importance of the elevator stiffness. Moreover, the proposed retrofitting strategy of using an inerter elevator can significantly mitigate the main structure displacement by about 18%∼23% for both far-field and near-fault earthquakes.

Under a strong earthquake, the axial force of shear walls in tall buildings may vary from compression to tension, but few studies have been conducted on this. Three low-aspect-ratio reinforced concrete (RC) wall specimens subjected to coupled variable axial tension-compression and lateral load were tested in this study, to investigate the effect of the fluctuating range of axial force and loading histories on the shear behavior of RC walls. The test results indicated that shear-compression failure occurred under the compressive-shear loading for all test wall specimens, and no obvious post-peak strength degradation in tension-shear loading. The hysteretic curves of test wall specimens were strongly affected by the loading histories; the shear strength and deformation capacity were mainly affected by the fluctuation of axial forces, especially for tension-shear strength. The equation of ACI 318-19 and JGJ 3-2010 conservatively predicted the shear strength of RC walls under the variable axial force, while the equation of ASCE/SEI 43-05 accurately predicted the shear strength with the mean values of the V^Test/V^ASCE of 0.97 and 0.94 for compression-shear and tension-shear strength, respectively. Comparison with an RC wall under constant axial tension revealed that the failure modes of RC walls were strongly dependent on the initial cracking patterns. Finally, a finite element (FE) model was developed, and parametric analyses were carried out to further estimate the effect of variable axial force on the cyclic shear behavior of RC walls.

Real-time hybrid simulation (RTHS) involves dividing a structural system into numerical and experimental substructures. The experimental substructure is challenging to model analytically and is therefore modeled physically in the laboratory. Analytical substructures are conventionally modeled using the finite element method. The two substructures are kinematically linked, and the governing equations of motion are solved in real-time. Thus, the state determination of the analytical substructure needs to occur within the timestep, which is of the order of a few milliseconds. All structural systems are supported by a soil-foundation system and any evaluation of the efficacy of response modification devices placed in the structure should consider soil-foundation structure interaction (SFSI) effects. SFSI adds compliance to a structural system, thereby altering the natural frequencies. Additionally, nonlinear behavior in the soil can result in residual deformations in the foundation and structure, as well as provide added damping. These effects can occur under both wind and earthquake loading. To overcome the barrier of the large computational effort required to model SFSI effects in real-time using the conventional finite element approach, a neural network (NN) model is combined with an explicit-based analytical substructure and experimental substructure with dampers to create a framework for performing RTHS with SFSI effects. The framework includes a block of long-short term memory (LSTM) layers that is combined with a parallel rectified linear unit (ReLU) to form a NN model of the soil-foundation system. RTHS of a tall 40-story steel building equipped with nonlinear viscous dampers and subjected to a windstorm are performed to illustrate the framework. It was found that a number of factors have an effect on the quality of RTHS results. These include: (i) the discretization of the wind loading into bins of basic wind speed; (ii) the extent of the NN model training as determined by the root mean square error (RMSE); (iii) noise in the restoring forces produced by the NN model and its interaction with the integration algorithm; and, (iv) the bounding of outliers of the NN model's output. Guidelines for extending the framework for the RTHS of structures subjected to seismic loading are provided.

This paper proposes a procedure to design low-rise base-isolated structures achieving a specific target level of earthquake-induced loss (e.g., dollars, downtime) while complying with a predefined minimum level of structural reliability. The procedure is “direct” since the target loss is specified at the first step of the process, and virtually no design iterations are required. Direct loss-based design (DLBD) is enabled by a simplified loss assessment module involving: (1) surrogate probabilistic seismic demand models representing the probability distribution of peak horizontal displacements and accelerations on top of the isolation layer conditional on different ground-motion intensity levels; (2) approximations of the superstructure response; (3) simplified consequence models for isolation system and superstructure based on damage-to-loss ratios (economic loss or repair time); (4) simplified consequence models for acceleration- and drift-sensitive non-structural components, based on storey loss functions of a potential inventory of components. Given some basic geometrical parameters of the superstructure, DLBD provides the isolation system's force-displacement curve and the required superstructure's strength complying with a selected loss target. The members' structural detailing follows the principles of direct displacement-based design, sectional analysis, and the general theory of base isolation. The procedure is illustrated by designing six reinforced concrete wall buildings (two-, three-, and four-storeys) base isolated with lead rubber bearings, to achieve predefined targets of expected repair time. Repair time is benchmarked against a more refined method adopting a cloud-based non-linear time history analysis, finding a maximum underestimation of 17%, thus confirming the dependability of DLBD. Such error is almost entirely attributable to the simplified estimation of peak floor accelerations, and it could be potentially eliminated by refining such estimation.

Experimental testing of full structural systems and their components is crucial for understanding their response to earthquakes. Since the 1960s, global interest in such testing has grown, supported by numerous national and international funding initiatives. This has resulted in valuable data that has improved understanding of structural behaviour, spurred the development of new mitigation solutions and helped validate numerical models critical for simulation studies. These advancements have enabled engineers to improve building codes and guidelines, and have allowed risk modellers to more accurately assess risk. With advanced computational resources, integrating experimental findings into broader initiatives becomes crucial. This article discusses a recent European initiative, Built Environment Data (BED) (https://builtenvdata.eu/), which currently offers a platform to store and manage data from experimental research, embodied carbon and simulated design services. BED aims to serve the European Plate Observing System (EPOS) distributed research infrastructure as one of its Thematic Core Services (TCSs). This paper focuses on the Experiments service for managing experimental data, compares it to similar global efforts and outlines the specific requirements and system architecture, including the web services and datasets currently offered. The Experiments service is expected to significantly support engineers worldwide by making experimental research and data more findable, accessible, inter-operable and re-usable.

The steel plate shear walls (SPSWs) have been proven effective in reinforced concrete frames (RCFs) as a lateral force-resistant structure. Despite of advancements, accurately predicting the ultimate shear capacity of RCFs with SPSWs remains challenging using current simplified models. Additionally, the flexural capacity design procedure for the boundary elements (beams and columns) in previous studies of RCF-SPSWs involved intricate iterative procedures, hindering its widespread implementation. To address the two issues, this paper investigates the pushover responses and the plate-frame interaction (PFI) of an RCF-SPSWs system using theoretical and numerical methods. There are three main contributions. First, a theoretical model of ultimate shear capacity for RCF-SPSWs is proposed, which can also be used to predict shear contributions of boundary frames in RCF-SPSWs. Calculation errors for ultimate shear capacity of RCF-SPSWs and shear contribution from the boundary frame are only 3.7% and 6.7% respectively, which are reduced dramatically compared with the traditional model. A simplified schematic diagram for the global collapse mechanism (uniform distribution of plastic hinges within a structure) of RCF-SPSWs is developed to facilitate the calculation of internal work and reaction forces. Secondly, a flexural capacity design method for the boundary elements to avoid in-span plastic hinges is proposed. The proposed method enables the achievement of direct estimation of the flexural demands that could trigger a global collapse mechanism, all without intricate iterative procedures. The applicability of current assumptions for the design of steel boundary frame in RCF-SPSWs system is discussed, and engineering suggestions are provided to ensure safer and more economic designs. Comparison results confirmed the applicability of the proposed design method, which can be adopted to achieve the global collapse mechanism for RCF-SPSW system. Thirdly, impacts of yielding panel actions on the flexural capacity of boundary elements of RCF-SPSWs are clarified. Comparison results demonstrated that adding SPSWs to an RCF alters the axial force on boundary elements and significantly impacts the flexural capacity. A design suggestion is made to emphasize the importance of avoiding the balanced failure of boundary elements. The proposed theoretical model can be used to economize the cross-section of boundary elements in RCF-SPSWs system under seismic loads due to accurate prediction of their shear contribution; the proposed flexural capacity design method can achieve a global collapse mechanism, and thus the structural safety and energy dissipation capacity are improved; moreover, the building design efficiency is also improved due to avoidance of intricate iterative procedures.

To manage structural responses under various external forces, the increasing incorporation of seismic isolation and supplementary damping systems in modern civil engineering necessitates post-installation performance assessments. The challenge of accurately inferring system information from these complex dynamical structures, especially with limited sensor deployment, could be significant. From the perspective of solving inverse problems, this challenge hinges on constructing an input-output mapping that assures unique solutions, achievable through theoretical observability or symmetry analysis. We introduce a unified algorithm framework designed to accommodate various definitions of Lie derivatives, specifically for observability and symmetry analysis in dynamic systems with affine, non-affine, and unknown inputs—capabilities not fully achieved in previous studies. We demonstrate its application across typical dynamic scenarios, including both linear and nonlinear examples. We also present a numerical example featuring complex isolation systems with limited sensor layouts, illustrating how uniform convergence can be achieved in estimating all system states when an observable input-output mapping is utilized. Furthermore, an experimental example employing shaking table tests showcases the potential complications that arise when an unobservable input-output mapping is used.

Tuned Mass Dampers (TMDs) are commonly used passive control devices in practical engineering applications. However, motion-limiting stoppers are usually installed to control the excessive TMD displacement due to the building space limitation, resulting in piecewise nonlinearity and detuning of TMD. This paper studies the influence of elastic motion-limiting stoppers on the optimal design of TMDs through a piecewise stiffness TMD (PSTMD) model. Performance of a PSTMD with classical design is first investigated and proven to be ineffective. To optimize the PSTMD parameters, the motion of PSTMD is decoupled from the controlled structure, and the frequency response equation of PSTMD is obtained analytically through the averaging method. Subsequently, the solution of the optimal design frequency for PSTMD is transformed into the solution of the jump frequency in the frequency response equation. With the optimal frequency of PSTMDs, the optimal damping and control performance of PSTMDs are discussed and analyzed compared with classical linear design, which fully showcases the effectiveness of the novel design method. Finally, the effectiveness of the novel design method is verified using a nine-story benchmark frame structure, and the results demonstrate that the control performance of the optimal PSTMD can be improved by nearly $��10�\%�$ under specific seismic excitation, compared to the PSTMD with classical linear method. In summary, the novel design method can effectively take into account the influence of piecewise nonlinearity caused by elastic motion-limiting stoppers and improve the optimal control performance of TMD in a more realistic engineering environment.

The UC San Diego large high-performance outdoor shake table (LHPOST), which was commissioned on October 1, 2004 as a shared-use experimental facility of the National Science Foundation (NSF) Network for Earthquake Engineering Simulation (NEES) program, was upgraded from its original one degree-of-freedom (LHPOST) to a six-degree-of-freedom configuration (LHPOST6) between October 2019 and April 2022. A mechanics-based numerical model of the LHPOST6 able to capture the dynamics of the upgraded 6-DOF shake table system under bare table condition is presented in this paper. The model includes: (i) a rigid body kinematic model that relates the platen motion to the motions of the components attached to the platen, (ii) a hydraulic dynamic model that calculates the hydraulic actuator forces based on all fourth-stage servovalve spool positions, (iii) a hold-down strut model that determines the pull-down forces produced by the three hold-down struts, (iv) Bouc-Wen models utilized to represent the dissipative forces in the shake table system, and (v) a rigid body dynamic model borrowed from robotic analysis governing the translational and rotational motions of the platen subjected to the forces from the various components attached to the platen. Extensive validation against experimental data shows excellent agreement for tri-axial and six-axial earthquake shake table tests. This validated model can be coupled with finite element models of test specimens to study the interaction between the shake table system and the specimens, and it offers potential for enhancing motion tracking performance through off-line controller tuning or advanced control algorithm development.