Earthquake Engineering & Structural Dynamics最新文献

Integral abutment bridges (IABs) generate strong soil–structure interaction (SSI) effects due to their high structural stiffness and transmission of inertial and thermal loads generated at the deck directly to the abutments. Despite an increasing number of experimental and numerical studies available in the literature, there is a lack of consolidated methodologies to model dynamic SSI phenomena for IABs, particularly in seismic regions where uncertainties associated with the induced ground motions render the problem harder to tackle. This study proposes an advanced strategy to model the seismic response of IABs, accounting for dynamic interaction between the structure, the abutment and the foundation, including piles and earth retaining walls. To this end, detailed finite-element studies were carried out employing OpenSees to simulate a recent experimental campaign on a scaled IAB model in a soil container (SERENA) carried out at EQUALS Lab, University of Bristol, in the framework of SERA/H2020 project. An extensive dataset in terms of recorded accelerations, displacements, strains and settlements are available from these tests, including earth pressures which are back-calculated from bending strain measurements. The objectives of this paper are threefold: firstly, the model parameters are explored and assessed critically by comparing the results from the numerical simulations against the experimental data; secondly, once the model is deemed sufficiently representative of the experiments, earth pressures are obtained numerically, as these are not directly measured in the tests; thirdly, the estimated static and dynamic earth pressures on the abutment wall are compared with the predictions of two simplified analytical procedures currently under consideration for inclusion in the new Eurocode 8. The results indicate that records and predictions match well for frequencies of up to 40 Hz at model scale (about 8 Hz in prototype scale) and confirm that the proposed modelling strategy can be used in practical applications. The quasi-elastic model proposed in this study is shown to provide dependable predictions for cases involving moderate strains in real-life applications.

Motion amplification devices utilized to amplify the motion of dampers can effectively improve the energy dissipation performance of dampers to reduce seismic responses of engineering structures. This study systematically develops a linear equivalence theory for motion amplification devices based on the proposed equivalent Maxwell model. This equivalent model accurately predicts the supplemental damping effect provided by motion amplification devices without approximation. Also, the equivalent model is capable of quantifying the amplification effect of motion amplification devices by means of deriving the analytical expressions of the equivalent damping and stiffness coefficients, which reveal that motion amplification devices simultaneously enhance the original damping and stiffness coefficients by $�{\overline{\alpha }}^2$, where $�\overline{\alpha }$ is the proposed rigidity motion amplification factor. The representative value of member stiffness $�k_p$ is developed to comprehensively evaluate the supporting stiffness of motion amplification devices. All the achieved results strongly support that the proposed linear equivalence theory provides a generic paradigm to explain, measure and compare different types of motion amplification devices in terms of their supplemental damping effects, and hence helps researchers and engineers gain valuable insight into the dynamic properties of motion amplification devices.

The growing concern over environmental impact and the significant improvement in the quality of engineered wood products have led to the rapid growth of the timber building industry in the last decades. Although traditional, yet recent, mass timber structural systems, such as cross-laminated timber walls, can provide satisfactory seismic performance during earthquakes in terms of life-safety, the crucial need for more resilient timber buildings has prompted the development of low-damage high-performance self-centring and dissipative solutions based on unbonded post-tensioned hybrid connections, referred to as Pres-Lam technology. The flexibility of design and construction speed, combined with the enhanced seismic performance, create a unique potential towards an earthquake-proof sustainable building system. Despite the growing popularity of the technology, a comprehensive framework for the fragility analysis, to be used in risk and loss modelling applications, has not yet been developed for both component and building levels.

This article aims to develop a framework for assessing the fragility curves of moment-resisting Pres-Lam frame systems, at both structural system and connection levels, by using and comparing different approaches that involve nonlinear static (pushover) and time history dynamic analyses. A Python-based parametric workflow was developed to evaluate fragility curves for a wide range of case-study buildings. Particularly, three distinct structures were selected, and their fragility curves were evaluated utilizing alternative methodologies at a building structural-system level. Finally, fragility models were fitted for individual structural connections using the results of time-history analyses. These models are intended for use in a component-based loss assessment.

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.