Earthquake Engineering & Structural Dynamics最新文献

In order to advance the post-earthquake rehabilitation for girder bridges with tall double-column bents, a critical infrastructure component in mountainous and canyon regions, the present study, motivated by the promising rocking self-centering (RSC) technology, proposes an innovative configuration employing an alternating uplift-rocking system to facilitate the implementation of the RSC technology in conventional tall bents. The proposed uplift-rocking tall double-column bent (UR-TDCB) integrates an extended foundation and external triangular steel plate dampers at the bottom of the tall bent to ensure adequate self-centering and energy-dissipative (ED) capacity, even in the absence of post-tensioned (PT) tendons. A displacement-constraint (DC) device ensures sufficient stability for the tall bent, such that the limited state of materials, rather than stability issues, is the predominant issue during infrequent earthquake events. Additionally, an analytical model considering the continuous variation in neutral axis depth was presented to characterize the hysteretic behavior of UR-TDCB, following validation by an optimized finite element (FE) model. This FE model significantly enhances the modeling efficiency and computational accuracy while also accounting for the influence of size effect on the rocking interface. Based on the design procedure and FE model, a case study of a double-span continuous girder bridge in the high-seismicity region, including nonlinear analysis under cyclic static loading and earthquake excitations, was conducted to comprehensively assess the seismic resilience of the UR-TDCB. Results confirm the superior performance of UR-TDCB in limiting both damage progression and residual deformation. Meanwhile, similar lateral stiffness, strength, and boundaries’ behaviors compared to the conventional tall bents underscore the potential for integrating this system in engineering applications.

This study presents an improved hybrid (empirical-stochastic) model for simulating non-stationary accelerograms based on filtered Gaussian white noise. A linear filter for the frequency domain and a modulating time function are used to generate a stochastic accelerogram based on target parameters. Arias intensity, strong-motion duration, and the lag time between S waves and P waves are used for the modulating function calibration. Universal empirical equations linking the time domain strong motion parameters and that of the modulating function are developed based on mathematical properties (inflection points) of the modulating function. The cumulative energy of the resultant modulation functions is assessed and compared to the cumulative energy of the target accelerogram. The central frequency and frequency bandwidth, determined from the physical spectrum of the target, are utilized for identifying the parameters of the linear filter. Empirical equations governing the frequency and damping ratio of the linear filter are proposed based on the specified spectral parameters. Stochastic accelerograms are simulated using proposed equations, resulting in notable improvements in the regeneration of target frequency characteristics, response spectra, and cumulative energy, as evidenced by comparisons to target records.

Nonlinear structural system inevitably experiences residual displacement (RD) following severe earthquake event, which compromises post-earthquake functionality and increases structural fragility. Despite its importance, RD has received limited attention compared to maximum displacement (MD). This study proposes an innovative procedure to evaluate RD-based seismic fragility using the total probability theorem with MD as an intermediate variable. The distribution of RD given MD is described by q-Weibull distribution in this procedure, and RD-based fragility is then determined through combining this distribution with the intensity measure (IM)-MD relationship obtained from cloud method. This approach not only mitigates the limitations of conventional cloud method but also significantly reduces computational efforts compared with incremental dynamic analysis (IDA). Additionally, the procedure is extended for dual-criteria seismic fragility assessment, incorporating both RD and MD. The effectiveness of the proposed q-Weibull-based model is validated against time history analysis results and is shown to outperform conventional bivariate lognormal models in capturing joint MD-RD distributions. Finally, application to a prototype global bridge with laminated rubber bearings demonstrates the procedure's accuracy and practicality for complex practical structures.

This paper proposes using a composite control device, termed tuned inerter-negative-stiffness dampers (TINSDs), for the longitudinal seismic control of long-span bridges with floating systems (LBFSs), and comprehensively investigates its optimization and control effectiveness. Initially, an analytical model for LBFS coupled with TINSD, referred to as the LBFS-TINSD system, is established, followed by the derivation of the corresponding equations of motion. Subsequently, two optimization strategies, namely, displacement- and energy-oriented $�H_2$ optimizations, are formulated to determine the design parameters of TINSD. By ignoring inherent damping, closed-form solutions for the optimal design parameters of TINSD are derived, and their accuracy is confirmed by contrasting them with numerical solutions. Parametric studies are then performed to investigate the influences of the stiffness ratio and inherent damping ratio of LBFS on the optimal design parameters of TINSD, while comparative analyses are conducted to investigate both optimization strategies. Finally, case studies are performed to numerically illustrate the effectiveness of TINSD in mitigating the responses of a classical cable-stayed bridge under different types of ground motions. In addition, the seismic control performances of TINSD are also compared with its counterparts, that is, tuned viscous mass damper (TVMD) and negative stiffness amplifying damper (NSAD). The results demonstrate that the energy-oriented $�H_2$ optimization achieves a more balanced performance in terms of girder displacement, girder acceleration, and energy dissipation compared to the displacement-oriented $�H_2$ optimization, albeit with a slight increase in control force. Furthermore, the TINSD exhibits superior performance over TVMD and NSAD, significantly reducing peak girder displacement response.

The intensity of seismic motion varies considerably with changes in direction, which is commonly known as the directionality of ground motion (GM). Different seismic design codes have adopted various methods for combining the intensity of horizontal GMs. These methods typically use the median spectral ordinate over all non-redundant orientations, referred to as RotD50, and the maximum spectral ordinate over all non-redundant orientations, referred to as RotD100. More recently, an intensity measure called MaxRotD50 has also been proposed and considered, which is calculated as the 50th percentile of the maximum spectral ordinates from two orthogonal horizontal directions for all non-redundant rotation angles. This measure, which always lies between RotD50 and RotD100, offers several advantages over other intensity measures. In contrast to the approach in ASCE 7 (2010, 2022), which uses RotD100 for the design of all structures, this study proposes to use RotD100 only for the design of axisymmetric structures, that is, structures with vertical cylindrical symmetry and similar properties in terms of mass, lateral stiffness and strength. It is also proposed to use MaxRotD50 for the design of structures where the probability of exceeding the intensity of GM in at least one of the two horizontal principal components is high. Likewise, this study complements and compares the RotD100/RotD50 and MaxRotD50/RotD50 ratios, which can be used as a multiplicative factor with the RotD50 predictions to predict the RotD100 or MaxRotD50 of the GM intensity. A database of 3853 seismic acceleration records from 283 events in the South American subduction region is used for this purpose. The influence of GM parameters such as moment magnitude, significant duration, rupture distance, and mean soil period, was evaluated. The results were compared with those of previous studies for different regions of the world. It was found that the RotD100/RotD50 ratios in South America are like those in other subduction regions such as Taiwan and Japan and that the Max RotD50/RotD50 ratios are comparable to other shallow crustal earthquakes in active tectonic regions. Finally, equations are also proposed to estimate ratios depending on the different parameters of the evaluated GM to account for the found influence on the ratios.

A confined precast prestressed hollow-core wall structure was proposed to improve the construction efficiency of the building. The system comprises three standardized components that are prestressed hollow-core wall panels, precast confined frames, and prestressed hollow-core floor slabs, with in-situ concrete for topping and beam–column joints. To verify the seismic performance of the system, a shaking table test was conducted on a full-scale three-story building that was designed using the proposed concept. The building was subjected to several shaking table tests with a range of intensity ground motions, incorporating both unidirectional and bidirectional loading. The test results showed that the structural system performed effectively during the intense series of tests. The building exhibited good seismic performance and achieved the performance objectives. The damages were mainly concentrated at the hollow-core wall toe and the horizontal and vertical connection joints between wall panels. The damage state was low and did not result in strength reduction of the building during DBE earthquakes. The test results validate the seismic safety of the system, demonstrating the proposed system is a reliable solution for precast construction.

Two-stage friction connections (TFCs) are proposed as lateral force-resisting components to enhance the stability of structures exhibiting negative postelastic stiffness under the P–Δ effect. A single point mass system composed of nonlinear springs, gap elements, and inherent damping, with varying ratios of initial sliding strength and length, is modelled. Time-history analyses (THAs) are conducted to investigate the behaviour of the structural system with TFC, in comparison with the system using the single-stage friction connection (SFC). Also, parameter studies are conducted considering different system postelastic stiffness ratios, r, considering initial strain hardening and P–Δ effects, T, and R. The displacement responses of a five-storey braced frame structure using SFC and TFC braces are compared. It is shown that the hysteresis curves exhibit two sliding strengths, corresponding to the frictional resistances at each end of the TFC. The initial sliding length is determined by the bolt slot at the weak end, and the model shows good agreement with experimental results. THA of TFC systems indicated that reductions in peak and residual displacements, Δ_p and Δ_r, respectively, were most significant when r was negative, compared to the SFC systems. Displacements were lowest when the strength ratio, β, which is the ratio of initial sliding strength to the higher sliding strength, was in the range strength of 0.5–0.7, and when the gap ratio, α, which is the ratio of the bolt movement in the slot in one direction to the elastic displacement, was 0.2–0.6. Median Δ_p and Δ_r reductions were up to 41% and 77%, respectively. The postshaking bolt location at the initial sliding end was 45% of the one-direction slot gap for the elastoplastic model, but 100% of this for significantly negative r. Lower r and larger R cause greater displacement reductions by using TFCs.