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Topographic effects significantly influence the propagation of seismic activity; however, research on the differences between mountainous and plateau terrains remains scarce. This paper focused on the 2008 Wenchuan earthquake, analyzing a five-span high-speed railway simply supported by a bridge through dynamic time-history analysis. Stations were categorized into mountainous and plateau groups based on their average shear wave velocity for the top 30m ($V_{s30})$ values and elevation, aiming to explore the impact of terrain differences on seismic actions by comparing structural responses between the two groups. This study revealed an exponential relationship between structural responses and the rupture distance ($R_{\mathrm{\text{rup}}}$)/peak ground acceleration (PGA), with a rapid decrease in response when $R_{\mathrm{\text{rup}}}$/PGA was below 100 and subsequent stabilization. Additionally, the sites were segmented into three zones according to the epicentral distance. The findings highlighted that the average PGA value of the mountain group was 2.7 times that of the plateau group in Region I, and the value decreased to 1.93 times that in Region II. However, the average PGA value of the plateau group slightly exceeded that of the mountain group in Region III. By comparing the PGA values of stations with similar fault distances within these regions, it was discovered that elevation could amplify seismic motion up to 4.59 times for smaller fault distances, with minimal amplification effects observed for larger fault distances. Finally, by examining damage to key components such as rails, beams, bearings, and piers and employing the kriging interpolation method to produce a regional seismic response cloud map, instances of high-speed railways constructed post-Wenchuan earthquake serve as evidence to corroborate the findings.

The overturning resistance of structures base-isolated using laminated rubber bearings (LRBs) is crucial to the stability of the structure due to the poor tensile performance of LRBs. Pounding occurs between the structure and moat wall, which can result in a reduction of the overturning resistance of the structure. This study aims to investigate the overturning resistance of a structure base-isolated by LRBs considering pounding against the moat wall based on numerical simulations. The influence of the gap size, pounding stiffness, and the horizontal stiffness of the isolation storey on the overturning resistance of the isolated structure was evaluated through parameter studies. The results indicate that poundings between the structure and moat wall result in short but large pounding forces. Pounding forces would amplify acceleration, inter-storey drifts of the isolated structure, and significantly increase the risk of overturning of the isolated structure. Increasing the gap ratio can improve the seismic performance of the structure. Larger pounding stiffness leads to greater pounding forces generated by the structure, and the risk of overturning of the structure increases. The coefficient of overturning resistance initially decreases, and then increases, as the stiffness of the isolation storey increases.

An inerter system, based on electromechanical similarity theory and vibration mitigation and isolation technology, represents a category of vibration damping systems. These systems typically improve damping performance by increasing mass or inertia, a method often found to be inefficient, leading to inadequate damping and limited applicability in real-world engineering scenarios. The lightweight inerter system (LwIS) introduced herein offers a more flexible and efficient means of altering structural inertia. Initially, this paper establishes the motion control equations for LwIS, followed by a stochastic analysis to derive the analytical expression for the root mean square displacement under Gaussian white noise excitation. A parametric analysis of LwIS is subsequently conducted, developing a displacement-based parametric strategy. Design examples for single-degree-of-freedom (SDOF) engineering structures under various requirements are provided, demonstrating the validity of LwIS’s optimal parameters through responses to simple harmonic excitation and seismic impacts. The findings indicate that the optimization approach of LwIS, unlike traditional methods, simultaneously addresses the displacement performance of the primary structure and the deformation efficiency of the damping element, thereby facilitating comprehensive optimization. Four optimal design parameters for LwIS are identified, underscoring its applicability to stochastic excitation and a broader range of load cases, thus enhancing its practicality in engineering contexts. LwIS’s design philosophy aims to improve deformation efficiency through an increased deformation enhancement coefficient in the damping element, enhancing damping performance, controlling seismic responses, and achieving superior energy dissipation. The optimal parameters, smaller in value, maximize the potential of the inerter system, aligning with the dual objectives of performance optimization and lightweight design, consequently reducing engineering costs.

The influence of surface Rayleigh waves (SRWs) on the seismic behavior of three archetype nonconforming reinforced concrete (RC) buildings including weak first story with four, six, and eight stories when subjected to earthquake ground motions (EQGMs) recorded during the strong September 19, 2017 $M_w$7.1 earthquake in Mexico City, is discussed in this paper. For this purpose, ground acceleration time histories corresponding to the retrograde and prograde components of SRWs were extracted from EQGMs collected at the accelerographic stations placed at the transition and soft soil sites. It was found that the SWRs contribute to about 50% of the median maximum IDR demand (IDR${}_{max}$) triggered by the as-recorded earthquake ground motions at the ground level of the four- and six-story building models, while their contribution is about 30% of IDR${}_{max}$ for the eight-story building model. It should be noted that that SRWs induce median IDR${}_{max}$ demands to the four-story building model larger than about 11% and 49% than those to the six- and eight-story models, respectively, for soft soil sites. Moreover, the prograde component can trigger IDR${}_{max}$ demands in the four-story building model larger than 73% and 45% than those for the six- and eight-story models, respectively, for the transition sites. Particularly, it was shown that SRWs induce median IDR${}_{max}$ demands in excess of 0.35% at the first level of the archetype building models, which is associated to the light cracking damage state of nonductile RC columns, and even in excess of IDR${}_{max}$ of 0.71% associated to the severe cracking damage state when the record-to-record variability is considered in the IDR${}_{max}$ demand (i.e. the 84th percentile of IDR${}_{max})$. Although the earthquake ground motion component of the surface Rayleigh waves was negligible in the median IDR${}_{max}$, this study showed that the effect of the directionality of IDR${}_{max}$ is important for the CH84 station, where significant polarity of spectral ordinates was identified in previous studies.

The effectiveness of sliding mode control on the seismic response of an isolated bridge with columns of irregular heights, which exhibit hysteretic behaviors at both the columns and isolators, is studied. The bridge of concern consists of a two-span continuous deck and three columns of irregular heights, adjoining two single-span approaches each at the two ends. The irregular isolated bridge is idealized by an equivalent model to reduce the number of degrees of freedom involved. Compared with typical isolated bridges, the irregular isolated bridge has more poles of sliding surface, which dominates the dynamic characteristics of the controlled system and should be determined for the sliding mode control. The particle swarm optimization-simulated annealing (PSO-SA) hybrid searching algorithm is thus employed and shown to outperform the PSO algorithm and a parametric approach in finding the best sliding surface. Numerical simulations reveal that the sliding mode control together with the PSO-SA hybrid searching algorithm provides a simple and powerful technique for controlling the nonlinear seismic responses of irregular isolated bridges. Such a technique combining the control and optimization technology can be applied to practical bridges or structures, which are generally complicated and should be idealized by sophisticated numerical models.

In this study, the seismic vulnerability of post-tensioned reinforced concrete box-girder highway bridges with moderate-to-large skew angles to various levels of ground motion intensity is investigated. The fragility curves are generated by performing incremental nonlinear dynamic analysis (IDA) on the bridges of skew angles of 0, 30, and 60°s. A total of 45 ground motion pairs are considered to develop the fragility curves. The damage states are presented and quantified based on the column rotational ductility and superstructure displacements at the abutments. Furthermore, the fragility curves constructed are compared against those recommended by HAZUS. It is demonstrated that as the skew angle increases, skew bridges become more vulnerable to seismically induced damages. It is also shown that the HAZUS fragility curves may not lead to a consistent prediction of the vulnerability of skewed bridges.

A new concept for establishing the damage model for high concrete dams under earthquakes based on damage mechanics is presented in this paper. Unlike the conventional approach of considering the residual deformation by means of plastic-damage coupling, the proposed approach relates the degraded apparent elastic moduli of loading and unloading directly to the material experimental data. As such, the nonlinear analysis of the seismic response of dam-foundation systems is simplified and more reasonable, with no recourse to plastic-damage coupling. To verify the proposed approach of damage–rupture process for high concrete dams, the seismic behaviors of the Koyna gravity dam in India and the Shapai RCC arch dam in China both subjected to strong earthquakes were examined. It is demonstrated that the proposed approach can be reliably used to study the damage–rupture behavior of concrete dams under strong earthquakes.

This paper introduces a new design of segmented nonbuckling brace member for use in frame structures to resist earthquake loading. The proposed segmented brace member consists of one or more segments connected by either tension-only or compressive force controlled joints. Because it cannot resist or can only resist a limited amount of compressive force, it is effective only under tension, but buckling would not be a failure mechanism of the brace. Its capability of mitigating seismic responses remains effective throughout the entire ground excitation duration. The other advantages of this new design include light weight, easy installation, easy replacement, controlled damage locations, and minimum or no residual structural deformation. The disadvantage is that full energy dissipations can be achieved only when it is in tension. Therefore they will be effective in a frame structure only when cross bracings are used. This paper presents experimental tests and numerical simulation results to examine the effectiveness of this innovative brace member in mitigating seismic responses of frame structures. Laboratory cyclic loading tests on a single brace member and on steel frames without bracing or with cross bracing by conventional brace or segmented brace are carried out. The testing results are analyzed and compared. The effectiveness of segmented brace members in mitigation of seismic loading effects on frame structures is demonstrated. Nonlinear response analyses are then carried out to investigate the performance of this new segmented brace applied to a steel frame structure subjected to ground motions of different amplitudes. The results demonstrate that this new design is effective in mitigating seismic loading effect throughout the entire ground motion duration.

Pipe-in-pipe (PIP) system can be considered as a structure-tuned mass damper (TMD) system by replacing the hard centralizers by the softer springs and dashpots to connect the inner and outer pipes. With properly designed connecting devices, PIP system therefore has the potential to mitigate the subsea pipeline vibrations induced by various sources, such as earthquake or vortex shedding. This study proposes using rotational friction hinge dampers with springs (RFHDSs) to connect the inner and outer pipes. The rotational friction hinge dampers (RFHDs) are used to absorb the energy induced by the external vibration sources and the springs are used to provide the stiffness to the TMD system and to restore the original locations of the inner and outer pipes. To investigate the effectiveness of this new design concept, detailed three-dimensional (3D) finite element (FE) model of the RFHD is developed in ANSYS and the hysteretic behavior of RFHD is firstly studied. The calculated hysteretic loop is then applied to the 3D PIP FE model to estimate the seismic responses. The effectiveness of the proposed system to mitigate seismic induced vibrations is examined by comparing the seismic responses of the proposed system with the conventional PIP system. The influences of various parameters, such as the preload on the bolt, the friction coefficient and the spring stiffness, on the RFHD hysteresis behavior and on the seismic responses of PIP system are investigated and some suggestions on the RFHDS design are made.

In the design of super-long-span suspension bridges, the floating system is commonly adopted. However, this system may lead to the excessive earthquake-excited longitudinal displacement (LD) at the end of the main girder, which in return could result in pounding damage at expansion joints. In this paper, Taizhou Bridge, the triple-tower suspension bridge with the longest main span in the world, is taken as an example to demonstrate the effectiveness of three different approaches (elastic links, viscous dampers, and their combination) of mitigating the possible excessive LD. The finite element code ABAQUS is used to build the numerical model of the bridge and calculate the dynamic characteristics as well as the seismic responses. Then, 24 cases with different parameters of elastic links and viscous dampers are investigated and it is observed that the mitigation effect of the 24 cases varies significantly with different parameters. To obtain the optimized mitigation effect for seismic responses, including the LD of the girder, the LD and shear force of all towers, in the 24 cases, the modified analytic hierarchy process (AHP) method is introduced to realize the compositive optimal control of the triple-tower suspension bridge. Results show that the 24th case is the optimal one in which the LD of the girder is reduced significantly while the inner force of towers does not get excessive increase.

The actual dead load of an arch dam should be applied gradually through staged construction and sequenced grouting. However, the cantilever- and integral-type dead loads commonly used in the analysis of arch dams represent simplified versions of the actual loading. In this paper, these two types of dead loads, i.e. cantilever and integral types, are presented based on the Lagrange multiplier method considering the nonlinear behaviors of contraction joints. Based on the finite element method and an appropriate contact model together with artificial viscoelastic boundary conditions, a dynamic analysis model of a dam–foundation–reservoir system is established in consideration of the interactions between the arch dam and foundation, the opening and closing of contraction joints, and the radiation damping effect of the far-field boundary. Taking a 300 m high arch dam in the strong earthquake area of West China as an example, a fine mesh finite element model with a total of approximately 3.5 million degrees of freedom is established. The separate effects of the cantilever and integral dead loads on the static and dynamic responses of the dam are studied. The results demonstrate that the distribution and magnitude of the contraction joint opening width and maximum tensile stress are different under the two different dead load simplifications.

The seismic isolation efficiency of different friction-based devices needs verification by shaking table test, but faces problems in scaling before the test due to their frictional nonlinearity. To solve the scaling problems, a simplified civil structure, isolated by a self-centering spring-friction device, was numerically scaled in different ways considering the effect of friction action. The seismic responses of the scaled models were scaled back to those of the prototype and compared with the seismic responses of the prototype. The scaling problems and solutions were validated by a shaking table test on simply supported bridges using friction pendulum bearings (FPBs). The results show that both the unscaled gravity on a shaking table and the unscaled non-uniform friction distribution cause an inaccurate friction force in the structural motion equations of scaled models, and thus causing the scaling errors. One new and valid solution, i.e. changing the friction coefficient and scaling the non-uniform friction distribution to keep an accurate friction force for the scaled models, is put forward to avoid the scaling errors thoroughly. Another new solution shows that an increasing peak ground acceleration (PGA) can increase the other forces, while weakening the ratio of inaccurate friction force in the structural motion equations of the scaled models, which therefore reducing the scaling errors of acceleration and relative displacement responses, but not the scaling errors of residual displacement responses. In addition, the time-varying friction, the interface separation and collision of bearings, and other complex factors are found to cause scaling errors and need further investigation.

Previous research has shown that the transient and partial footing separation is one of the effective methods to reduce the impact of earthquakes on bridge structures. The separation will not only temporarily stop the transfer of seismic load to structures, but also activate rigid-like body motions of the bridge piers. Most of current investigations involving footing uplift only focused on straight bridges. The influence of skew angle is rarely considered. Even though skewed bridges are common and more vulnerable to seismic load. This work reveals the simultaneous influence of skew angle and footing uplift on soil on seismic response of bridges. A bridge with a 30^∘ or 45^∘ skew angle, in addition to a straight bridge, was excited using a large-scale shake table. The ground excitations were stochastically simulated based on design spectrum of New Zealand standard. The result revealed that with increasing skew angle bridges will have frequent footing uplifts. In the case of a straight bridge, although allowing footing uplift is beneficial in reducing the bending moment at the pier support, it increases the longitudinal girder displacement. In contrast, in the case of 30^∘ and 45^∘ skewed bridges, uplifts increase the bending moments of piers and the displacements of the girder, especially in the transverse direction.

The seismic response of curved concrete bridges is complex because of the geometric irregularity and induced planar rotation of the deck, which can magnify the displacement of the deck and deformation of the bearings. To control the planar rotation and thus the seismic response of the curved bridge, an orthogonally separated isolation system (OSIS) is proposed, which consists of the upper and lower isolation parts. With this, the planar relative displacement of the common isolation system is decomposed into the relative displacement of the upper part in one direction and the relative displacement of the lower isolation part in the orthogonal direction. Therefore, the planar rotation can be restrained and the seismic demand of the isolation bearing is decoupled. The analytical models of a curved bridge and the OSIS are established in OpenSees. A suite of 118 ground motions, of which 80 are ordinary and 38 are pulse-like, is selected as input with 24 different angles of incidence so as to consider the seismic variation. Nonlinear dynamic time-history analyses of the two models are conducted to evaluate the effectiveness of the OSIS. The results show that the OSIS can effectively decrease the deck displacement, the bearing deformation and the pier column shear force, especially under the ground motions with higher intensities, while the shear force increases slightly on the abutment.

As a generalized version of the base isolation, the inter-story isolation has increasing applications in tall buildings due to its better adaptivity. Compared with the seismic response of the base-isolated building, that of the inter-story isolated building is more complex because it is affected by dynamic characteristics of the lower structure (LS), isolation layer (IL) and upper structure (US), which deserves the in-depth study. This study presents a comprehensive investigation on the reduced model and the seismic response of the inter-story isolated building. The equations of motion are established using modal displacements of the linear lower and upper structures, as well as the displacement of the isolation layer with the nonlinear hysteretic restoring force character. In light of the contribution of the generalized stiffness, a method of selecting the adequate participating modes of lower and upper structures is proposed. The nonlinear time history analysis of example tall buildings to seismic excitations shows that the reduced building model can provide accurate estimation for important seismic responses. Based on the reduced building model, the influence of dimensionless parameters including frequency ratio, mass ratio, damping ratio, second stiffness ratio (i.e. ratio of the post-yield over pre-yield stiffness) and the ratio of yielding force to total weight of upper structure on structural responses are investigated systematically. Finally, the equivalent linearization method being suitable for the base-isolated structure is evaluated for the inter-story isolated structure, and the filter effect of the lower structure is emphasized.

The Compositive Passive Control method (CPC method) of “interlayer seismic isolation” + “shock absorption between adjacent towers” is applied to Multi-Tower Building (MTB) with a large podium. Taking the total vibration energy of the structure as the optimal control objective, the response expressions of a multi-DOF layer shear model and an equivalent single-DOF layer shear model are derived. The rationality of the equivalent model is demonstrated from the perspective of mode characteristics and time history response. Based on the Kanai–Tajimi spectral seismic motion model, the control effect and the optimal control parameters of the CPC method are studied. Compared with the conventional seismic scheme and the interlayer seismic isolation scheme, the influence of the CPC method on the structure natural vibration characteristics and dynamic response under different parameters of the connecting control device is discussed and analyzed. The numerical analysis proves that the CPC method provides a significant damping effect compared with the interlayer seismic isolation scheme. It maintains the advantages of the interlayer seismic isolation scheme and reduces the defect of the response amplification caused by the interlayer isolation. This analysis constitutes a good reference for the follow-up study of the CPC method of MTB.

A cantilever beam with multiple rotation spring-dampers was utilized to simulate the damped outrigger system. Two new methods, namely, the “Maxwell dampers type method” and the “virtual small mass method,” were proposed to present the simplified seismic response analysis of the damped outrigger system. Corresponding dynamic characteristic equations based on the proposed methods were also given. Subsequently, $H_{\infty }$ performance index was employed to obtain the optimal damper parameters. The numerical analysis shows that the proposed methods agree well with the finite-element method and have relatively accurate results. Stiffness ratios of the perimeter columns have a significant effect on the pseudo frequencies and system damping ratios. Lower stiffness ratios of the perimeter columns commonly lead to higher pseudo frequencies and system damping ratios. Furthermore, the damped outrigger system has excellent seismic mitigation performance when applied with appropriate damping parameters based on $H_{\infty }$.

It is generally perceived that ground motion duration has an effect on structural seismic response and damage, despite the neglect of current seismic codes. Based on friction SDOF systems, this paper investigates the duration effect of ground motions on seismic responses and damage of sliding bearings. Ground motions are divided into long-duration (LD) and short-duration (SD) cases, taking the significant duration of 25s as the boundary. Each case consists of natural records and spectrally equivalent artificial ground motions to decouple duration from other earthquake characteristics. Results from response history analyses implicate that duration has hardly any effect on seismic responses of the system exhibiting an approximate linear elasticity. Nevertheless, for systems with distinct frictional nonlinearity, selecting LD ground motions as seismic inputs usually leads to a conservative result. By performing incremental dynamic analysis (IDA), nonlinear systems in SD cases bear 10% higher damage risk than those in LD cases without considering the influence of temperature rise. The same is true for systems with a small friction coefficient of 0.005 when earthquakes are in the low intensity range. It was also found that damage exceedance probabilities of these small friction coefficient systems are almost unaffected by the duration as the peak ground acceleration increases to more than 0.6$g$. When the effect of temperature rise caused by friction is considered, the damage exceedance probability in LD cases is higher than SD cases. The damage probability of friction SDOF system under LD earthquake will be underestimated without considering the influence of temperature rise.

To accurately and rapidly predict seismic responses, including the maximum displacement (MaxD) and maximum acceleration (MaxA), of the isolated structure considering the soil–structure interaction (SSI), five ensemble learning models, i.e. random forest (RF), gradient boosting regression tree (GBRT), extreme gradient boosting (XGBoost), light gradient boosting machine (LightGBM) and stacking model, are constructed. Firstly, a total of 96 000 nonlinear time history analyses of the isolated structure considering the SSI are conducted with the aid of OpenSees. The generated database is used for training and testing ensemble learning models. The ensemble learning models have 12 input variables in four categories, i.e. ground motion parameters, structural parameter, isolation parameters and soil parameter, and two output variables, i.e. MaxD and MaxA. The study shows that all ensemble learning models have excellent prediction performance for both training and testing datasets. The determination coefficients are larger than 0.96 and root-mean-square errors (RMSEs) are relatively small. Among the five ensemble learning models, the stacking model exhibits the best performance. In addition, the calculation method of feature importance score for the stacking model is provided. According to the feature importance analysis, the ground motion parameters have greater impact on seismic responses than other three categories of inputs. Finally, six ground motions are randomly selected to verify the generalization ability of the proposed ensemble learning models. The results show that the stacking model has a favorable generalization ability with relatively small prediction errors.

Compared to ground supported tank, column supported tank has the advantages of saving land space, having strong adaptability and making gas transmission cost small. It can be mass-produced in the center of a city, which has been widely used in practices. However, its seismic responses are much different from those of cylindrical tank. Limited research works and standard codes involve uplift effect and retrofitting measure of column supported tanks. Therefore, a shaking table test is conducted with a model tank designed by quasi-dimensional analysis method. To solve the problem of the anchored tank that may suffer damage under severe earthquake, a designed resilient tank is presented with mild steel dampers. The seismic responses of those two tanks are compared with each other, including the structural displacement parallel to excitation direction, the strain of tank walls and columns, the uplift displacement and the structural force. The results show that due to the uplift effect and the energy dissipation of dampers, the resilient tank has larger horizontal displacement, but less base shear and overturning moment than the anchored tank. Its strains of columns and walls in excitation direction decrease obviously, while those in perpendicular direction increase but with small variation, resulting in more balanced force allocation of the resilient tank. When encountering plastic failure, the dampers can be replaced in a very short time, making the normal use of the tank quickly even extreme condition. The resilient tank can save repairing time and cost. It can help resume the gas supply function of a city quickly after severe earthquake.