Three-dimensional Ground Motion Research Articles

Failure mechanisms and seismic fragility analysis of overhead transmission lines incorporating pile-soil-structure interaction

Overhead transmission lines (OTLs) are responsible for long-distance electric power transmission from power plants to end-users, inevitably passing through seismically active regions. A thorough literature review regarding seismic design and assessment of various structures underscores the significance of incorporating soil-structure interaction (SSI) and depth-varying spatial effect (DVSE). However, previous studies typically assumed that OTLs are fixed directly to the ground, and depth-varying ground motions (DVGMs) are oversimplified as uniform excitations, which may yield questionable structural performance estimations. To address this concern, this paper focuses on investigating the SSI effect on the seismic response and failure mechanism of an OTL subjected to DVGMs. Prior to this investigation, two commonly used methods for modeling the SSI effect in software ABAQUS are compared, with a nonlinear spring-based modeling method deems comparable in accuracy yet superior in efficiency. Subsequently, a refined finite element model of an OTL-soil-pile system is developed utilizing this simplified modeling method, and a group of three-dimensional ground motions varying within layered soils is stochastically synthesized. The influences of SSI and DVSE are systematically explored in terms of the seismic responses, failure mechanisms, and fragility probabilities of the OTL. The results expose the potential of the SSI effect to weaken the seismic capacity of the OTL and increase the risk of failure, while disregarding the DVSE is likely to lead to overestimated outcomes. This research is expected to raise awareness of considering SSI and DVSE in the seismic design and analysis of OTLs.

A comparison of ground motions predicted through one-dimensional site response analyses and three-dimensional wave propagation simulations at regional scales

One-dimensional (1D) site response analysis (SRA), which considers vertically propagating seismic waves from the bedrock to the surface, has been a common technique among geotechnical engineers to examine site-specific ground shaking. However, observations from past earthquakes and analytical studies indicate that idealizations ingrained in 1D SRA may be too severe to capture the ground truth, such as the omissions of spatial variability of soil properties, surface topography, and basin and directivity effects. Physics-based three-dimensional ground motion simulations (GMSs) can incorporate these factors and yield more reliable predictions. In this study, we utilize ground motions from 57 physics-based broadband (from 0 to 8–12 Hz) GMS for a region of Istanbul. A total of 2912 sites with experimentally measured soil profiles that are distributed over the 30 km-by-12.5 km area are also modeled as soil columns and analyzed through 1D SRA. The ground responses from 1D SRA and three-dimensional (3D) GMS are then compared for all 57 earthquake scenarios. These systematic comparisons are then used for examining model features that are correlated with variations in the ratios of various ground motion intensity measures (IMs) and for developing regression-based formulas that can be used for determining simple factors for the considered region to correctly scale (up or down) the site-specific ground motion intensities obtained from 1D SRA, including peak ground acceleration (PGA), peak ground velocity (PGV), and spectral acceleration ( Sa) values.

Evaluation of isolation performance of, reticulated shell structures with curvature-consistent frictional pendulum isolation system through shaking table tests

In this study, we investigated the isolation effect of a curvature-consistent frictional pendulum bearing isolation system (CC-FPB-IS) on a long-span spatial structure. Considering a typical spherical reticulated shell in a long-span spatial structure as the research object, we conducted shaking table tests on a scaled reticulated shell structure equipped with fixed hinge bearings and CC-FPBs. In addition, a refined finite element simulation method was established to analyze to the seismic impact on an actual reticulated shell structure with isolation layers under different isolation conditions. The variations in the isolation effect on the dynamic responses under horizontal unidirectional, vertical, and three-dimensional ground motions were compared. The results indicated that the isolation layer comprising the CC-FPB can notably reduce the horizontal dynamic response of a reticulated shell structure under horizontal seismic action while retaining its elastic state during rare earthquakes. With increasing loading amplitude, the isolation rate of the long-span spatial structure increased and gradually reached the optimal value. However, the proposed CC-FPB-IS did not effectively reduce the dynamic response of the vertical component, and the isolation rate was relatively small. When subjected to a three-dimensional earthquake, the structure exhibited an isolation effect because of the coupling of earthquake components in different directions. Thus, the CC-FPB-IS has notable effects on the dynamic response of the overall structure.

Key technologies research on of soil-structure interaction base story isolated structure response in 3D seismic zone

The development of karst in Karst area leads to poor stability of stratum. If earthquake occurs, the area will produce destructive disaster. In order to improve the stability capacity of the grassroots in the region, this study investigates the seismic response of inter-story isolation structures considering soil-structure interaction (SSI) in three-dimensional earthquakes. A model of the inter-story isolation structure incorporating SSI was developed, and one-dimensional, two-dimensional, and three-dimensional ground motions were applied to compare the seismic response under different input conditions. A three-dimensional isolation system was introduced and compared with traditional horizontal isolation structures to address excessive tensile and compressive stresses on the isolation structure during three-dimensional ground motion. The results demonstrate that the seismic response to three-dimensional earthquakes surpasses one-dimensional and two-dimensional inputs. Furthermore, adding a three-dimensional isolation structure effectively isolates vertical ground motion and reduces structural seismic response. Moreover, it minimizes soil stresses on the foundation compared to traditional horizontal isolation structure, enhancing foundation stability. This study will provide theoretical value and practical guidance for the research on key technology of SSI base story isolation structure response in Karst Plateau 3D Seismic zone.

Analysis of Damage Mechanism of Heihe Bridge during the Maduo Earthquake

It is of great significance to discuss the earthquake damage mechanism of the bridge. In this paper, the seismic damage mechanism of Heihe Bridge is analyzed based on the post earthquake data. Firstly, the seismic response of Heihe Bridge is analyzed based on the finite element software Midas/Civil, and the model of Heihe Bridge (upward) is established using the data of Dawu strong earthquake records near the bridge site; Then, the influence of bridge connecting plates on the seismic response of small and medium span simply supported girder bridges is studied, and the models with and without connecting plates are established. Finally, through the experimental analysis of the ground motion response, the internal force relationship between the connecting plate and the substructure of the bridge is discussed. The results show that:1)Abutment plays an important role in restraining the displacement of main beam along the bridge. Bridge connecting plate is an important seismic measure. (2) Using the three-dimensional ground motion simulation method of random finite faults, the seismic response analysis of the given USGS ground motion can better simulate the failure mechanism of the bridge. (3)The seismic response of the structural system is determined by the different layout of the bridge deck.

Seismic fragility assessment of traditional air-cooled support structure and air-cooled support energy dissipation structure based on IDA method

In this paper, the effectiveness of the modeling method is verified by the finite element analysis of the preliminary test. Three finite element models of traditional air-cooled support structure, ‘large diameter RC tubular columns + LBRB’ energy dissipation structure and ‘small diameter RC tubular columns + LBRB’ energy dissipation structure are established. Based on IDA method, the fragility of air-cooled support structure and energy dissipation structures is studied. The study shows that the addition of LBRB can effectively improve the horizontal-torsional coupling phenomenon of the structure, improve the ductility and seismic performance, and reduce the failure probability of the structure. Adding LBRBs and reducing the diameter of RC tubular columns can play the role of LBRB energy dissipation to a greater extent, so that the structure can obtain stronger anti-collapse capacity and better economy, which is more conducive to the realization of seismic performance-based fortification goal. It is suggested that three-dimensional ground motion input should be used for fragility analysis. If the dimension of ground motion input is reduced, the assessment results will be biased to danger.

A two-step approach combining FK with SE for simulating ground motion due to point dislocation sources

It has been well established that source-path-site effects have had an essential impact on the seismic analysis of major infrastructure over the past few decades, where the accurate and efficient modeling of seismic wave propagation can become a critical issue. In this study, a two-step approach combining the frequency-wavenumber (FK) technique with the spectral element (SE) method is developed based on the concept of domain reduction to simulate three-dimensional (3D) ground motion due to point dislocation sources. In the first step, the seismic responses for the dislocations in a layered half-space crustal model are solved exactly using the FK method and converted into effective input seismic loads around the region of interest. In the second step, the local wavefields of a 3D complex site are finely simulated using the SEM, while absorbing conditions are imposed at five boundaries of the SE model to achieve absorption of the outward scattered energy. The semi-analytical FK method is well-matched to the propagation frequencies because it allows the broadband synthesis associated with engineered systems to be addressed without additional calculations. When the FK is combined with the SEM, it is feasible to efficiently simulate earthquake ground motions covering a broad range of frequencies in the region of interest. Comparisons with the results of existing studies and the traditional SEM show that our approach is accurate and robust for arbitrary geometries and point sources. To further illustrate the efficiency and general applicability of the proposed method, three examples are presented. The results demonstrate that the two-step approach can consider the effects of the seismic source, propagation path, and local site geological conditions on the earthquake ground motions and serve as an effective forward modeling tool for reducing the computational cost.

AN EARTHQUAKE INTENSITY MEASURE FOR HIGH-RISE STRUCTURES UNDER THREE-DIMENSIONAL EARTHQUAKE GROUND MOTIONS

High-rise concrete structures are long and flexible cantilever structures which are commonly used as chimneys, water towers and TV towers. The existing earthquake intensity measures (IMs) mainly focus on building structures under one-dimensional or two-dimensional input ground motions, but high-rise concrete structures are sensitive to vertical ground motions. Based on a chimney and a water tower, it proposes a combined earthquake intensity measure which considers both the higher-mode effect and period elongation effect. The sufficiency and efficiency of the IM are investigated for three-dimensional far-field ground motions and near-fault ground motions with the pulse-like effect. A comparison is made among fifteen existing IMs, and the results indicate that the proposed IM is suitable for such kind of structures. Consequently, this IM is a promising intensity measure in the seismic assessment of high-rise structures under three-dimensional ground motions.

Modeling nonlinear site effects in physics-based ground motion simulations of the 2010–2011 Canterbury earthquake sequence

This study examines the performance of nonlinear total stress one-dimensional (1D) wave propagation site response analysis for modeling site effects in physics-based ground motion simulations of the 2010–2011 Canterbury, New Zealand earthquake sequence. This approach explicitly models three-dimensional (3D) ground motion phenomena at the regional scale, and detailed site effects at the local scale. The approach is compared with a more commonly used empirical VS30-based method of computing site amplification for simulated ground motions, as well as prediction via an empirical ground motion model. Site-specific ground response analysis is performed at 20 strong motion stations in Christchurch for 11 earthquakes with 4.7≤ MW≤7.1. When compared with the VS30-based approach, the wave propagation analysis reduces both overall model bias and uncertainty in site-to-site residuals at the fundamental period, and significantly reduces systematic residuals for soft or “atypical” sites that exhibit strong site amplification. The comparable performance in ground motion prediction between the physics-based simulation method and empirical ground motion models suggests the former is a viable approach for generating site-specific ground motions for geotechnical and structural response history analyses.

Strong ground motion over a large area in northern Taiwan caused by the northward rupture directivity of the 2019 Hualien earthquake

An Mw 6.2 earthquake struck Hualien on the eastern coast of Taiwan on April 18, 2019. Its focal mechanism was determined to be a thrust fault with a depth of 18.8 km. A wide range of strong ground shaking with an intensity value from 4 (25–80 Gal) to 7 (greater than 400 Gal) occurred in northern Taiwan, which is unusual for earthquakes of this size. Here we show a source model as determined by local seismic waveform inversion. Two asperities were found, the smaller one occurred at the hypocenter and the larger one was found 10 km north of the hypocenter with a depth of 18–25 km. The initial rupture started from the hypocenter and then rapidly propagated all the way to the large asperity in the north. A near supershear speed of close to 4.0 km/s was found to have occurred during this northward rupture process. The inverted source model was evaluated using forward three-dimensional ground motion simulations. The results show strong agreement with island-wide observed displacement waveforms and peak ground acceleration for periods from 3.0 to 20.0 s. The rapid northward rupture caused a strong directivity effect coupled with the specific source radiation pattern, resulting in a large area of strong ground shaking in northern Taiwan, even though the Hualien earthquake was a moderately-sized event.

Three-dimensional ground motion modelling in the Kachchh rift zone, Gujarat, India

The strong motion dataset of the 6 April 2006 Bhuj aftershock of Mw5.5 from 16 three-component accelerograph stations are used here to perform a detailed ground motion modelling in the Kachchh rift basin. First, we estimate the 1-D velocity structure model down to the bedrock at 16 accelerograph sites, through the Genetic Algorithm inversion of strong motion waveforms. Then, a 3-D velocity structure model of the basin is constructed using the modelled 1-D velocity structure and constraints from earlier seismological, Vs30 estimation (by PS logging and MASW), and seismic exploration studies in the region. We modelled low-frequency (0.1–1 Hz) ground motions excited by the 6 April 2006 event, using the finite difference method (FDM) assuming a point source, to access the robustness of the constructed velocity structure model. At most of the stations, the observed and simulated velocity waveforms are found to be in good agreement in terms of both amplitude and ground motion duration. We also computed synthetic ground velocities at numerous locations within the basin, for both the 2001 Bhuj mainshock (finite-fault source) and the 2006 aftershock (point source) cases, using the 3-D velocity structure model. For both the cases, we notice significant amplifications of amplitudes and elongation of shaking at stations lying within the basin while smaller amplifications are noticed at stations away from the basin. Our FDM modelling for the 2001 Bhuj mainshock at lower frequency (<1 Hz) predicted a peak ground motion velocity (PGV) of 50–110 cm/s at locations just over the causative fault of the 2001 mainshock. Our study reveals that the presence of low velocity sediments within the Kachchh rift basin plays a key role in modifying the ground motions in 0.1–1.0 Hz, thus, these effects should be quantitatively considered for future seismic hazard analysis in this region.

Source rupture process of the 2018 Hokkaido Eastern Iburi earthquake deduced from strong-motion data considering seismic wave propagation in three-dimensional velocity structure

The source rupture process of the 2018 Hokkaido Eastern Iburi earthquake (MJMA 6.7) was analyzed by a kinematic waveform inversion method using strong-motion data in 0.04–0.5 Hz. This earthquake occurred close to the Hidaka Collision Zone and the Ishikari depression, where the crustal structure is rather complex. Thus, we used a three-dimensional velocity structure model to compute the theoretical Green’s functions by the finite difference method. A source fault model with strike-angle variation was set based on the spatial distribution of the early aftershocks. The strong-motion stations used for the source inversion were selected based on the result of forward ground motion simulation of a moderate aftershock. The slip in the first 5 s was relatively small, but an area of significant slip with peak slip of 1.7 m was found in the depth range from 22 to 32 km. The rupture propagated upward mainly in the southwest direction. Based on the regional crustal structure and the configuration of the Moho discontinuity, the large-slip area was thought to be located in the lower crust, and its rupture did not reach the upper part of the continental crust. Most of the early aftershocks occurred around the large-slip area. The later aftershocks at the depth shallower than 20 km occurred outside the causative source fault of the mainshock. Three-dimensional ground motion simulation demonstrated that the heterogeneous source process and the three-dimensional basin and crustal velocity structure brought a large velocity pulse to an area to the southwest of the source fault, where the largest PGV was observed during the mainshock. The spatial distribution of the simulated PGV resembled the observed PGV distribution except some sites located inside the Ishikari depression where thick Quaternary soft low-velocity sediments exist at the top of the basin.

Probabilistic seismic demand and capacity models and fragility curves for reticulated structures under far-field ground motions

This paper aims to develop probabilistic seismic demand models (PSDMs), probabilistic seismic capacity models (PSCMs) and fragility curves for the widely-constructed reticulated structures using far-field earthquake records. The ground motion variability and prevailing uncertainties in structural design and modeling are considered, via performing incremental dynamic analyses (IDAs) on sample models of eighteen generic reticulated shells under forty far-field three-dimensional ground motions. A seismic energy demand-based damage index (DIE) is introduced and then employed together with the peak ground acceleration (PGA), to develop PSDMs and PSCMs for the reticulated shells considered, on the basis of statistical evaluation of the IDA results. The effects of two key structural design parameters, i.e., rise-to-span (or -width) ratio and roof load, on the PSDMs are investigated, and the normalized values for the PSCMs are also recommended. Fragility curves are derived and plotted to examine the difference among reticulated shells with different design parameters. It is concluded that DIE has strong correlation with PGA, and is more appropriate for developing PSDMs for the reticulated shells; and it also suggests that the reticulated shells with bigger rise-to-span (or -width) ratios or larger roof loads are more likely to damage or collapse during earthquakes. These results and conclusions will facilitate the performance-based seismic design and seismic vulnerability assessment of reticulated structures.

Static Test and Seismic Dynamic Response of an Innovative 3D Seismic Isolation System

Seismic isolation is an efficient strategy to protect structures from the effects of moderate to severe earthquake shaking. Conventional isolation devices can reduce the structural response in horizontal directions only; however, three-dimensional (3D) ground motions have been observed in earthquake records. In this paper, an innovative 3D seismic isolator is proposed. A new kind of asymmetric oblique hysteretic model is illustrated, and a quasistatic compression test of a model device using three lead rubber bearings (LRBs) is conducted. The test results and theoretical model results match well. A significant asymmetric property is observed in the hysteretic curves. The proposed hysteretic model can efficiently simulate the vertical mechanical behavior of a 3D seismic isolation system. The effects of different parameters are highlighted based on the theoretical mechanical model. The inclination angle, friction coefficient, and second shape factor of the inclined LRBs strongly influence the vertical behavior of the proposed device. A dynamic response analysis of the substructure of a nuclear power plant (NPP) is conducted. The hysteretic curves have the shape of an asymmetric quadrangle; this shape is similar to that observed in the test results. The vertical acceleration response of the vertical isolation structure is reduced by 33% compared with that of a fixed-base structure and reduced by 58% compared with that of a horizontal isolation structure. The proposed 3D isolator can sufficiently isolate the seismic input.

Elastic-plastic behavior of AP1000 nuclear island structure under mainshock-aftershock sequences

This paper studies dynamic responses of AP1000 nuclear island structure in strong earthquake sequences. A numerical model to simulate nuclear structural behaviors in earthquake is validated by comparison with data from a previous study on a nonlinear dynamic analysis of a reinforced concrete shield building. The validated numerical model is then used to carry out a series of parametric analyses with 112 computational cases so as to determine influence of strong aftershocks on structural elastic-plastic behavior considering input of three-dimensional ground motions. The results indicate that the influence of aftershocks on structural horizontal/vertical dynamic responses is very small in design basis earthquake sequences. However, the influence must be considered seriously in beyond-design basis earthquake sequences as values of RMVs (Ratio of Mean Value) deviating IPRs (Input Peak Ratio) obviously, which means structural dynamic responses are greatly changed in strong aftershocks. Damage aggravating effect induced by strong aftershocks can cause severe damage of structural members and it is found the greater the magnitude of aftershocks, the severer the aggravation effect. Although earthquake input energy is mostly dissipated by damping energy, plastic damage energy plays considerable role in strong aftershocks as it shares beyond 8 percent of the total input energy, which is 10 times more compared to design basis earthquake sequences.

Simulation of multi-support depth-varying earthquake ground motions within heterogeneous onshore and offshore sites

This paper presents a novel approach to model and simulate the multi-support depth-varying seismic motions (MDSMs) within heterogeneous offshore and onshore sites. Based on 1D wave propagation theory, the three-dimensional ground motion transfer functions on the surface or within an offshore or onshore site are derived by considering the effects of seawater and porous soils on the propagation of seismic P waves. Moreover, the depth-varying and spatial variation properties of seismic ground motions are considered in the ground motion simulation. Using the obtained transfer functions at any locations within a site, the offshore or onshore depth-varying seismic motions are stochastically simulated based on the spectral representation method (SRM). The traditional approaches for simulating spatially varying ground motions are improved and extended to generate MDSMs within multiple offshore and onshore sites. The simulation results show that the PSD functions and coherency losses of the generated MDSMs are compatible with respective target values, which fully validates the effectiveness of the proposed simulation method. The synthesized MDSMs can provide strong support for the precise seismic response prediction and performance-based design of both offshore and onshore large-span engineering structures.

Damage assessment of older highway bridges subjected to three-dimensional ground motions: Characterization of shear–axial force interaction on seismic fragilities

This study presents the influence of vertical ground motions on the seismic response and fragility of typical older highway bridges. The fragility is investigated using a set of functions that estimate exceedance probabilities of structures under seismic events. For this purpose, this study selects a typical older two-span single frame concrete box-girder bridge constructed in California in 1967. The bridge column has insufficient design details such as wide spacing of transverse reinforcement and low ratio of shear span to section depth resulting in an increased potential of shear–axial failure. The column shear response model accounts for the fluctuation in column axial force using an existing Zeus-NL material model and is validated through comparison of simulated and experimental results reported in the literature. Using this shear–axial force interaction model, a bridge system model is created in Zeus-NL to perform nonlinear time-history analyses. The response results are used to generate demand models, and component and system fragility curves of the bridge. Finally, fragility curves are compared for two bridge models with column shear model under constant axial force and with column shear model under axial force variation. The comparative results indicate that the shear model accounting for varying axial force increases the probability of exceeding the severe damage state by about 10% across the entire range of an intensity measure and reduces the median intensity measure by more than 15%. This observation highlights the importance of shear–axial force interaction in the seismic performance of older bridges.

Response of Transmission Lines under Three-Dimensional Seismic Excitations

The behavior of transmission line under three-dimensional seismic excitations is studied by numerical simulation. According to a practical engineering, the transmission towers are modeled by frame elements and the transmission lines are modeled by cable element account for the nonlinearity of the cable. The effects of single-dimensional, two-dimensional and three-dimensional ground motions on the responses of transmission line are investigated using nonlinear time history analysis method, respectively. The results indicate that the longitudinal maximum response of transmission lines can be obtained considering longitudinal ground motion excitation only. The transverse maximum response of transmission lines can be obtained considering transverse ground motion excitation only. Neglecting multiple nature of ground motion in analysis will significantly underestimate the vertical responses of the transmission lines. To obtain an accurate seismic response of transmission lines, three-dimensional ground motion inputs are required.

Influence of Soil-Pile Interaction on Seismic Mitigation Effectiveness with FPB for Curved Girder Bridge

The seismic response of curved girder bridge is more complex because of its irregular plane shape. Friction pendulum bearing (FPB) has a positive effect on structural seismic response. The seismic response mitigation effectiveness of FPB to curved girder bridge with soil-pile interaction considered is needed to research. The three-dimensional calculation model of a curved continuous girder bridge is established, and FPB are added at the positions of sliding bearings with soil-pile interaction. The influence of soil-pile interaction on seismic response mitigation effectiveness of FPB is computed and analyzed under three-dimensional ground motion action. The results show that the seismic response mitigation effectiveness of FPB is quite obvious with or without soil-pile interaction considered. Furthermore, seismic response mitigation effectiveness of FPB increases for the internal force of piers after soil-pile interaction considered. FPB has great and positive mitigation effectiveness on the seismic longitudinal displacement of the main girder of curved girder bridge, but with soil-pile interaction considered the mitigation effectiveness decreases a bit.

Analysis on Seismic Pounding of Curved Bridge

Based on the impact phenomenon between the end of the beam and the bridge abutment of the curved continuous bridge during earthquakes, a spatial finite element calculating model with collision element is presented. The law of collision is studied by the nonlinear contact time history analysis method under two three-dimensional ground motions. The variation laws of relative displacement and the internal force at the bottoms of piers are researched. In addition the changing of displacement and internal force at the end diaphragm are studied. The results show that the pounding action can easily lead to significant collision forces between the end beam and the abutment of the curved bridge which increases the axial force of girder evidently. The collision forces and longitudinal displacements from the inner to outer of the diaphragm generally are showed by an increasing trend, and the pounding action is more fierce under Elcentro ground motion than that under Tianjin ground motion.There is no relative displacement of consolided pier, bending moment and shear force of the consolided pier are greater than that of the mobile pier.The conclusions from the present study may serve as a reference base for seismic design of continuous curved bridges.