Effects Of Ground Motions Research Articles

Effect of Base Isolation using LRB on Stepped Building

Abstract: The base isolation design strategy uncouples the superstructure from the foundation, reducing the effects of earthquake ground motion. The structure is isolated from the ground motion by a flexible base. Installing base isolators in columns. The structural response accelerations are usually less than the ground motion acceleration. In general, base isolation reduces storey shear and acceleration while simultaneously increasing time period, and storey drift, allowing rigid buildings to be more flexible by dispersing energy to the foundation. The basic seismic isolation design provides a shielding technique, allowing the structure to function without harm even after significant earthquakes. The current study explores the seismic effects of a G+6 stepped building with an LRB isolator. An isolator with a lead rubber bearing was used. E-tabs is used to conduct the base isolation study and seismic analysis. The reaction of the structure, lateral shear force, time period, and base shear, was observed. This paper presents time-history analysis and performance assessment analyses on a base isolated stepped building using Bhuj Earthquake ground motion data.

Effects of Ground Motion Duration on the Seismic Performance of a Two-Storey Balloon-Type CLT Building

The effects of long duration ground motions on the seismic performance of a newly constructed two-storey balloon-type cross-laminated timber (CLT) building located in Vancouver, Canada, was studied. A three-dimensional numerical model of the building was developed in OpenSees. The connection and shear wall models were validated with test data. Twenty-four pairs of long and short duration records with approximately the same amplitude, frequency content, and rate of energy build-up were used for nonlinear dynamic analyses. Fragility curves were developed based on the results of incremental dynamic analysis to assess the building’s collapse capacity. At design intensity level, ground motion duration was shown not to be a critical factor as the difference in inter-storey drift ratio between the two sets of records was negligible. However, due to the larger number of inelastic cycles, the long duration motions increased the median probability of collapse by 9% when compared with the short duration motions. Further research is required to evaluate the duration effects on taller and platform-type CLT buildings.

Fragility curves for light damage of clay masonry walls subjected to seismic vibrations

The probability of light damage to unprepared, unreinforced masonry structures exposed to induced seismicity due to gas extraction in the north of the Netherlands is still under investigation. Repeated light seismic excitations caused by frequent, light and nearby earthquakes have been linked to economical losses and societal unrest in particular, with extensive damage claims. Moreover, the damaging potential of the seismic events has been related to the condition of the structure, especially if damage corresponding to settlement causes is already present. A comprehensive testing campaign oriented towards the initiation and progression of light damage of replicated clay brick masonry has been conducted at Delft University of Technology. Based on these tests, calibrated finite element models have been produced. This article uses the calibrated non-linear time-history models to simulate the effect of earthquake ground motion on a variety of initial conditions, wall geometry, material properties, and number, type and intensity of earthquakes. The results are then used to regress a relationship between damage and these parameters. This is subsequently employed to run a MonteCarlo simulation and produce fragility curves where the probability of exceeding specific damage values for various initial damage levels is presented against the seismic hazard. The vulnerability or fragility curves show that visible damage, with cracks wider than 0.1 mm, appears, with a 10% exceedance probability, at 13 mm/s of peak ground velocity; but, if the masonry had already undergone some light, yet imperceptible damage, a PGV of 6 mm/s was sufficient to aggravate it into visible cracks. To attain a 1% probability of exceeding light damage however, for which the masonry would need more invasive repair, it was observed that PGVs larger than 15 mm/s were required. These fragility curves were finally compared to graphs from other authors and found to capture well the variability in the range assigned to light damage.

Effects of near-fault pulse-type ground motions on high-speed railway simply supported bridge and pulse parameter analysis

Based on an innovative high-speed railway simply supported bridge (HSRSSB) model, the potential influence of near-fault pulse-type ground motions on HSRSSB is analyzed. Eighty-five original records of such ground motions are imposed on the simulation model. The dynamic responses of the bridge are calculated, including girder displacement, rail displacement, pier bending moment, bearing deformation, and residual displacement. Linear regression analysis reveals the relationship between the dynamic response and intensity measures (IMs). Moreover, six typical ground motions are chosen from these eighty-five records as prototypes in order to perform a pulse parameter analysis. Through an artificial ground motion synthesis, the effects of parameters, such as pulse amplitude, pulse period, and pulse number, on the behavior of HSRSSB are investigated and discussed. It is concluded that the response of HSRSSB depends on the acceleration-type IMs and presents a strong linear relationship with spectral IMs at the fundamental period of the structure. Regarding the pulse parameters, the HSRSSB dynamic response shows a positive correlation relationship with pulse amplitude, but a negative correlation with pulse period.

Nonlinear seismic fragility analysis of a resilient precast post-tensioned segmental bridge pier

ABSTRACT The use of precast post-tensioned segmental (PPS) piers is growing in the bridge industry, particularly in Accelerated Bridge Construction (ABC). To increase their use in high-seismicity regions, this study focuses on the seismic performance of the PPS piers under pulse-like near-field earthquakes. Two ensembles of 40 pulse-like near-field ground motions and 44 far-field ground motions along with three bridge piers of various heights are used in a series of incremental dynamic analyses. The piers are analysed under the original pulse-like near-field ground motions, their extracted pulse ground motions, and their corresponding non-pulse ground motions. It is found that the effect of the pulse ground motion is pronounced, when the pulse period is in proximity to the natural period of the pier. It is also seen that pulse-like near-field and far-field ground motions generally have similar effects on the response of PPS piers.

Stochastic ground motion simulation and seismic damage performance assessment of a 3-D subway station structure based on stochastic dynamic and probabilistic analysis

In practical engineering of underground structures, it is well-known that the randomness of earthquake generation and a structure's seismic response need to be considered for the safety of the project. The dynamic response and reliability level of a subway station are analyzed from the perspective of random vibration and the effect of stochastic ground motions on seismic responses is considered in this paper. This research proposes a model that can generate completely nonstationary ground motions and combines it with the probability density evolution method (PDEM) to analyze the seismic response and reliability level of a subway station. First, combining random function spectrum representation and evolutionary power spectrum density function, a probability model of nonstationary ground motion is established. According to the code (Gb 50909-2014), the model parameters of 5 sites are suggested, and the efficiency and accuracy are verified. A series of intensity–frequency nonstationary stochastic earthquakes are generated for the seismic response analysis. Then, a 3-D finite element analysis is performed for the deterministic dynamic response of the Daikai subway station, and the second-order statistics of three evaluation indicators (interstory drift, relative settlement, damage area ratio) are attained. Finally, the stochastic dynamic response and reliability level of the station structure are obtained by processing the data with the PDEM. The limit state related to the three evaluation indicators is established through probability density function (PDF) and cumulative distribution function (CDF). In addition, this probability evaluation system is more intuitive and effective than conventional methods. The statistical and probabilistic results show that the characteristics of earthquakes have a significant influence on the seismic response of subway stations, furthermore, the stochastic earthquakes generated by the intensity–frequency nonstationary ground motion model match well with the target value and the PDEM can comprehensively evaluate the seismic performance and reliability level of subway stations. Therefore, combing the stochastic earthquake and PDEM is an effective way to analyze the seismic response of subway stations.

Near‐fault ground motion effects on pounding and unseating using an example of a three‐span, simply supported bridge

AbstractA simple model of a three‐span, simply supported bridge consisting of three rigid decks supported by two axially rigid piers and rigid abutments at two ends is analyzed by solving the dynamic differential equations. The response spectrum method is not considered, and it is assumed that there is no soil–structure interaction. The bridge is acted upon by the acceleration of gravity, g, and excited by differential horizontal‐, vertical‐, and point‐ and cord‐rocking components of near‐fault ground motion. The model's in‐plane linear response shows that the vertical and rocking ground‐motion components have no noticeable effect on the maximum pounding force between bridge segments when computed for horizontal ground motion only. For the model with system periods longer than 1 s subjected to the strong motion pulse corresponding to magnitude M = 7, the vertical ground‐motion component contributes to the destabilizing effect of the gravity. For bridge periods longer than 0.5 s, the simultaneous action of horizontal and vertical ground‐motion components can noticeably increase the minimum gap size required to prevent pounding and the minimum seating length to avoid the unseating of bridge segments when computed for horizontal ground motion only. For system periods shorter than 1 s, the time delay of input ground motion has a significant effect on the minimum gap size to prevent pounding as well as on the minimum seating length to avoid unseating of the deck. The response of the bridge subjected to differential horizontal, vertical, and point‐rocking ground‐motion components is almost the same as the response under differential horizontal and vertical components of the ground motion. The main contribution to changes in the response, which is computed for horizontal ground motion only, is caused by the vertical and cord rocking of the ground motion. The minimum seating length to avoid the unseating of bridge segments suggested in seismic Iranian Code, No: 463 (Road and railway bridges seismic‐resistant design code, 2008), is conservative for pulses with magnitudes M = 5 and 6, but not conservative for bridge periods longer than about 0.6 s and a near‐field pulse with M = 7 magnitude.

A hybrid characterization framework for structure-significant pulse-like features in ground motions

In earthquake engineering and engineering seismology, it is fundamental to identify pulse-type ground motions and characterize their pulse-like features, as seismologists relate them to the fault rupture and engineers relate them to the structural response. Pulse-type ground motions have been observed to exhibit peculiar attributes both in the response spectrum and in the time series. The existing pulse identification methods rarely leverage the distinct feature in response spectrum sufficiently, and consequently only the mimicry in time series sometimes loses the impulsive effect of the original ground motion on the structures. Based on the self-similarity revealed by dimensional analysis, the current study developed a hybrid pulse characterization framework that starts from subregion-to-subregion similarity matching in response spectral space and finally achieves resemblance in time domain, for pulse-like features in either ground velocity or acceleration. The framework directly identifies the pulses that dominate the structural response. The framework is versatile in terms of allowing various pulse waveforms, switching among different types of response spectra, and coping with the ground motions that contain multiple structure-significant pulse-like features.

Impact of directional effect of strong ground motion on scenario-based earthquake hazards: preliminary results

Scenario-based earthquake hazards are useful for social planning and disaster mitigation. In this study, general attenuation properties of earthquake events are analysed empirically with respect to the direction of seismic rupture from the epicentre. The study is primarily focused on presenting a relationship between fault source characteristics and the most credible direction of any earthquake that occurs at that source. Since such a direction is not only a function of source but also is dependent on site parameters, several ground motion prediction equations are utilised in congregation with methods to evaluate site parameters. The method involves a graphical relationship between scenario spectral ordinates and polar coordinates to estimate the most credible direction for that scenario. An analysis illustrating the method is presented here for the Himalayan megathrust fault, the Main Boundary Thrust.

ANALYSIS OF MINING-INDUCED TERRAIN DEFORMATION USING MULTITEMPORAL DISTRIBUTED SCATTERER SAR INTERFEROMETRY

Abstract. This work addresses a methodology based on the Interferometric Synthetic Aperture Radar (InSAR) to analyse and monitor ground motion phenomena induced by underground mining activities, in the Legnica-Glogow Copper District, south-western Poland. Two stacks of ascending and descending Sentinel-1 Synthetic Aperture Radar (SAR) images are processed with a small baseline multitemporal approach. A simple method to select interferograms with high coherence and eliminated images with low redundancy is implemented to optimize the interferogram netwrork. The estimated displacement maps and time series show the effect of both linear and impulsive ground motion and are validated against Global Navigation Satellite System (GNSS) measurements.

Earthquake-induced landslide erosion coupled to tectonics and river incision, and effects of ground motion on coupled patterns

Landslide erosion and long-term denudation for the natural surface erosion processes in tectonically active mountain ranges are coupled to tectonics and river incision. However, such relationships have rarely been quantified in earthquake-induced landslides. Here we assess seismic landslide erosion caused by the Wenchuan earthquake in the Longmen Shan and explore relationships between tectonic uplift, river incision, and earthquake-induced landslide erosion yields and thus evaluate the effects of ground motion on coupled patterns. We show that nonlinear correlations exist between seismic landslide erosion rates and topographic metrics (mean slope gradient and normalized channel steepness) under various shaking conditions (peak ground acceleration PGA > 0.4 g). The areas with stronger shaking cause greater landslide erosion yields, higher erosion efficiency, weaker nonlinearity, and lower mean landslide slope although they have a similar threshold hillslope. Taken together, these analyses support an emerging view that the stronger ground motion reduces the equivalent rock mass strength on the hillslope and breaks the topographic threshold, which consequently produces a systematic increase in landslide erosion below or above the threshold state and results in nonlinearity variation. Our finding demonstrates that earthquake-induced landslide erosion is coupled to tectonics and river incision under various shaking conditions and presents a quantitative relationship between seismic landslide erosion rates and topographic metrics, providing potentially important implications for mountain belt evolution.

Seismic behaviour of structures under bidirectional ground motion: Does the angle of incidence have any influence?

Inelastic seismic behaviour of structures is needed to be predicted as accurately as possible. As during the seismic design, structures are allowed to undergo a stipulated amount of inelastic deformation in the dual design philosophy and its further extension of performance-based design. To obtain reasonably accurate behaviour in post-elastic ranges has manifold issues to be addressed together. The simultaneous effect of bidirectional ground motion is one of the major factors that need to be considered, and many studies also did the same. However, hardly any of them did consider the interaction between the deformations along two principal orthogonal directions on the yield criteria, post-elastic range excursion and the criteria of unloading. The present study makes an attempt to address these issues. Further, a few more studies mentioned that the angle of incidence of such orthogonal components of ground motion might influence the response of the structure. Hence, along with incorporating the effect of bidirectional interaction in the post elastic range, the issue of incidence angle is also studied extensively to reach a conclusive end. The detailed results presented in the study not only help to develop the physical insight but also maybe help in fine-tuning the design provisions.

A Multi-Temporal Small Baseline Interferometry Procedure Applied to Mining-Induced Deformation Monitoring

This work addresses a methodology based on the interferometric synthetic aperture radar (InSAR) applied to analyze and monitor ground-motion phenomena induced by underground mining activities in the Legnica-Glogow copper district, south-western Poland. The adopted technique employs an InSAR processing chain that exploits a stack of Sentinel-1 synthetic aperture radar (SAR) images using a small baseline multitemporal approach. Interferograms with small temporal baselines are first selected, then their network is optimized and reduced to eliminate noisy data, in order to mitigate the effect of decorrelation sources related to seasonal phenomena, i.e., snow and vegetation growth, and to the radar acquisition geometry. The atmospheric disturbance is mitigated using a spatio-temporal filter based on the nonequispaced fast Fourier transform. The estimated displacement maps and time series show the effect of both linear and impulsive ground motion and are validated against global navigation satellite system (GNSS) measurements. In this context, a significant threat to the built environment is represented by seismic tremors triggered by underground mining activities, which are analyzed using the proposed method to integrate the information gathered by in situ seismometer devices.

A New Model for Vertical-to-Horizontal Response Spectral Ratios for Central and Eastern North America

ABSTRACT It is a well-known fact that critical structures are required to be designed for the vertical effects of earthquake ground motions as well as the horizontal effects. We developed a new model for the spectral ratio of vertical-to-horizontal components of earthquakes (V/H ratio) for central and eastern North America (CENA). The proposed V/H ratio model has the advantage of considering the earthquake magnitude, source-to-site distance, and the shear-wave velocity of soil deposits in the upper 30 m of the site for peak ground acceleration and a wide range of spectral periods (0.01–10.0 s). The model evaluation is based on a comprehensive set of regression analysis of the compiled Next Generation Attenuation-East database of the available CENA recordings with M ≥ 3.4 and Rrup<1000 km. The median value of the geometric mean of the orthogonal horizontal motions rotated through all possible nonredundant rotation angles, known as the RotD50, is used along with the vertical component to perform regression using the nonlinear mixed-effect regression. We excluded the earthquakes and recording stations in the Gulf Coast region due to their different ground motion attenuation (Dreiling et al., 2014). To compute V/H ratios for the Gulf Coast region, we refer the readers to the study of Haji-Soltani et al. (2017). Moreover, we excluded the National Earthquake Hazard Reduction Program site class E sites from consideration because of their complex site response characteristics and their potential for nonlinear site effects. The predicted V/H ratios from the proposed model are compared with recently published V/H ratio models. We suggest our model to be used for developing the vertical response spectra for CENA sites.

Effects of near-fault pulse-like ground motions on seismically isolated buildings

Forward-directivity effects create distinct velocity pulse in the fault-normal direction of near-fault ground motions. It has been shown that this pulse period governs the structural response of fixed base buildings. The present study examines the effects of the near-fault pulse-like ground motions on seismically isolated buildings, considering different effective isolation period to pulse period ratios. Three sets for near-fault ground motions with varying pulse periods are employed to determine the effects of pulse-like ground motions on isolator displacements, superstructure drift ratios, and superstructure load distributions. These effects are categorized as spectral shape and amplification. It is seen that the pulse period forms the spectral shape of records. Spectral acceleration relatively decreases in the short periods and increases in the long periods by enhancing the pulse period. This phenomenon reduces isolator displacement demand for near-fault ground motions with the large and medium pulse periods considering ASCE 7–16 scaling range. An intensity measure parameter is modified to indicate the spectral shape effect of pulse-like records on the isolated buildings. Also, the amplification ratio for the isolator displacement caused by the pulse period is obtained, excluding the spectral shape effect and considering the pulse period to effective isolation period ratio. Further, the R-μ-T relation of the first-floor acceleration, transferred acceleration to the superstructure, is acquired to determine the pulse period effect on superstructures. The results show that the superstructure ductility demand is very sensitive to the pulse period, and the effectiveness of the isolation system considerably decreases by enhancing the pulse period. Also, it is demonstrated that the pulse period governs the lateral load distribution for the superstructure.

Effect of Elastomeric Bearings in Bridge Piers

In this paper, the influence of elastomeric bearings is investigated in terms of seismic responses and presented under effects of severe ground motions. For this purpose, seismic performance of an isolated pier system is analytically studied by using time history analyses. The isolation system is assembled by elastomeric bearings composed of rubber layers and steel-shims. The bearings are located between pier-top ends and box-girder of the bridge deck. Seismic solutions are obtained for isolated system and non-isolated pier system known as rigid connection. Time-dependent response quantities are obtained in transverse direction for two strong quakes. Additionally, nonlinear static procedure is carried out to obtain lateral seismic capacity. Thus, the displacement and shear force capacity are determined for the considered pier systems. Seismic responses are comparatively presented in terms of superstructure and base response values. Thanks to the isolation system, the bearings have yielded lower peak displacements and base responses with seismic demand as well. On the other hand, higher seismic capacity has been obtained in case of isolation system and the results are presented by computed lateral capacity curves. The results show that the elastomeric bearing is an effective tool in lateral strength and modal behavior of the pier system as well.

Prediction and Modeling for Local Site Amplification Effect of Ground Motion: Exploring Optimized Machine Learning Approaches

Prediction and Modeling for Local Site Amplification Effect of Ground Motion: Exploring Optimized Machine Learning Approaches

Modeling of non-ductile RC structure under near-fault ground motions: A nonlinear finite element analysis

The old existing reinforced concrete (RC) structures in Taiwan are susceptible to severe damage under earthquakes because of the soft-story mechanism. Moreover, the effects of near-fault ground motions often contain a long period of velocity pulse and permanent ground displacement. This study is based on the tri-axial shaking table test conducted at the National Center for Research on Earthquake Engineering in Taiwan and a series of seismic performance evaluations of a non-ductile RC structure in Taiwan. Finite element analysis (FEA) will be conducted to simulate the linear and nonlinear behavior of the seven-story building. This accommodates the damage plasticity model for concrete and the elastic-perfectly plastic model for reinforcement. Comparison of the results between the experimental test and numerical model showed that the similarity of the vibration period has a great influence on the simulation results. The findings showed that the data of acceleration and displacement behavior corresponded with the experimental results in a satisfactory margin. Also, the damage mode is very similar to the shaking table test results. The study found that using FEA can satisfactorily simulate the seismic performance of mid-rise buildings under a near-fault earthquake.

State-of-Art-Review: Latest Advancements in Seismic Isolation of Structures

Seismic isolation is effected by providing an interface between the foundations of the building and superstructure which may consist of stories above the ground level by inserting devices. Those are meant to reduce the effect of ground motions generated by an earthquake or/ and wind load. In this process, the period of the whole structure including base isolators is elongated so that ground waves containing large energy contents in the horizontal components of the earthquake may be deflected conveniently. An updated state-of-art review of isolation techniques and the design of isolated buildings is presented in this paper. The research findings in the comprehensive form are extracted out of the large volume of research papers published during the last five decades, where only some limited quality papers are selected for the preparation of this manuscript. The review generally covered papers on the analysis and design of structures with base isolation. Review is not confined to buildings with friction pendulum isolators only, but also includes the study of structural response to some other types of base isolators and dampers to seismic attacks.

New conditional, scenario-based, and traditional peak ground velocity models for interface and intraslab subduction zone earthquakes

The Pacific Earthquake Engineering Research (PEER) Center next-generation attenuation relationships for subduction zone earthquakes (NGA-Sub) ground motion database is used to develop new conditional ground motion models (CGMMs), several scenario-based ground motion models (GMMs), and a traditional GMM to estimate the peak ground velocity ( PGV) for subduction zone (interface, intraslab) earthquakes. The PGV estimate in the CGMMs is conditioned on the rupture distance ( Rrup), magnitude ( Mw), time-averaged shear wave velocity in the top 30 m ( V s30) and pseudo-spectral acceleration PSA( T PGV). The period T PGV in the CGMMs is magnitude dependent to account for the magnitude dependence of the earthquake source corner frequency in the Fourier amplitude spectrum. Several scenario-based models are developed by combining the CGMM with PSA GMMs to directly estimate PGV given an earthquake scenario and site condition. Scenario-based models capture the complex ground motion effects in the underlying PSA GMMs and ensure the consistency with a design PSA spectrum, which is desired in engineering practice. In addition, a traditional PGV GMM is developed using Bayesian hierarchical regression. Finally, we compare all of these models and find that the scenario-based models are consistent with the traditional model developed in this study giving confidence to their use. The conditional and traditional PGV GMMs developed in this study benefit the performance-based design of engineering systems affected by subduction earthquakes when PGV is an important intensity measure.