Components Of Earthquake Ground Motion Research Articles

Seismic Performance Evaluation of Multi-Storey Residential Building with Friction Pendulum Bearings: Indonesia case study

The methodology for seismic performance evaluation of a residential building in Indonesia with the use of seismic isolation is considered. An 8-storey reinforced concrete frame residential building with shear wall structural system was selected as a case study. Nonlinear methods of seismic response analysis were used to calculate the response of the structure: nonlinear static (Pushover) and Nonlinear-Time History Analysis, NLTHA. The analysis is performed in STERA 3D freeware. The nonlinear time history analysis was performed for seven pairs of horizontal components of earthquake ground motions, selected according to the parameters of possible earthquakes for the considered site (Bandung city). The selected earthquake records were modified using the spectral matching procedure for design spectrum. Friction-pendulum bearings developed by Nippon Steel Corporation of Japan were used as seismic isolation. The results of nonlinear time history analysis show that shallow earthquakes result in greater damage compared to megathrust earthquakes, with both scenarios providing a life safety (LS) performance level. The use of seismic isolation can reduce seismic loads, as evidenced by the reduction in top-level accelerations and shear forces at the base.

Directionality of FIV3 ground-motion intensities during the 6 February 2023 Kahramanmaraş, Türkiye earthquake doublet

At present time, ground-motion prediction models neglect the directionality observed in horizontal components of earthquake ground motions, that is, the important changes in ground-motion intensity that occur with changes in azimuth. This study presents an investigation of the directionality of a recently proposed measure of ground-motion intensity during the 6 February 2023, Mw 7.8 Pazarcık and Mw 7.5 Elbistan earthquake doublet in the Kahramanmaraş region of Türkiye, which resulted in the collapse of more than 35,000 buildings and caused almost 60,000 fatalities. The studied intensity measure is referred to as FIV3, which has been shown to be better correlated with structural collapse than the spectral acceleration at the fundamental period of the structure. The improved intensity measure is period-dependent and is computed as the sum of the three largest incremental velocities with the same polarity obtained from the area under segments of a low-pass filtered ground acceleration time series. The following aspects are studied in this article: variation of FIV3 intensity with changes in the orientation; variation of FIV3 intensity with changes in the period of vibration; attenuation of FIV3 intensities with increasing distance; and spatial distribution of the orientation of maximum FIV3 intensity. This study is based on 231 pairs of records from the Mw 7.8 main event and 222 pairs of records from the Mw 7.5 event. Similarly to the directionality of spectral ordinates, it is found that the directionality of FIV3 intensity also increases with increasing period. Strong directionality occurred not only in the near field but up to distances as large as 400 km from the epicenter. The orientation of maximum FIV3 intensity is found to occur close to the transverse orientation, consistent with observations for the orientation of maximum spectral ordinates during strike-slip earthquakes.

Soil-Pile-Structure Interaction (SPSI) in Bridges: A Review

Response of soil influencing motion of pile supported structures or vice-versa is called Soil-Pile-Structure Interaction (SPSI). A part of SPSI is considered beneficial for the structure wherein it increases damping, and period of vibration. This study provides a comprehensive review addressing SPSI in bridge structures. Past research in this field has typically emphasised on Soil-Structure Interaction (SSI), rather than SPSI. An attempt is made here to compile the work done so far in this field. Detailed study, based on discretising the considered models in various articles, and the method for determining the stiffness of the underlying soil was carried out. The articles in this study were carefully chosen such that even if they have not considered SPSI, their models were worth reporting in this study. Response of soil and structure on the application of earthquake ground motion was also studied and discussed here with emphasis given on calculation of stiffness of soil and the interaction between them. It was observed that the material/spring used for modelling of soil is of utmost importance. The theories for the calculation of stiffness of the soil material for different locations of the pile length are also discussed. Few studies have also considered the vertical component of earthquake ground motion in the past. A detailed justification regarding the selection of method of analysis such as linear or non-linear analysis, and adopted approaches for analysis such as discrete or continuous approaches, and their overall influence on the study was observed, and reported here in a concise manner. This article primarily aims to summarize the previously published researches on SSI and SPSI, including their advantages and issues over the structure.

Impact of the Vertical Component of Earthquake Ground Motion in the Performance Level of Steel Buildings

This study discusses the impact of the vertical component of earthquake ground motion in the performance level of steel building subjected to earthquake excitations. Analyses are carried out for the strong column-weak beam philosophy because the structural performance is focused on these elements. A realistic steel frame is also considered to investigate the impact of including the seismic vertical component in the non-linear response of the building. The main findings of this study are: (1) When an analysis is performed by considering the horizontal and vertical components of ground motion acting simultaneously (near the causative fault), larger plastic rotations in the beams are obtained as compared to those resulting by considering only the horizontal component. (2) Due to the previous finding, if a codified criterion to inspect the steel beams performance in terms of the plastic rotation is considered, the beam performance could lie within a different acceptation criterion (i.e., from immediate occupancy to collapse prevention) if the vertical component is included in the analysis.

Seismic Response of Simply Supported Base-Isolated Bridge with Different Isolators

The seismic response of simply supported base-isolated bridge with different isolators is presented. The isolated bridge deck is idealized using simplified model of a simply supported rigid deck with three degrees-of-freedom, two lateral translational, mutually orthogonal and one rotational. The rotational degree-of-freedom of the bridge deck may arise because of the dissimilarity in properties of different seismic isolation devices such as elastomeric and sliding systems supporting the bridge deck. The sources of dissimilarity in the isolators considered here are the isolation stiffness and the yield force. The flexibility of abutments and bridge deck is ignored and two horizontal components of earthquake ground motion are applied, considering bi-directional interaction of the seismic response. The governing equations of motion for the uncoupled and torsionally coupled bridge are derived and solved using Newmark's method of integration to obtain the seismic response. The parametric studies are conducted for different system configurations, isolation systems and frequency ratios during torsionally coupled and uncoupled conditions. The seismic response of base-isolated bridge is seen to be considerably altered due to the dissimilarity in the isolator properties. The eccentricity arose due to the isolation stiffness affects more than that due to the isolator yield forces. The effectiveness of isolation reduces at higher eccentricities and the torsionally coupled response diminishes with the increase of uncoupled torsional to lateral frequency ratio.

Seismic response and failure modes of steel silos with isotropic stepped walls: The effect of vertical component of ground motion and comparison of buckling resistances under seismic actions with those under wind or discharge loads

Steel silos are one of the main structures for bulk solids handling and storage in many industries and agricultural sectors. A growing body of research suggests the importance of including the vertical component of earthquake ground motion in seismic analysis and design of certain structures. In the case of steel silos, this may induce additional meridional compression to exacerbate buckling failures in such thin shells. Accordingly, this paper investigates the buckling behavior of three cylindrical steel silos (i.e., a squat, an intermediate slender and a slender silo) with stepped walls subjected to horizontal only (H) and horizontal and vertical (HV) ground accelerations to address this point. Seven pairs of seismic records, each scaled to multiple levels of the peak ground acceleration (PGA), were applied to the silos. Using Incremental Dynamic Analyses (IDA), the critical base shear, base moment and the PGA at the buckling instant were evaluated for each structure. Moreover, the normal pressures and frictional tractions induced from ensiled material on silo walls were extracted under seismic conditions to reveal the influence of including the vertical component of seismic records on contact pressures.In accordance to the analyses performed, two different buckling modes were observed under seismic actions. Squat and intermediate slender silos buckled in the elastic range characterized by local diagonal shear wrinkles in the upper parts of the shell walls, while slender silo showed an elastic-plastic elephant’s foot buckling mode at the base. Considering the obtained critical values, the observed dynamic buckling modes and the extracted pressure distributions, it is concluded that including the vertical component of seismic records in calculations has quite marginal effects on seismic response of the silos.In order to provide a helpful insight into governing action in silos design, as a supplementary section to the paper, the buckling capacities of sample silos under seismic actions were compared with those evaluated under wind actions or discharge loads. Regarding to the different seismicity levels of Europe, governing action was determined for each silo in the context of Eurocode limit state design. The results obtained highlight the importance of considering the seismic action in buckling design of steel silos.

Scaling of Vertical Component of Seismic Ground Motion

Three-dimensional time history analysis has become a demand for the majority of updated building codes. A vast literature has addressed the selecting and scaling of horizontal component of earthquake ground motion. Meanwhile, the scaling of vertical component has been less of a concern. This paper investigates the suggestion of using the same scaling factor of horizontal component of ground motion to scale its vertical counterpart. A data set consists of 6409 mainshock records with vertical and orientation independent geometric rotated (GMRotD50) response spectra with 5% damping is used. Even though ASCE7-16 among other international codes recommends to use the same scaling factor for horizontal component and its vertical counterpart, this paper shows that scaling factor of vertical component trends an extreme variation from its horizontal counterpart for various soil classes, different magnitudes and over a wide range of Joyner-Boore distances. Results illustrate that the ratio of vertical to horizontal scaling factors has a strong negative relationship with the ratio of vertical to horizontal peak ground acceleration. Earthquake magnitude has no significant role on the ratio of vertical to horizontal scaling factors. A gradual increase is observed in the studied ratio over a wide range of Joyner-Boore distances. The paper ends up with simplified equations to calculate the scaling factor of vertical component in regards with the scaling factor of its GMRotD50 horizontal counterpart based on the (V/H)PGA ratio of the recorded components. Robust statistics manifest the goodness of the developed equations.

Seismic Analysis of Steel Cylindrical Liquid Storage Tank Using Coupled Acoustic-Structural Finite Element Method For Fluid-Structure Interaction

A seismic analysis of ground-supported, three-dimensional (3-D) rigid-base steel cylindrical liquid storage tank is investigated, using a coupled acoustic-structural finite element (FE) method for fluid-structure interaction (FSI). In this method, the contained liquid in the tank is modelled using acoustic elements and the cylindrical tank is modelled using shell elements. The impulsive and convective terms are estimated separately by using the appropriate boundary conditions on the free surface of the liquid. The convergence and validation studies of the proposed FE model are conducted by comparing the results reported in the literature. The parametric studies are performed for rigid and flexible tanks for the varying slenderness of the open roof tanks. The sloshing displacement and base shear time history responses are evaluated for the 3-D tanks subjected to harmonic unidirectional ground motions. Further, the results are compared with the commonly used two and three lumped-mass models of the tank. Moreover, the seismic response quantities of the tank subjected simultaneously to the bi-directional horizontal components of earthquake ground motion are also investigated using the 3-D FE model, and the response quantities are compared with the lumped-mass models. The results obtained from the 3-D FE model and lumped-mass model are in close agreement. The average percentage difference in the 3-D FE and lumped-mass models for maximum sloshing displacement prediction is 15 percent to 20 percent and that for the base shear is about 4 to 10 percent, in the case of the uni-directional harmonic ground motions. It is concluded that the sloshing displacement is not affected by the tank flexibility, but the impulsive hydrodynamic pressure and the impulsive component of the base shear increases with the tank flexibility.

Numerical study of base-isolated cylindrical liquid storage tanks using coupled acoustic-structural approach

A numerical study of the base-isolated ground-supported cylindrical liquid storage tank is carried out using finite element method (FEM). The coupled acoustic-structural (CAS) approach in the FEM is used for the analysis of the base-isolated tanks with rigid and flexible walls with varying parameters. Base isolation systems used in the present study are laminated rubber bearing (LRB) and friction pendulum system (FPS). The effects of aspect ratio (liquid height to radius) of the tank, and the isolation time period on the seismic response of the base-isolated tank is considered for investigation. For this study, the broad and slender tanks with three different isolation time periods are considered, which exhibit their relative flexibility. The sloshing displacement, base shear, hydrodynamic pressure, and bearing displacement responses are evaluated for three-dimensional (3-D) rigid and flexible tanks subjected to bi-directional components of earthquake ground motions. Moreover, the FE results are compared with the commonly used mechanical lumped-mass model of the base-isolated tank. The results show that as the time period of the isolator increases, i.e. increased flexibility, the base shear response is considerably reduced in both the rigid and flexible, broad and slender tanks. The reduction in the impulsive component causing base shear is more as compared to the convective (sloshing) component in the base-isolated tanks. The sloshing displacement increases with increase in the time period of the base isolation systems in both the rigid and flexible tanks. The impulsive hydrodynamic pressure along the tank wall is reduced with introduction of the isolation systems and the reduction is significantly more in case of the flexible isolators. The bearing displacement increases with increase in the time period of the isolation system adopted.

Determination of seismic compression of sand subjected to two horizontal components of earthquake ground motions

The objective of this Technical Note is to investigate the ratio of seismic compression of sand subjected to two mutually perpendicular horizontal components of earthquake ground motions simultaneously to its counterpart for single component of horizontal motions. By using a verified, fully coupled and inelastic finite element procedure, sand specimens with various relative densities (Dr=45%, 60% and 100%) are subjected to each of the horizontal components of motion separately, and then simultaneously, with the vertical strains and corresponding ratio computed for each case. In total, 296 shallow crustal horizontal motions (i.e. 148 sets of horizontal motions) with various earthquake magnitudes, site to source distances, durations, and site conditions recorded in active tectonic regions are used in the analyses. The results showed that the ratio generally ranges from 1.52 to 2.32, and it increases with earthquake magnitude and relative density of sand but decreases with epicentral distance. These results can be used in conjunction with seismic compression correlations for single component of motion to estimate its counterpart for multiple components of motion, thereby increasing the accuracy in predicting the severity of seismic compression under multi-directional seismic motions.

On the design of a dense array to extract rotational components of earthquake ground motion

Data recorded from dense seismic arrays such as the Large Scale Seismic Testing array in Lotung, Taiwan, are used for multiple purposes, including development of attenuation and coherency functions, computing dynamic strains in soil, and estimating rotational components of ground motion. The required footprint of a seismic array deployed to compute rotational components of ground motion is a function of the method used for the computations and site specific characteristics, including the apparent seismic wave velocity and the frequency content of expected ground motions. A design procedure for a general two-dimensional seismic array is presented together with a site-specific example using the Surface Distribution Method to extract the rotational components of ground motion. A sensitivity study is performed to determine how the location of recording stations of translational motion in a dense array affects the computed rotational components of earthquake ground motion.

Acceleration response spectra for Tbilisi city with site effects

The utilization of time histories of earthquake ground motion has grown considerably in the field of earthquake engineering. It is very unlikely, however, that recordings of earthquake ground motion will be available for all sites and conditions of interest. Hence, there is a need for efficient methods for the simulation of strong ground motion for a given region. Due to lack of the real strong ground motion records the objective of this research is to develop a methodology for rapid generation of horizontal and vertical components of earthquake ground motion at any site for Tbilisi city. The model developed in this study provides simulation of ground motion over a wide range of magnitudes and distances at 8 earthquake sources zones of Tbilisi region (within 50 km). The research includes three main topics: (i) the stochastic simulation of earthquake ground motion at a given site of the city of Tbilisi; (ii) the estimation of acceleration time histories at a given site using the direct method of engineering seismology considering soil conditions based on the theory of the reflected waves and (iii) calculation of horizontal and vertical acceleration elastic response spectra for main sites of Tbilisi territory. The simulation procedure typically consists of multiplying deterministic modulating function with a stationary process of known power spectral density. The obtained results in the terms of normalized elastic response spectra can be widely applied in the practice of earthquake engineering in Georgia.

Characterizing rotational components of earthquake ground motion using a surface distribution method and response of sample structures

Rotational components of strong earthquake ground motion (rocking and torsion) have not been measured directly by instruments deployed in the free field and such components are rarely considered, if at all, in the seismic analysis and design of buildings, bridges, infrastructure and safety-related nuclear structures. The effect of rotational components of ground motion on these structures is therefore unknown. Indirect methods of extracting rotational components from recorded translational data have been developed: a Single Station Procedure (SSP) uses data recorded at one station; and a multiple station procedure (MSP) uses data recorded at a number of closely co-located recording stations (the seismic array). An advantage of MSPs is that site-specific geologic data are not required for the calculations. The Geodetic Method (GM) is a MSP but it cannot retain important high frequencies in the rotational components. The Acceleration Gradient Method (AGM) retains higher frequencies than the GM with the upper limit on frequency being a function of the physical dimensions of the seismic array. A new procedure, the Surface Distribution Method (SDM), is shown to capture high frequencies but some site-specific data are required for the calculations. Results are presented to enable a comparison of SSP, GM, AGM and SDM. The SDM can be used to estimate the three rotational components of ground motion at a reference station across a wide range of frequencies using data recorded in a seismic array. Rotational seismic excitations calculated using the SDM are used to assess their effect on structural response. Three example structures, namely, a chimney, a base-isolated building and the associated fixed-base building are considered. Results indicate that rotational ground motions can significantly affect the response of structures.

Damping Scaling Factors for Vertical Elastic Response Spectra for Shallow Crustal Earthquakes in Active Tectonic Regions

This paper develops a new model for a damping scaling factor (DSF) that can be used to adjust elastic response spectral ordinates for the vertical component of earthquake ground motion at a 5% viscous damping ratio to ordinates at damping ratios between 0.5% and 30%. Using the extensive NGA-West2 database of recorded ground motions from worldwide shallow crustal earthquakes in active tectonic regions, a functional form for the median DSF is proposed that depends on the damping ratio, spectral period, earthquake magnitude, and distance. Standard deviation is a function of the damping ratio and spectral period. The proposed model is compared to the DSF for the “average” horizontal component. In general, the peak in DSF is shifted toward shorter periods and is farther from unity for the vertical component. Also, the standard deviation of DSF for vertical motion is slightly higher than that observed for the “average” horizontal component.

DAMAGE POTENTIAL OF EARTHQUAKE GROUND MOTIONS RECORDED IN SOUTHERN CENTRAL AMERICA

A total of 18 different components of earthquake ground motion recorded in Central America were selected to conductan evaluation oftheir damage potential. Emphasis was placed in ground motions recorded during recent seismic activity inCosta Rica. For the purpose of comparison, five records obtained in different parts ofthe world were included in the study. Asa mean ofidentif)'ing the damage potential ofthe records, the input energy as well as the plastic hysteretic energy speCtra werecalculated for different levels of displacement ductility and a viscous damping coefficient ~=0.05. The effect of duration ofground motion was studied by introducing the non dimensional parametery and the target ductility μTAR. The parameteryis a function of the maximum displacement and the plastic hysteretic energy dissipation demands. The calculations wereperformed for single-degree-of-freedom systems with an elastoplastic hysteretic behavior. Other response quantities consideredwere the constant strength ductility demands and constant ductility strength demands. The results are contrasted withthe current seismic design recommendations for the region as presented in the latest building codes available.

Damage potential of earthquake ground motions recorded in southern Central America

A total of 18 different components of earthquake ground motion recorded in Central America were selected to conductan evaluation oftheir damage potential. Emphasis was placed in ground motions recorded during recent seismic activity inCosta Rica. For the purpose of comparison, five records obtained in different parts ofthe world were included in the study. Asa mean ofidentif)'ing the damage potential ofthe records, the input energy as well as the plastic hysteretic energy speCtra werecalculated for different levels of displacement ductility and a viscous damping coefficient ~=0.05. The effect of duration ofground motion was studied by introducing the non dimensional parametery and the target ductility μTAR. The parameteryis a function of the maximum displacement and the plastic hysteretic energy dissipation demands. The calculations wereperformed for single-degree-of-freedom systems with an elastoplastic hysteretic behavior. Other response quantities consideredwere the constant strength ductility demands and constant ductility strength demands. The results are contrasted withthe current seismic design recommendations for the region as presented in the latest building codes available.

Extracting rotational components of earthquake ground motion using data recorded at multiple stations

ABSTRACTRotational components of earthquake ground motion have not been considered for seismic analysis, design and performance assessment because recordings of these components are unavailable. A number of procedures have been proposed to extract rotational components of ground motion from translational time series recorded at multiple, closely spaced recording stations. In this paper, a new procedure that is capable of capturing higher frequency content in rotational time‐series is presented. The frequencies at which numerical errors are introduced in the solution, which are a function of apparent wave velocity and array dimension, are identified. Results are presented for the proposed procedure, the widely accepted geodetic method, and a single‐station procedure developed by the authors, all using data recorded at the Lotung array in Taiwan. Copyright © 2012 John Wiley & Sons, Ltd.

Estimating Rotational Components of Ground Motion Using Data Recorded at a Single Station

Seismic analysis, design, and performance assessment of buildings, bridges, and safety-related nuclear structures is based on two or three translational components of earthquake ground motion. Although rotational components (rocking and torsional) may contribute significantly to translational and torsional response and damage, they are not considered in design and assessment because their intensity and frequency content are not measured by accelerograms deployed in the free field. A method for developing rotational time series by first deconstructing the three translational time series of a ground motion recorded at one station into body waves is presented in this paper. The body waves are then reassembled to generate rotational time series. Point and line source representations of the fault rupture are considered. Results of the single station procedure are presented using rotational acceleration spectra and compared with the multiple-station-based geodetic method. The spectra are similar at periods greater than 1s. The spectral ordinates computed using the geodetic method are significantly smaller at shorter periods, which is attributed to the underlying assumption of a plane surface for the recorded data at any time instant in the method.

Dynamic Analysis of Suspension Bridges and Full Scale Testing

This paper is concerned with the earthquake analysis of suspension bridges, in which the effects of large deflections are taken into account. The first part of the study deals with an iteration scheme for the nonlinear static analysis of suspension bridges by means of tangent stiffness matrices. The concept of tangent stiffness matrix is then introduced in the frequency equation governing the free vibration of the system. At any equilibrium stage, the vibrations are assumed to take place tangent to the curve representing the force-deflection characteristics of the structure. The bridge is idealized as a three dimensional lumped mass system and subjected to three orthogonal components of earthquake ground motion producing horizontal, vertical and torsional oscillations. By this means a realistic appraisal is achieved for torsional response as well as for the other types of vibration. The modal response spectrum technique is applied to evaluate the seismic loading for the combination of these vibrations. Various numerical examples are introduced in order to demonstrate the method of analysis. The procedure described enables the designer to evaluate the nonlinear dynamic response of suspension bridges in a systematic manner.

Adjustments for baseline shifts in far-fault strong-motion data: An alternative scheme to high-pass filtering

Traditional processing methods of accelerometric strong-motion records rely on band-pass filtering to remove contaminating noise. While filtering of low-frequency noise is often desirable to reduce the distortion of displacement and velocity waveforms, application of crude filtering can lead to the loss of long-period components of earthquake ground motion. This paper focuses on a baseline adjustment algorithm, which reduces noise-induced distortion of ground-motion accelerometric signals, and unlike high-pass filtering, retains potentially useful information at long periods. A brief description of the state of the art techniques in strong-motion data processing is presented, followed by a detailed formulation of the proposed baseline adjustment algorithm and some examples of its applications to recently recorded accelerograms. This method is found effective for high-quality far-fault data where the amplitude of the recorded signal is of structural engineering significance.