Ground Motion Acceleration Research Articles

A new method for online identification of civil structures: Virtual synchronization

SummaryThis paper presents a new approach, named Virtual Synchronization Method (VSM), for online identification of stiffness and viscous damping in a civil structure while it is subjected to a harmonic ground motion acceleration. It is assumed that displacement and velocity of the structure relative to the ground are measured in real time. They are used to define a virtual system similar to the actual structure. Proper controllers and estimation functions are designed to force the states of this virtual system to follow those of the actual structure. Theoretical results are derived to study on what conditions, after the two systems synchronized, the estimation functions converge to the true stiffness and damping of the actual structure. Provided numerical examples show that VSM is a promising method for online identification of civil structures and should be the subject of further studies.

WINSTON-BATAN: A SEISMOLOGICAL GROUND-MOTION ANALYSIS CODE

A thorough understanding of an earthquake is very important to provide a descriptive knowledge and in the same time as a prescriptive knowledge for the future development. In particular, it is essential for site selection and structural design development of nuclear reactor and other critical facilities. Ground motion acceleration time history is an important raw information to understand the earthquake and specific geological condition of where the data is recorded. This paper presented the development of strong-motion analysis code, called Winston-BATAN, which able to interpret ground motion time history. The analysis scope of the code including the ground motion parameters such as peak ground acceleration, several additional seismic intensity parameters, strong motion duration, its frequency content via Fast Fourier Transformation and response spectra analysis. Being developed based on an open source Python programming language, Winston-BATAN is flexible for exploratory study to exploit the ground motion time history and easily improve to accommodate additional features. This code able to read input from PEER NGA type file or a simple time and acceleration data type of ground motion. Analysis results of Winston-BATAN shows a very good agreement compare to the results from the standard tools Seismosignal® 2018 Software, in addition flexibility of this code, in particular, to explore the response spectra from the ground motion time history is demonstrated.

POD-based dimension reduction representation of stochastic ground motion fields

In this paper, two kinds of proper orthogonal decomposition (POD) representations for simulating the non-stationary stochastic vector processes are derived based on the basic theory of POD, namely the orthogonal-random-variables-based POD representation and the random-phase-angles-based POD representation. It is clarified that the random-phase-angles-based scheme is a special case of the orthogonal-random-variables-based scheme, and the differences between them are analyzed from the number of elementary random variables and the constraint conditions. It is found that the randomness degree (the number of elementary random variables) of the non-stationary stochastic vector processes could be greatly reduced by introducing some appropriate constraint conditions. To this end, the efficient dimension reduction simulation of the non-stationary stochastic vector processes with just two elementary random variables is realized through introducing more rigorous constraints on the orthogonal random variables in the orthogonal-random-variables-based scheme. Also, the complete probability information of the stochastic processes is fully emerged. Through the numerical analysis of the ground motion stochastic field simulation, it is obtained that the relative errors of the mean and standard deviation, evolutionary power spectrum and coherence function of the non-stationary ground motion acceleration vector process are all in good agreement with the corresponding target values, which shows that the proposed method is effective and accurate. Meanwhile, in order to further verify the applicability of this method in terms of engineering characteristics upon ground motion, according to the five classes of the typical soil sites divided in “Seismic ground motion parameters zonation map of China”, 920 strong motion records are selected for comparing and analyzing the response spectrum and the Fourier amplitude spectrum of ground motion acceleration, respectively. The research shows that the simulation results of the proposed method have good consistency with the strong motion records, which lays a solid foundation for this proposed method applied in engineering applications.

Dynamic response and damage character of road embankment under strong earthquake

Dynamic response of road embankment under strong earthquake was explored by site investigation, shaking table tests, and discrete element method simulations, which shows that the distribution of responded accelerations strongly depends on the amplitude of input ground motion and the height of road embankment. When the peak ground acceleration of ground motion is small, peak ground acceleration amplification factors will linearly increase from the toe to the top of the slope; then, it will step into non-linear amplification; when the peak ground acceleration of ground motion is large enough, it will transform from amplification to attenuation. There is a logarithmic relationship between the magnitude of acceleration and the slope amplification factor, and the critical acceleration making the peak ground acceleration transform from amplification to attenuation increases with the raise of embankment height and connects with spectral characteristics of ground motion. There is a logarithmic relationship between the input ground acceleration and the amplification ratio of slope top to toe, and the critical acceleration making the peak ground acceleration transform from amplification to attenuation increases with the raise of embankment height and connects with spectral characteristics of ground motion. The results found should be useful for aseismic of road embankment as well as railway subgrade.

Seismic Fragility Analysis of Steel Frame Structures Containing Initial Flaws in Beam-Column Connections

The objective of this paper was to evaluate the influence of initial flaws in the beam-column connections on the seismic performance of steel frame structures. The finite element models were constructed with different initial flaw lengths by ABAQUS. The initial flaw length was 0, 8, and 16 mm, respectively. The dynamic elastic-plastic time history analysis and the pushover analysis were conducted to obtain the probabilistic characteristics of seismic demand and seismic capacity. Seismic demands are quantified in terms of the maximum drift angle (RDA) and the displacement ductility ratio $$ \left( {\mu_{d} } \right) $$ . Moreover, the peak ground acceleration (PGA) was used for the pushover analysis. Formulas considering the influence of initial flaws on failure probability of a structure were derived for each length using different design basic acceleration of ground motion. The fragility curves were further constructed based on the data of seismic demand and capacity. The results show that the fragility of steel frame structures is similar across different seismic demand parameters. In addition, the analyses of fragility curves obviously indicate that the seismic fragility of steel frame structures increases as flaw length increases. Finally, the fragility of steel frame structures with initial flaws is consistent using different design basic acceleration of ground motion.

Prediction of earthquake-induced slope displacements considering 2D topographic amplification and flexible sliding mass

The Newmark approach is commonly used in predicting earthquake-induced displacements as an index of slope stability under seismic loading. However, this method is limited to a rigid block assumption in which the incident wave fails to interact with either the slope geometry or the sliding mass. In reality, ground motions are amplified near the slope crest due to the topographic effect or de-amplified at deep failure planes that consider the overlying deformable sliding mass. Therefore, a series of 2-dimensional (2D) dynamic analyses are performed to characterize this interaction behavior in this study. A general prediction model for slope response that considers both the topographic effect and flexible sliding mass is developed based on peak ground acceleration and mean period of incident ground motions conditioned on the natural period of sliding mass and the slope angle. Consequently, the predicted displacement of the 2D slope under seismic loading is achieved using the proposed prediction model of slope response in conjunction with the previously developed rigid displacement prediction model.

Cluster Analysis of Earthquake Ground-Motion Records and Characteristic Period of Seismic Response Spectrum

ABSTRACTClassification of earthquake ground-motion records is carried out in this article using K-means cluster technique. Two kinds of cluster attributes are introduced, which are augmented by the frequency band of energy concentration and by the magnitude distance of earthquake ground motions. The effectiveness of cluster analysis is testified through the investigation of 7692 earthquake ground-motion records. It is revealed that the clustered ground-motion records show significant group discrepancies in spectral properties. A new seismic response spectrum is then suggested taking account of the influences of magnitude, propagation distance, and site class. An optimization criterion is introduced to identify the characteristic period of the suggested seismic response spectrum, through a comparative study between the mean response spectrum of the clustered ground-motion accelerations and the seismic response spectrum in provisions. It provides a comprehensive argument for characterizing the spectral properties of ground motions not only with respect to specific site but also with respect to specific magnitude and propagation distance. Numerical investigations indicate that the cluster analysis technique has the benefit of dealing with massive ground-motion records, whereby the suggested seismic response spectrum and associated characteristic periods are applicable of integrated design of seismic structures.

Response of anisotropic porous layered media with uncertainsoil parameters to shear body-and Love-waves

The present study is dedicated to investigate the SH body-as well as Love-waves propagation effects in porous media with uncertain porosity and permeability. A unified formulation of the governing equations for one-dimensional (1-D) wave propagation in anisotropic porous layered media is presented deterministically. The uncertainties around the above two cited parameters are taken into account by random fields with the help of Monte Carlo Simulations (MCS). Random samples of the porosity and the permeability are generated according to the normal and lognormal distribution functions, respectively, with a mean value and a coefficient of variation for each one of the two parameters. After performing several thousands of samples, the mathematical expectation (mean) of the solution of the wave propagation equations in terms of amplification functions for SH waves and in terms of dispersion equation for Love-waves are obtained. The limits of the Love wave velocity in a porous soil layer overlaying a homogeneous half-space are obtained where it is found that random variations of porosity change the zeros of the wave equation. Also, the increase of uncertainties in the porosity (high coefficient of variation) decreases the mean amplification function amplitudes and shifts the fundamental frequencies. However, no effects are observed on both Love wave dispersion and amplification function for random variations of permeability. Lastly, the present approach is applied to a case study in the Adapazari town basin so that to estimate ground motion accelerations lacked in the fast-growing during the main shock of the damaging 1999 Kocaeli earthquake.

Quantification of the amplitude variability of the ground motion in Argostoli, Greece. Variability of linear and non-linear structural response of a single degree of freedom system.

The term “spatial variability of seismic ground motions” denotes the differences in the amplitude and phase content of seismic motions. The effect of such spatial variability on the structural response is still an open issue. In-situ experiments may be helpful in order to answer the questions regarding both the quantification of the spatial variability of the ground motion within the dimensions of a structure as well as the effect on its dynamic response. The goal of the present study is to quantify the variability of the seismic ground motion accelerations in the shallow sedimentary basin of Argostoli, Greece, and thereafter to identify its effect on the linear and non-linear elasto-plastic response of a single degree of freedom system in terms of spectral displacements. Around 400 earthquakes are used, recorded by the 21-element very dense seismological array deployed in Argostoli with inter-station spacing ranging from 5 to 160 meters. The seismic motion variability, evaluated in terms of spectral accelerations, is found to be significant and to increase with inter-station distance and frequency. Thereafter, the amplitude variability in terms of spectral displacements, which is indeed the linear response of a single degree of freedom (SDOF) system with various fundamental periods, is compared with the amplitude variability of a SDOF with non-linear elasto-plastic response. The variability of the maximum top displacement of the linear single degree of freedom system is estimated to be on average 12% with larger variabilities to be observed within two narrow frequency ranges (between 1.5 and 1.7 Hz and between 3 and 4 Hz). Such high variabilities are caused by locally edge-generated diffracted surface waves. The non-linear perfectly elasto-platic structural response of the SDOF system shows that although the variability has the same trends as in the case of linear response, it is almost constantly increased by 5%.

Real-Time Substructure Tests and Numerical Simulation of Mechanical Characteristics of Natural Rubber-Laminated Bearings

Natural rubber lamination is a kind of seismic isolation of bearings often used in civil engineering. The advantage of laminated bearings is large vertical stiffness and small lateral stiffness. In seismic regions, structural periods would be extended and the effect of seismic forces can be lowered using bearings. In previous tests, the static cyclic loading method was mainly used that failed to take account of the loading rate. The real-time substructure testing is proposed to simulate true seismic loads. This testing and test setup were first introduced, and the effect of the loading rate was studied. Then the effects of vertical pressure and peak acceleration of ground motion were studied. At last the test results were simulated by the finite element method, and an accurate method to calculate seismic responses of bridges with laminated bearings was proposed.

Generation of stochastic earthquake ground motion in western Saudi Arabia as a first step in development of regional ground motion prediction model

Earthquake ground motion model is an essential part of seismic hazard assessment. The model consists in several empirical ground motion prediction equations (GMPEs) that are considered to be applicable to the given region. When the recorded ground motion data are scarce, numerical modeling of ground motion based on available seismological information is widely used. We describe results of stochastic simulation of ground motion acceleration records for western Saudi Arabia. The simulation was performed using the finite fault model and considering peak ground acceleration and amplitudes of spectral acceleration at natural frequencies 0.2 and 1.0 s. Based on the parameters of the input seismological model that were accepted in similar previous studies, we analyze influence of variations in the source factor (stress drop) and in the local attenuation and amplification factors (kappa value, crustal amplification). These characteristics of the model are considered as the major contributors to the ground motion variability. The results of our work show that distribution of simulated ground motion parameters versus magnitude and distance reveals an agreement with the GMPEs recently used in seismic hazard assessment for the region. Collection of credible information about seismic source, propagation path, and site attenuation parameters using the regional ground motion database would allow constraining the seismological model and developing regional GMPEs. The stochastic simulation based on regional seismological model may be applied for generation of ground motion time histories used for development of analytical fragility curves for typical constructions in the region.

Seismic Response Characteristics of Stabilizing Pile Based on Elastic‐Plastic Analysis

Stabilizing pile is widely used in the landslide controlling projects and shows excellent seismic performance under the action of earthquake. Therefore, in order to improve seismic design theory, it is of importance to study the seismic response characteristics of stabilizing pile based on elastic‐plastic analysis. In view of this, elastic‐plastic constitutive model was established to deduce the plastic zone of stabilizing pile. Based on elastic‐plastic analysis, the seismic response characteristics and the influence of different section sizes, material strengths, and peak ground motion acceleration (PGA) were analyzed by ANSYS 3D. Resultantly, the elastic‐plastic fourth‐order tensor was deduced, which can be used to calculate plastic strain of stabilizing pile under loading. Compared with Chinese code, the material of stabilizing pile working with elastic‐plastic state will be decreased under the same section size and the same property. Furthermore, stabilizing pile is in the elastic stage at the beginning under the action of earthquake. With the increase of ground motion time, the section starts to exhibit elastic‐plastic state and then the plastic zone expands gradually. Finally, the plastic zone runs through the whole section, resulting in the performance loss of the pile. In addition, under the different design parameters, pile shows different seismic response characteristics; namely, changing these parameters reasonably can improve the seismic design.

Quantification of response spectra of pulse-like near-fault ground motions

This study aims to quantify the acceleration and displacement response spectra of pulse-like near-fault ground motions, which can be further employed to derive the seismic force demands of a structure system or structural member. The spectra are computed based on a set of pulse type ground motions, and the spectral shapes are derived by normalizing the spectra with the spectral values at the pulse periods. The normalized spectral values exhibit very small variations at periods larger than the pulse period but very large dispersions at periods shorter than the pulse periods. In a bi-normalization coordinate, an empirical function is developed for simulating the normalized spectral shape, in which the damping effect is included. Moreover, another empirical function for estimating the spectral value at the pulse period is constructed. The two-step procedure finally leads to a function for estimating acceleration spectral values based on the structural period, structural damping and pulse period of ground motion. The displacement spectra of high damping systems are further developed by employing the damping modification factors for acceleration and displacement spectra. On average, the spectra estimated by the proposed model are in agreement with the true spectra. Combined with the prediction of key parameters of ground motions in near-fault zones, the proposed record-based spectral model is expected to produce a design spectrum better than code-based design spectra.

11.44: An integrated experimental and numerical assessment of force‐based design for concentrically braced steel frames

ABSTRACTThis study uses an integrated experimental and numerical approach to assess the use of the force‐based design (FBD) methodology presented in Eurocode 8 (EC8) for multi‐storey steel concentrically‐braced frames (CBFs).In the EC8 approach, the design seismic action is defined by first generating an elastic response spectrum. This spectrum is reduced to create the design spectrum by applying an appropriate behavioural factor (q) to account for energy dissipation. The value of q chosen depends on the form of the lateral‐load resisting structure, the structural material(s) to be used, the ductility class and the degree of irregularity in the structural layout. The design base shear force calculated from the design spectrum is used to estimate the seismic forces on the structure and hence determine the final member cross‐section sizes.In this study, the FBD approach to the design of structures presented in Eurocode 8 is described and applied to 4‐ and 8‐storey CBF structures. Both dissipative (Ductility Class High – DCH) and non‐dissipative (Ductility Class Low – DCL) design is considered for each structure.A numerical modelling approach developed using the OpenSees seismic analysis software and validated from a series of full‐scale experimental tests of single‐storey CBFs is outlined. The two‐dimensional reference model assigns appropriate out‐of‐plane rotational stiffnesses to the ends of the bracing members based on the strength and geometry of gusset plates specified.The experimental work used to validate the model, carried out as part of the BRACED transnational research project funded by the European Commission's Seventh Framework Programme (FP7) is briefly described. The experimental observations support model validation at different levels of earthquake ground motion including elastic, inelastic and ultimate response conditions.The validated numerical modelling approach is used to perform a series of non‐linear time history analyses (NLTHA) of the designed 4‐ and 8‐storey frames by subjecting them to appropriately scaled simulated ground motion accelerations. The key recorded responses of the NLTHA of the modelled frames (displacements, drift, brace forces and ductility demands) are compared, and the implications of the assumed energy dissipations are discussed.

Investigation on the seismic retrofit positions of FRP jackets for RC frames using multi-objective optimization

Abstract This research aims to achieve an optimal seismic retrofit method using fiber reinforced polymer (FRP) jackets and to investigate the distributions of retrofit positions and the amount of FRP using the solutions obtained by the proposed method. This method utilizes two objective functions. The first minimizes the amount of FRP reinforcement for economic feasibility, and the second maximizes the spectral acceleration of ground motion that causes the collapse of a structure to reduce the collapse risk. The proposed method is tested on a 3-story reinforced concrete (RC) frame example structure. The amount of FRP used in schemes to retrofit only columns is less than the amount used in schemes to retrofit both columns and beams. In addition, retrofit schemes to differentiate the retrofit level according to the retrofit position are proposed as optimal solutions.

Empirical Attenuation relationship for Peak Ground Horizontal Acceleration for North-East Himalaya

Empirical Attenuation relationship for Peak Ground Horizontal Acceleration for North-East Himalaya

INCORPORATING DIFFERENT SOURCE RUPTURE CHARACTERISTICS INTO SIMULATIONS OF STRONG GROUND MOTION FROM THE 1867, M7.0 EARTHQUAKE ON THE ISLAND OF LESVOS (NE AEGEAN SEA, GREECE)

We apply the stochastic method for finite-faults (Beresnev and Atkinson, 1997, 1998) to simulate strong ground motion acceleration from the 1867 earthquake that devastated the Island of Lesvos in NE Aegean Sea. Recent geological data are taken into account to construct realistic models of the earthquake source, while a first-order approximation of the site effect variation throughout the entire island of Lesvos is achieved following an empirical approach suggested by Wald and Allen (2007). We test several source models including different segments of the Agia Paraskevi fault, which is most probably the seismogenic fault of the 1867 earthquake. Stronger ground motion is predicted in the central part of the island, i.e. around the assumed seismogenic structure. A significant site effect is evident along the eastern coast of Lesvos, where the capital of Mytilene lies, strongly hit by the 1867 earthquake, and around the gulfs of Kalloni and Geras in the south and southeast parts of the island. Synthetic peak ground acceleration values are converted to macroseismic intensities through an empirical relation and discussed in comparison with available reports on the macroseismic effects of the 1867 earthquake.

Vibration Control of an existing building through the Vibrating Barrier

Vibration control of structures is normally addressed through devices such as isolators, dampers and tuned mass dampers. Although those devices are technically sound their use might become unpractical in existing buildings such as heritage structures, whereas the alteration of part of the structure is forbidden for various socio-economic issues. In this context, a novel passive control device called Vibrating Barrier (ViBa) has been recently proposed. The Vibrating Barrier is a massive structure, hosted in the soil and detached from the existing building, calibrated for absorbing portion of the ground motion input energy. The working principle is based on the generally know structure-soil-structure interaction between two vibrating structures and the soil.In this paper the Vibrating Barrier is designed to control the vibration of an existing masonry structure forced by ground motion acceleration. The structure, the soil and the ViBa are assumed to be linear behaving and modelled through a pertinent Finite Element approach. The design is pursued through a simplified discrete model of the structure and the ViBa in which the soil is represented by linear elastic springs. Significant reduction of the dynamic response has been achieved manifesting the potential of the Vibrating Barrier to be a valid alternative whereas the traditional vibration control techniques cannot be applied.

Seismic Source Modeling in the Shores of Western Makran

Makran is an active subduction zone with a lower activity rate in comparison with other similar subduction zones. In the extent of Makran seismotectonic province, from coastline up to 70 Km distance onshore, the earthquakes are shallow whilst further inland, focal depths of the earthquakes are deeper. Con-sidering the low seismic activity rate, lack of adequate and reliable seismic data and uncertainty about earthquake hazard contribution ratio of subduction segments and faults, it is intended in this article to determine the most accurate method of seismic source modelling. Estimation of the maximum strong ground motion in this province has been assessed by assuming various combinations of activity rate contribution ratios, i.e. independent activity of either subduction source or faults or simultaneous activity of subduction source and faults. According to the obtained results, the maximum and minimum limits of the strong ground motion acceleration is related to the independent seismic activity models and when subduction source and faults are assumed to be contributing simultaneously to the activity rate of the region, the resultant ground motion acceleration will be between the limits obtained based on independent activity models.

Experimental and analytical investigation of the inelastic behavior of structures isolated using friction pendulum bearings

Current American and European code provisions prohibit yielding of base-isolated structures. Therefore, the majority of existing base-isolated structures are designed elastically. This study aims at investigating the necessity of the elastic design of these structures through the analytical and experimental investigation of their inelastic behavior.This analytical investigation is performed using a two-degree-of-freedom model of a base-isolated structure. The bilinear hysteretic behavior of the structure and the isolator is simulated via a Bouc-Wen model. Numerous simulations of the response to strong ground motion excitations were performed using Matlab and Opensees models.The experimental investigation performed in this study is based on the response of a reduced-scale base-isolated steel structure to strong recorded ground motion accelerations applied using the shaking table of the IBK Structural Testing laboratory of ETH Zurich. The part of the structure designed to develop inelastic behavior is a pair of steel coupons that can be easily replaced after such damage. The structure is base-isolated using four friction pendulum bearings provided by MAGEBA.The experimentally observed inelastic behavior of base-isolated structures is compared to the analytically simulated behavior. A relation between experimentally obtained strength and displacement ductility of these structures is presented. The influence of a wide range of response parameters is quantified and presented. The experimentally obtained data is compared to an analytically derived strength-ductility-period relation for seismically isolated structures. This comparison serves to validate the proposed analytical relation and to increase the understanding of the behavior of inelastic seismically isolated structures.