Anaxagoras Elenas

Correlation between seismic acceleration parameters and overall structural damage indices of buildings

This article describes the interdependency between several seismic acceleration parameters and the behavior of the reinforced concrete frame structures in the form of correlation coefficients. The structural behavior is expressed in form of overall structural damage indices. After the numerical evaluation of several seismic parameters, a nonlinear dynamic analysis is carried out to provide the total damage status of a structure. The aim is to select those, which have drastic influence on structural damage. Furthermore, the design philosophy of aseismic codes can be verified. The attention is focussed on the earthquake acceleration time histories of the worldwide well-known sites with a strong seismic activity.

Seismic intensity parameters for fragility analysis of structures with energy dissipating devices

The aim of the study is to develop a procedure for the identification of seismic intensity parameters, which make it possible to relate the fragility of linear and non-linear systems for a given design response spectrum, with the fragility for a set of different recorded accelerograms. The correlation between the response parameters of the studied systems and seismic intensity parameters is estimated. For the considered linear systems the higher the correlation coefficient for a given seismic intensity parameter, the closer the fragility line for recorded accelerograms to those for the considered spectrum. For the studied non-linear systems with energy dissipating devices the value of the correlation coefficient do not relate to the sequence of the fragility curves and consequently cannot be used as a single indicator of the appropriateness of the predictive linear equations. In this connection a criterion of appropriateness of the seismic intensity parameter is formulated as the ratio of the correlation coefficient to the coefficient of variation of the seismic intensity parameters. The proposed criterion helps to cluster the seismic intensity parameters, which exhibit the most appropriate predictive equations. Next, the predictive equations of all the parameters with highest values of the proposed criterion should be examined to obtain the intensity parameter the most relevant for the particular non-linear system and design spectrum. The results show that the spectral pseudo-velocity and the Kappos spectral intensity for the linear systems and the peak ground velocity, the mean spectral pseudo-velocity and the Kappos spectral intensity for the non-linear systems could be recommended as seismic intensity parameters for fragility analysis.

Interdependence between damage indices and ground motion parameters based on Hilbert-Huang transform

Feature extraction from seismic accelerograms is a key issue in characterization of earthquake damage in structures. Until today, a number of effective classical parameters such as peak ground acceleration (PGA) and Arias intensity have been proposed for analyzing the earthquake motion records. The aim of this paper is to search for new crucial characteristic seismic parameters which provide information pertinent to the damage indicators of the structures. The first proposed parameter is the maximum amplitude (AHHT max) and the second is the mean amplitude (AHHT mean). Emphasis of our work has been placed on the use of the Hilbert‐Huang transform (HHT). A set of 13 natural accelerograms from worldwide well-known sites with strong seismic activity have been used. The HHT has been applied to the nonlinear and non-stationary data (earthquake recordings). Each complex seismic accelerogram is decomposed into several simple components called intrinsic mode functions (IMFs). Using the IMFs a three-dimensional time‐frequency distribution of earthquake excitation is computed and two new seismic parameters are proposed and evaluated. After the numerical computation of all the seismic parameters (classical and proposed), nonlinear dynamic analysis is carried out to provide the post-seismic damage status of the structure under study. Two structural damage indices are utilized and the degree of interrelation among them and the seismic parameters is provided by correlation coefficients. Furthermore, two different reinforced concrete structures are examined. Results indicate the high correlation of the new seismic parameters (AHHT max ,A HHT mean) with the damage indices and confirm that HHT is a promising tool for extracting information to characterize damage in structures.

Intelligent Seismic Acceleration Signal Processing for Damage Classification in Buildings

Three new pattern recognition methods, based on fuzzy logic techniques that are suitable for seismic acceleration signal classification, are proposed in this paper. The classification of unknown signals is carried out according to the structural or architectural damage that is produced by the seismic signals. A set of 400 natural accelerograms, which have been recorded in various regions with well-known strong seismic activity, has been used for evaluation of the proposed methods. The seismic accelerograms are first treated as graphs; the similarity between them is exploited in order to perform the classification. In the second approach, a set of parameters are derived from each signal through computer analysis. These describe effectively the intensity measure of the seismic excitation, and they are used instead of the accelerograms. Similarity between them is appropriately utilized. Finally, a method that depends purely on fuzzification of the accelerograms parameters is also described. Classification results are presented for each method, and correct classification rates up to approximately 85% are recorded. The contribution of this paper to seismic signal classification lies in the methodology that allows for classification of seismic signals according to the damage in buildings. This process depends strongly on the structural parameters of the specific building, and therefore, given a building and a seismic signal, each signal can be classified into one of the four well-defined and scientifically approved damage classes. Consequently, the proposed paper contributes an effective method for engineers to test the response of a building to seismic signals, produced by earthquakes.

Interdependency between seismic acceleration parameters and the behaviour of structures

Abstract The first part of this article describes some strong motion acceleration parameters of seismic excitations. Furthermore, a classification of the ground motions at a site according to their damage potential is presented. The second part deals with a nonlinear dynamic analysis of a six storey reinforced concrete plane frame. Damage indicators in the form of cross sectional ductility demand are evaluated and correlated with the strong motion characteristics. The aim is to extract among the several seismic parameters, those which have drastic affection on the damage indicators of the structures. The attention is focused on earthquake acceleration time histories, recorded in Greece, Central and North America, which are well-known sites with strong seismic activity.

Seismic Intensity Feature Construction Based on the Hilbert–Huang Transform

An increasing number of seismic parameters for the representation of the severity of earthquake signals have been proposed in recent years. Considering the complex nature of seismic accelerograms, there is an obvious need for a more effective representation. The destructiveness of a seismic wave cannot be always described using a single feature of the examined ground motion. Moreover, the level of structural damage caused by a severe earthquake depends on the characteristics of the oscillated structure. The aim of this study is to propose new crucial ground-motion parameters, which reflect the damage potential of the seismic excitations. The Hilbert-Huang transform (HHT) is applied to a set of 70 natural accelerograms. Through the HHT, the complex earthquake signals are decomposed into several simple components called intrinsic mode functions. After a thorough analysis, eight new seismic parameters are extracted. The key novelty of this paper is that the frequency-based new seismic parameters are associated with the eigenfrequency of the oscillated structures. By studying the correlation between the new seismic parameters and well-known damage indices (DIs), their interdependence is confirmed. The achieved high levels of correlation indicate that the proposed parameters are directly related to structural damage. Furthermore, the application of the HHT improves the correlation coefficients between the widely used classical earthquake parameters and DIs. The quality of the proposed HHT-based parameters is consolidated by the use of minimal-redundancy-maximal-relevance feature selection. A subset of six seismic parameters is tested by the use of a support vector machine classifier, providing a 91.4% classification performance. Results indicate that the new seismic features along with the proposed optimized classical parameters can be considered highly competitive descriptors of the seismic damage potential.

Seismic Response Parametric Study of Ancient Rocking Columns

ABSTRACT This study examines the seismic response of free-standing, monolithic rocking columns, taking into account different ground motion intensity measures (IMs). The primary scope of this article is to investigate the effect of the IMs, among 23 considered, on the rocking response of the examined structural system. The seismic vulnerability of the examined structural systems is based on the probabilistic seismic demand model (PSDM), in which the degree of uncertainty depends on the used IM. Thus, concluding to the most efficient one is of major importance. A performance-based analysis has been performed, using three limit states, and fragility curves are generated in terms of the most efficient univariate and bivariate IMs, considering the maximum rocking rotation normalized to the critical overturning rotation, as engineering demand parameter. Time domain analyses are numerically performed, by solving the equation of rocking motion, given a set of 35 natural seismic records. The results indicate that the velocity based as well as the frequency content IMs exhibit a strong correlation with the seismic behavior of free-standing rocking columns. Moreover, the acceleration based IMs can describe with great efficiency the rocking response only as a bivariate IM combined with the frequency content of the ground motions.

Intensity Parameters as Damage Potential Descriptors of Earthquakes

This paper provides a methodology to quantify the interrelationship between the seismic intensity parameters and the structural damage. First, a computer-supported elaboration of the accelerograms provides several peak, spectral and energy seismic parameters. After that, nonlinear dynamic analyses are carried out to provide the structural response for a set of seismic excitations. Among the several response characteristics, the overall structure damage indices after Park/Ang and the maximum inter-storey drift ratio are selected to represent the structural response. Correlation coefficients are evaluated to express the grade of interrelation between seismic acceleration parameters and the structural damage. The presented methodology is applied to a six-story reinforced concrete frame building, designed according to the rules of the recent Eurocodes. As seismic input for the nonlinear dynamic analysis, a set of spectrum-compatible synthetic accelerograms has been used. As the numerical results have shown, the spectral and energy parameters provide strong correlation to the damage indices. Due to this reason, spectral and energy related parameters are better qualified to be used for the characterization of the seismic damage potential.

Classification of Seismic Damages in Buildings Using Fuzzy Logic Procedures

It is well-known that damage observations on buildings after severe earthquakes exhibit interdependence with the seismic intensity parameters. Numerical elaboration of structural systems quantified the interrelation degree by correlation coefficients. Further, the seismic response of buildings is directly depended on the ground excitation. Consequently, the seismic response of buildings is directly depended on the used accelerogram and its intensity parameters. Among the several response quantities, the focus is on the overall damage. Thus, the Maximum Inter-Storey Drift Ratio and the damage index of Park/Ang are used. Intervals for the values of the damage indices are defined to classify the damage degree in low, medium, large and total. This paper presents an Adaptive Neuro-Fuzzy Inference System for the damage classification. The seismic excitations are simulated by artificial accelerograms. Their intensity is described by seismic parameters. The proposed system was trained and tested on a reinforced concrete structure. The results have shown that the proposed fuzzy technique contributes to the development of an efficient blind prediction of seismic damages. The recognition scheme achieves correct classification rates over 90%.

Synthesis of artificial spectrum-compatible seismic accelerograms

The Hilbert–Huang transform is used to generate artificial seismic signals compatible with the acceleration spectra of natural seismic records. Artificial spectrum-compatible accelerograms are utilized instead of natural earthquake records for the dynamic response analysis of many critical structures such as hospitals, bridges, and power plants. The realistic estimation of the seismic response of structures involves nonlinear dynamic analysis. Moreover, it requires seismic accelerograms representative of the actual ground acceleration time histories expected at the site of interest. Unfortunately, not many actual records of different seismic intensities are available for many regions. In addition, a large number of seismic accelerograms are required to perform a series of nonlinear dynamic analyses for a reliable statistical investigation of the structural behavior under earthquake excitation. These are the main motivations for generating artificial spectrum-compatible seismic accelerograms and could be useful in earthquake engineering for dynamic analysis and design of buildings.According to the proposed method, a single natural earthquake record is deconstructed into amplitude and frequency components using the Hilbert–Huang transform. The proposed method is illustrated by studying 20 natural seismic records with different characteristics such as different frequency content, amplitude, and duration. Experimental results reveal the efficiency of the proposed method in comparison with well-established and industrial methods in the literature.