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Luis A. Montejo - One of the best experts on this subject based on the ideXlab platform.

  • An improved CWT-based algorithm for the generation of Spectrum-compatible records
    International Journal of Advanced Structural Engineering, 2013
    Co-Authors: Luis A. Montejo, Luis E. Suarez
    Abstract:

    The seismic Design of most civil structures is usually accomplished using the response Spectrum approach or simplified equivalent lateral force methods. However, some special tasks require the use of dynamic time history analyses. In the nuclear industry, for example, dynamic analyses are required in the Design verification and seismic assessment of critical buildings and in the development of floor response spectra and free-field ground response spectra. The input motion for these analyses requires acceleration time series whose response Spectrum matches a target Design Spectrum. This article revises the continuous wavelet transform (CWT) approach to generate Spectrum-compatible records from the modification of acceleration time histories recorded in actual seismic events. The computational efficiency of the algorithm is increased greatly by performing the wavelet decomposition and details reconstruction via fast convolution using fast Fourier transforms. The new algorithm is evaluated using a typical Design Spectrum from the nuclear industry and different seed records.

  • Applications of the wavelet transform in the generation and analysis of Spectrum-compatible records
    Structural Engineering and Mechanics, 2007
    Co-Authors: Luis E. Suarez, Luis A. Montejo
    Abstract:

    A wavelet-based procedure to generate artificial accelerograms compatible with a prescribed seismic Design Spectrum is described. A procedure to perform a baseline correction of the compatible accelerograms is also described. To examine how the frequency content of the modified records evolves with time, they are analyzed in the time and frequency using the wavelet transform. The changes in the strong motion duration and input energy Spectrum are also investigated. An alternative way to match the Design Spectrum, termed the "two-band matching procedure", is proposed with the objective of preserving the non-stationary characteristics of the original record in the modified accelerogram.

  • Generation of artificial earthquakes via the wavelet transform
    International Journal of Solids and Structures, 2005
    Co-Authors: Luis E. Suarez, Luis A. Montejo
    Abstract:

    AbstractA wavelet-based procedure is presented to generate an accelerogram whose response Spectrum is compatible with a target Spectrum. The acceleration time history of a recorded ground motion is decomposed into a number of component time histories. Next, each of the time histories is appropriately scaled so that its response Spectrum matches a specified Design Spectrum at selected periods. The modified components are used to reconstruct an updated accelerogram, its Spectrum is compared with the target Spectrum and the process is repeated until a reasonable match is obtained. To achieve this goal, a new wavelet, based on the impulse response function of an underdamped oscillator is proposed. The proposed procedure is illustrated by modifying five recorded accelerograms with different characteristics so that their spectra match a seismic Design Spectrum prescribed in the 1997 Uniform Building Code for a seismic zone 3 and soil type SB (rock)

Luis E. Suarez - One of the best experts on this subject based on the ideXlab platform.

  • An improved CWT-based algorithm for the generation of Spectrum-compatible records
    International Journal of Advanced Structural Engineering, 2013
    Co-Authors: Luis A. Montejo, Luis E. Suarez
    Abstract:

    The seismic Design of most civil structures is usually accomplished using the response Spectrum approach or simplified equivalent lateral force methods. However, some special tasks require the use of dynamic time history analyses. In the nuclear industry, for example, dynamic analyses are required in the Design verification and seismic assessment of critical buildings and in the development of floor response spectra and free-field ground response spectra. The input motion for these analyses requires acceleration time series whose response Spectrum matches a target Design Spectrum. This article revises the continuous wavelet transform (CWT) approach to generate Spectrum-compatible records from the modification of acceleration time histories recorded in actual seismic events. The computational efficiency of the algorithm is increased greatly by performing the wavelet decomposition and details reconstruction via fast convolution using fast Fourier transforms. The new algorithm is evaluated using a typical Design Spectrum from the nuclear industry and different seed records.

  • Applications of the wavelet transform in the generation and analysis of Spectrum-compatible records
    Structural Engineering and Mechanics, 2007
    Co-Authors: Luis E. Suarez, Luis A. Montejo
    Abstract:

    A wavelet-based procedure to generate artificial accelerograms compatible with a prescribed seismic Design Spectrum is described. A procedure to perform a baseline correction of the compatible accelerograms is also described. To examine how the frequency content of the modified records evolves with time, they are analyzed in the time and frequency using the wavelet transform. The changes in the strong motion duration and input energy Spectrum are also investigated. An alternative way to match the Design Spectrum, termed the "two-band matching procedure", is proposed with the objective of preserving the non-stationary characteristics of the original record in the modified accelerogram.

  • Generation of artificial earthquakes via the wavelet transform
    International Journal of Solids and Structures, 2005
    Co-Authors: Luis E. Suarez, Luis A. Montejo
    Abstract:

    AbstractA wavelet-based procedure is presented to generate an accelerogram whose response Spectrum is compatible with a target Spectrum. The acceleration time history of a recorded ground motion is decomposed into a number of component time histories. Next, each of the time histories is appropriately scaled so that its response Spectrum matches a specified Design Spectrum at selected periods. The modified components are used to reconstruct an updated accelerogram, its Spectrum is compared with the target Spectrum and the process is repeated until a reasonable match is obtained. To achieve this goal, a new wavelet, based on the impulse response function of an underdamped oscillator is proposed. The proposed procedure is illustrated by modifying five recorded accelerograms with different characteristics so that their spectra match a seismic Design Spectrum prescribed in the 1997 Uniform Building Code for a seismic zone 3 and soil type SB (rock)

Pol D. Spanos - One of the best experts on this subject based on the ideXlab platform.

  • A stochastic approach for deriving effective linear properties of bilinear hysteretic systems subject to Design Spectrum compatible strong ground motions
    2011
    Co-Authors: Agathoklis Giaralis, Ioannis A. Kougioumtzoglou, Pol D. Spanos
    Abstract:

    A novel statistical linearization based approach is proposed to derive effective linear properties (ELPs), namely damping ratio and natural frequency, for bilinear hysteretic oscillators subject to seismic excitations specified by an elastic response/Design Spectrum. First, an efficient numerical scheme is adopted to derive a power Spectrum, satisfying a certain statistical criterion, which is compatible with the considered seismic Spectrum. Next, the thus derived power Spectrum is used in conjunction with a frequency domain higher-order statistical linearization formulation to substitute a bilinear hysteretic oscillator by a third order linear system. This is done by minimizing an appropriate error function in the least square sense. Then, this third-order linear system is reduced to a second order linear oscillator characterized by a set of ELPs by enforcing equality of certain response statistics of the two linear systems. The ELPs are utilized to estimate the peak response of the considered hysteretic oscillator in the context of linear response Spectrum-based dynamic analysis. In this manner, the need for numerical integration of the nonlinear equation of motion is circumvented. Numerical results pertaining to the European EC8 elastic response Spectrum are presented to demonstrate the applicability and usefulness of the proposed approach. These results are supported by Monte Carlo analyses involving an ensemble of 250 non-stationary artificial EC8 Spectrum compatible accelerograms. The proposed approach can hopefully be an effective tool in the preliminary aseismic Design stages of yielding structures following either a force-based or a displacement-based methodology.

  • Determination of non-stationary stochastic processes compatible with seismic response/Design spectra
    Proceedings of the 6th International Conference on Computational Stochastic Mechanics(CSM-6), 2011
    Co-Authors: Agathoklis Giaralis, Pol D. Spanos
    Abstract:

    In this paper the problem of deriving non-stationary stochastic processes defined by a parametric evolutionary power Spectrum (EPS) compatible with a given (target) Design Spectrum is addressed. An inverse stochastic dynamics problem is formulated and solved in a least-square sense to determine the requisite EPS. This involves the incorporation of a “peak factor” which is used to relate statistically the target Spectrum to the EPS. Special attention is focused on deriving Design Spectrum compatible processes of specific “effective duration” as commonly defined in the field of earthquake engineering. Specifically, the Design Spectrum of the Chinese GB 50011 aseismic code is considered as a paradigm of a target Spectrum. Comprehensive Monte Carlo analyses are undertaken to numerically estimate GB 50011-compatible median peak factor spectra, given in a polynomial form. These spectra are associated with the first passage problem for linear oscillators excited by uniformly modulated colored non-stationary processes of various durations. The derived peak factor spectra used in conjunction with the herein adopted stochastic formulation yield an excellent level of agreement between the GB 50011 Spectrum and the ensemble average response spectra of simulated EPS-compatible accelerograms of different effective durations. Additional numerical results pertaining to the Design spectra of the European EC8 code and the GB 50011 code are included to show how the behavior of the target Spectrum in the range of long periods affects the choice of the assumed spectral form of the EPS. It is envisioned that the herein derived stochastic processes can be used to facilitate the aseismic Design of structures regulated by contemporary code provisions in a Monte Carlo-based or random vibration-based context of analysis.

  • Effective linear damping and stiffness coefficients of nonlinear systems for Design Spectrum based analysis
    Soil Dynamics and Earthquake Engineering, 2010
    Co-Authors: Agathoklis Giaralis, Pol D. Spanos
    Abstract:

    A stochastic approach for obtaining reliable estimates of the peak response of nonlinear systems to excitations specified via a Design seismic Spectrum is proposed. This is achieved in an efficient manner without resorting to numerical integration of the governing nonlinear equations of motion. First, a numerical scheme is utilized to derive a power Spectrum which is compatible in a stochastic sense with a given Design Spectrum. This power Spectrum is then treated as the excitation Spectrum to determine effective damping and stiffness coefficients corresponding to an equivalent linear system (ELS) via a statistical linearization scheme. Further, the obtained coefficients are used in conjunction with the (linear) Design Spectrum to estimate the peak response of the original nonlinear systems. The cases of systems with piecewise linear stiffness nonlinearity, along with bilinear hysteretic systems are considered. The seismic severity is specified by the elastic Design Spectrum prescribed by the European aseismic code provisions (EC8). Monte Carlo simulations pertaining to an ensemble of nonstationary EC8 Design Spectrum compatible accelerograms are conducted to confirm that the average peak response of the nonlinear systems compare reasonably well with that of the ELS, within the known level of accuracy furnished by the statistical linearization method. In this manner, the proposed approach yields ELS which can replace the original nonlinear systems in carrying out computationally efficient analyses in the initial stages of the aseismic Design of structures under severe seismic excitations specified in terms of a Design Spectrum.

  • Synthesis of accelerograms compatible with the Chinese GB 50011-2001 Design Spectrum via harmonic wavelets: artificial and historic records
    Earthquake Engineering and Engineering Vibration, 2009
    Co-Authors: Pol D. Spanos, Agathoklis Giaralis
    Abstract:

    A versatile approach is employed to generate artificial accelerograms which satisfy the compatibility criteria prescribed by the Chinese aseismic code provisions GB 50011-2001. In particular, a frequency dependent peak factor derived by means of appropriate Monte Carlo analyses is introduced to relate the GB 50011-2001 Design Spectrum to a parametrically defined evolutionary power Spectrum (EPS). Special attention is given to the definition of the frequency content of the EPS in order to accommodate the mathematical form of the aforementioned Design Spectrum. Further, a one-to-one relationship is established between the parameter controlling the time-varying intensity of the EPS and the effective strong ground motion duration. Subsequently, an efficient auto-regressive moving-average (ARMA) filtering technique is utilized to generate ensembles of non-stationary artificial accelerograms whose average response Spectrum is in a close agreement with the considered Design Spectrum. Furthermore, a harmonic wavelet based iterative scheme is adopted to modify these artificial signals so that a close matching of the signals’ response spectra with the GB 50011-2001 Design Spectrum is achieved on an individual basis. This is also done for field recorded accelerograms pertaining to the May, 2008 Wenchuan seismic event. In the process, zero-phase high-pass filtering is performed to accomplish proper baseline correction of the acquired Spectrum compatible artificial and field accelerograms. Numerical results are given in a tabulated format to expedite their use in practice.

  • Determination of Design Spectrum compatible evolutio- nary spectra via Monte Carlo peak factor estimation
    2009
    Co-Authors: Agathoklis Giaralis, Pol D. Spanos
    Abstract:

    The problem of generating ensembles of artificial non-stationary earthquake accelerograms compatible with a given (target) response/Design Spectrum is cast on a stochastic basis. The Design Spectrum of the European aseismic code provisions (EC8) for various soil conditions and damping ratios is used as a paradigm of a Design/target Spectrum. The generated accelerograms are construed as realizations of a non-stationary random process; they are char- acterized in the frequency domain by a parametrically defined evolutionary power Spectrum (EPS). An appropriate least squared optimization problem is formulated for the determination of the parameters of the EPS. The solution of this problem involves the incorporation of a "peak factor" which is used to re- late the target Spectrum to the EPS in a probabilistic context. To this end, a comprehensive Monte Carlo study is undertaken to estimate numerically the statistical properties of the peak factor from appropriately computed popula- tions, and to derive polynomial expressions for the median frequency- dependent peak factors (peak factor spectra). These expressions are used in conjunction with the herein adopted optimization problem to determine EPSs compatible with the EC8 Design Spectrum. The derived median peak factor spectra yield an excellent level of agreement between the EC8 Spectrum and the ensemble average and median response spectra of simulated EPS- compatible ensembles of accelerograms.

Agathoklis Giaralis - One of the best experts on this subject based on the ideXlab platform.

  • A stochastic approach for deriving effective linear properties of bilinear hysteretic systems subject to Design Spectrum compatible strong ground motions
    2011
    Co-Authors: Agathoklis Giaralis, Ioannis A. Kougioumtzoglou, Pol D. Spanos
    Abstract:

    A novel statistical linearization based approach is proposed to derive effective linear properties (ELPs), namely damping ratio and natural frequency, for bilinear hysteretic oscillators subject to seismic excitations specified by an elastic response/Design Spectrum. First, an efficient numerical scheme is adopted to derive a power Spectrum, satisfying a certain statistical criterion, which is compatible with the considered seismic Spectrum. Next, the thus derived power Spectrum is used in conjunction with a frequency domain higher-order statistical linearization formulation to substitute a bilinear hysteretic oscillator by a third order linear system. This is done by minimizing an appropriate error function in the least square sense. Then, this third-order linear system is reduced to a second order linear oscillator characterized by a set of ELPs by enforcing equality of certain response statistics of the two linear systems. The ELPs are utilized to estimate the peak response of the considered hysteretic oscillator in the context of linear response Spectrum-based dynamic analysis. In this manner, the need for numerical integration of the nonlinear equation of motion is circumvented. Numerical results pertaining to the European EC8 elastic response Spectrum are presented to demonstrate the applicability and usefulness of the proposed approach. These results are supported by Monte Carlo analyses involving an ensemble of 250 non-stationary artificial EC8 Spectrum compatible accelerograms. The proposed approach can hopefully be an effective tool in the preliminary aseismic Design stages of yielding structures following either a force-based or a displacement-based methodology.

  • Determination of non-stationary stochastic processes compatible with seismic response/Design spectra
    Proceedings of the 6th International Conference on Computational Stochastic Mechanics(CSM-6), 2011
    Co-Authors: Agathoklis Giaralis, Pol D. Spanos
    Abstract:

    In this paper the problem of deriving non-stationary stochastic processes defined by a parametric evolutionary power Spectrum (EPS) compatible with a given (target) Design Spectrum is addressed. An inverse stochastic dynamics problem is formulated and solved in a least-square sense to determine the requisite EPS. This involves the incorporation of a “peak factor” which is used to relate statistically the target Spectrum to the EPS. Special attention is focused on deriving Design Spectrum compatible processes of specific “effective duration” as commonly defined in the field of earthquake engineering. Specifically, the Design Spectrum of the Chinese GB 50011 aseismic code is considered as a paradigm of a target Spectrum. Comprehensive Monte Carlo analyses are undertaken to numerically estimate GB 50011-compatible median peak factor spectra, given in a polynomial form. These spectra are associated with the first passage problem for linear oscillators excited by uniformly modulated colored non-stationary processes of various durations. The derived peak factor spectra used in conjunction with the herein adopted stochastic formulation yield an excellent level of agreement between the GB 50011 Spectrum and the ensemble average response spectra of simulated EPS-compatible accelerograms of different effective durations. Additional numerical results pertaining to the Design spectra of the European EC8 code and the GB 50011 code are included to show how the behavior of the target Spectrum in the range of long periods affects the choice of the assumed spectral form of the EPS. It is envisioned that the herein derived stochastic processes can be used to facilitate the aseismic Design of structures regulated by contemporary code provisions in a Monte Carlo-based or random vibration-based context of analysis.

  • Effective linear damping and stiffness coefficients of nonlinear systems for Design Spectrum based analysis
    Soil Dynamics and Earthquake Engineering, 2010
    Co-Authors: Agathoklis Giaralis, Pol D. Spanos
    Abstract:

    A stochastic approach for obtaining reliable estimates of the peak response of nonlinear systems to excitations specified via a Design seismic Spectrum is proposed. This is achieved in an efficient manner without resorting to numerical integration of the governing nonlinear equations of motion. First, a numerical scheme is utilized to derive a power Spectrum which is compatible in a stochastic sense with a given Design Spectrum. This power Spectrum is then treated as the excitation Spectrum to determine effective damping and stiffness coefficients corresponding to an equivalent linear system (ELS) via a statistical linearization scheme. Further, the obtained coefficients are used in conjunction with the (linear) Design Spectrum to estimate the peak response of the original nonlinear systems. The cases of systems with piecewise linear stiffness nonlinearity, along with bilinear hysteretic systems are considered. The seismic severity is specified by the elastic Design Spectrum prescribed by the European aseismic code provisions (EC8). Monte Carlo simulations pertaining to an ensemble of nonstationary EC8 Design Spectrum compatible accelerograms are conducted to confirm that the average peak response of the nonlinear systems compare reasonably well with that of the ELS, within the known level of accuracy furnished by the statistical linearization method. In this manner, the proposed approach yields ELS which can replace the original nonlinear systems in carrying out computationally efficient analyses in the initial stages of the aseismic Design of structures under severe seismic excitations specified in terms of a Design Spectrum.

  • Synthesis of accelerograms compatible with the Chinese GB 50011-2001 Design Spectrum via harmonic wavelets: artificial and historic records
    Earthquake Engineering and Engineering Vibration, 2009
    Co-Authors: Pol D. Spanos, Agathoklis Giaralis
    Abstract:

    A versatile approach is employed to generate artificial accelerograms which satisfy the compatibility criteria prescribed by the Chinese aseismic code provisions GB 50011-2001. In particular, a frequency dependent peak factor derived by means of appropriate Monte Carlo analyses is introduced to relate the GB 50011-2001 Design Spectrum to a parametrically defined evolutionary power Spectrum (EPS). Special attention is given to the definition of the frequency content of the EPS in order to accommodate the mathematical form of the aforementioned Design Spectrum. Further, a one-to-one relationship is established between the parameter controlling the time-varying intensity of the EPS and the effective strong ground motion duration. Subsequently, an efficient auto-regressive moving-average (ARMA) filtering technique is utilized to generate ensembles of non-stationary artificial accelerograms whose average response Spectrum is in a close agreement with the considered Design Spectrum. Furthermore, a harmonic wavelet based iterative scheme is adopted to modify these artificial signals so that a close matching of the signals’ response spectra with the GB 50011-2001 Design Spectrum is achieved on an individual basis. This is also done for field recorded accelerograms pertaining to the May, 2008 Wenchuan seismic event. In the process, zero-phase high-pass filtering is performed to accomplish proper baseline correction of the acquired Spectrum compatible artificial and field accelerograms. Numerical results are given in a tabulated format to expedite their use in practice.

  • Determination of Design Spectrum compatible evolutio- nary spectra via Monte Carlo peak factor estimation
    2009
    Co-Authors: Agathoklis Giaralis, Pol D. Spanos
    Abstract:

    The problem of generating ensembles of artificial non-stationary earthquake accelerograms compatible with a given (target) response/Design Spectrum is cast on a stochastic basis. The Design Spectrum of the European aseismic code provisions (EC8) for various soil conditions and damping ratios is used as a paradigm of a Design/target Spectrum. The generated accelerograms are construed as realizations of a non-stationary random process; they are char- acterized in the frequency domain by a parametrically defined evolutionary power Spectrum (EPS). An appropriate least squared optimization problem is formulated for the determination of the parameters of the EPS. The solution of this problem involves the incorporation of a "peak factor" which is used to re- late the target Spectrum to the EPS in a probabilistic context. To this end, a comprehensive Monte Carlo study is undertaken to estimate numerically the statistical properties of the peak factor from appropriately computed popula- tions, and to derive polynomial expressions for the median frequency- dependent peak factors (peak factor spectra). These expressions are used in conjunction with the herein adopted optimization problem to determine EPSs compatible with the EC8 Design Spectrum. The derived median peak factor spectra yield an excellent level of agreement between the EC8 Spectrum and the ensemble average and median response spectra of simulated EPS- compatible ensembles of accelerograms.

Hendrawan Soeleman - One of the best experts on this subject based on the ideXlab platform.

  • ACM Great Lakes Symposium on VLSI - Digital CMOS logic operation in the sub-threshold region
    Proceedings of the 10th Great Lakes Symposium on VLSI - GLSVLSI '00, 2000
    Co-Authors: Hendrawan Soeleman, Kaushik Roy
    Abstract:

    Numerous efforts in balancing the trade-off between power, area and performance have been carried out in the medium performance, medium power region of the Design Spectrum. However, not much study has been done at the two extreme ends of the Design Spectrum, namely, the ultra-low power with acceptable performance at one end, and high performance with power within limit at the other. In this paper, we focus on the ultra-low power end of the Spectrum where performance is of secondary importance. One solution to achieve the ultra-low power requirement is to operate the digital logic gates in sub-threshold region. In this paper, we analyze both CMOS and Pseudo-NMOS logic operating in sub-threshold region. We compare the results with CMOS in normal strong inversion region and with other known low-power logic, namely, energy recovery logic. Results show energy/switching reduction of two orders of magnitude from an 8×8 carry-save array multiplier when it is operated in the sub-threshold region.

  • ultra low power digital subthreshold logic circuits
    International Symposium on Low Power Electronics and Design, 1999
    Co-Authors: Hendrawan Soeleman
    Abstract:

    Numerous efforts in balancing the trade-off between power, area and performance have been done in the medium performance, medium power region of the Design Spectrum. However, not much study has been done at the two extreme ends of the Design Spectrum, namely the ultra-low power with acceptable performance at one end (the focus of this paper), and high performance with power within limit at the other. One solution to achieve the ultra-low power requirement is to operate the digital logic gates in the subthreshold region. We analyze both CMOS and Pseudo-NMOS logic families operating in the subthreshold region. We compare the results with CMOS in the normal strong inversion region and with other known low-power logic, namely, energy recovery logic. Our results show an energy per switching reduction of two orders of magnitude for an 8/spl times/8 carry save array multiplier when it is operated in the subthreshold region.

  • ISLPED - Ultra-low power digital subthreshold logic circuits
    Proceedings of the 1999 international symposium on Low power electronics and design - ISLPED '99, 1999
    Co-Authors: Hendrawan Soeleman, Kaushik Roy
    Abstract:

    Numerous efforts in balancing the trade-off between power, area and performance have been done in the medium performance, medium power region of the Design Spectrum. However, not much study has been done at the two extreme ends of the Design Spectrum, namely the ultra-low power with acceptable performance at one end (the focus of this paper), and high performance with power within limit at the other. One solution to achieve the ultra-low power requirement is to operate the digital logic gates in the subthreshold region. We analyze both CMOS and Pseudo-NMOS logic families operating in the subthreshold region. We compare the results with CMOS in the normal strong inversion region and with other known low-power logic, namely, energy recovery logic. Our results show an energy per switching reduction of two orders of magnitude for an 8/spl times/8 carry save array multiplier when it is operated in the subthreshold region.