CQC modal combination rule for high‐frequency modes
ABSTRACT The CQC rule for modal combination is extended to include the quasi-static contribution of truncated modes and the effects of input narrow-bandedness and cut-off frequency. A simple measure of the error in approximating a high-frequency modal response by its quasi-static contribution is derived. The extended rule is applicable to structures with high-frequency modes and to seismic inputs which may not be regarded as wide band. Numerical examples demonstrate the significance of input bandwidth and cut-off frequency on modal cross-correlation coefficients, and on the error resulting from truncation of high-freqeuncy modes.
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ABSTRACT: Assessment of structural performance under stochastic dynamic loadings requires estimation of the extremes of stochastic response components and the resultant responses as their linear and nonlinear combinations. This paper addresses the evaluations and combination rules for the extremes of scalar and vectorial resultant responses from two response components that may show non-Gaussian characteristics. The non-Gaussian response process is modeled as a translation process from an underlying Gaussian process. The mean crossing rates and extreme value distributions of resultant responses are calculated following the theory for vector-valued Gaussian processes. An extensive parameter study is conducted concerning the influence of statistical moments of non-Gaussian response components on the extremes of resultant responses. It is revealed that the existing combination rules developed for Gaussian processes are not applicable to the case of non-Gaussian process. New combination rules are suggested that permit predictions of the extremes of resultant responses directly from the extremes of response components. Keywords: Scalar combination; vectorial combination; non-Gaussian process; extreme value distribution; upcrossing theory; peak factor; combination rule Read More: http://www.worldscientific.com/doi/abs/10.1142/S0219455413500764International Journal of Structural Stability and Dynamics 04/2014; 14(3):1350076-1 - 1350076-36. · 0.68 Impact Factor
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ABSTRACT: The role played by the modal analysis in the framework of structural dynamics is fundamental from both deterministic and stochastic point of view. However the accuracy obtained by means of the classical modal analysis is not always satisfactory. Therefore it is clear the importance of methods able to correct the modal response in such a way to obtain the required accuracy. Many methods have been proposed in the last years but they are meaningful only when the forcing function is expressed by an analytical function. Moreover in stochastic analysis they fail for white noise excitation. In the paper a method able to give a very accurate response for both deterministic and stochastic input is presented. This method is based upon the use of Ritz vectors together with the classical modal analysis. Numerical applications for both deterministic and stochastic inputs show the great accuracy of the proposed method.Computers & Structures 11/2001; 79(26):2471-2480. · 2.18 Impact Factor
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ABSTRACT: Several investigations have been concerned with the statistics of peaks in the seismic response of multi-degree-of-freedom (MDOF) structures when all the peaks are arranged in decreasing level of amplitude. The present paper suggests improvements in the probabilistic formulation adopted in such studies. With these improvements, the probabilistic spectrum superposition approach becomes more accurate and convinient to use in practical applications. By computing the response of a five-story example building excited by several real accelograms with differing frequency and nonstationary characteristics, it is shown that the probabilistic approach is able to predict accurately the amplitudes of several significant response peaks, corresponding to the strong-motion stationary part of input excitation.Soil Dynamics and Earthquake Engineering 01/1998; 17(1):1-11. · 1.28 Impact Factor