摘要:

AbstractAsymmetrically yielding single‐degree‐of‐freedom elastoplastic systems are subjected to simulated accelerograms based on El Centro‐NS, 1940 ground motion (wide frequency band) to calculate the corresponding ductility demands. Results are compared with those corresponding to simulated accelerograms of the SCT‐EW, 1985 Mexico earthquake (narrow frequency band) obtained in a previous work. Results obtained reveal that the characteristics of the excitation influence the response of asymmetrically yielding structures and that the differences found on responses corresponding to both earthquakes are due to frequency content, duration and/or intensity of motion. The effect of the latter concepts is studied using modulating sinusoidal excitations as well as accelerograms recorded on soft and hard soils of Mexico City.Two alternate expressions are proposed to evaluate the increase in ductility demands of structures with asymmetric force‐displacement curves with respect to symmetric ones. Those expressions take into account motion intensity and duration, as well as seismic design

ISSN:0098-8847    

DOI:10.1002/eqe.4290200102

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA systematic procedure to develop a consistent lumped‐parameter model with real frequency‐independent coefficients to represent the unbounded soil is developed. Each (modelled) dynamic‐stiffness coefficient in the frequency domain is approximated as a ratio of two polynomials, which is then formulated as a partial‐fraction expansion. Each of these terms is represented by a discrete model, which is the building block of the lumped‐parameter model. A second‐order term, for example, leads to a discrete model with springs and dampers with two internal degrees of freedom, corresponding to two first‐order differential equations, or, alternatively, results in a discrete model with springs, dampers and a mass with one internal degree of freedom, corresponding to one second‐order differential equation.The lumped‐parameter model can easily be incorporated in a general‐purpose structural dynamics program working in the time domain, whereby the structure can even be non‐linear. A thorough evaluation shows that highly accurate results are achieved, even for dynamic systems wi

ISSN:0098-8847    

DOI:10.1002/eqe.4290200103

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA systematic procedure to develop consistent (symmetric) stiffness, damping and mass matrices with real coefficients to represent any unbounded soil is developed. These property matrices are based on the lumped‐parameter models of Reference 1. Either stiffness and damping matrices corresponding to first‐order differential equations involving the internal degrees of freedom and those on the structure‐soil interface result or, alternatively, in addition mass matrices are introduced, corresponding to second‐order differential equations, which reduce the number of internal degrees of freedom by a factor 2.The stiffness, damping and mass matrices can easily be incorporated in a general‐purpose structural dynamics program working in the time domain, whereby the structure can even be n

ISSN:0098-8847    

DOI:10.1002/eqe.4290200104

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe estimation of site intensity occurrence probabilities in low seismic activity regions has been studied from different points of view. However, no method has been definitively established because several problems arise when macroseismic historical data are incomplete and the active zones are not well determined. The purpose of this paper is to present a method that estimates site occurrence probabilities and at the same time measures the uncertainties inherent in these probabilities in low activity regions. The region to be studied is divided into very broad seismic zones. An exponential intensity probability law is adjusted for each zone and the degree of uncertainty in the assumed incompleteness of the catalogue is evaluated for each intensity. These probabilities are used to establish what may be termed ‘prior site occurrence models’. A Bayesian method is used to improve ‘prior models’ and to obtain the ‘posterior site occurrence models’. Epicentre locations are used to recover spatial information lost in the prior broad zoning. This Bayesian correction permits the use of specific attenuation for different events and may take into account, by means of conservative criteria, epicentre location errors. Following Bayesian methods, probabilities are assumed to be random variables and their distribution may be used to estimate the degree of uncertainty arising from (a) the statistical variance of estimators, (b) catalogue incompleteness and (c) mismatch of data to prior assumptions such as Poisson distribution for events and exponential distribution for intensities. The results are maps of probability and uncertainty for each intensity. These maps exhibit better spatial definition than those obtained by means of simple, broad zones. Some results for Catalonia (NE of Iberian Peninsula

ISSN:0098-8847    

DOI:10.1002/eqe.4290200105

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA series of parametrically defined experimental model structures has been tested under earthquake base loading using the SERC national U.K. earthquake simulator. The models have been designed with variable ratios of torsional to lateral stiffness, and with both symmetric and asymmetric mass distributions. This paper first describes the tests carried out to determine the basic dynamic model properties and the establishment of idealized analytical models which give accurate predictions of model behaviour under steady‐state loading and free‐vibration conditions. Secondly, a detailed discussion is made of the two highly coupled structural models having uncoupled torsional to lateral frequency ratioRf= 1.2, commenting on the ability of the modal analysis procedures to predict accurately the maximum recorded responses. It is concluded that the theory underestimates the significance of the fundamental torsional mode of vibration in the combined structural response, and overestimates the contribution of the first lateral mode. These effects compensate each other on the side of the structure which is most severely affected by torsional response, but produce large inaccuracies on the side of the building which is commonly assumed to be affected beneficially by torsional coupl

ISSN:0098-8847    

DOI:10.1002/eqe.4290200106

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper addresses some fundamentally contradictory conclusions drawn by Tso and Ying1and the authors2regarding the additional seismic ductility demand in asymmetric building structures and the adequacy of certain code torsional provisions. It also clarifies a number of issues arising from the different approaches employed in the two studies. The Mexico 76 and 87 code torsional provisions are taken as examples. Results show that the structural element at the stiff edge is the more critical and that the Mexico 76 code torsional provisions (among others) are inadequate, substantially underestimating the strength demand of this element. On the other hand, the Mexico 87 code torsional provisions are found to be over‐conservative. Recommendations are also given for improving the form and effectiveness of these code torsional provision

ISSN:0098-8847    

DOI:10.1002/eqe.4290200107

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0098-8847    

DOI:10.1002/eqe.4290200108

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0098-8847    

DOI:10.1002/eqe.4290200101

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY