摘要:

AbstractNon‐linear seismic response of soil is studied by comparing the spectral ratios of surface to downhole horizontal accelerations on weak and strong motion. Data from two boreholes are analysed. One is drilled in the alluvial deposits in the south–west quadrant of the SMART 1 array. The second one penetrates Pleistocene terrace deposits in the northern part of the SMART2 array. Observed weak and strong motion spectral ratios are compared with the theoretical ones predicted by the geotechnical soil model which postulates a hysteretic constitutive law. A significant non‐linear response is found at the first site for the events with surface peak acceleration exceeding roughly 0–15g. Deamplification of the strong motion occurred in the frequency range from approximately 1 to 10 Hz. The maximum observed difference between the average weak and strong motion amplification functions of an 11 m‐thick near‐surface stratum is a factor of 2–3. Nonlinear response characteristics are in qualitative agreement with the model. An additional corollary is that the amplification function calculated from the shear wave coda is equivalent to the average amplification calculated over the ensemble of small earthquakes. No statistically significant non‐linear response is detected on the second array, that is tentatively accounted for by the stiffer soil conditions and weaker accelerations achieved at the SMART2 site. The results indicate that the non‐linear amplification can be detectable at certain soil conditions above a threshold a

ISSN:0098-8847    

DOI:10.1002/eqe.4290240302

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFor the identification of multi‐degree‐of‐freedom structures, it is not practical to identify all of the parameters included in the structures because enormous computation time is required and because identifiability may not be possible. In this paper, a localized identification approach through substructuring is formulated in the frequency domain. A technique of spectral smoothing is incorporated in the approach to deal with noise‐corrupted data. The proposed approach can be used to identify the structural parameters in any part of interest in a structure. The numerical investigations for a lumped mass‐spring‐dashpot system indicate that faster convergence and higher accuracy are achieved and the noise influences on the identified results are reduced greatly by spectral smoothing. The approach also applies to whole‐structure identification if the required records available and the numerical example shows that higher accuracy results are obtained with less cpu time and more poorly guessed initial values as compared with the general complete‐structure

ISSN:0098-8847    

DOI:10.1002/eqe.4290240303

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn this paper a comprehensive investigation on the dynamic characteristics of turbine–generator–foundation systems is performed. All the major components of the system, including turbine–generator casing, shaft, rotors, journal bearings, deck, piers, foundation mat, piles, and soil medium, have been included. Full interaction between the turbine–generator set, the foundation superstructure, and the soil medium, is considered.A hybrid method is used to establish the mathematical model for the turbine–generator‐foundation system. The analysis is conducted in the frequency domain through complex frequency response analysis. The response in the time domain is obtained by Fourier transform. The seismic excitation is represented as the control motion on the ground surface, which is generated as an artificial earthquake.A 300 MW turbine‐generator‐foundation system is analysed under excitations from rotor unbalances and earthquakes. The influence of turbine‐generator casing and soil anisotropy on the response of the system is explored. It is found that the presence of casing and soil anisotropy strongly influences the displacements and internal forces of the system under rotor unbalance excitation. Under seismic excitation, however, although the presence of casing and soil anisotropy does affect the displacements of the system, their effect on the internal forces of the

ISSN:0098-8847    

DOI:10.1002/eqe.4290240304

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe incident steady‐state SH waves in the neighbourhood of a boundary node point are first expanded in terms of a few plane waves at different incident angles, the motion of the boundary point is then related to those of its adjacent node points to form the multi‐directional transmitting boundary conditions, which reduce reflections from the boundary over the entire range of incident angles. This feature of the boundaries is demonstrated by finite element computations of SH motions of a layer fixed at its base, in which the incident wave may travel parallel to the boundary as the frequency of excitation approaches one of the natural frequencies of the sys

ISSN:0098-8847    

DOI:10.1002/eqe.4290240305

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA suitable model material was developed to construct scaled models of a 30 m high prototype concrete gravity dam monolith and the experimental technique perfected for testing the models, till failure, on the EPSRC earthquake simulator at Bristol University. A series of shaking table tests was performed with the aim of assessing the possible failure mechanisms of medium to low height dams under simple motions and simulated earthquakes. Tests were conducted with and without the presence of hydrostatic pressure. The hydrodynamic pressure was simulated using Westergaard's added mass approach. Base cracking was observed to be the main failure mechanism and a tendency of the models to slide and rock after the full crack development at the interface was also observed in some cases.

ISSN:0098-8847    

DOI:10.1002/eqe.4290240306

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper investigates the non‐linear inelastic seismic response of existing single‐span simply supported bridges having bearings which can remain stable and slide after their anchor bolts are ruptured. A simplified equivalent model is developed for the inelastic analysis of these single‐span simply supported bridges. Non‐linear inelastic time‐history analyses are conducted for various acceleration inputs. It is found that narrower bridges with longer spans may have considerable sliding displacements and fall off their supports if adequate seat width is not provided. It is also found that for the same ratio of friction coefficient to peak ground acceleration, the sliding displacement of a structural system is linearly proportional to the amplitude of the peak ground acceleration beyond a certain threshold value. This is also demonstrated analytically from an energy approach point of view. The distribution of the energy content of an earthquake, which is related to its velocity time history, can be an indication of the propensity of an earthquake to cause high sliding displacements. Ground motions with high frequency content or high Ap/Vpratio may produce smaller sliding displacements than ground motions with relatively lower Ap

ISSN:0098-8847    

DOI:10.1002/eqe.4290240307

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThrough an energy formulation and the use of a large deflection theory, it is shown that if a thin plate has a slight initial preform, and if its edges are constrained against in–plane displacements, then all of the natural frequencies of the plate will be shifted upward. For a uniform thin plate, the amount of frequency shift depends on the type of boundary conditions and the ratio of the amplitude of preform to the thickness of the plate. Examples of square and rectangular plates preformed in the shape of their first mode shapes are presented. The method holds the promise of shifting or essentially removing a troublesome vibration mod

ISSN:0098-8847    

DOI:10.1002/eqe.4290240308

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe dynamic behaviour of a system of three‐dimensional, massless, rigid, surface foundations of arbitrary shape perfectly bonded to the elastic half‐space is numerically studied with the frequency domain boundary element method. This method employs the dynamic Green's function for the surface of the half‐space and this results in a discretization of only the soil‐foundation interfaces. In addition, use of isoparametric quadratic quadrilateral boundary elements increases the accuracy of the method, which is confirmed by comparison with other known numerical solutions. Externally applied loads, harmonically varying with time, are considered. The through the soil coupling effect between the foundations as a function of distance and frequency is assessed through extensive parametric studies involving two and four rigid foundations being isolated or interconnected. It is found that the assertion of ATC‐3 regulations that omission of coupling effects leads to conservative results is not always correct for all fr

ISSN:0098-8847    

DOI:10.1002/eqe.4290240309

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractExperiments were conducted to measure the damping in low‐aspect‐ratio, reinforced concrete shear walls with the specific intent of obtaining a better understanding of how this parameter changes with increasing stress levels. These experiments and the corresponding results are presented, along with a description of the methods used to estimate damping from measured input and response data and a summary of a numerical study that was undertaken to assess the relative accuracy of these methods. Also presented are the testing methods used in this study, including static cyclic tests, experimental modal analyses, and simulated seismic testing on a shake table. The results are summarized and compared with those obtained by other investigators. In conclusion, an empirical relationship is developed for equivalent viscous damping in low‐aspect‐ratio shear walls as a function of the peak nominal base shear stress the shear wall experiences during a seismi

ISSN:0098-8847    

DOI:10.1002/eqe.4290240310

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0098-8847    

DOI:10.1002/eqe.4290240311

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY