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The response of an elastic circular wedge on a flexible foundation embedded into a half-space is investigated in the frequency domain for incident pane SH-waves. The problem is solved by expansion of the motion in all three media (wedge, foundation and half-space) in cylindrical wave functions (Fourier-Bessel series). The structural model is simple, but accounts for both differential motions of the base and for the effects of soil-structure interaction. Usually, structural models in earthquake engineering consider either differential ground motion, but ignore soil-structure interaction, or consider soil-structure interaction, but for a rigid foundation, thus ignoring differential ground motion. The purpose of the study is to find how stiff the foundation should be relative to the soil so that the rigid foundation assumption in soil-structure interaction models is valid. The shortest wavelength of the incident waves considered in this study is one equal to the width of the base of the wedge. It is concluded that, for this model, a foundation with same mass density as the soil but 50 times larger shear modulus behaves as ‘rigid’. For ratio of shear moduli less than 16, the rigid foundation assumption is not valid. Considering differential motions is important because of additional stresses in structures that are not predicted by fixed-base and rigid foundation models. 相似文献
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Antiplane response of a dike with flexible soil-structure interface to incident SH waves 总被引：2，自引：0，他引：2
Abdul Hayir Maria I. Todorovska Mihailo D. Trifunac 《Soil Dynamics and Earthquake Engineering》2001,21(7)
Studies of the effects of differential ground motions on structural response generally do not consider the effects of the soil-structure interaction. On the other end, studies of soil-structure interaction commonly assume that the foundation of the structure (surface or embedded) is rigid. The former ignore the scattering of waves from the foundation and radiation of energy from the structure back to the soil, while the latter ignore quasi-static forces in the foundations and lower part of the structure deforming due to the wave passage. This paper studies a simple model of a dike but considers both the soil-structure interaction and the flexibility of the foundation. The structure is represented by a wedge resting on a half-space and excited by incident plane SH-waves. The structural ‘foundation’ is a flexible surface that can deform during the passage of seismic waves. The wave function expansion method is used to solve for the motions in the half-pace and in the structure. The displacements and stresses in the structure are compared with those for a fixed-base model shaken by the free-field motion. The results show large displacements near the base of the structure due to the differential motion of the base caused by the wave passage. 相似文献
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The system damping, the system frequency, the relative building response and the base rocking response peak amplitudes are studied, as those depend on the building mass and height, the flexibility of the soil, the structural damping, the type of incident waves and their angle of incidence. A linear two-dimensional model is used, which assumes the soil to be a homogeneous isotropic half-space, the foundation supporting the building to be a rigid embedded cylinder, and in which the building model is an equivalent single-degree-of-freedom oscillator. The system frequency and the system damping ratio are determined by measuring the width and the frequency of the peak in the transfer function of the oscillator relative response, using the analogy with the half-power method for a single-degree-of-freedom fixed-base oscillator. Previous similar studies are for dynamic soil-structure interaction only, and for simplified models in which the stiffness of the soil and the damping due to radiation are represented by springs and dashpots. The study in this paper differs from the previous studies in that the wave passage effects (or the kinematic interaction) are also included, and that no additional simplifications of the model are made. Results are shown for excitation by plane P- and SV-waves. 相似文献
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M. D. Trifunac S. S. Ivanovi M. I. Todorovska 《Soil Dynamics and Earthquake Engineering》2003,23(1):65-75
This paper presents low frequency wavenumbers in a seven-storey reinforced concrete building estimated from its recorded response to eleven earthquakes, one of which (1994 Northridge) caused visible structural damage, and two of which are its aftershocks. The wavenumbers, Ki,j(f), are estimated from pairs (i,j) of records at neighboring recording sites in the building, distributed vertically or horizontally. Changes in Ki,j(f) from one event to another are compared in the undamaged (lower) and in the damaged (upper) part of the building, with the aim to find whether trends in Ki,j(f) can indicate damage. The results suggest significant and permanent increase of the wavenumbers in the damaged parts for the 1994 Northridge earthquake and its aftershocks, which is not the case for the other events in the damaged parts, and for all eleven events in the undamaged parts of the building. This increase in wavenumbers in the damaged parts can be explained by reduced wave velocities through the damaged structural members, and by scattering of waves from the discontinuities created by the damage. It is concluded from this qualitative analysis that wavenumbers estimated from strong motion recordings in a building can indicate location of damage, and that it would be useful to refine further this method (extend it to higher frequencies, and add the capability to quantify the damage). However, this would require more dense strong motion instrumentation in buildings than currently available. Deployment of dense arrays in selected buildings would provide data for further work on this subject. 相似文献
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The effects of variable speeds of spreading of submarine slides and slumps on near-field tsunami amplitudes are illustrated. It is shown that kinematic models of submarine slides and slumps must consider time variations in the spreading velocities, when these velocities are less than about 2cT, where
is the long period tsunami velocity in ocean of constant depth h. For average spreading velocities greater than 2cT, kinematic models with assumed constant spreading velocities provide good approximation for the tsunami amplitudes above the source. 相似文献
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The 1994 Northridge earthquake occurred underneath a densely populated metropolitan area, and was recorded by over 200 strong motion stations in the metropolitan area and vicinity. This rare coincidence made it an ideal case to study, in statistical sense, the correlation of damage to structures with the level of strong shaking, in particular with respect to (1) instrumental characteristics of shaking and (2) the reported site intensity scale. In this paper, statistics for the incidence of red-tagged building in 1 × 1 km2 blocks in San Fernando Valley and Los Angeles is presented and analyzed, as function of the observed peak ground velocity or the local intensity of shaking. The ‘observed’ peak velocity is estimated from contour maps based on the recorded strong motion. The intensity of shaking is estimated from the published intensity map and from our modification of this map to make it more consistent with observed high damage to buildings in some localized areas. Finally, empirical scaling equations are derived which predict the average density of red-tagged buildings (per km2) as a function of peak ground velocity or site intensity of shaking. These scaling equations are specific to the region studied, and apply to Wooden Frame Construction, typical of post World War II period, which is the prevailing building type in the sample studied. These can be used to predict the density of red-tagged buildings per km2 in San Fernando Valley and in Los Angeles for a scenario earthquake or for an ensemble of earthquakes during specified exposure, within the framework of probabilistic seismic hazard analysis. Such predictions will be useful to government officials for emergency planning, to the insurance industry for realistic assessment of insured losses, and to structural engineers for assessment of the overall performance of this type of buildings. 相似文献
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Shaking hazard compatible methodology for probabilistic assessment of permanent ground displacement across earthquake faults 总被引：2，自引：0，他引：2
A methodology for probabilistic hazard assessment of permanent displacement across faults caused by earthquake rupture is presented, compatible with region specific models for ground shaking hazard in California, developed earlier by the authors and coworkers. Assessment of permanent dislocations across faults is important for the design and retrofit of highway bridges and tunnels crossing faults, as well as for other lifelines crossing faults, such as aqueducts, water and gas lines, etc. The methodology is illustrated for two strike-slip faults (prototypes of Class A and Class B faults in California), for 50 years exposure. The illustrations show that, for given seismic moment rate, the hazard estimates are quite sensitive to how the seismic moment is distributed over earthquake magnitudes. They also show that the hazard is small even for very small levels of displacement, in contrast to ground shaking hazard, which is due to the fact that only one fault contributes to the hazard and not every event on that fault necessarily affects the site. 相似文献
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Maria I. Todorovska 《地震工程与结构动力学》1998,27(10):1031-1051
A mathematical model for a three-component accelerograph is presented that accounts for the effects of transducer misalignment and cross-axis sensitivity. The former refers to departures in the alignment of the transducer penduli (typically of the order of few degrees) from an ideal orthogonal system, and the latter to a transducer recording components of motion in directions other than its principal sensitivity axis. Transducer misalignment magnifies the effects of cross-axis sensitivity. These effects are significant only for large amplitude recordings (peak acceleration close to 1g), for example in the near-field of the 1994 Northridge, California, earthquake. The misalignment angles and the angular amplification constant can be determined by a static tilt test, performed in the field, and solving a generalized inverse problem. This paper presents an algorithm for solution of this inverse problem on a routine basis. Practical implementation of the algorithm and results for 76 instruments of the Los Angeles Strong Motion Array are presented in a separate paper. © 1998 John Wiley & Sons, Ltd. 相似文献