Defining equivalent stationary PSDF to account for nonstationarity of earthquake ground motion   总被引：1，自引：0，他引：1  

I.D. Gupta  M.D. Trifunac 《Soil Dynamics and Earthquake Engineering》1998,17(2):89-99

This paper presents three approaches to defining the stationary power spectrum density function (PSDF) of strong ground acceleration, for prediction of structural response corresponding to the strong-motion stationary part of the input excitation. The first approach defines the PSDF in terms of the Fourier amplitude spectrum and a stationary duration of ground acceleration. The PSDF obtained by this approach predicts accurately the response of structures with low to intermediate natural periods. In the second approach, we introduce the concept of stationary duration of response, which is defined as a function of the natural period and damping ratio of the oscillator. Using this approach, it is possible to get accurate estimates of response amplitudes for the broad range of natural periods. However, it is not convenient in practical applications to deal with several stationary durations for a given input excitation. Further, to evaluate these durations it is necessary to specify both the Fourier and the response spectra of ground accelerations; whereas the common engineering practice is to specify the response spectrum only. Therefore, the third approach suggests the use of the response ‘spectrum compatible’ PSDF. The paper presents several improvements in the general methodology used for this purpose. The improvements mainly relate to using more accurate peak factors and to using the transient nature of response. The spectrum compatible PSDFs, as evaluated in the present study, provide realistic specification of strong ground motion for stochastic seismic response analyses of structures.  相似文献   

冻土断裂力学在桩基冻拔稳定计算中的应用   总被引：11，自引：2，他引：9  

李洪升 《冰川冻土》1998,20(2):112-115

对桩基冻拔的冻土工程问题进行了断裂力学分析,并给出简化模。在此基础上讨论了断裂判据以及应力强度因子的计算表达式。  相似文献   

合肥地区超压密粉土-砂层的性状与地基评价   总被引：1，自引：0，他引：1  

郭恒久 《安徽地质》1998,(1)

本文论述了合肥地区超压密粉土—砂层的分布及其物理力这性质。通过多种方法计算对比,综合确定了地基承载力与桩的端阻力。认为可以作为中高层建筑的桩基或箱（筏）基持力层。并对地层时代归属作了探讨。  相似文献   

A palaeolimnological study of Tugulnuit Lake, British Columbia, Canada, with special emphasis on river influence as recorded by chironomids in the lake's sediment     

Andrea Rück  Ian R. Walker  Richard Hebda 《Journal of Paleolimnology》1998,19(1):63-75

Sediments from Tugulnuit Lake in the Okanagan Valley of British Columbia, Canada, were examined for chironomid assemblages. The chironomid stratigraphy obtained encompasses the last 4000 to 5000 years and suggests a warm and fairly stable climate typical for a temperate lake at low- to mid-elevation. This is indicated by the even distribution of warm-water taxa, such as Cladopelma, Dicrotendipes, Polypedilum, Pentaneurini, Stempellina, Stempellinella/Zavrelia and Pseudochironomus throughout the core. Very few cold-water taxa occurred in the sediments. However, stream inputs have had a major impact on Tugulnuit Lake. Sandy sediments and the appearance of Simuliidae and stream-inhabiting chironomid taxa (e.g., Brillia/Euryhapsis, Eukiefferiella/Tvetenia, Rheocricotopus) indicate that a stream intruded into the current lake's basin ca. 3800 yr Before Present (BP). Sediments deposited prior to, and after, the stream's intrusion show a distinctly different chironomid assemblage exhibiting chironomid taxa more typical for lentic habitats. This result indicates that chironomids can serve to detect past stream influences on lake environments. Thus, rheophilic chironomids preserved in lake cores provide a new alternative for reconstructing stream palaeoenvironmental records.  相似文献   

地下工程洞体突然涌水条件的力学分析     

孙峰根  潘国营 《水文地质工程地质》1998,25(2):30-33

本文依据力学原理分析了地下工程洞体形成前后岩体内应力、应变特征,总结出松弛断裂型和底鼓突破型两类突水的力学条件。并提出了集中力在岩体内形成应力的静态液压分布原理。  相似文献   

黄河晋陕峡谷河流阶地和鄂尔多斯高原第四纪构造运动   总被引：47，自引：5，他引：42       下载免费PDF全文

程绍平  邓起东  闵伟  杨桂枝 《第四纪研究》1998,18(3):238-239

本文通过黄河晋陕峡谷河段21个地点的阶地横剖面观察和阶地对比研究,确定出6级宽谷阶地序列,同时,依据17个放射性测年数据对阶地定年。6级宽谷阶地序列揭示了鄂尔多斯高原第四纪区域造陆隆起和局部构造变形,区域造陆隆起的发生时间比之青藏高原隆起要滞后0．113～0．25Ma,而且,平均区域造陆隆起量比之青藏高原的内部和边缘的隆起量小得多。晋陕峡谷河段发生过3期加积作用幕,指示着造陆隆起景观中的气候变化时间线。渭河盆地北缘的韩城断裂悬崖带记录着构造基准面下降,影响的河流长度仅为21～127km。  相似文献   

Dark halo mergers and the formation of a universal profile     

Syer  & Simon D. M. White 《Monthly notices of the Royal Astronomical Society》1998,293(4):337-342

We argue that a universal density profile for dark matter haloes arises as a natural consequence of hierarchical structure formation: it is a fixed point in the process of repeated mergers. We present analytic and numerical arguments for the emergence of a particular form of the central cusp profile. At small radii, the density should vary as r ^−α, with α determined by the way in which the characteristic density of haloes scales with their mass. If small haloes are dense, then α is large. The mass–density relation can be related to the power spectrum of initial fluctuations, P ( k ), through 'formation time' arguments. Early structure formation leads to steep cusps. For P ( k ) ∼  k ⁿ we find α ≃ 3(3 +  n )/(5 +  n ). The universal profile is generated by tidal stripping of small haloes as they merge with larger objects.  相似文献   

Capture of Halley-type comets from the near-parabolic flux     

V. V. Emel'yanenko  & M. E. Bailey 《Monthly notices of the Royal Astronomical Society》1998,298(1):212-222

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Unified analytical solutions to two-body problems with drag   总被引：3，自引：0，他引：3  

S. Breiter  & A. A. Jackson 《Monthly notices of the Royal Astronomical Society》1998,299(1):237-243

The two-body problem with a generalized Stokes drag is discussed. The drag force is proportional to the product of the velocity vector and the inverse square of the distance. The generalization consists of allowing two different proportionality constants for the radial and the transverse components of the force. Under the 'generalized Robertson transformation', the equation of the orbit takes the form of the Lommel equation and admits solutions in terms of Bessel and Lommel functions. The exact, analytical solutions for this type of drag reveal a paradoxical effect of increasing eccentricity for all trajectories. The Poynting–Robertson drag and Poynting–Plummer–Danby problems are discussed as particular cases of the general solution.  相似文献   

The mass of the Pleiades     

Pinfield  Jameson  & Hodgkin 《Monthly notices of the Royal Astronomical Society》1998,299(4):955-964

A membership catalogue for the Pleiades is divided into four mass bins, and a tidally truncated King profile is fitted to each bin with good agreement with the data. The tidal radius of the cluster is found to be 13.1 pc, and the total mass of the cluster down to the stellar limit is calculated to be 735 M. The spread of stars in each bin, as well as the relaxation and crossing times, shows the Pleiades to be an approximately relaxed cluster with equilibrium between the density and velocity distributions. The cluster kinetic energy and binding energy are consistent with the virial theorem, indicating no large unseen population of brown dwarfs. However, the 1 σ errors in the cluster parameters provide an upper limit to the mass of any brown dwarf population of 131 M, which would show up in deep CCD surveys as ≤ 5.5 brown dwarfs per 10 × 10 arcminute field in the cluster centre.  相似文献