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Nicolas Luco Yasuhiro Mori Yosuke Funahashi C. Allin Cornell Masayoshi Nakashima 《地震工程与结构动力学》2003,32(14):2267-2288
Predictors (or estimates) of seismic structural demands that are less computationally time‐consuming than non‐linear dynamic analysis can be useful for structural performance assessment and for design. In this paper, we evaluate the bias and precision of predictors that make use of, at most, (i) elastic modal vibration properties of the given structure, (ii) the results of a non‐linear static pushover analysis of the structure, and (iii) elastic and inelastic single‐degree‐of‐freedom time‐history analyses for the specified ground motion record. The main predictor of interest is an extension of first‐mode elastic spectral acceleration that additionally takes into account both the second‐mode contribution to (elastic) structural response and the effects of inelasticity. This predictor is evaluated with respect to non‐linear dynamic analysis results for ‘fishbone’ models of steel moment‐resisting frame (SMRF) buildings. The relatively small number of degrees of freedom for each fishbone model allows us to consider several short‐to‐long period buildings and numerous near‐ and far‐field earthquake ground motions of interest in both Japan and the U.S. Before doing so, though, we verify that estimates of the bias and precision of the predictor obtained using fishbone models are effectively equivalent to those based on typical ‘full‐frame’ models of the same buildings. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Scalar and vector intensity measures are developed for the efficient estimation of limit‐state capacities through incremental dynamic analysis (IDA) by exploiting the elastic spectral shape of individual records. IDA is a powerful analysis method that involves subjecting a structural model to several ground motion records, each scaled to multiple levels of intensity (measured by the intensity measure or IM), thus producing curves of structural response parameterized by the IM on top of which limit‐states can be defined and corresponding capacities can be calculated. When traditional IMs are used, such as the peak ground acceleration or the first‐mode spectral acceleration, the IM‐values of the capacities can display large record‐to‐record variability, forcing the use of many records to achieve reliable results. By using single optimal spectral values as well as vectors and scalar combinations of them on three multistorey buildings significant dispersion reductions are realized. Furthermore, IDA is extended to vector IMs, resulting in intricate fractile IDA surfaces. The results reveal the most influential spectral regions/periods for each limit‐state and building, illustrating the evolution of such periods as the seismic intensity and the structural response increase towards global collapse. The ordinates of the elastic spectrum and the spectral shape of each individual record are found to significantly influence the seismic performance and they are shown to provide promising candidates for highly efficient IMs. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Granulite- and amphibolite-facies metabasites occur within the Archaean Marydale Group (3.0 Ga) along the western edge of the mid-Proterozoic Kheis Tectonic Subprovince (1.8–1.3 Ga) of South Africa. At the northern end of the exposed Marydale Group, the metabasites are infolded with overlying quartzites from which they are separated by a low-angle fault contact. They contain two pyroxenes, hornblende and bytownite, but show widespread retrogression to coronas of almandine and hornblende. Geothermometric data for these assemblages indicate peak equilibration of the two-pyroxene assemblage at 690–760°C, and retrograde equilibration of garnet-hornblende pairs at 600–650°C. Barometric data are more uncertain though an estimate of 3–5 kbar is made from a consideration of hornblende chemistry. Using previously published data, a near-isobaric retrograde P-T path is inferred.
Rb---Sr ages of whole-rock hypersthene tonalites and mylonitized granites yield ages of 1353 ± 33 and 1355 ± 20 Ma, respectively, interpreted as the age of isotopic resetting during granulite-facies metamorphism. K---Ar hornblende ages of 1228 ± 61 and 1070 ± 48 Ma are recorded from fresh and sheared granulite-facies metabasites, respectively. These ages data the P-T path and show that the granulite-facies metamorphism predates the adjacent Namaqua orogeny that reset Rb---Sr systematics at ±1210 Ma. 相似文献
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Statistical methods are available which predict the maximum response of simple oscillators given the peak acceleration (Ap), peak velocity (Vp) or peak displacement (Dp) of seismic ground motions. An alternative parameter, namely an ordinate (or ordinates) of the Fourier amplitude spectrum of ground motion acceleration, FS(f), may in fact be a preferred predictor of peak response, especially in a frequency range close to f. Other statistical methods (attenuation laws) use distance R and other parameters such as magnitude (M), Modified Mercalli epicentral Intensity (Io) and Modified Mercalli site Intensity (MMI or Is) to predict spectral velocity (Sv(f)), etc. In using such approaches, it is most desirable to know the total uncertainty in the predicted peak response of the system given the starting parameter values. An extensive strong motion data set is used to study these questions, The most direct prediction models are found to be preferable (have lower prediction dispersion) but data may not be available in all regions to permit their use. 相似文献
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David H. Cornell 《Earth and Planetary Science Letters》1977,37(1):117-123
The metabasic Marydale Formation of the Kheis Group occupies a zone of contact between the Sanama and Kaapvaal structural provinces of South Africa. Stratigraphic relationships between the two provinces are not well understood. Whilst the well-known Kaapvaal basement and supracrustal succession yield radiometric ages older than 1900 m.y., Sanama Province ages reflect a Kibaran(1200 ± 200m.y.) tectogenetic cycle. The age of the Marydale, stratigraphically the oldest Sanama formation, has been variously estimated at2500m.y., about 2000 m.y., or Kibaran, based on controversial field interpretations or on available radiometric data.Rb-Sr data are presented for Marydale samples from a nappe-like body which, having been thrust over the Kaapvaal basement, was shielded from metamorphism. Two types of alteration are described and possible causes of isotopic homogenisation are discussed. It is concluded that an isochron age of 1899± 57m.y. (I = 0.7040 ± 0.0003) represents the age of extrusion of the Marydale volcanics.The stratigraphic controversy is thus resolved, Kheis Group formations being approximately coeval with the Matsap, the youngest formation of the Kaapvaal Precambrian succession. The implications of this and other recent work to theories of crustal evolution are considered. It is suggested that the continental crust of Sanama Province originated partly during the Eburnian(2000 ± 100m.y.) period of African orogeny and partly during the Kibaran tectogenetic cycle during which the province became cratonised and was added to the Southern African cratonic block. 相似文献
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We introduce a general decision analysis procedure based on stochastic dynamic programming in the post‐quake aftershock environment. The damage sustained by the building due to the mainsheet, the time‐varying aftershock rates and the potential for further damage progression in the post‐quake environment are all factors taken into consideration in the proposed methodology. This procedure enables the optimal decision after the mainshock to be selected based on the minimization of expected financial losses, subject to a constraint on a minimal level of individual life‐safety, using a consistent probabilistic framework to explicitly quantify the uncertainties in the variables. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
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The 2220 Ma Kalahari Manganese field of South Africa is the world's largest Mn resource and a major producer. Current models for its origin rely on those developed for Phanerozoic deposits, invoking a submarine redox boundary and water movements across a continental shelf, precipitating Mn oxides from the sea. Here we report the discovery of major hydrothermal alteration in the thick andesitic volcanic pile beneath the Mn ore. This and other evidence shows that the Kalahari manganese is actually a volcanic exhalative deposit, analogous in some respects to those forming at present day mid-ocean ridges. Important differences in depth and oxygen supply account for the smaller area and high grade of the Kalahari Manganese Field, compared with the widespread but thinly developed modern ocean floor Mn deposits. 相似文献