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91.
Energy serves as an alternative index to response quantities like force or displacement to include the duration‐related seismic damage effect. A procedure to evaluate the absorbed energy in a multistorey frame from energy spectra was developed. For low‐ to medium‐rise frames, it required a static pushover analysis of the structure to determine the modal yield force and ductility factor of an equivalent single‐degree‐of‐freedom system for the first two modes. The energy spectra were then used to determine the energy contribution of each mode. A procedure was also developed to distribute the energy along the frame height based on energy shapes. This study showed that the second‐mode response in some cases needs to be considered to reflect the energy (or damage) concentration in the upper floors. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
92.
The Vincent Thomas Bridge in the Los Angeles metropolitan area, is a critical artery for commercial traffic flow in and out of the Los Angeles Harbor, and is at risk in the seismically active Southern California region, particularly because it straddles the Palos Verdes fault zone. A combination of linear and non‐linear system identification techniques is employed to obtain a complete reduced‐order, multi‐input–multi‐output (MIMO) dynamic model of the Vincent Thomas Bridge based on the dynamic response of the structure to the 1987 Whittier and 1994 Northridge earthquakes. Starting with the available acceleration measurements (which consists of 15 accelerometers on the bridge structure and 10 accelerometers at various locations on its base), an efficient least‐squares‐based time‐domain identification procedure is applied to the data set to develop a reduced‐order, equivalent linear, multi‐degree‐of‐freedom model. Although not the main focus of this study, the linear system identification method is also combined with a non‐parametric identification technique, to generate a reduced‐order non‐linear mathematical model suitable for use in subsequent studies to predict, with good fidelity, the total response of the bridge under arbitrary dynamic environments. Results of this study yield measurements of the equivalent linear modal properties (frequencies, mode shapes and non‐proportional damping) as well as quantitative measures of the extent and nature of non‐linear interaction forces arising from strong ground shaking. It is shown that, for the particular subset of observations used in the identification procedure, the apparent non‐linearities in the system restoring forces are quite significant, and they contribute substantially to the improved fidelity of the model. Also shown is the potential of the identification technique under discussion to detect slight changes in the structure's influence coefficients, which may be indicators of damage and degradation in the structure being monitored. Difficulties associated with accurately estimating damping for lightly damped long‐span structures from their earthquake response are discussed. The technical issues raised in this paper indicate the need for added spatial resolution in sensor instrumentation to obtain identified mathematical models of structural systems with the broadest range of validity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
93.
A new method is presented for the computation of the gravitational attraction of topographic masses when their height information is given on a regular grid. It is shown that the representation of the terrain relief by means of a bilinear surface not only offers a serious alternative to the polyhedra modeling, but also approaches even more smoothly the continuous reality. Inserting a bilinear approximation into the known scheme of deriving closed analytical expressions for the potential and its first-order derivatives for an arbitrarily shaped polyhedron leads to a one-dimensional integration with – apparently – no analytical solution. However, due to the high degree of smoothness of the integrand function, the numerical computation of this integral is very efficient. Numerical tests using synthetic data and a densely sampled digital terrain model in the Bavarian Alps prove that the new method is comparable to or even faster than a terrain modeling using polyhedra. 相似文献
94.
Nikola Stražičić 《GeoJournal》1996,38(4):445-453
Croatia, through its geographic position, is a Mediterranean/Adriatic and Central European/Danube state. As an Adriatic coastal state, it has a long maritime tradition, which is apparent in its well-developed shipping (2.4 million GT), the high-quality ship-building industry (among the top six in the world) and through its numerous sea ports, of which many were established in ancient times. The leading national port is Rijeka, which is at the same time an important transit port for Austria, Hungary, Slovakia and the Czech Republic.The exceptionally indented Croatian Adriatic coast with its attractive archipelagos and favorable climatic and oceanographic conditions in the coastal sea offers very advantageous conditions for comprehensive tourist utilization. This is particularly true of nautical tourism, which is complimented by a larger number of constructed and well-equipped yachting ports/marinas on the coast and islands. 相似文献
95.
The Carpatho-Balkanides and adjacent area: a sector of the Tethyan Eurasian metallogenic belt 总被引:3,自引:1,他引:3
S. Janković 《Mineralium Deposita》1997,32(5):426-433
The Tethyan Eurasian metallogenic belt (TEMB) was formed during Mesozoic and post-Mesozoic times in the area of the former
Tethyan ocean on the southern margin of Eurasia, with the Afro-Arabian and Indian plates to the south. It extends from western
Mediterranean via the Alps and southeastern Europe through the Lesser Caucasus, the Hindu Kush, and the Tibet Plateau to Burma
and SW Indonesia, linking with the West Pacific metallogenic belt. The Carpatho-Balkan region is one of the sectors of the
TEMB, characterized by some specific features. The emplacement of ore deposits is related to a definite time interval, and
to specific tectonic settings such as:
1. Late Permian-Triassic intracontinental rifting along the northern margin of Gondwanaland and/or fragments already separated.
This setting involves volcanogenic and volcano-sedimentary deposits (iron, lead/zinc, manganese, antimony, mercury, barite),
skarn deposits associated with volcano-plutonic complexes of bimodal magmatism, and low temperature carbonate-hosted lead/zinc
deposits.
2. Jurassic intraoceanic rifting – ophiolite complexes: This setting hosts major magmatic (particularly podiform chrome deposits)
and volcano-sedimentary deposits, mainly of the Cyprus type.
3. Subduction-related setting involves porphyry copper deposits, lesser skarn deposits (iron, locally Pb-Zn), massive sulphide
Cu (e.g. Bor) accompanied locally by Pb-Zn of replacement type, epithermal gold deposits, associated with calc-alkaline igneous
complexes of the Early Tertiary-Late Cretaceous, and the Neogene gold/silver and base metals deposits.
4. Post-collision continent-continent setting includes deposits of Pb-Zn, Sb, As, Au-Cu associated with volcano-plutonic complexes
of calc-alkaline affinity.
Several major Alpine metallogenic units are developed in the Carpatho-Balkanides and adjacent area, each characterized by
specific development, mineral associations, and types of ore deposits.
Received: 3 June 1996 / Accepted: 10 January 1997 相似文献
96.
A methodology for improving geopotential models has been developed. Theoretical relations have been derived converting coefficients in harmonic expansions for radial distortions due to geopotential models into geopotential Stokes coefficients. Terms of the order of 10
–10
in magnitude have been retained. 相似文献
97.
The magnetic susceptibility has been used as a quantitative or semi‐quantitative proxy for reconstructing the summer monsoon intensity in the Chinese Loess Plateau based on extensive studies on climatic or/and environmental mechanisms producing the magnetic susceptibility signatures. However, the precise nature of the link between past climates and the susceptibility signatures has remained uncertain primarily due to lack of our understanding in the ?nalizing and preserving processes of the signatures. This paper attempts to examine the reliability or acceptability of this summer monsoon proxy from non‐magnetic perspectives of soil‐forming processes. We chose nine sections along two transects: one across the western part of the Chinese Loess Plateau and another across the eastern part. Several conclusions can be drawn from our analytical data. First, clay translocation within the S1 palaeosol pro?les, as indicated by ?eld‐observed clay coatings on ped faces in Bt and Bk horizons and demonstrated by laboratory‐analysed clay contents, must have moved some of the magnetic minerals downward so that the susceptibility re?ects only the post‐translocation distribution of the magnetic‐susceptibility‐producing minerals. Second, the best‐developed palaeosol S1S3 at most of the sections studied is not expressed by the magnetic susceptibility because this palaeosol developed in underlying coarse loess (L2) and coarse textures tend to lower the susceptibility. Third, carbonate concentration is normally negatively correlated with the magnetic susceptibility or simply suppresses the magnetic susceptibility peak when the susceptibility enhancement exceeds the carbonate dilution effect. To conclude, extreme caution must be observed when using magnetic susceptibility signatures to retrieve high‐resolution records of the last interglacial palaeoclimate in the Chinese Loess Plateau. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
98.
In this study a procedure for determining the optimum size and location of viscoelastic dampers is proposed using the eigenvalue assignment technique. Natural frequencies and modal damping ratios, required to realize a given target response, are determined first by the convex model. Then the desired dynamic structural properties are realized by optimally distributing the damping and stiffness coefficients of viscoelastic dampers using non‐linear programming based on the gradient of eigenvalues. This optimization method provides information on the optimal location as well as the magnitude of the damper parameters. The proposed procedure is applied to the retrofit of a 10‐story shear frame, and to a three‐dimensional structure with an asymmetric plan. The analysis results confirm that the responses of model structures retrofitted by the proposed method correspond well with the given target response. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
99.
This study investigates an electric‐type active mass driver (AMD) system for structural vibration control. Composed primarily of an electric servomotor and a ball screw, the electrical AMD system is free from noise problems, oil leakage, and labor‐intensive maintenance that commonly are associated with hydraulic AMD systems. The desired stroke amplification of the mass and the power demand of the servomotor can be adjusted via the ball screw pitch, which in turn affects the effectiveness and efficiency of the system. Meanwhile, an instantaneous optimal direct output feedback control algorithm is adopted. Numerical simulation is performed using a five‐story steel frame as the object structure under the conditions of the 1940 El Centro earthquake. The AMD system proves to be effective and efficient within a certain range of the ball screw pitch. The reductions of the peak responses can reach as high as 70% if properly designed. Requiring only the velocity measurement of the top floor for on‐line feedback control, the proposed control algorithm is recommended for practical implementation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
100.
The Elusive AD 1826 Tsunami, South Westland, New Zealand 总被引:1,自引:0,他引:1
James R. Gofr Andrew Wells Catherine Chagu‐Goff Scott L. Nichol Robert J.N. Devoy 《New Zealand geographer》2004,60(2):28-39
In AD 1826 sealers reported earthquake and tsunami activity in Fiordland, although, contemporary or near‐contemporary accounts of tsunami inundation at the time are elusive. A detailed analysis of recent sediments from Okarito Lagoon builds on contextual evidence provided by earlier research concerning past tsunami inundation. Sedimentological, geochemical, micropalaeontological and geochronological data are used to determine palaeoenvironments before, during and after what was most probably tsunami inundation in AD 1826. The most compelling chronological control is provided fry a young cohort of trees growing on a raised shoreline bench stranded fry a drop in the lagoon water level following tsunami inundation. 相似文献