Using Bézier curves to model gradual stiffness transitions in nonlinear elements: Application to self‐centering systems     

Constantin Christopoulos 《地震工程与结构动力学》2011,40(14):1535-1552

A number of techniques are available for modelling nonlinear elements, but most available hysteretic rules do not capture the gradual stiffness changes that are typical of physical systems. In particular, there has not previously been a hysteretic rule with rounded hysteretic corners that could be used to model self‐centering elements, where multiple stiffness changes occur within one loading cycle. This paper presents a new hysteretic rule that allows the gradual stiffness transitions that occur in real systems to be modelled. In this paper, the rule is formulated for flag‐shaped hystereses, but it is shown that the same model also produces hystereses that can be used to model systems that are not self‐centering. The same technique could also be applied to round the corners of different backbone hystereses. A previous study has shown how abrupt stiffness changes can cause very large acceleration spikes, particularly in self‐centering systems. This paper shows that acceleration spikes due to stiffness changes may be reduced by designing systems to change stiffness more gradually, and that this typically has little effect on other aspects of the seismic response. When modelling structural systems, especially if they are self‐centering, sharp‐cornered hysteretic models may be used for initial analysis, but round‐cornered hysteretic models should be considered when using nonlinear rotational springs or when accelerations are of particular importance. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Informational decision support for risk reduction related to hailstorm in Oltenia region: Romania     

Constantin Şulea  Gheorghe Manolea  Dan Selişteanu 《Natural Hazards》2013,66(2):835-850

This paper deals with the design of a system for decisional support dedicated to an anti-hail system. It is proposed a specific system for Romania anti-hail network, which completes the existing systems with specific information in order to identify the best solutions for both coordination and launch. The main topics refer to the system structure, information handled in the system and reconstruction of a signal based on Bayes criterion. The system comprises two main components: a subsystem of launch decision and a subsystem for assisting the launch decision. In order to achieve this system, the following important issues are considered: the use of communication via GPRS, monitoring the parameters throughout all operating period, log-values, status and alarms, operator actions logs, friendly graphical interface and the generation of tabular and graphical reports for any period. The system enables an increased efficiency by shortening the time for action, a good organization and a high degree of security.  相似文献   

Process of serpentinization in the ultramafic massif of Beni Bousera (internal Rif,Morocco)     

Zaineb?HajjarEmail author  Amina?Wafik  Marc?Constantin  Mohamed?Bhilisse 《Arabian Journal of Geosciences》2016,9(6):471

The Beni Bousera massif forms part of the Sebtide units in the internal Rif Mountain (Morocco). It is mainly composed of mantle peridotites surrounded by crustal metamorphic rocks (kinzigites, micaschists, and schists). The serpentinization affects all of peridotite massif to various degrees. Serpentinization is concentrated at the top of the peridotites, along the mylonitized zone, and in the NE part of the massif. It is manifested by the formation of mesh and hourglass textures along the tectonic foliation in the highly serpentinized peridotites; and brecciated texture in the least serpentinized peridotites. Pyroxene minerals are still intact hosting few serpentine veins. These petrographic features are consistent with the geochemical data, marked by the increasing of LOI and decreasing of MgO and FeO toward the top of the massif and Aaraben fault. The Raman characterization of serpentine with the brecciated mesh and hourglass textures correspond to lizardite type whereas the serpentine with the vein texture is formed by lizardite + chrysotile.  相似文献   

The distribution of late-Quaternary woody taxa in northern Eurasia: evidence from a new macrofossil database     

Heather A. Binney  Katherine J. Willis  Mary E. Edwards  Shonil A. Bhagwat  Patricia M. Anderson  Andrei A. Andreev  Maarten Blaauw  Freddy Damblon  Paul Haesaerts  Frank Kienast  Konstantin V. Kremenetski  Sergey K. Krivonogov  Anatoly V. Lozhkin  Glen M. MacDonald  Elena Y. Novenko  Pirita Oksanen  Tatiana V. Sapelko  Minna Väliranta  Ludmila Vazhenina 《Quaternary Science Reviews》2009,28(23-24):2445-2464

We present a database of late-Quaternary plant macrofossil records for northern Eurasia (from 23° to 180°E and 46° to 76°N) comprising 281 localities, over 2300 samples and over 13,000 individual records. Samples are individually radiocarbon dated or are assigned ages via age models fitted to sequences of calibrated radiocarbon dates within a section. Tree species characteristic of modern northern forests (e.g. Picea, Larix, tree-Betula) are recorded at least intermittently from prior to the last glacial maximum (LGM), through the LGM and Lateglacial, to the Holocene, and some records locate trees close to the limits of the Scandinavian ice sheet, supporting the hypothesis that some taxa persisted in northern refugia during the last glacial cycle. Northern trees show differing spatio-temporal patterns across Siberia: deciduous trees were widespread in the Lateglacial, with individuals occurring across much of their contemporary ranges, while evergreen conifers expanded northwards to their range limits in the Holocene.  相似文献   

Transients of Giggenbach’s ‘Na‐K‐Mg‐Ca Geoindicators’ preceding the 27 October 2004, Mw = 6.0 earthquake in Vrancea area (Romania)     

Horia Mitrofan  Constantin Marin  Dorel Zugr&#x;vescu  Alin Tudorache  Lucian Beu?iu  Mihaela Radu 《地学学报》2008,20(2):87-94

The Na, K, Mg and Ca contents of certain deep‐origin groundwater discharges have been used by Giggenbach (1988) to define a series of ‘geoindicators’, which may provide hints on the up‐flow depth of origin, on the duration of the fluid ascent to the ground surface and on the associated CO₂ flux. On occurrence of a M_w = 6.0 Vrancea earthquake, significant fluctuations of Giggenbach’s geoindicators have been recorded in a saline spring, some 50 km away from the epicentre. A pre‐seismic overall anomaly was monitored for 1 year and a half, the sharpest variations occurring about 3 months before the earthquake. Processes controlling the geoindicator fluctuations assumedly took place at 7–8 km depth, while the earthquake hypocenter depth was about 100 km. This could be an evidence for a mechanical coupling still existing between the seismogenic body in the lithosphere and the overlying crust.  相似文献   

The physics of thundercloud and lightning discharge. Comment on the note by Earle Williams and Sharon Stanfill The physical origin of the land–ocean contrast in lightning activity     

Constantin Pontikis  Elizabeth Hicks  Nathalie Michalon 《Comptes Rendus Geoscience》2004,336(15):1409-1412

The arguments and conclusions of the commented Williams and Stanfill article in relation to the validity of the thermal and aerosol hypotheses advanced in order to explain the land–ocean contrast in lightning activity are critically re-examined. This re-examination reveals that the analysis presented by these authors is incomplete, thus weakening the corresponding conclusions. To cite this article: C. Pontikis et al., C. R. Geoscience 336 (2004).  相似文献   

Comparative study of statistical methods to identify a predictor for discharge at Orsova in the Lower Danube Basin     

Ileana Mares  Constantin Mares  Venera Dobrica  Crisan Demetrescu 《水文科学杂志》2020,65(3):371-386

ABSTRACT

The aims of this study are to investigate the influence of large-scale atmospheric circulation quantified by indices such as the North Atlantic Oscillation index (NAOI), the Greenland-Balkan Oscillation index (GBOI) and blocking-type indices on the Lower Danube discharge. We separately analysed each season for the 1948–2000 period. In addition to the statistical linear procedure, we applied methods to quantify nonlinear connections between variables, as mutual information between predictors and predictand, using Shannon’s information entropy theory. The nonlinear correlation information between climate indices and discharge is higher than that obtained from the linear measure, providing more insight into real connections. Also, the non-stationarity of the link between variables is highlighted by spectral coherence based on wavelet analysis. For the physical interpretation, we analyse composite maps over the Atlantic-European region. The most significant influence on the discharge of the Lower Danube Basin is given by the GBOI and blocking-type atmospheric circulation over Europe.  相似文献   

Use of carbon rather than dry weight to assess the DNA content and nutritional condition index of sole larvae   总被引：1，自引：1，他引：1  

Bergeron  Jean-Pierre; Ruyet  Jeannine Person-Le; Koutsikopoulos  Constantin 《ICES Journal of Marine Science》1997,54(1):148-151

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Trace Element Data for Gold, Iridium and Silver in Seventy Geochemical Reference Materials     

Marc Constantin 《Geostandards and Geoanalytical Research》2009,33(1):115-132

New concentrations for Au, Ir and Ag obtained by instrumental neutron activation analysis are presented for seventy geochemical reference materials. Results in agreement with literature values for Au and Ir down to concentrations of a few ng g⁻¹ were obtained. For Au and Ir concentrations above 10 ng g⁻¹, the repeatability of replicate analyses of reference materials was mostly better than 10%. For concentrations between 1 and 10 ng g⁻¹ the RSD for Ir was 10–30%, whereas for Au it was higher and more variable (20–50%). In addition, concentrations for Cd and Hg are presented for some of the same reference materials. The high RSD at relatively high concentrations seen in gold for some RMs (e.g., WMG-1, WMS-1) did not exist for Ir and suggests homogeneity for this platinum-group element at the sub-sample size used in this study. For the following eight RMs, mostly ultramafic rocks (CHR-Pt+, OREAS-13P, OREAS-14P, PCC-1, UMT-1, WMG-1, WMS-1, WPR-1), Ir measurements agreed within ± 10% of mostly certified or recommended concentrations, which ranged from 2 ng g⁻¹ to 6 μg g⁻¹. For the reference material UB-N, iridium concentration compared favourably to published results obtained by isotope dilution ICP-MS methods and a previously unrecognised heterogeneity is inferred for Au, Hg and Sb, but not for the other measured elements.  相似文献   

Reinforced concrete beam–column joints with crossed inclined bars under cyclic deformations     

Constantin E. Chalioris  Maria J. Favvata  Chris G. Karayannis 《地震工程与结构动力学》2008,37(6):881-897

This experimental study investigates the effectiveness of crossed inclined bars (X‐bars) as joint shear reinforcement in exterior reinforced concrete beam–column connections under cyclic deformations. Test results of 20 joint subassemblages with various reinforcement ratios and arrangements including X‐bars in the joint area are presented. The X‐type, non‐conventional reinforcement is examined as the only joint reinforcement and in combination with common stirrups or vertical bars. The experimental results reported herein include full loading cycle curves, energy dissipation values and a categorization of the observed damage modes. Based on the comparisons between the overall hysteretic responses of the tested specimens, it is deduced that joints with X‐bars exhibited enhanced cyclic performance and improved damage mode since a distinct flexural hinge was developed in the beam–joint interface. Further, the combination of crossed inclined bars and stirrups in joint area resulted in enhanced hysteretic response and excellent performance capabilities of the specimens. However, in some specimens with X‐bars as the only joint shear reinforcement, the deformations of the bent anchorage of the beam's bars caused considerable damages at the back of the joint area. Discussion for a potential replacement of the joint stirrups with X‐type reinforcement in some cases of exterior joints is also included. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献