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21.
This paper presents a macroelement formulation for the prediction of the planar dynamic response of inelastic deformable rocking bodies. The formulation is based on a previous macroelement developed by the authors able to describe the cyclic response of inelastic rocking bodies, which takes into account the deformability both along the height of the member, as well as near the rocking end. Modifications of this formulation to account for other motion modes of rocking members during their dynamic response, namely, sliding and upthrow, as well as modifications to account for damping in a uniform manner during the whole motion, including impacts, are introduced. The dynamic response predicted by the macroelement for free-standing rigid and deformable rocking bodies is presented and compared with existing theoretical solutions, and the effect of deformability, damping, inelasticity, and friction on the response is discussed. 相似文献
22.
Constantinos C. Repapis Petros P. Mimoglou Vicky V. Dimakopoulou Ioannis N. Psycharis Ioannis M. Taflampas 《地震工程与结构动力学》2020,49(5):479-497
The special interest produced by near-field directivity records and their effect on structural response has given a new significance in the velocity time history, its pulse-like content, and relevant parameters and indices. Recent research has shown that directivity pulses inherent in these records govern the linear and the nonlinear response of a wide range of structures. Based on this observation, it is suggested in this paper that a truncated ground motion, limited to the duration of the predominant velocity pulse, can be efficiently used to predict the structural response, instead of the base motion with the total duration, reducing significantly the required runtimes. The proposed methodology is verified for a series of medium to high rise reinforced concrete buildings, for which nonlinear time-history analyses are performed for a vast suite of pulse-like near-field records applied as base excitations with their total duration and the proposed truncated one. Comparison of the results for the response displacements and forces shows very good agreement, permitting the acceptance of the pulse duration as the efficient strong motion time interval of the original record, which determines the response and, thus, it can be used for nonlinear structural analyses. 相似文献
23.
Kelly M. Darnell Tim J. B. Carruthers Patrick Biber Ioannis Y. Georgiou Thomas C. Michot Ronald G. Boustany 《Estuaries and Coasts》2017,40(5):1288-1300
Seagrasses are submerged marine plants that are anchored to the substrate and are therefore limited to assimilating nutrients from the surrounding water column or sediment, or by translocating nutrients from adjacent shoots through the belowground rhizome. As a result, seagrasses have been used as reliable ecosystem indicators of surrounding nutrient conditions. The Chandeleur Islands are a chain of barrier islands in the northern Gulf of Mexico that support the only marine seagrass beds in Louisiana, USA, and are the sole location of the seagrass Thalassia testudinum across nearly 1000 km of the coastline from west Florida to central Texas. Over the past 150 years, the land area of the Chandeleur Islands has decreased by over half, resulting in a decline of seagrass cover. The goals of this study were to characterize the status of a climax seagrass species at the Chandeleur Islands, T. testudinum, in terms of leaf nutrient (nitrogen [N] and phosphorus [P]) changes over time, from 1998 to 2015, and to assess potential drivers of leaf nutrient content. Thalassia testudinum leaf nutrients displayed considerable interannual variability in N and P content and molar ratios, which broadly mimicked patterns in annual average dissolved nutrient concentrations in the lower Mississippi River. Hydrological modeling demonstrated the potential for multiple scenarios that would deliver Mississippi River water, and thus nutrients, to T. testudinum at the Chandeleur Islands. Although coastal eutrophication is generally accepted as the proximate cause for seagrass loss globally, there is little evidence that nutrient input from the Mississippi River has driven the dramatic declines observed in seagrasses at the Chandeleur Islands. Rather, seagrass cover along the Chandeleur Islands appears to be strongly influenced by island geomorphological processes. Although variable over time, the often elevated nutrient levels of the climax seagrass species, T. testudinum, which are potentially driven by river-derived nutrient inputs, raises an important consideration of the potential loss of the ecosystem functions and services associated with these declining seagrass meadows. 相似文献
24.
Nonstationary stochastic response of structural systems equipped with nonlinear viscous dampers under seismic excitation 总被引:1,自引:0,他引:1 下载免费PDF全文
Nonlinear viscous dampers are supplemental devices widely used for enhancing the performance of structural systems exposed to seismic hazard. A rigorous evaluation of the effect of these damping devices on the seismic performance of a structural system should be based on a probabilistic approach and take into account the evolutionary characteristics of the earthquake input and of the corresponding system response. In this paper, an approximate analytical technique is proposed for studying the nonstationary stochastic response characteristics of hysteretic single degree of freedom systems equipped with viscous dampers subjected to a fully nonstationary random process representing the seismic input. In this regard, a stochastic averaging/linearization technique is utilized to cast the original nonlinear stochastic differential equation of motion into a simple first‐order nonlinear ordinary differential equation for the nonstationary system response variance. In comparison with standard linearization schemes, the herein proposed technique has the significant advantage that it allows to handle realistic seismic excitations with time‐varying frequency content. Further, it allows deriving a formula for determining the nonlinear system response evolutionary power spectrum. By this way, ‘moving resonance’ effects, related to both the evolutionary seismic excitation and the nonlinear system behavior, can be observed and quantified. Several applications involving various system and input properties are included. Furthermore, various response parameters of interest for the seismic performance assessment are considered as well. Comparisons with pertinent Monte Carlo simulations demonstrate the reliability of the proposed technique. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
25.
In this paper a recently developed multimode pushover procedure for the approximate estimation of structural performance of asymmetric in plan buildings under biaxial seismic excitation is evaluated. Its main idea is that the seismic response of an asymmetric multi-degree-of-freedom system with \(N\) degrees of freedom under biaxial excitation can be related to the responses of \(N\) ‘modal’ equivalent single-degree-of-freedom (E-SDOF) systems under uniaxial excitation. The steps of the proposed methodology are quite similar to those of the well-known modal pushover analysis. However, the establishment of the (E-SDOF) systems is based on a new concept, in order to take into account multidirectional seismic effects. The proposed methodology does not require independent analysis in the two orthogonal directions and therefore the application of simplified superposition rules for the combination of seismic component effects is avoided. After a brief outline of the theoretical background and the application process, an extensive evaluation study is presented, which shows that, in general, the proposed methodology provides a reasonable estimation for the vast majority of the calculated response parameters. 相似文献
26.
A selected assortment of Archaic‐Hellenistic tableware samples from Solunto, a Phoenician‐Punic site located 20 km east of Palermo (Sicily), has been subjected to thin‐section petrography and chemical analysis (XRF). In this settlement several ceramic kilns remained operative over a long time period (7th to 3rd century B.C.). The main goal of this analytical study is to distinguish the ceramics manufactured locally from regional and off‐island imports. Analytical results were matched to similar data concerning local natural clay sources and to coeval tableware productions from other sites in the same area. The ceramic pastes used by the ancient craftsmen of Solunto in the case of this class of pottery could be differentiated clearly by their petrochemical characteristics. We conclude that ceramics were locally produced far beyond satisfying just internal consumption needs, indicating interaction of Solunto with neighboring Greek colonies, indigenous people, and Phoenician‐Punic colonies of Sicily. © 2009 Wiley Periodicals, Inc. 相似文献
27.
Coastal imagery obtained from a coastal video monitoring station installed at Faro Beach, S. Portugal, was combined with topographic
data from 40 surveys to generate a total of 456 timestack images. The timestack images were processed in an open-access, freely
available graphical user interface (GUI) software, developed to extract and process time series of the cross-shore position
of the swash extrema. The generated dataset of 2% wave run-up exceedence values R
2 was used to form empirical formulas, using as input typical hydrodynamic and coastal morphological parameters, generating
a best-fit case RMS error of 0.39 m. The R
2 prediction capacity was improved when the shore-normal wind speed component and/or the tidal elevation η
tide were included in the parameterizations, further reducing the RMS errors to 0.364 m. Introducing the tidal level appeared
to allow a more accurate representation of the increased wave energy dissipation during low tides, while the negative trend
between R
2 and the shore-normal wind speed component is probably related to the wind effect on wave breaking. The ratio of the infragravity-to-incident
frequency energy contributions to the total swash spectra was in general lower than the ones reported in the literature E
infra/E
inci > 0.8, since low-frequency contributions at the steep, reflective Faro Beach become more significant mainly during storm
conditions. An additional parameterization for the total run-up elevation was derived considering only 222 measurements for
which η
total,2 exceeded 2 m above MSL and the best-fit case resulted in RMS error of 0.41 m. The equation was applied to predict overwash
along Faro Beach for four extreme storm scenarios and the predicted overwash beach sections, corresponded to a percentage
of the total length ranging from 36% to 75%. 相似文献
28.
29.
The current design of seismically isolated bridges usually combines the use of bearings and stoppers, as a second line of
defence. The stoppers allow the development of the in-service movements of the bridge deck, without transmitting significant
loads to the piers and their foundations, while during earthquake they transmit the entire seismic action. Despite the fact
that stoppers, which restrain the transverse seismic movements of the deck, are used frequently in seismically isolated bridges,
the use of longitudinal stoppers is relatively rare, mainly due to the large in-service constraint movements of bridges. The
present paper proposes a new type of external longitudinal stoppers, which are installed in stiff sub-structures-boundaries,
aiming at limiting the bridge seismic movements. The parametric investigation, which was conducted in order to identify the
seismic efficiency of the external stoppers, showed that the interaction of the bridge with the stiff boundaries can lead
to significant reductions in the seismic movements of the bridge. Serviceability is appropriately arranged in the paper by
expansion joints and approach slabs. 相似文献
30.
Tunnels are believed to be rather “insensitive” to earthquakes. Although a number of case histories seem to favor such an argument, failures and collapses of underground
structures in the earthquakes of Kobe (1995), Düzce–Bolu (1999), and Taiwan (1999) have shown that there are exceptions to
this “rule”. Among them: the case of tunnels crossed by fault rupture. This paper presents the analysis and design of two highway cut-and-cover
tunnels in Greece against large tectonic dislocation from a normal fault. The analysis, conducted with finite elements, places
particular emphasis on realistically modeling the tunnel-soil interface. Soil behavior is modeled thorough an elastoplastic
constitutive model with isotropic strain softening, which has been extensively validated through successful predictions of
centrifuge model tests. A primary conclusion emerging from the paper is that the design of cut-and-cover structures against
large tectonic deformation is quite feasible. It is shown that the rupture path is strongly affected by the presence of the
tunnel, leading to development of beneficial stress-relieving phenomena such as diversion, bifurcation, and diffusion. The
tunnel may be subjected either to hogging deformation when the rupture emerges close to its hanging-wall edge, or to sagging deformation when the rupture is near its footwall edge. Paradoxically, the maximum stressing is not always attained with
the maximum imposed dislocation. Therefore, the design should be performed on the basis of design envelopes of the internal
forces, with respect to the location of the fault rupture and the magnitude of dislocation. Although this study was prompted by the needs of a specific project, the method of analysis,
the design concepts, and many of the conclusions are sufficiently general to merit wider application. 相似文献