Response spectrum techniques for three-component earthquake design     

Stavros A. Anagnostopoulos 《地震工程与结构动力学》1981,9(5):459-476

An evaluation is made of response spectrum techniques as applied to seismic analysis and design of steel template offshore platforms. Such structures are designed as braced space frames for several loading conditions, including the simultaneous action of three earthquake components. Base shears as well as gross forces and combined stresses in members of three different platforms are computed for 30 real, three-component earthquakes and response spectrum predictions, obtained by several modal-spatial combination methods, are compared to time history solutions. Results are presented in the form of error statistics. The three approximations examined are: (a) combination of modes for one component input, (b) combination of the three partial responses to obtain estimates of total response and (c) combination of gross forces to derive maximum design stresses at a section. Attention is focused on corner piles because these are among the most heavily penalized members by three-component excitations. It is shown that commonly used spatial combination rules may underestimate gross forces in design controlling corner members by 15–30 per cent on the average. This is attributed to correlations between motion components that create additive effects along certain directions. Typical estimates of combined stresses, however, are found to be slightly conservative.  相似文献   

Experimental evidence of a unique flow rule of non-cohesive soils under high-cyclic loading     

T. Wichtmann  A. Niemunis  Th. Triantafyllidis 《Acta Geotechnica》2006,1(1):59-73

The presented results of cyclic triaxial tests on sand demonstrate that the cumulative effects due to small cycles obey a kind of flow rule. It mainly depends on the average stress ratio about which the cycles are performed. This so-called “cyclic flow rule” is unique and can be well approximated by flow rules for monotonic loading. Amongst others it is shown that the cyclic flow rule is only moderately influenced by the average mean pressure, by the strain loop (span, shape, polarization), the void ratio, the loading frequency, the static preloading and the grain size distribution curve. A slight increase of the compactive portion of the flow rule with increasing residual strain (due to the previous cycles) was observed. These experimental findings prove that the cyclic flow rule is an essential and indispensable concept in explicit (N-type) accumulation models.  相似文献   

Diffraction effects between foundations due to incident rayleigh waves     

Th. Triantafyllidis  Th. Neidhart 《地震工程与结构动力学》1989,18(6):815-835

The dynamic behaviour of a finite number of rigid, adjacent foundations on the surface of a linear-elastic, isotropic and homogeneous halfspace due to a far-field excitation of the Rayleigh type is the subject of the present work. The dynamic behaviour of this system differs from that of a single foundation subjected to the same excitation due to the existence of the natural coupling between adjacent foundations caused by the wave propagation through the underlying soil. For the determination of the diffraction forces acting on the foundations an analytical procedure is followed. The stresses at the interfaces between the foundations and subsoil are approximated by series expansions of orthogonal polynomials. It is interesting to notice that, apart from the loads appearing in the direction of incidence, additional loads perpendicular to the given incidence direction act on the foundations due to scattered waves. Their intensity depends on the excitation frequency and the distance between the foundations. The method followed here can be applied for the determination of the dynamic loads acting on fixed foundations in the case of a seismic excitation of relatively long duration.  相似文献   

Liapunov instability of the hypoplastic model for soils     

Andrzej Niemunis  Theodor Triantafyllidis 《Soil Dynamics and Earthquake Engineering》2004,24(1):35-48

The hypoplastic constitutive model is known for its numerous application to the problems of soil mechanics and also for its excessive ratcheting. The paper shows that this deficiency can be interpreted as Liapunov instability in dynamic case. This is demonstrated with a simple one-dimensional swinger. Infinitesimally small as well as finite oscillations are analytically examined and the variability of stiffness upon a single cycle is considered. Several methods to circumvent the problem of ratcheting are discussed: implementation of ‘elastic’ range by means of so-called intergranular strain, usage of overlay modelling with parallel coupling of hypoplastic materials as originally proposed by Valanis in his endochronic theory and a special coupling of hypoplastic models based on comparison of partial stiffnesses.  相似文献   

Towards an integrated environmental assessment for wetland and catchment management   总被引：4，自引：0，他引：4  

R Kerry Turner  Stavros Georgiou  Roy Brouwer  Ian J Bateman  I J Langford 《The Geographical journal》2003,169(2):99-116

This paper develops a decision support system for evaluation of wetland ecosystem management strategy and examines its, so far partial, application in a case study of an important complex coastal wetland known as the Norfolk and Suffolk Broads, in the east of England, UK. Most managed ecosystems are complex and often poorly understood hierarchically organized systems. Capturing the range of relevant impacts on natural and human systems under different management options will be a formidable challenge. Biodiversity has a hierarchical structure which ranges from the ecosystem and landscape level, through the community level and down to the population and genetic level. There is a need to develop methodologies for the practicable detection of ecosystem change, as well as the evaluation of different ecological functions. What is also required is a set of indicators (environmental, social and economic) which facilitate the detection of change in ecosystems suffering stress and shock and highlight possible drivers of the change process. A hierarchical classification of ecological indicators of sustainability would need to take into account existing interactions between different organization levels, from species to ecosystems. Effects of environmental stress are expressed in different ways at different levels of biological organization and effects at one level can be expected to impact other levels, often in unpredictable ways. The management strategy, evaluation methodologies and indicators adopted should also assess on sustainability grounds whether any given management option is supporting, or reducing, the diversity of functions which are providing stakeholders with the welfare benefits they require.  相似文献   

Ethnic residential shifts: The Greek population of Akron, Ohio, 1930–2005     

Stavros T. Constantinou 《GeoJournal》2007,68(2-3):253-265

The purpose of this paper is to apply the framework of transnationalism to the study of the Akron, Ohio Greek community through the spatio-temporal changes in the residential patterns. Church records for the period 1930 to 2005 form the basis of the study. The first Greek immigrants arrived in Akron, Ohio in the latter part of the nineteenth century and settled around the commercial zone in the central city. Additional immigrants, mostly young males with little education, arrived during the early decades of the twentieth century to seek employment in the growing industries, especially the tire factories. The establishment of a sizable colony made it possible to form a parish church in close proximity to the place of work. In addition to the place of worship, ethnic stores, and coffee houses became foci of ethnic life. Although this central city cluster was undergoing minor residential shifts to the suburbs, it was identifiable until the early 1970s. By then most of its immigrant residents as well as their American born children moved to the suburbs, especially in the northwestern part of the city, because of economic improvement. Post-1965 immigrants bypassed the central city cluster and settled in the suburbs. Anecdotal information suggests that these immigrants, individually and collectively as a group, maintain a variety of economic, social, and cultural connections with their place of origin as well as the Akron Greek community. Thus, transnationalism is an appropriate framework to study recent immigrants who maintain concurrent connections to the United States and Greece.  相似文献   

Strain accumulation in sand due to cyclic loading: Drained cyclic tests with triaxial extension   总被引：1，自引：0，他引：1  

T. Wichtmann  A. Niemunis  Th. Triantafyllidis   《Soil Dynamics and Earthquake Engineering》2007,27(1):42-48

This paper presents results of numerous drained cyclic tests with triaxial extension. The influence of the strain amplitude, the average stress and the number of load cycles on the accumulation rate was studied. A simple cyclic flow rule was observed. Most findings confirm a previous study with cyclic triaxial compression tests. The test results serve as the basis of an explicit accumulation model.  相似文献   

Large Scale Tests on Jointed and Bedded Rocks Under Multi-Stage Triaxial Compression and Direct Shear     

Maximiliano R. Vergara  Peter Kudella  Theodoros Triantafyllidis 《Rock Mechanics and Rock Engineering》2015,48(1):75-92

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Estimated SLR station position and network frame sensitivity to time-varying gravity   总被引：1，自引：1，他引：0  

Nikita P. Zelensky  Frank G. Lemoine  Douglas S. Chinn  Stavros Melachroinos  Brian D. Beckley  Jennifer Wiser Beall  Oleg Bordyugov 《Journal of Geodesy》2014,88(6):517-537

This paper evaluates the sensitivity of ITRF2008-based satellite laser ranging (SLR) station positions estimated weekly using LAGEOS-1/2 data from 1993 to 2012 to non-tidal time-varying gravity (TVG). Two primary methods for modeling TVG from degree-2 are employed. The operational approach applies an annual GRACE-derived field, and IERS recommended linear rates for five coefficients. The experimental approach uses low-order/degree $4\times 4$ coefficients estimated weekly from SLR and DORIS processing of up to 11 satellites (tvg4x4). This study shows that the LAGEOS-1/2 orbits and the weekly station solutions are sensitive to more detailed modeling of TVG than prescribed in the current IERS standards. Over 1993–2012 tvg4x4 improves SLR residuals by 18 % and shows 10 % RMS improvement in station stability. Tests suggest that the improved stability of the tvg4x4 POD solution frame may help clarify geophysical signals present in the estimated station position time series. The signals include linear and seasonal station motion, and motion of the TRF origin, particularly in Z. The effect on both POD and the station solutions becomes increasingly evident starting in 2006. Over 2008–2012, the tvg4x4 series improves SLR residuals by 29 %. Use of the GRGS RL02 $50\times 50$ series shows similar improvement in POD. Using tvg4x4, secular changes in the TRF origin Z component double over the last decade and although not conclusive, it is consistent with increased geocenter rate expected due to continental ice melt. The test results indicate that accurate modeling of TVG is necessary for improvement of station position estimation using SLR data.  相似文献   

Modelling of earth and water pressure development during diaphragm wall construction in soft clay     

R. Schfer  Th. Triantafyllidis 《国际地质力学数值与分析法杂志》2004,28(13):1305-1326

The influence of a diaphragm wall construction on the stress field in a soft clayey soil is investigated by the use of a three‐dimensional FE‐model of seven adjacent wall panels. The installation procedure comprises the excavation and the subsequent pouring of each panel taking into account the increasing stiffness of the placed fresh concrete. The soft clay deposit is described by a visco‐hypoplastic constitutive model considering the rheological properties and the small‐strain stiffness of the soil. The construction process considerably affects the effective earth and pore water pressures adjacent to the wall. Due to concreting, a high excess pore water pressure arises, which dissipates during the following construction steps. The earth pressure finally shows an oscillating, distinct three‐dimensional distribution along the retaining wall which depends on the installation sequence of the panels and the difference between the fresh concrete pressure and the total horizontal earth pressure at rest. In comparison to FE‐calculations adopting the earth pressure at rest as initial condition, greater wall deflections and surface ground settlements during the subsequent pit excavation can be expected, as the average stress level especially in the upper half of the wall is increased by the construction procedure of the retaining structure. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献