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41.
42.
Modelling of R/C members accounting for shear failure localisation: Finite element model and verification 下载免费PDF全文
Reinforced concrete (R/C) frame buildings designed according to older seismic codes represent a large part of the existing building stock worldwide. Their structural elements are often vulnerable to shear or flexure‐shear failure, which can eventually lead to loss of axial load resistance of vertical elements and initiate vertical progressive collapse of a building. In this study, a computationally efficient member‐type finite element model for the hysteretic response of shear critical R/C frame elements up to the onset of axial failure is presented; it accounts for shear‐flexure interaction and considers, for the first time, the localisation of shear strains, after the onset of shear failure, in a critical length defined by the diagonal failure plane. Its predictive capabilities are verified against experimental results of column and frame specimens and are shown to be accurate not only in terms of total response, but also with regard to individual deformation components. The accuracy, versatility, and simplicity of this finite element model make it a valuable tool in seismic analysis of complex R/C buildings with shear deficient structural elements. 相似文献
43.
Modelling of R/C members accounting for shear failure localisation: Hysteretic shear model 下载免费PDF全文
Reinforced concrete (R/C) frame buildings designed according to older seismic codes represent a large part of the existing building stock worldwide. Their structural elements are often vulnerable to shear or flexure‐shear failure, which can eventually lead to loss of axial load resistance of vertical elements and initiate vertical progressive collapse of a building. In this study, a hysteretic model capturing the local shear response of shear‐deficient R/C elements is described in detail, with emphasis on post‐peak behaviour; it differs from existing models in that it considers the localisation of shear strains after the onset of shear failure in a critical length defined by the diagonal failure planes. Additionally, an effort is made to improve the state of the art in post‐peak shear response modelling, by compiling the largest database of experimental results for shear and flexure‐shear critical R/C columns cycled well beyond the onset of shear failure and/or up to the onset of axial failure, and developing empirical relationships for the key parameters defining the local backbone post‐peak shear response of such elements. The implementation of the derived local hysteretic shear model in a computationally efficient beam‐column finite element model with distributed shear flexibility, which accounts for all deformation types, will be presented in a companion paper. 相似文献
44.
Existing loading protocols for quasi-static cyclic testing of structures are based on recordings from regions of high seismicity. For regions of low to moderate seismicity they overestimate imposed cumulative damage demands. Since structural capacities are a function of demand, existing loading protocols applied to specimens representative of structures in low to moderate seismicity regions might underestimate structural strength and deformation capacity. To overcome this problem, this paper deals with the development of cyclic loading protocols for European regions of low to moderate seismicity. Cumulative damage demands imposed by a set of 60 ground motion records are evaluated for a wide variety of SDOF systems that reflect the fundamental properties of a large portion of the existing building stock. The ground motions are representative of the seismic hazard level corresponding to a 2 % probability of exceedance in 50 years in a European moderate seismicity region. To meet the calculated cumulative damage demands, loading protocols for different structural types and vibration periods are developed. For comparison, cumulative seismic demands are also calculated for existing protocols and a set of records that was used in a previous study on loading protocols for regions of high seismicity. The median cumulative demands for regions of low to moderate seismicity are significantly less than those of existing protocols and records of high seismicity regions. For regions of low to moderate seismicity the new protocols might therefore result in larger strength and deformation capacities and hence in more cost-effective structural configurations or less expensive retrofit measures. 相似文献
45.
Spatial and temporal characteristics of wet spells in Greece 总被引:6,自引:1,他引:6
Summary This study examines the characteristics of wet spells in Greece, using daily rainfall gauge data, over a 40-year period (1958–1997). The longest wet spells, computed for two different thresholds (0.1mm and 1mm), were observed in Western Greece and Crete, whereas the shortest ones were found in the central and south Aegean. A detailed analysis of the wet spells, dividing them into three classes, shows that on an annual basis their highest frequencies were observed in Western and Northwestern Greece. The seasonal results are also quite similar. The trends and the variability of the mean length of the wet spells were also analyzed. Negative trends were found in the case of the year-to-year analysis and during winter. Finally, this study presents an evaluation of two theoretical distribution models; the second order Markov Chains (MC2) and the Negative Binomial Distribution (NBD), by their adjustment to the empirical data. Both models can be used in the future for an estimation of the wet spells in the area under study. 相似文献
46.
Simulating maximum and minimum temperature over Greece: a comparison of three downscaling techniques 总被引:1,自引:0,他引:1
E. Kostopoulou C. Giannakopoulos C. Anagnostopoulou K. Tolika P. Maheras M. Vafiadis D. Founda 《Theoretical and Applied Climatology》2007,90(1-2):65-82
Summary Statistical downscaling techniques have been developed for the generation of maximum and minimum temperatures in Greece. This
research focuses on the four conventional seasons, and three downscaling approaches, Multiple Linear Regression using a circulation
type approach (MLRct), Canonical Correlation Analysis (CCA) and Artificial Neural Networks (ANNs), are employed and compared
to assess their performance skills. Models were developed individually for each variable (Tmax, Tmin), station and season. The accuracy of downscaled values has been quantified in terms of a number of performance criteria,
such as differences of the mean and standard deviation ratios between observed and modelled data, the correlation coefficients
of the two sets, and also the RMSEs of the downscaled values relative to the observed. All methods revealed that during the
cool season Tmax tends to be better reproduced, whereas Tmin is overestimated, particularly over western Greece, which is characterised by higher orography. With respect to the warm
season, the simulation of Tmax reveals greater divergence, whereas Tmin is better generated. The distinction between the three techniques is somewhat blurred. None of the methods were found to
be superior to the others and each has been shown to be a good estimator in some cases. This study concludes that all proposed
methods comprise useful tools for simulating daily temperatures, as the high correlation coefficients, between observed and
downscaled values, have demonstrated. However, the importance of local factors, which affect the natural variability of temperature,
has been emphasised indicating that the geography of a region constitutes an important and rather complex factor, which should
be included in models to improve their performance. 相似文献
47.
Rajat M. Thomas Saleem Zaroubi Benedetta Ciardi reas H. Pawlik Panagiotis Labropoulos Vibor Jeli Gianni Bernardi Michiel A. Brentjens A. G. de Bruyn Geraint J. A. Harker Leon V. E. Koopmans Garrelt Mellema V. N. Pandey Joop Schaye Sarod Yatawatta 《Monthly notices of the Royal Astronomical Society》2009,393(1):32-48
48.
Geraint Harker Saleem Zaroubi Gianni Bernardi Michiel A. Brentjens A. G. de Bruyn Benedetta Ciardi Vibor Jeli Leon V. E. Koopmans Panagiotis Labropoulos Garrelt Mellema ré Offringa V. N. Pandey Joop Schaye Rajat M. Thomas Sarod Yatawatta 《Monthly notices of the Royal Astronomical Society》2009,397(2):1138-1152
49.
Zheng Li Panagiotis Kotronis Sandra Escoffier Claudio Tamagnini 《国际地质力学数值与分析法杂志》2018,42(12):1346-1365
Batter piles are widely used in geotechnical engineering when substantial lateral resistance is needed or to avoid the interference with existing underground constructions. Nevertheless, there is a lack of fast numerical tools for nonlinear soil‐structure interactions problems for this type of foundation. A novel hypoplastic macroelement is proposed, able to reproduce the nonlinear response of a single batter pile in sand under monotonic and cyclic static loadings. The behavior of batter piles (15°, 30°, and 45°) is first numerically investigated using 3D finite element modeling and compared with the behavior of vertical piles. It is shown that their response mainly depends on the pile inclination and the loading direction. Then, starting from the macroelement for single vertical piles in sand by Li et al (Acta Geotechnica, 11(2):373‐390, 2016), an extension is proposed to take into account the pile inclination introducing simple analytical equations in the expression describing the failure surface. 3D finite element numerical models are adopted to validate the macroelement that is proven able to reproduce the nonlinear behavior in terms of global quantities (forces‐displacements) and to significantly reduce the necessary computational time. 相似文献
50.
He Ziguang Nguyen Hoang Vu Thai Ha Zhou Jian Asteris Panagiotis G. Mammou Anna 《Acta Geotechnica》2022,17(4):1257-1272
Acta Geotechnica - Soft soils are considered as disadvantages in construction, especially in clay layers. It requires many advanced techniques to treat the soft soils before construction, aiming to... 相似文献