钢筋混凝土梁抗震性能指标分析     

万海涛  韩小雷 《华南地震》2010,30(3):21-26

采用软件ABAQUS对钢筋混凝土梁进行有限元模拟,即可获取梁的荷载-位移骨架曲线。将试验结果和模拟结果进行对比,结果表明,有限元可以较准确地模拟试验情况。然后同样采用软件ABAQUS来模拟146根梁,并获取该批梁的弯矩-转角骨架曲线。将曲线按照不同因素进行分类,并由这些曲线得出梁的性能参数:塑性转角限值。塑性转角限值能为梁的性能评估提供定量的参考指标。  相似文献   

Experimental verification of bridge seismic damage states quantified by calibrating analytical models with empirical field data     

Swagata Banerjee  Masanobu Shinozuka 《地震工程与工程振动(英文版)》2008,7(4):383-393

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Displacement limits and performance displacement profiles in support of direct displacement‐based seismic assessment of bridges          下载免费PDF全文

Donatello Cardone 《地震工程与结构动力学》2014,43(8):1239-1263

Displacement limits and performance displacement profiles (PDPs) for the direct displacement‐based assessment of existing bridges are proposed. The PDPs are defined as the bridge inelastic deformed shapes associated with the attainment of selected damage states in some critical elements of the bridge. In the paper, displacement limits are provided for piers, abutments, joints, bearing devices and shear keys. Moreover, different approaches for the definition of the PDP are examined, including adaptive pushover analysis, effective modal analysis, and rational analysis of simplified bridge models. In the paper, the key aspects and modeling assumptions of the proposed direct displacement‐based assessment procedure are presented first. This is followed by some examples of application to typical Italian highway bridge configurations, differing in pier layout, deck type, and pier‐deck connections. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Estimating palaeo-water depth from the physical rock record     

Adrian Immenhauser   《Earth》2009,96(1-2):107-139

Palaeo-water depth and its change with time is a key factor in environmental analysis and in sedimentology in general. The literature published on this topic and on related subjects, however, is substantial albeit scattered within and between different communities (geologists, oceanographers, engineers, physicists etc.). Here I focus on proxies for palaeo-bathymetry as obtained from the physical rock record. Floral, faunal and chemical evidence for palaeo-water depth, being equally important, must be dealt with elsewhere. An assessment of the main depth-related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed. The outcome reveals the full complexity of this topic. There is, for example, no such thing as an average wave-base depth applicable to a wide range of fossil case settings. This because wave and current climates in general, and particularly so in neritic and coastal settings, are intriguingly complex. Furthermore, observations from modern oceans are not a priori applicable to fossil ones. Acknowledging these problems and limitations, critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed.  相似文献   

Residual and Fully Softened Strength Evaluation of Soils using Artificial Neural Networks     

Abidin Kaya 《Geotechnical and Geological Engineering》2009,27(2):281-288

A backpropagation artificial neural network (ANN) model is developed to predict the secant friction angle of residual and fully softened soils, using data reported by Stark et al. (J Geotech Geoenviron Eng ASCE 131:575–588, 2005). In the ANN model, index properties such as liquid limit, plastic limit, activity, clay fraction and effective normal stress are used as input variables while secant residual friction angle is used as output variable. The model is verified using data that were not used for model training and testing. The results also indicate that the secant residual friction angle of cohesive soils can be predicted quite accurately using liquid limit, clay fraction and effective normal stress as input variables with R ² = 0.93. The sensitivity analysis results indicate that plastic limit and activity have no appreciable effect on ANN predicted secant friction angles. The secant friction angle predictions of the ANN model were also compared with those of Stark’s et al. (2005) curves and the empirical formulas suggested for the same data sets by Wright (Evaluation of soil shear strengths for slope and retaining wall stability with emphasis on high plasticity clays, 2005). The comparison shows that the ANN model predictions are very close to those suggested by the Stark et al. (2005) curves but much better than the prediction of Wright’s (2005) empirical equations. The results also show that ANN is an alternative powerful tool to predict the secant friction angle of soils.  相似文献   

Snow hydrology signatures for model identification within a limits‐of‐acceptability approach          下载免费PDF全文

Bettina Schaefli 《水文研究》2016,30(22):4019-4035

Discharge simulation from snow‐dominated catchments seems to be an easy task. Any spatially explicit precipitation–runoff model coupled to a temperature‐index snow model generally yields simulations that mimic well the observed daily discharges. The robustness of such models is, however, questionable: in the presence of strong annual discharge cycles, small model residuals do not guarantee high explanatory power of the underlying model. This paper proposes a methodology for snow hydrological model identification within a limits‐of‐acceptability framework, where acceptable model simulations are the ones that reproduce a set of signatures within an a priori specified range. The signatures proposed here namely include the relationship between the air temperature regime and the discharge regime, a new snow hydrology signature that can be readily transferred to other Alpine settings. The discriminatory power of all analysed signatures is assessed with a new measure of their discriminatory power in the model prediction domain. The value of the proposed snow hydrology signatures and of the limits‐of‐acceptability approach is demonstrated for the Dischma river in Switzerland, whose discharge shows a strong temporal variability of hydrologic forcing conditions over the last 30 years. The signature‐based model identification for this case study leads to the surprising conclusion that the observed discharge data contains a multi‐year period that cannot be reproduced with the model at hand. This model‐data mismatch might well result from a yet to be identified problem with the discharge observations, which would have been difficult to detect in a classical residual‐based model identification approach. Overall, the detailed results for this case study underline the robustness of the limits‐of‐acceptability approach in the presence of error‐prone observations if it is applied in combination with relatively robust signatures. Future work will show whether snow hydrology signatures and their limits‐of‐acceptability can be regionalized to ungauged catchments, which would make this model selection approach particularly powerful for Alpine environments. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

关于软弱粉质粘土地震液化或震陷的判别标准     

辛鸿博  周锡元 《世界地震工程》2011,27(1)

文中简要介绍了判别细粒土地震液化分析方法的发展历程,指出了工程建设中考虑细粒土地震液化问题的必要性。基于已有研究成果,阐述了可用于工程设计的软弱粉质粘土地震液化简化判别方法,并对建筑抗震设计新规范中增加的相关条款进行了说明解释。  相似文献   

Reinterpreting Rotherslade,Gower Peninsula: implications for Last Glacial ice limits and Quaternary stratigraphy of the British Isles     

John F. Hiemstra  Kenneth F. Rijsdijk  Richard A. Shakesby  Danny McCarroll 《第四纪科学杂志》2009,24(4):399-410

Rotherslade on the Gower Peninsula in south Wales has been viewed as a key site for the reconstruction of Quaternary depositional environments in the British Isles. Since the early 20th century, and certainly since the 1980s, the accepted view has been that Rotherslade is the most westerly location on the south Gower coast where there is in situ basal till exposed and that, logically, this location marks the position of the LGM ice limit. However, reinvestigation of the sediments and their architecture, and analysis of clast fabrics and thin sections of critical sedimentary units, show that none of the exposed sediments has properties diagnostic of subglacial deposition or deformation. We postulate here that LGM ice terminated at the western side of Swansea Bay, a few kilometres to the north‐east of Rotherslade, and propose that the sedimentary sequence comprises Early to Middle Devensian periglacial sediments, overlain by a complex of Late Devensian, ice‐proximal outwash fan deposits, an assemblage of paraglacial debris and, finally, periglacial mass movement deposits. The proposed repositioning of the Late Devensian ice limit and the associated new subaerial interpretation of the sediments suggest that a reassessment of sedimentary sequences (Hunts Bay, Western Slade) and landforms (Paviland Moraine) farther west on Gower, which have attained similar stratigraphical status, is now warranted. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The last ice sheet in Snowdonia     

Danny Mccarroll  Colin K. Ballantyne 《第四纪科学杂志》2000,15(8):765-778

In Snowdonia there is a marked contrast between weathered summits, often with well‐developed blockfields or tors, and lower ice‐moulded terrain. The boundary is interpreted as a trimline marking the upper surface of the last ice sheet. This interpretation is supported by the presence of gibbsite, an end‐product of prolonged weathering, at the base of soils above but not below the trimline. The reconstructed ice surface reaches about 850 m above present sea‐level along an ice divide running NE–SW through the massif. There is no evidence to support the popular view that ice centred further south extended over Snowdonia, and breaching to form the major glacial troughs can be explained by the action of local ice. The field evidence presented here demonstrates that most models of the southern British and Irish Sea ice sheets are significantly flawed, the earliest being far too thick and the most recent far too thin. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Latitudinal gradients and poleward expansion of mangrove ecosystems in South Africa: 50 years after Macnae’s first assessment     

N Peer  A Rajkaran  NAF Miranda  RH Taylor  B Newman  F Porri 《African Journal of Marine Science》2018,40(2):101-120

Mangroves occur in South African estuaries at their poleward distribution limits, extending into temperate habitats. In 1963, William Macnae published the first comprehensive assessment of mangrove swamps in South Africa and made firsthand observations of these mangrove ecosystems. This article reassesses South African mangrove habitats, highlighting changes since Macnae’s assessment, through a literature review of research done in the past 50 years and using the results of a dedicated mangrove survey spanning 2012–2017. Until now, changes have been recorded mostly for mangrove vegetation, including a change in mangrove cover and a poleward shift of mangrove species. While some mangrove-associated fauna have disappeared from most sites (e.g. the gastropod Terebralia palustris), others, such as fiddler crabs, have spread farther south. The effects of decreasing diversity with an increase in latitude were not observed along the South African coast. Instead, habitat quality and estuarine mouth state seem to exert greater influence on species diversity in the mangroves, and a poleward shift in species distribution is now evident not just for the mangrove flora but for the fauna as well. South African mangrove research needs to include a continuous monitoring plan, especially if we are to contribute to global knowledge on blue carbon, the effects of sea-level rise, and the resilience of the mangrove ecosystem.  相似文献