Seismic Design of Symmetric Structures for Accidental Torsion   总被引：5，自引：0，他引：5  

Silvia L. Dimova  Ilia Alashki 《Bulletin of Earthquake Engineering》2003,1(2):303-320

The paper presents an analytical estimation of the dynamic effects, caused by the shifting of the centre of mass with accidental eccentricity in symmetric structures. The approximate analytical solution proves, that even under small accidental eccentricities the symmetric structures exhibit “irregular behaviour” and the accidental torsional effects cannot be described properly by static application of torsional moments. The prescribed application rule by Eurocode 8 for multimodal analysis underestimates the accidental torsional effects up to 21% for 5% eccentricity for the structures considered in the paper. An expression for the correction of member responses is derived. It is proved by numerical simulations of the dynamic response of three-dimensional models of symmetric structures, that the proposed correction coefficient gives accurate results in cases of single-storey and multi-storey structures. It gives a convenient way for the design practice to estimate accurately the accidental torsional effects on planar and 3-D models of symmetric structures. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Inversion of local S-wave velocity structures from average H/V ratios, and their use for the estimation of site-effects   总被引：2，自引：1，他引：2  

D. Fäh  F. Kind  D. Giardini 《Journal of Seismology》2003,7(4):449-467

H/V spectral ratios from microtremors areused to retrieve the S-velocity structurefrom a single ambient vibration record, byusing its relation to the ellipticity ofthe fundamental mode Rayleigh wave and theamplitude of observed H/V ratio.Constraints are needed in order to restrictthe possible range of solutions, and theinversion is applied to sites where thethickness of the unconsolidated sedimentsis approximately known from boreholeinformation. Within the uncertainty, theinverted structures agree well with theresults from other S-wave measuringtechniques such as downhole and cross-holemeasurements, and the analysis of ambientvibrations measured on an array.The influence of the inversion uncertaintyon site-amplification estimates forearthquakes is then investigated. For allinverted models, site response is computedfor a large number of events, which allowsto define the uncertainty by the aprioriunknown source position and mechanism of afuture earthquake. In most cases thevariability between the results obtainedfor the different models is much smallerthan the variability introduced by theunknown source position. The accuracy withwhich S-wave velocity structures can beretrieved from observed H/V ratios istherefore sufficient for an application ofthe method in seismic hazard analysis for aspecific site.  相似文献   

Flow hydraulics and geomorphic effects of glacial‐lake outburst floods in the Mount Everest region,Nepal     

Daniel A. Cenderelli  Ellen E. Wohl 《地球表面变化过程与地形》2003,28(4):385-407

Glacial‐lake outburst floods (GLOFs) on 3 September 1977 and 4 August 1985 dramatically modified channels and valleys in the Mount Everest region of Nepal by eroding, transporting, and depositing large quantities of sediment for tens of kilometres along the flood routes. The GLOF discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff, glacier meltwater, and monsoonal precipitation (referred to as seasonal high flow floods, SHFFs). Specific stream power values ranged from as low as 1900 W m^?2 in wide, low‐gradient valley segments to as high as 51 700 W m^?2 in narrow, high‐gradient valley segments bounded by bedrock. Along the upper 16 km of the GLOF routes, the reach‐averaged specific stream power of the GLOFs was 3·2 to 8·0 times greater than the reach‐averaged specific stream power of the SHFFs. The greatest geomorphic change occurred along the upper 10 to 16 km of the GLOF routes, where the ratio between the GLOF specific stream power and the SHFF specific stream power was the greatest, there was an abundant supply of sediment, and channel/valley boundaries consisted primarily of unconsolidated sediment. Below 11 to 16 km from the source area, the geomorphic effects of the GLOFs were reduced because of the lower specific stream power ratio between the GLOFs and SHFFs, more resistant bedrock flow boundaries, reduced sediment supply, and the occurrence of past GLOFs. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

土地利用变化对水文系统的影响研究   总被引：22，自引：0，他引：22  

王建群  卢志华 《地球科学进展》2003,18(2):292-298

以秦淮河流域为研究区域，利用现代遥感、地理信息系统等多种数字技术，获取流域空间分布的下垫面信息和中间状态信息，细致地刻画了流域内的水文过程，建立了研究区域数字水文模型。利用所建立的数字水文模型，对定义的土地利用变化情景进行了模拟。模拟结果表明，模型可以定性和定量地反映各种土地利用变化对水资源系统尤其是对水量平衡和防洪情势的影响程度。  相似文献   

洛湛线岩溶路基注浆加固与检测   总被引：2，自引：0，他引：2  

倪宏革  王星华  李锦平 《水文地质工程地质》2003,30(1):84-87

洛湛铁路益娄段地处岩溶发育区,水文工程地质条件复杂。为此,施工和设计中确定了相应的岩溶路基加固原则,探索出最佳的注浆工艺,运用多种手段对注浆质量进行了全面检测,结果完全满足工程和环境的要求。  相似文献   

流域水文模型和GIS集成技术研究现状与展望   总被引：11，自引：0，他引：11  

朱雪芹  潘世兵  张建立 《地理与地理信息科学》2003,19(3):10-13

该文综述了流域水文数值模拟模型与遥感、地理信息系统集成技术的发展和研究现状，讨论了四种类型集成技术特点、应用和存在的问题。提出了高层次共实体的时空概念框架，以实现水文模型与GIS完全集成，指出水文模型与GIS集成技术研究发展方向。  相似文献   

渭干河流域水资源及其水文特征分析   总被引：6，自引：0，他引：6  

满苏尔·沙比提  玉素甫江·如素力  阿布拉江·苏来曼 《山地学报》2003,21(2):195-200

渭干河是新疆11大河之一，是渭干河一库车河三角洲绿洲的塑造者，该绿洲的生存和发展与渭干河水资源的变化趋势有密切关系。本文根据渭干河流域各水文站历年水文统计资料及近几年来实际水文调查，通过流域概况、气温、蒸发、降水、冰川、补给、年内和年际变化、泥沙、冰倩、水质、地下水资源等方面的分析和论述渭干河多年来的水资源及水文特征变化规律，试图查清渭干河流域水资源量的收支情况。  相似文献   

小波域多时相干涉SAR数据融合     

岳焕印  郭华东  王长林  廖静娟  阎福礼 《遥感学报》2002,6(6):501-506

大气因素和高斯白噪声对由星载干涉SAR系统获取的干涉图相位有很大的影响，可能会极大地降低结果DEM的精度，提出了一种对多时相干涉SAR数据生成的独立DEM进行权重融合的方法，该算法在小波域当中估计了大气和高斯噪声的误差功率，并对多时相DEM进行权重融合。用河北省尚义县地区的ERS-1和ERS-2数据的研究表明，此算法可以很好地提高由干涉SAR获取的DEM的精度。  相似文献   

Towards a more ecologically relevant assessment of the impact of heavy metals on the photosynthesis of the seagrass, Zostera capricorni     

Catriona M. O. Macinnis-Ng  Peter J. Ralph 《Marine pollution bulletin》2002,45(1-12)

This in situ study used photosynthetic activity (measured as chlorophyll a fluorescence) and photosynthetic pigment concentrations to assess the effect of copper, cadmium, lead and zinc on the seagrass Zostera capricorni. Custom-made portable in situ exposure (PIE) chambers were developed so seagrasses could be dosed within the meadow. Z. capricorni was exposed to 0.1 and 1 mg l⁻¹ of metal solutions for 10 h. During this time and for the subsequent four-day recovery period, the effective quantum yield of photosystem II (PS II) (ΔF/Fm^′) was measured. While the results were variable, copper and zinc exposed samples had a depressed ΔF/Fm^′ during the exposure period. Samples exposed to zinc recovered to pre-exposure levels but those exposed to copper did not. Cadmium and lead did not impact on the chlorophyll a fluorescence and the chlorophyll pigment data supported these findings. This study presents an innovative new application of chlorophyll a fluorescence stress assessment.  相似文献   

Influences of a Microcystis aeruginosa Kützing bloom on zooplankton populations in Jacarepaguá Lagoon (Rio de Janeiro, Brazil)     

Aloysio S. Ferro-Filho  Patricia Domingos  Sandra M.F.O. Azevedo 《Limnologica》2002,32(4)

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