Yield frequency spectra and seismic design of code‐compatible RC structures: an illustrative example

The seismic design of an eight‐story reinforced concrete space frame building is undertaken using a yield frequency spectra (YFS) performance‐based approach. YFS offer a visual representation of the entire range of a system's performance in terms of the mean annual frequency (MAF) of exceeding arbitrary global ductility or displacement levels versus the base shear strength. As such, the YFS framework can establish the required base shear and corresponding first‐mode period to satisfy arbitrary performance objectives for any structure that may be approximated by a single‐degree‐of‐freedom system with given yield displacement and capacity curve shape. For the eight‐story case study building, deformation checking is the governing limit state. A conventional code‐based design was performed using seismic intensities tied to the desired MAF for safety checking. Then, the YFS‐based approach was employed to redesign the resulting structure working backwards from the desired MAF of response (rather than intensity) to estimate an appropriate value of seismic intensity for use within a typical engineering design process. For this high‐seismicity and high‐importance midrise building, a stiffer system with higher base shear strength was thus derived. Moreover, performance assessment via incremental dynamic analysis showed that while the code‐design did not meet the required performance objective, the YFS‐based redesign needed only pushover analysis results to offer a near‐optimal design outcome. The rapid convergence of the method in a single design/analysis iteration emphasized its efficiency and practicability as a design aid for practical application. Copyright © 2017 John Wiley & Sons, Ltd.     

Protracted river response to medieval earthquakes

Mountain rivers respond to strong earthquakes by rapidly aggrading to accommodate excess sediment delivered by co-seismic landslides. Detailed sediment budgets indicate that rivers need several years to decades to recover from seismic disturbances, depending on how recovery is defined. We examine three principal proxies of river recovery after earthquake-induced sediment pulses around Pokhara, Nepal's second largest city. Freshly exhumed cohorts of floodplain trees in growth position indicate rapid and pulsed sedimentation that formed a fan covering 150 km² in a Lesser Himalayan basin with tens of metres of debris between the 11th and 15th centuries AD. Radiocarbon dates of buried trees are consistent with those of nearby valley deposits linked to major medieval earthquakes, such that we can estimate average rates of re-incision since. We combine high-resolution digital elevation data, geodetic field surveys, aerial photos, and dated tree trunks to reconstruct geomorphic marker surfaces. The volumes of sediment relative to these surfaces require average net sediment yields of up to 4200 t km^–2 yr^–1 for the 650 years since the last inferred earthquake-triggered sediment pulse. The lithological composition of channel bedload differs from that of local bedrock, confirming that rivers are still mostly evacuating medieval valley fills, locally incising at rates of up to 0.2 m yr^–1. Pronounced knickpoints and epigenetic gorges at tributary junctions further illustrate the protracted fluvial response; only the distal portions of the earthquake-derived sediment wedges have been cut to near their base. Our results challenge the notion that mountain rivers recover speedily from earthquakes within years to decades. The valley fills around Pokhara show that even highly erosive Himalayan rivers may need more than several centuries to adjust to catastrophic perturbations. Our results motivate some rethinking of post-seismic hazard appraisals and infrastructural planning in active mountain regions. © 2018 John Wiley & Sons, Ltd.     

遥感估算水稻产量Ⅱ.用光谱数据和陆地卫星图像估算水稻产量

本文介绍了采用更系统的生物学方法,根据水稻在整个生长期的叶面积指数轨线,按叶面积指数的一次测量值,结合气象和光谱数据及陆地卫星MSS图像,估算大面积水稻产量的方法。 在产量与总截获的关系中,叶面积指数是最重要的参量之一。文中重点分析了由水稻在MSS波段内的光谱数据构成的绿度指数和Suits模式估算叶面积指数的结果。表明,用Suits模式计算的叶面积指数有较高的相关系数和较低的剩余标准差。并用这个方法计算了不同田块的叶面积指数,再根据这些数据和MSS图像建立关系。本文比较了卫星数据和多种绿度指数的关系,认为垂直植被指数(PVI)是估算叶面积指数的最好参量,因为它消除了土壤背景的影响,并用它求出了大面积水稻的叶面积指数分布。再根据已建立的叶面积指数轨线和作物截获的有效光合辐射(TIPAR)关系,计算了TIPAR,编制了产置分布图。文章分析了计算结果,并以1983年的例子进一步讨论了该方法的适用性。结果表明,预测的水稻产量和实测产量间的相关系数为0.9左右。     

Application of USLE in a GIS environment to estimate soil erosion in the Irga watershed,Jharkhand, India

A comprehensive methodology that integrates the Universal Soil Loss Equation (USLE) and Geographic Information System (GIS) was adopted in this study to determine the soil erosion and sediment yield of the Irga watershed in Jharkhand, India. Based on the availability and applicability of data in a GIS-environment, the original equations for the model input parameters were, however, modified by researchers. In the present study, a power-law equation was generated to estimate the rainfall erosivity (R) factor, and the Nash-Sutcliffe model efficiency coefficient used to determine the accuracy of the modified R factor. Average annual soil erosion in the Irga watershed is estimated to be 4.3 t ha^?1 yr^?1. On the other hand, average annual sediment yield of the watershed, estimated using the sediment delivery ratio, was found to be 1.2 t ha^?1 yr^?1. Low sediment yield indicates that most of the eroded soil was deposited within the watershed.     

RCP8.5气候变化情景下21世纪印度粮食单产变化的多模式集合模拟

基于跨部门影响模型比较计划（ISI-MIP）中20种气候模式与作物模型组合的模拟结果,预估了RCP 8.5排放情景下21世纪印度小麦和水稻单产变化。研究发现：① 多模式集合模拟结果基本再现了印度小麦和水稻单产的空间差异;同时,再现了小麦和水稻单产对温度和降水变化的响应特征：与温度呈负相关,与降水呈正相关。② RCP 8.5情景下,水稻和小麦生长季温度和降水均呈增加趋势,小麦生长季的温度、降水增加幅度大于水稻。空间上,温度增加幅度自北向南逐渐减小,降水增幅则逐渐增加,并且小麦种植区升温幅度大于非种植区,降水增幅则少于非种植区,水稻种植区升温幅度小于非种植区,降水增幅则多于非种植区。③ RCP 8.5情景下,小麦和水稻单产均呈下降趋势,21世纪后半叶尤为明显。小麦单产的下降速度明显大于水稻,其中21世纪前半叶小麦和水稻单产下降速度约分别为1.3%/10a （P < 0.001）和0.7%/10a （P < 0.05）,后半叶分别增至4.9%/10a （P < 0.001）和4.4%/10a （P < 0.001）。小麦和水稻单产变化存在明显的空间异质性,小麦单产的最大下降幅度出现在德干高原西南部,降幅约60%,水稻单产最大下降幅度出现在印度河平原北部,降幅约50%。这意味着未来气候变化情景下印度粮食供给将面临较大的挑战。     

Characterizing the changing environment of cropland in the Songnen Plain,Northeast China,from 1990 to 2015

Journal of Geographical Sciences - Quantitative characterization of environmental characteristics of cropland (ECC) plays an important role in maintaining sustainable development of agricultural...     

东北地区县域粮劳变化耦合模式与乡村发展类型

本文选取2001年、2008年和2015年3期截面数据,综合运用标准差椭圆等空间分析法和非参数检验等数理统计法,对东北地区183个县域粮食产量与农业劳动力变化的耦合模式及其表征的乡村发展类型进行研究。结果表明：① 2001—2015年东北地区总的粮劳变化耦合模式在2008年发生转折,2001—2008年为粮增劳减模式,2008—2015年为粮劳同增模式,这实际上是一种在多因素综合作用下发生的退化。② 县域层面,2008年前后两时段东北地区粮增劳减耦合模式的比例由45.90%下降为37.16%,同时粮减劳增与粮劳同减耦合模式的比例明显上升。从空间格局看,粮劳变化耦合模式转换的差异明显。③ 县域粮劳变化耦合模式可以较好的表征相应的乡村发展类型。县域乡村发展类型实际上具有一定的层级性和结构演进规律。④ 东北地区各县域乡村发展类型所面临的约束和机遇不同,应有针对性的采取差别化的推进策略。     

On the compression behavior of remolded cement-admixed soft clay

Although extensive research has been performed on the mechanical properties of cement-stabilized clays, quite a few attempts have been made on the compression behavior of remolded cement-admixed clays. The results from oedometer tests have been discussed to investigate the compressibility of remolded cement-admixed clays, taking into consideration cement amount and curing time. The findings show that the difference in shape and position of compression curves is attributed to cement amount and curing time. Most compression index (C_c) values of remolded cement-admixed clays are greater than those of untreated clay due to the presence of remolded yield stress σ′_yr that is closely related to initial water content and clay fabric. Based on the obtained test data, the relationships of C_c vs. e₀, C_c vs. w₀, C_c vs. e₁, C_c vs. e_yr, and σ′_yr vs. e_yr are preliminarily discussed and quantitatively established. Especially, an important divergence of void index I_v at effective stress σ′_v less than remolded yield stress σ′_yr can be observed at different cement amounts and curing durations. Being independent on cement amount, curing time, and initial state of soil, an excellent convergence occurs at stress σ′_v greater than yield stress σ′_yr. The normalized compression curves of I_v vs. σ′_v at σ′_v?>?σ′_y can be expressed by a unique line that agrees well with intrinsic compression line (ICL) and extended ICL.     

长江中上游土壤自然侵蚀量及其估算方法

首先阐述了土壤侵蚀可分为自然侵蚀和人为加速侵蚀,自然侵蚀是自地球形成以来就普遍存在的一种自然现象;继而从夷平面、河流阶地、沉积盆地等侵蚀和堆积地貌形迹论述了第四纪以来长江中上游土壤自然侵蚀存在的佐证事实;在此基础上,依据侵蚀沉积相关原理,利用沉积物的厚度、面积和沉积时段分别计算了洞庭湖流域、鄱阳湖流域和古云梦泽流域全新世以来的自然侵蚀量,它们分别为264.2t/km² · a、 312.5t/km² · a和297.0t/km² · a;同时,本文还辅以川西和三峡地区的对比实验小区资料,现代自然侵蚀量分别为342.0t/km² · a、 75~270t/km² · a佐证历史自然侵蚀量。长江上中游区域的自然侵蚀量介于264.0t/km² · a ~342.0t/km² · a之间。流域平均自然侵蚀量是现代侵蚀量的50%~60%之间;本研究成果有助于对长江中上游现代土壤侵蚀的属性、演变过程有一个科学的认识;同时可为生态保护、环境友好建设目标提供背景参照物。     

漳河流域气象水文预报模型研究

通过对漳河产流、汇流、河道汇流和水库调洪演算,建立了漳河流域气象水文预报模型。本模型可根据实测降水量预报未来一定时期内入库洪水总量、洪峰、峰现时间、入库洪水过程,考虑水库出流及串联水库水量交换,经调洪演算得出水库水位变化过程。同时,也可输入气象预报的降水量或人工估算的未来可能降水量,进行水库未来洪水的可能发展趋势预测。