考虑强地面运动持时影响的概率地震需求模型

选择合理的持时衰减关系,利用Monte-Carlo方法,抽取持时样本,根据震级M、震中距R和局部场地土壤条件S以及持时样本,选择符合条件的实际地震波记录,并进行合理的调值,对一座钢筋混凝土桥墩进行了非线性动力时程分析.对比强地面运动持时与能量需求参数和累积破坏参数的相关性,发现:幅值、频谱和持时对能量需求参数和累积破坏参数的影响是强烈耦合的,且强地面运动持时对两者的影响比较显著;在选择结构第一模态周期谱加速度和合理的能量需求参数,并分别作为地面运动强度参数IM和EDP建立概率地震需求模型时,要考虑持时的影响.     

高层混合结构滞回耗能比的研究

基于结构层间弯曲屈服强度的概念,提出了高层混合结构滞回耗能比的简化计算公式,该公式综合体现了结构以及地震动特征参数对结构滞同耗能比的影响。研究表明,结构滞回耗能比随地震动的峰值速度与峰值加速度的比值的增大而增大;随着地震动幅值的增大,滞回耗能比也线性增加;对于短持时地震动,滞回耗能比与强震持时之间没有一定的规律性,但对于长持时地震动,结构滞回耗能比会随强震持时的增大而线性增加。随着结构弯曲屈服强度系数的增大,结构滞回耗能比呈凹函数下降,结构的自振周期越大,同一弯曲屈服强度系数对应的滞回耗能比越小;钢框架与混凝土剪力墙承载力比值的增加能够降低结构的滞回耗能比。     

Seismic upgrading of old masonry buildings by seismic isolation and CFRP laminates: a shaking-table study of reduced scale models

The efficiency of improving the seismic resistance of old masonry buildings by means of seismic isolation and confining the structure with CFRP laminate strips has been investigated. Five models of a simple two-story brick masonry building with wooden floors without wall ties have been tested on the shaking table. The control model has been built directly on the foundation slab. The second model has been separated from it by a damp-proof course in the form of a PVC sheet placed in the bed-joint between the second and the third course, whereas the third model has been isolated by rubber isolators placed between the foundation slab and structural walls. Models four and five have been confined with CFRP laminate strips, simulating the wall ties placed horizontally and vertically at floor levels and corners of the building, respectively. One of the CFRP strengthened models has been placed on seismic isolators. Tests have shown that a simple PVC sheet damp-proof course cannot be considered as seismic isolator unless adequately designed. Tests have also shown that the isolators alone did not prevent the separation of the walls. However, both models confined with CFRP strips exhibited significantly improved seismic behavior. The models did not collapse even when subjected to significantly stronger shaking table motion than that resisted by the control model without wall ties.     

利用阿拉斯加台阵资料分析2008年汶川大地震的破裂过程

2008年5月12日,四川省汶川县发生M_S8.0地震.我们利用美国阿拉斯加区域台网的部分宽频带地震台构成广义台阵, 应用非平面波台阵技术——迁移叠加方法,获得了这次地震的高频（>0.1 Hz）能量辐射源随时间和空间变化的图像.图像表明,这次地震破裂从震中开始向北东方向扩展约300 km,震源过程至少长达90 s,平均破裂速度为3.4 km/s;整个过程可分为两大阶段,前段持续时间50 s,破裂长度约110 km,破裂传播的平均速度为2.2 km/s,后段持续时间约40 s,长度约190 km,平均破裂速度为4.8 km/s.这意味着地震过程的后期似乎发生了超S波破裂,而且后段很可能为前段动态触发所致.     

An analysis of non-normal Markovian extremal droughts

In many arid and semi-arid environments of the world, years of extended droughts are not uncommon. The occurrence of a drought can be reflected by the deficiency of the rainfall or stream flow sequences below the long-term mean value, which is generally taken as the truncation level for the identification of the droughts. The commonly available statistics for the above processes are mean, coefficient of variation and the lag-one serial correlation coefficient, and at times some indication of the probability distribution function (pdf) of the sequences. The important elements of a drought phenomenon are the longest duration and the largest severity for a desired return period, which form a basis for designing facilities to meet exigencies arising as a result of droughts. The sequences of drought variable, such as annual rainfall or stream flow, may follow normal, log-normal or gamma distributions, and may evolve in a Markovian fashion and are bound to influence extremal values of the duration and severity. The effect of the aforesaid statistical parameters on the extremal drought durations and severity have been analysed in the present paper. A formula in terms of the extremal severity and the return period ‘T’ in years has been suggested in parallel to the flood frequency formula, commonly cited in the hydrological texts. © 1998 John Wiley & Sons, Ltd.     

地震总输入能量与瞬时输入能量谱的研究

现有的抗震设计理论大多是基于承载力或强度的设计方法,与其相应的反应谱理论最大的缺陷是无法反映地震动持时的影响,而以地震动能量作为设计参数时就能弥补现有抗震理论的不足。本文按照反应谱理论的思路建立了线性单自由度体系的地震动总输入能量谱和瞬时输入能量谱。研究发现,阻尼比为5%时的地震动总输入能量谱和最大瞬时输入能量谱的等价速度谱可以分别用阻尼比为0.5%和10%下的拟速度谱来近似获得;地震波的V/A值大于0.15时,总输入能量谱的Δt谱峰值与地震波的强震持时呈线性增长关系,V/A值小于0.15时,两者间的关系无规律性。最大瞬时输入能量谱的Δt谱峰值基本不受地震波的V/A值与强震持时的影响;输入能量谱(总输入能量谱与最大瞬时输入能量谱)的特征周期随地震波V/A值的增大而增大,根据分析结果本文提出了线性单自由度体系输入能量谱的简化计算方法,方法简便,计算结果偏安全。     

玉米净作和间作植株间光强的时空分布(英文)

作物多样性种植能够有效减少病虫危害,显著增加产量,但其中的机理尚不清楚。太阳辐射是最重要的影响因子之一。本试验研究了玉米净作(A)及玉米/大豆2:2(B,2行玉米2行大豆)和2:4(C,2行玉米4行大豆)两种间作模式下,玉米冠层内太阳辐射强度的时空变化。研究结果表明,多样性种植可在不同高度上对玉米植株间的受光强度和受光时间产生明显影响。在玉米穗期,相比净作,在30cm高度上,B和C模式下光强都超过了2倍,在70cm高度上,光强超过10倍。花粒期,在110、160和210cm位置上,相比净作,B和C模式下光强分别提高了5倍、2倍和12%,而且随着测量高度的下降,间作模式下光强下降较为缓慢。从第7–18叶,相比净作,各叶位间作模式下光强平均增加2倍,而且日有效辐射时间平均提高了5小时。此外,玉米的一些生物学性状,如千粒重、每株产量和穗位叶叶面积等也表现出间作B和C模式都显著高于净作。因此,间作提高了玉米的受光强度和有效辐射时间,是改善玉米生物学性状的重要因子。     

典型岩溶区潜在蒸散发变化及其影响因素

蒸散发过程是联系大气过程和陆面水文过程的关键环节,对区域/流域水循环过程和水量平衡具有重要影响。岩溶区,地表生态环境脆弱,对气候变化响应敏感,蒸散发可能是联系大气、水、热交换和碳循环的关键生态水文过程。准确地估算蒸散发对于深入研究岩溶水循环响应气候变化、碳循环、生态修复等具有重要作用。本文选择典型岩溶区桂林市为研究对象,基于1951~2015年桂林市气象站逐日气象数据,采用Penman- Monterith方法计算了潜在蒸散发量,利用Mann- Kendall非参数检验法和相关性分析研究桂林市潜在蒸散发的变化趋势及其影响因素。研究结果表明,桂林市潜在蒸散发具有明显的年、年际和季节尺度变化特征。1951~2015年桂林市潜在蒸散发呈显著的减小趋势,变化速率为-8. 02 mm/10a;夏季、秋季和冬季潜在蒸散发呈下降趋势,而春季呈微弱的上升趋势;夏季潜在蒸散发的显著减小是影响年蒸散发下降的主要原因;桂林市潜在蒸散发在1967和2003年左右发生突变;通过Mann- Kendall趋势检验和相关性分析得出,桂林市平均气温、最高、最低气温呈显著的上升趋势,而风速、相对湿度、日照时数呈显著的下降趋势;日照时数是影响桂林市潜在蒸散发变化的主要因素,其次是风速。     

Evaluation of the WEPP model and digital elevation grid size,for simulation of streamflow and sediment yield in a heterogeneous catchment

The paper presents the result of an application of the GeoWEPP model in a heterogeneous semi‐agricultural catchment located in the northern Italian Apennines mountain range. The objectives were: (a) to evaluate the GeoWEPP model in a heterogeneous catchment in a Mediterranean climate and (b) to examine the effect of digital elevation model grid size on hydrological and sediment yield simulations. The catchment is characterized by large heterogeneity in geology, soil type, vegetation cover and topography. In addition, 10% of its area is occupied by calanchi (badlands), characterized by steep, bare soil and accentuated erosion. Experimental streamflow data were compared with those simulated by GeoWEPP for a period of eight years and the results were evaluated by means of statistical indices, with the analysis of the flow duration curve. Simulated sediment yields were compared with experimental data for one year. The streamflow cumulative annual results were satisfactory with NSE oscillating between 0.40 and 0.83 and RMSE between 1.1 and 2.9 mm. Also, the performance of the model with daily streamflow data was positive (NSE = 0.68 and RMSE = 1.9 mm). The flow duration curve indicated that GeoWEPP could represent the experimental streamflow for fluxes over 1 mm d^?1. The model performance for simulation of sediment yield was satisfactory with both digital elevation models of different grid sizes (NSE = 0.84 and 0.87). Indeed, the sensitivity analysis tests of the model showed that there was no statistically significant improvement in the accuracy of the digital elevation model between 10 and 2 m resolution. These results were confirmed for both streamflow as well as sediment yield. Additional sensitivity analysis of other model parameters performed on the entire catchment and badlands hillslopes showed that bedrock hydraulic conductivity primarily affected the model in both settings. Copyright © 2014 John Wiley & Sons, Ltd.     

近50年新疆日照时数时空变化分析

利用新疆101 个气象站1961-2010 年的逐月日照时数、总云量和低云量资料,使用线性趋势分析、Mann-Kendall 检测以及基于ArcGIS 的混合插值法对春、夏、秋、冬四季和年日照时数的变化趋势、突变特征以及日照时数多年平均值和突变前后变化量的空间分布及其与云量的关系进行了分析,结果表明：（1）新疆春季日照时数总体呈现“从东北向西南递减”的空间分布特点;夏季为“北疆多,南疆少,东部多、西部少,平原和盆地多,山区少”的格局;秋季呈现“由东南向西北递减”的分布格局;冬季具有“东部多,西部少”的特点。新疆各地年日照时数2450~3450 h,其空间分布总体呈现“东部多,西部少;平原和盆地多,山区少”的格局。（2）1961-2010 年,除春季日照时数呈不显著的略增趋势外,新疆夏季、秋季、冬季和年日照时数分别以-4.27 h·（10a）^-1、-4.30 h·（10a）^-1、-14.36 h·（10a）^-1和-19.42 h·（10a）^-1的倾向率呈显著的减少趋势。并且,夏季、秋季、冬季和年日照时数分别于1988 年、1986 年、1987 年和1982 年发生了突变。突变年前后,全疆各地日照时数的变化具有明显的区域性差异,以年日照时数为例,1982 年后较其之前,除吐鲁番、哈密盆地,塔里木盆地南缘等少部分区域年日照时数有所增多外,全疆大部为减少的态势。（3）云量是影响新疆日照时数的主要因素,总体来说,新疆总云量和低云量较少的区域日照时数相对较多;反之,亦然。近50a,新疆总云量变化不明显,但低云量明显增多,这是导致日照时数减少的主要成因。