Torsional balance as new design criterion for asymmetric structures with energy dissipation devices

Lateral–torsional coupling in asymmetric‐plan buildings leads to correlated translations and rotations of the building plan, which generate uneven distributions of deformation demand among resisting planes. The deformation demand of a resisting plane depends on the relative magnitude of the plan translation and rotation and on the correlation between the two signals. Thus, small rotations highly correlated with building translation may lead to significantly different deformations of the resisting planes at the building edges. Consequently, the use of supplemental dampers is intended not only to reduce the magnitude of the plan translation and rotation, but also the correlation between these motions. For the sake of simplicity, linear viscous dampers are used in this investigation, which properly located in plan lead to a minimum response of the geometric center, thus achieving the same mean‐square value of the displacements at the building edges. Mathematically, this condition may be understood as creating zero correlation between the translations and rotation at the geometric center of the plan, which represents an uncoupling in the mean‐square sense. Results show that the optimal damper location depends on the static eccentricity and frequency ratio of the bare structure, the total amount of supplemental damping considered, and the frequency content of the excitation. Through a final 6‐story model example, the torsional balance concept is demonstrated to work on multistory buildings subjected to bidirectional ground motions. Copyright © 2009 John Wiley & Sons, Ltd.     

Two-dimensional finite volume method for dam-break flow simulation

A numerical model based upon a second-order upwind ceil-center f＇mite volume method on unstructured triangular grids is developed for solving shallow water equations. The assumption of a small depth downstream instead of a dry bed situation changes the wave structure and the propagation speed of the front which leads to incorrect results. The use of Harten-Lax-vau Leer （HLL） allows handling of wet/dry treatment. By usage of the HLL approximate Riemann solver, also it make possible to handle discontinuous solutions. As the assumption of a very small depth downstream oftbe dam can change the nature of the dam break flow problem which leads to incorrect results, the HLL approximate Riemann solver is used for the computation of inviscid flux functions, which makes it possible to handle discontinuous solutions. A multidimensional slope-limiting technique is applied to achieve second-order spatial accuracy and to prevent spurious oscillations. To alleviate the problems associated with numerical instabilities due to small water depths near a wet/dry boundary, the friction source terms are treated in a fully implicit way. A third-order Runge-Kutta method is used for the time integration of semi-discrete equations. The developed numerical model has been applied to several test cases as well as to real flows. The tests are tested in two cases： oblique hydraulic jump and experimental dam break in converging-diverging flume. Numerical tests proved the robustness and accuracy of the model. The model has been applied for simulation of dam break analysis of Torogh in Iran. And finally the results have been used in preparing EAP （Emergency Action Plan）.     

3维GIS融入控制性详细规划的理论研究和实现

随着城市建设的快速发展,城市规划管理的复杂程度、管理难度的逐渐增加,控制性详细规划在城市空间形态控制上的缺陷日益显现,由于缺少有效的控制手段,对3维空间考虑相对较少,很难对建筑形体和城市形态方面进行引导和控制。3维GIS形象真实地描述了城市3维地理空间的内容,它不仅具有虚拟现实表现的真实感,而且具有真实的地理坐标,具有空间分析和空间运算能力,能为控详规划提供强有力的技术手段。如何将3维GIS融入到控制性详细规划中,利用3维GIS技术手段,解决控详规划管理过程中的实际问题,是本文研究和阐述的关键问题。     

中国的荒漠化及其防治策略

中国作为世界上受荒漠化影响最为严重的国家之一,旱地面积约332万km2(占国土面积的34.6％,包括干旱区、半干旱区和亚湿润干旱区),其中超过262万km2归属联合国防治荒漠化公约定义的“荒漠化土地”;主要分布在全国18个省、区、市.超过4亿人生活在荒漠化地区,每年因荒漠化造成的直接经济损失超过640亿元.中国治沙的实践可以追溯到20世纪50年代.特别是最近30年,先后通过“三北防护林”工程(1978年启动)、全国防沙治沙工程(1990年启动)、环京津风沙源治理工程和退耕还林还草工程(2000年启动)等一系列国家级生态治理工程的实施,以年均0.024％ GDP的投入,治理和修复了大约20％的荒漠化土地.目前,以现有技术评估,可治理的沙化土地约有50×104 km2.考虑到全球变暖的影响,预测未来50年需要治理的荒漠化土地面积大致在55×104-100×104 km2之间.若按照每年1.5×104-2.2×104 km2的治理速度,大约需要45 -70年之久.规划安排到2015年治理完成22×104 km2,到2030年治理面积新增33×104 kim2,到2050年治理完成45×104 km2.基于国家生态修复投资战略的总体安排,未来防沙治沙决策应从以下四个方面着眼:一是强化多部门协作的综合治理;二是确立优先治理区,并在适当地方建立“生态特区”;三是改变投资模式,由目前政府直接投资植树改为投资买林、买绿;四是完善土地承包制度(70年权属不变)和实行生态补偿.     

Effects of hillslope geometry on spatial infiltration using the TOPMODEL and SCS-CN models

ABSTRACT

The estimation of infiltration is a main issue in runoff simulation. The geometry of hillslopes (plan shape and profile curvature) may affect the responses, as well as infiltration over the hillslopes. In this study, the equations of TOPMODEL (a topography-based model) were applied to complex hillslopes to develop the complex TOPMODEL. This model was coupled with the SCS-CN (Soil Conservation Service Curve Number) model to examine the effects of geometry on infiltration and derive a saturation excess-based curve number (CN). The effects of plan shape and profile curvature upon the spatial distribution of CN and infiltration were studied. The results show that convergent hillslopes have 15.4% less infiltration and divergent hillslopes have 7.8% more infiltration than parallel ones. The infiltration over concave hillslopes is 13.5% lower and infiltration over convex hillslopes 5.8% higher than for straight ones. The degree of convergence/divergence has a greater effect on the CN compared to that of profile curvature.     

城市居住区规划评价的群决策一致方法

从抗震防灾的角度对城市建成居住区评价的群决策方法进行了研究,建立了基于各不同评价角度相关群体对于候评区域的每个属性,依据自己的判断提出各自差异的个体决策信息,采用乘性加权集结算子构造群体决策矩阵,并判断群体决策矩阵与个体决策矩阵之间的相似度差异值,指导个体决策矩阵的修正,完成个体意见的一致化,得到了初始居住区规划方案评价群决策的计算模型。实例分析的结果表明,采用群决策评价的一致方法有利于提高多利益主体对居住规划方案评价群决策的综合满意度。     

The status of freshwater pearl mussel in the Czech Republic: Several successfully rejuvenated populations but the absence of natural reproduction

The freshwater pearl mussel was historically abundant in many streams and rivers in the Elbe, Oder, and Danube Basins in the Czech Republic, Central Europe. By the 21st century, the mussels had become extinct in the lower and middle altitudes, and current populations are only present near the upper limit of their natural range. The current population of this mussel is estimated to be only 1% of the historical abundance. The population decline was related to the negative impacts of pollution from industry, intense agriculture, forestry, and sewage water. The freshwater pearl mussel habitat has also been impacted by watercourse regulations and has been fragmented by dams and weirs. All of these impacts have resulted in failure of the reproductive cycle; the last significant cohort of juveniles settled approximately 30 – 40 years ago. Therefore, this species is considered critically endangered, and an action plan was developed to conserve the populations in the Czech Republic. Special measures were conducted between 1984 and 2005 to improve the age structure of elderly populations. Fish infected with millions of glochidia were released in two locations, and over 53,000 captive-bred juveniles that were three to five years old were released in seven locations. Only the latter approach resulted in a small number of subadults that gradually emerged from the substratum to the bottom surface, as confirmed by monitoring efforts. Despite simultaneous efforts to restore mussel habitat over the last 25 years, natural reproduction still does not occur in the Czech Republic. Therefore, complete restoration of oligotrophic streams is the key to the future presence and natural reproduction of freshwater pearl mussels in the Czech Republic.     

Displacement-based seismic design of hysteretic damped braces for retrofitting in-elevation irregular r.c. framed structures

A displacement-based design procedure is proposed for proportioning hysteretic damped braces (HYDBs) in order to attain, for a specific level of seismic intensity, a designated performance level of a reinforced concrete (r.c.) in-elevation irregular framed building which has to be retrofitted. To check the effectiveness and reliability of the design procedure, a numerical investigation is carried out with reference to a six-storey r.c. framed building, which, originally designed according to an old Italian seismic code (1996) for a medium-risk zone, has to be retrofitted by inserting of HYDBs to attain performance levels imposed by the current Italian code (NTC08) in a high-risk zone. To simulate a vertical irregularity, a change of use of the first two floors, from residential to office, is also supposed; moreover, masonry infill walls, regularly distributed along the perimeter, are substituted with glass windows on these floors. Nonlinear dynamic analyses of unbraced (UF), infilled (IF) and damped braced infilled (DBIF) frames are carried out considering sets of artificially generated and real ground motions, whose response spectra match those adopted by NTC08 for different performance levels. To this end, r.c. frame members are idealized by a two-component model, assuming a bilinear moment–curvature law whose ultimate bending moment depends on the axial load, while the response of an HYDB is idealized by a bilinear law, to prevent buckling. Finally, masonry infills are represented as equivalent diagonal struts, reacting only in compression, with an elastic–brittle linear law.     

浅谈科技期刊如何服务于我国防灾减灾事业

科技期刊是传播创新成果的主要媒介,是我国防灾减灾宣传工作中的主流媒体之一。从当今科技期刊的特征入手,分析了科技期刊在我国防灾减灾事业中发挥的作用,并对科技期刊今后如何更好地服务于我国防灾减灾事业进行了设想。     

Influence of earthquake direction on the seismic response of irregular plan RC frame buildings

The nonlinear response of structures is usually evaluated by considering two accelerograms acting simultaneously along the orthogonal directions. In this study, the infl uence of the earthquake direction on the seismic response of building structures is examined. Three multi-story RC buildings, representing a very common structural typology in Italy, are used as case studies for the evaluation. They are, respectively, a rectangular plan shape, an L plan shape and a rectangular plan shape with courtyard buildings. Nonlinear static and dynamic analyses are performed by considering different seismic levels, characterized by peak ground acceleration on stiff soil equal to 0.35 g, 0.25 g and 0.15 g. Nonlinear dynamic analyses are carried out by considering twelve different earthquake directions, and rotating the direction of both the orthogonal components by 30° for each analysis(from 0° to 330°). The survey is carried out on the L plan shape structure. The results show that the angle of the seismic input motion signifi cantly infl uences the response of RC structures; the critical seismic angle, i.e., the incidence angle that produces the maximum demand, provides an increase of up to 37% in terms of both roof displacements and plastic hinge rotations.