The application of range of variability approach to the assessment of a check dam on riverine habitat alteration

This report uses the intermediate disturbance hypothesis to assess the influence of constructing a check dam on river environment. HEC-HMS and HEC-RAS programs were used to generate hydraulic parameters such as flow discharge, water depth, velocity, water surface width and sediment discharge. Indicators of hydrologic alteration (IHA) and indicator of habitat alteration (IHabA) were used to evaluate the flow and habitat conditions before and after check dam construction. The range of variability approach was used to calculate the degree of hydrologic alteration for each IHA, degree of habitat alteration and overall alteration for IHabA. Variability of river habitats before and after check dam construction was contrasted. Alteration became larger the closer to the dam body. An assessment method for check dam construction is offered which does not require ecological investigation data and combines ecology concepts and hydraulics.     

Extreme pressure due to expanded cylindrical and spherical cavity in a limitless medium: applications in soil mechanics

The extreme net pressure resulting from an expansion in a cylindrical or spherical cavity within a limitless medium is studied. Performing the static and kinematic approaches of yield design theory, analytical solutions of the extreme net pressure are established for cohesive–frictional as well as for purely cohesive medium. In the case of a cylindrical cavity, the identification between the analytical extreme net pressure and limit net pressure leads to the prediction of shear strength characteristics of soil. As useful result, in soil mechanics, the assessment of correlations using pressuremeter data has been discussed. Also, some assumptions for designing foundations, from pressuremeter data, have been highlighted.     

Convergence-control approach for rock tunnels reinforced by grouted bolts,using the homogenization concept

The scope of this paper is to introduce a method for the analysis of rock tunnels reinforced by grouted bolts, based on the convergence-control approach. The analytical formulations presented in this paper refers to an elasto-plastic behavior of the rock mass and the latest Hoek and Brown yield criterion (Version 2002). In order to model the reinforced plastic zone, the equivalent material approach was taken into account such that the apparent strength of the rock mass is improved as a consequence of the bolting effect. The general design guides and examples presented are intended to facilitate the comprehension and application of the proposed analytical solution in practice.     

Urbanization and water management in Ho Chi Minh City,Vietnam-issues,challenges and perspectives

The management of water resources is an unfinished effort of the international community. Rapid urbanization has transcended the management capacity of governments in developing countries. Since the renovation policy launched in 1986, Ho Chi Minh City, Vietnam, has experienced the fastest urbanization and industrialization process. This has placed severe constraints on the use of water resources and management capacity of the local government. The abstraction of groundwater has exceeded the limiting volume (520,000 m³/day) and the annual drawdown of water table is 2–3 m. In addition, the quality of urban water bodies is increasingly exacerbated by a huge volume of untreated industrial and domestic wastewater. These are hampering water demand, use and the capacity of the municipal authority in managing water resources. The purpose of this paper is to analyze the impact of urbanization on water resources. Current issues and challenges in the management practices of water resources are discussed. It will propose a new paradigm of water management in Ho Chi Minh City.     

Rigid‐plastic seismic design of reinforced concrete structures

In this paper a new seismic design procedure for Reinforced Concrete (R/C) structures is proposed—the Rigid‐Plastic Seismic Design (RPSD) method. This is a design procedure based on Non‐Linear Time‐ History Analysis (NLTHA) for systems expected to perform in the non‐linear range during a lifetime earthquake event. The theoretical background is the Theory of Plasticity (Rigid‐Plastic Structures). Firstly, a collapse mechanism is chosen and the corresponding stress field is made safe outside the regions where plastic behaviour takes place. It is shown that this allows the determination of the required structural strength with respect to a pre‐defined performance parameter using a rigid‐plastic response spectrum, which is characteristic of the ground motion alone. The maximum strength demand at any point is solely dependent on the intensity of the ground motion, which facilitates the task of distributing required strength throughout the structure. Any artificial considerations intended to adjust results according to empirical observations are avoided, which, from a conceptual point of view, is considered to be an advantage over other simplified design procedures for seismic design. The procedure is formulated using a step‐by‐step format followed by a design example of a 4‐storey‐R/C‐plane‐frame. Results are compared with refined NLTHA and found to be extremely encouraging. Copyright © 2006 John Wiley & Sons, Ltd.     

An earthquake scenario for the microzonation of Sofia and the vulnerability of structures designed by use of the Eurocodes

The study of the site effects and the microzonation of a part of the metropolitan Sofia, based on the modelling of seismic ground motion along three cross-sections are performed. Realistic synthetic strong motion waveforms are computed for scenario earthquakes (M=7) applying a hybrid modelling method, based on the modal summation technique and finite differences scheme. The synthesized ground motion time histories are source and site specific. The site amplification is determined in terms of response spectra ratio (RSR). A suite of time histories and quantities of earthquake engineering interest are provided. The results of this study constitute a “database” that describes the ground shaking of the urban area. A case study of experiment-based assessment of vulnerability of a cast-in-situ single storey, industrial, reinforced concrete frame, designed according to Eurocodes 2 and 8 is presented. The main characteristics of damage index and storey drift are discussed for the purposes of microzonation.     

2003年渭河流域5次致洪暴雨过程的水汽场诊断分析

利用实况高空探测和地面观测资料、NCEP/NCAR再分析资料, 从水汽输送、水汽收支以及水汽含量等方面着手, 对2003年发生在渭河流域的5次致洪暴雨过程进行了对比分析, 结果表明:强降水发生时, 降水区700 hPa上的比湿值均不低于7 g/kg; 在垂直结构上, 强降水地区低层水汽含量在降水前6~12 h出现峰值, 强降水出现在高层比湿的峰值附近; 致洪暴雨过程的水汽通道与西太平洋副热带高压的位置有着明显的相关性; 渭河流域南边界是水汽的主要输入方, 主要的水汽输送层在850~700 hPa, 西边界是水汽的主要输出方。     

Hazard rate estimation of a mixture model with censored lifetimes

This paper is intended to compare the hazard rate from the Bayesian approach with the hazard rate from the maximum likelihood estimate (MLE) method. The MLE of a parameter is appropriate as long as there are sufficient data. For various reasons, however, sufficient data may not be available, which may make the result of the MLE method unreliable. In order to resolve the problem, it is necessary to rely on judgment about unknown parameters. This is done by adopting the Bayesian approach. The hazard rate of a mixture model can be inferred from a method called Bayesian estimation. For eliciting a prior distribution which can be used in deriving a Bayesian estimate, a computerized-simulation method is introduced. Finally, a numerical example is given to illustrate the potential benefits of the Bayesian approach.