The Wall in Recent Architectural Form: A Pattern of Evolution Toward Autonomy

Architectural design during the past twenty-five years has exhibited an increasingly pronounced tendency to treat the building wall as an autonomous designed object, independent of the building volume with which it is associated. There is a continuum of approaches, ranging from surface elaboration of the wall through low relief and high relief, to full design autonomy. Architects employ two main strategies toward this end: the expanded frontal wall plane, which exaggerates the building's monumentality, and the concentric shell or colonnade, which tends to the opposite result of an elaborated and more approachable design. In this article, I explore and illustrate these points with the support of an extensive series of specific examples.     

钢管脚手架支撑结构类型及破坏模式之探讨

钢管脚手架(鹰架)为台湾地区高挑空建筑工地常用之模板支撑构材,由于目前可供设计及施工参考之规范甚为缺乏,工地常是凭借着施工经验来架设支撑,致使常有倒塌意外发生。本文介绍台湾地区常用之钢管鹰架,并提出五种可能引致钢管鹰架模板支撑失败的模式供营建工程界参考,期能降低钢管鹰架模板支撑之倒塌意外     

Seismic response of multi-storey buildings including foundation interaction and P-Δ effects

This paper presents a method of seismic analysis of multi-storey buildings when both soil-structure interaction and P-Δ effects have been taken into account. The additional overturning moment at each storey due to P-Δ effects is replaced by two fictitious horizontal forces acting in opposite directions at the upper and lower ends of each storey. Then, the governing equation for each floor is developed in which these fictitious horizontal forces are incorporated along with seismic inertia forces. Considering the footing as a rigid disc resting on the surface of an elastic half-space, two equations expressing the equilibrium of the building as a whole in translation and rotation complete the set of equations in terms of floor displacements and two rigid body base displacements. Recognizing that the superstructure alone admits classical normal modes, floor governing equations are uncoupled and substituted into the remaining equations, which results in two coupled integro-differential equations in terms of two rigid body displacements. These two equations can be solved using numerical procedures. The method is applied to two unbraced steel buildings and numerical results are presented for different foundation soil conditions. The influence due to P-Δ effects and soil-structure interactions on the responses of these buildings is discussed.     

Numerical simulation of a jointed rock block mechanical behavior adjacent to an underground excavation and comparison with physical model test results

Mechanical behavior of a jointed rock mass with non-persistent joints located adjacent to a free surface on the wall of an excavation was simulated under without and with support stress on the free surface using approximately 0.5 m cubical synthetic jointed rock blocks having 9 non-persistent joints of length 0.5 m, width 0.1 m and a certain orientation arranged in an en echelon and a symmetrical pattern using PFC^3D software package. The joint orientation was changed from one block to another to study the effect of joint orientation on strength, deformability and failure modes of the jointed blocks. First the micro-mechanical parameters of the PFC^3D model were calibrated using the macro mechanical properties of the synthetic intact standard cylindrical specimens and macro mechanical properties of a limited number of physical experiments performed on synthetic jointed rock blocks of approximately 0.5 m cubes. Under no support stress, the synthetic jointed rock blocks exhibited the same three failure modes: (a) intact rock failure, (b) step-path failure and (c) planar failure under both physical experiments and numerical simulations for different orientations. The jointed blocks which failed under intact rock failure mode and planar or step-path failure mode produced high and low jointed block strengths, respectively. Three phases of convergence of free surface were discovered. The joint orientation and support stress played important roles on convergence magnitude. The average increment of jointed block strength turned out to be about 10, 7.9 and 6.6 times the support stress when support stresses of 0.06 MPa, 0.20 MPa and 0.40 MPa were applied, respectively. The modeling results offer some guideline in support design for underground excavations.     

隔离病房气流分布模拟与评价

采用CFD数值模拟的方法,利用相关评价指标对四种不同气流分布方式进行了比较分析,认为天花板顶送异侧下排是较为理想的气流分布方式。建立了实体模型,对这种气流分布方式的排污效果进行了实验测试,结果令人满意。     

The extinction of fires in aircraft jet engines — Part I,small-scale simulation of fires

Three modes of combustion are possible in an aircraft engine fire, and these have been simulated separately in a small wind tunnel.     

Component and system reliability analysis of nonlinear reinforced concrete grids with multiple failure modes

The bending moment redistribution is an inherent behavior in reinforced concrete grids, which increases the number of possible critical cross-sections susceptible to reach a limit state. Despite the fact that its influence could be important, the high number of failure cross-sections is not often considered in reinforced concrete reliability analyses. In this paper, a local approach of reliability analysis applied to grid structures is developed by taking into account the dominant failure modes. This approach is based on random sampling coupled with finite element analysis, through the use of a localized response surface technique. A mode selection strategy has been developed to capture the individual failure modes in order to classify their importance in the global system reliability. For large-scale systems, this procedure intends to reduce the global computational time in the reliability analysis. Numerical applications aim to show the effect of internal force redistribution, as well as the efficiency of the proposed approach and the interest of considering multiple failure modes.     

反倾岩质边坡次生倾倒机理及稳定性分析

倾倒破坏是反倾边坡的一种常见破坏模式,其中次生倾倒是反倾岩质边坡倾倒破坏的主要诱因。建立了反倾岩层在坡后土体作用下次生倾倒破坏的地质力学模型,基于室内物理模拟试验,分析了反倾岩层上覆土压力分布规律、岩层的破坏模式和整体破坏面的形状与位置。根据库仑主动土压力理论得到下卧岩层表面各点法向压力的理论值与实测值基本相符,土体中存在土拱效应导致两者存在差异,随着上覆土体厚度及堆载作用的加大,土拱效应越明显。各岩层可能的破坏模式包括弯拉破坏、弯滑破坏和滑动破坏。下卧反倾岩层的整体破坏面是一通过坡脚的近似平面,整体破坏面与岩层层面法线方向呈0°～25°的夹角。基于叠合悬臂梁模型,引入岩层横截面上节理面的黏聚力和岩石抗拉强度随岩层嵌入深度的折减系数,改进了反倾岩层的极限平衡分析方法,推导了坡体任意岩层下推力的理论公式,定义了任意岩层变形破坏的安全系数和边坡整体倾倒破坏的综合安全系数。提出了下卧反倾岩层潜在整体破坏面的理论计算方法,并确定了影响潜在整体破坏面位置的敏感因素。     

From Neural Networks to Qualitative Models in Environmental Engineering

As an alternative to physical models, artificial neural networks (ANNs) are a valuable forecast tool in environmental sciences. They can be used effectively due to their learning capabilities and their low computational costs. Once all relevant variables of the system are identified and put into the network, it works quickly and accurately. However, one of the major shortcomings of neural networks is that they do not reveal causal relationships between major system components and thus are unable to improve the explicit knowledge of the user. Another problem is due to the fact that reasoning is only done from the inputs to the outputs. In cases where the opposite is requested (i.e., deriving inputs leading to a given output), neural networks can hardly be used. To overcome these problems, we introduce a novel approach for deriving qualitative information out of neural networks. Some of the resulting rules can directly be used by a qualitative simulator for producing possible future scenarios. Because of the explicit representation of knowledge, the rules should be easier to understand and can be used as a starting point for creating models wherever a physical model is not available. Moreover, the resulting rules are well adapted to be used in decision support systems. We illustrate our approach by introducing a network for predicting surface ozone concentrations and show how rules can be derived from the network and how the approach can be naturally extended for use in decision support systems.     

Simulating impacts of wind farms on local hydrometeorology

Wind power is one of the fastest growing energy sources in the world, most of the growth being in large wind farms that are often located on agricultural land near residential communities. This study explores the possible impacts of such wind farms on local hydrometeorology using a mesoscale model equipped with a rotor parameterization based on data from a commercial wind turbine. Results show that wind farms significantly affect near-surface air temperature and humidity as well as surface sensible and latent heat fluxes. The signs of the impacts, i.e., increase or decrease, depend on the static stability and total water mixing ratio lapse rates of the atmosphere. The magnitudes of these impacts are not only constrained by the hub-height wind speed but also depend to some extent on the size of the wind farms. Wind farms also affect the hydrometeorology of an area up to 18-23 km downwind. More work is required to conclusively estimate the length-scale of wind farm wakes. This study is one of the first few to provide realistic estimates of possible impacts of wind farms. The model developed and used in this study can help in assessing and addressing the environmental impacts of wind farms thereby ensuring the long-term sustainability of wind power.     

Deployment of Fiber-Optic Lane Use Indication Signs Using a Distributed Control Architecture

This article reviews the basic signing technologies available to the traffic engineer for dynamically changing sign displays. An example installation of dynamic lane assignment in Houston, Texas, is reviewed and referenced as the motivation for developing a simple traffic signal cabinet interface for dynamic lane assignment signs. The failure modes of these dynamic lane assignment signs are identified so that suitable control models can be selected. Various candidate control architectures are summarized, and a distributed control model is recommended because of the simple cabinet retrofit and the inherent malfunction management capabilities. The article concludes by describing the distributed computing design comprised of the sign-control interface (SCI) residing in the cabinet and the sign-control modules (SCM) residing in each sign. Photographs of the SCI and SCM prototypes are included.     

Reliability analysis of ground–support interaction in circular tunnels using the response surface method

The first-order and the second-order reliability method (FORM/SORM) are used to evaluate the failure probability of three performance functions of the ground–support interaction in circular tunnels subjected to hydrostatic stresses. The response surface method (RSM) is used to enable reliability analysis of the implicit convergence-confinement method. The friction angle, cohesion and elastic modulus of the rock mass are considered as basic random variables and are first assumed to obey normal distributions. The quadratic polynomial with cross terms is employed as response surface function to approximate the limit state surface (LSS) at the design point. The strategies for the RSM are presented. The failure probability with respect to different criteria are obtained from FORM/SORM and compared to those generated from Monte Carlo simulations. The results show that the support installation position has great influence on the probability of the three failure modes under consideration. Comparison between analysis using correlated and uncorrelated friction angle and cohesion indicates that the influence of the correlation on the reliability analysis depends on the support installation position and the orientation of the LSS. The reliability analysis involving correlated non-normal distributions and the reliability-based design of the support are also investigated.     

An experimental investigation of the failure mechanism of simulated transversely isotropic rocks

This paper presents the results of an experimental investigation of the failure mechanism, including failure process and failure modes, of transversely isotropic rock. This paper employs a rotary scanner to obtain the “unrolled” images of rock specimens at different stress levels during the uniaxial compressive tests. The unrolled image constitutes a circumferential surface image of the cylindrical specimen in a single picture and facilitates the study of failure processes and failure modes. Based on the experimental results, the failure of simulated transversely isotropic rock with varied orientations at different confining pressures is classified into one of two modes: (a) sliding failure along the discontinuities and (b) non-sliding failure along the discontinuities. The latter can be further classified into one of the following three sub-failure modes: (1) tensile fracture across the discontinuities, (2) tensile-split along the discontinuities, and (3) sliding failure across the discontinuities. The failure processes of these modes are also examined in this study. Failure criterion proposed by Tien and Kuo is found to predict accurately the strength and failure modes of simulated transversely isotropic rocks.     

Mining-induced stress change and consequences of stress path on excavation stability — a case study

For stability assessments as well as for support design, it is important to understand the factors leading to detrimental stress changes. Stress changes not only influence the demand on the rock support, they also change the support capacity of frictional support components such as plain cablebolts. Stress and stress changes are commonly predicted by numerical models but it is rarely possible to verify these predictions. This study presents a practical example illustrating the usefulness of stress change measurements in providing an accurate picture of the mining-induced stress changes and their value for numerical model calibration. Stress changes, associated with mining of the 565#6 stope at Winston Lake Mine, were measured by four CSIRO HI stress cells, two in the hangingwall and two in the back of a sill drift. In order to obtain the full stress history of the hangingwall, stresses at the installation time were calculated by use of a three-dimensional boundary element program — MAP3D. Two types of rockmass failure were observed at this mine: hangingwall delamination and collapse leading to ore dilution, and wedge-like failures in the backs of sill drifts. All stress cells were located such that they were affected by these failure mechanisms. Using measured and predicted stress paths, this study explains the nature of these two failure modes, as experienced at Winston Lake Mine. Excellent correspondence between measured and predicted stresses is achieved for both the hangingwall and the back of the sill drifts. Modelled stress rotations in the hangingwall follow closely the stress rotations determined in the field, except at the end of the monitoring campaign when the stress cells were affected by inelastic straining of the host rock. These measurements assist in understanding the failure processes and in defining the limitations of the adopted numerical models.     

浸水条件下有限土体土压力试验研究与数值分析

采用自主设计自动控制模型箱,开展了墙后有限宽度浸水无粘性土体在绕墙底转动、平动及绕墙顶转动3种位移模式下的主动土压力试验,并通过ABAQUS进行数值模拟,分析研究了墙后不同宽度土体的破坏形式及其土压力分布规律。研究结果表明,3种位移模式下,有限土体宽度较窄时破裂面被固定挡墙截断,随着填土宽度的增加破裂面开始延伸至填土表面,并最终稳定于库伦破裂面内侧。3种位移模式下的有限土体土压力分布均明显小于水土分算值,且随填土宽度的增加而逐渐接近水土分算理论值;绕墙底转动时土压力分布接近三角形分布,平动时土压力随土体宽度增加渐呈“勺型”分布,而绕墙顶转动时则呈“S”型分布规律。     

Design of a robust controller for doubly fed induction generator to damp low frequency oscillations in emerging distribution systems

Emerging distribution systems accommodate a large number of dynamic devices such as distributed energy resources, their controllers and other smart devices. Complex interactions among these dynamic devices may result in a number of instability issues. One of the important instability concerns is the small signal instability caused by oscillatory modes with lower values of frequency and damping ratios. In such cases, a suitable control methodology must be applied to ensure the stability of an emerging distribution system. In this paper, a robust control methodology for a doubly fed induction generator (DFIG) is proposed for the enhancement of system stability. The impact of active and reactive power of the DFIG on a low damped mode is assessed. The effectiveness of the controller is tested in an IEEE 43 bus distribution system with distributed generation units. Results show that the proposed robust controller for the DFIG can support damping of critical modes.     

两相邻建筑“结构土结构体系”的动力特性

为了研究建筑群中相邻结构存在导致结构动力特性的变化,将上部结构简化为等效单自由度模型,采用刚性基础明置于均质土层上,系统地研究两个相同结构所构成三维结构土结构体系中,邻近结构存在对结构动力特性的影响。根据结构土结构相互作用下体系存在两阶频率相近相位相反振动模态的现象,提出了孪生频率的概念。随后,探讨了孪生频率随结构与土层的频率比、结构之间的相对距离、基础宽度与土层厚度比等因素的变化规律,以反映两结构通过土体耦合对结构动力特性的影响。在此基础上,进行了行波地震输入下结构土结构相互作用体系动力反应计算,结果表明,由于孪生频率的存在,易于使结构和场地产生拍的现象。     

深基坑工程中锚桩支护结构的设计

文章将岩土锚固技术用于基坑支护结构中,利用锚杆锚固和排桩支护技术相结合的方法提出基坑排桩一锚杆支护体系,通过详细论述这种支护体系的工作机理和破坏形式,着重分析了深基坑工程中类似结构的设计要点。     

季节性气候变化对填埋场温度分布影响的研究

基于热传导理论,根据能量守恒原理与傅立叶定律,建立了填埋场内温度传输的数学模型,并利用有限单元法进行了数值求解.数值模拟结果显示:在夏季,随着深度的增加,温度逐渐降低;冬季则相反.这是由于垃圾土的热传导系数不高,比热较大,而且使得温度的分布在空间上产生了滞后.在填埋场表层及浅层区域,由于受到传热效应的作用,其温度值几乎与外界大气温度一致.所建立的数值模型可以仿真填埋场内温度在空间上的分布变化规律,不仅为填埋气体产量和环境评价的研究提供理论依据,而且可为填埋场的气体收集系统和相关设计提供技术支持.     

Features of surface modes in metamaterial layers

In this paper, we present a study of the waveguiding properties of metamaterial layers. We pay particular attention to peculiar features that have not yet been given sufficient consideration in previous publications, with an emphasis on the physical interpretation of these results. We attempt to follow the transition of waves guided by a solitary “metamaterial–vacuum” boundary (the so-called true surface wave—TSW) to modes guided by the metamaterial layer. We considered the way TSW of different types (forward, backward and degenerated) transform to the layer modes and examined the features arising in the dispersion curves. For example, “pulling” of the dispersion curve into the frequency region where TSWs do not exist separately, presence of the bend for all modes produced by backward TSWs, existence of the waves with complex conjugate propagation constants, etc.