Ski Jump Hydraulics

Ski jumps are a major element of each dam spillway because these are the only structures able to accomplish satisfactory energy dissipation for takeoff velocities in excess of some 20?m/s. This research aims to add to several hydraulic problems with ski jumps that have not yet been systematically solved so far. Based on an experimental campaign, the following problems were addressed: (1) pressure head maximum and pressure distribution along a circular-shaped flip bucket; (2) takeoff characteristics for a certain bucket deflection and a relative bucket curvature including the jet trajectories of both the lower and the upper nappes; (3) impact characteristics in a prismatic tailwater channel with details of shock wave formation and height of recirculation depth; (4) energy dissipation across the ski jump, from the upstream channel to downstream of jet impact; and (5) choking flow conditions by the flip bucket. These results demonstrated the significant effect of the approach Froude number, the relative bucket curvature and the bucket angle. The results allow immediate application to the design of ski jumps in hydraulic engineering.     

Stability of Ballasted Woody Debris Habitat Structures

An important component of stream restoration in the Pacific Northwest is the reintroduction of large woody debris (LWD) and construction of LWD habitat structures in degraded systems. A significant problem faced by engineers involved in stream restoration is a lack of physically based guidelines for design and construction of ballasted LWD habitat structures. A simple theoretical approach is developed that forms the basis for determining ballast requirements for three types of LWD structures. Field monitoring and assessment were undertaken to test the approach and to compare predicted and observed stability for approximately 90 ballasted LWD structures. The results indicate that the stability of single-LWD and single-LWD with root wad structures can be successfully predicted by the theory. The stability of the multiple-LWD structures proved to be more complex to predict because numerous design and construction-related factors influence stability. A design approach based on factors of safety is recommended.     

岩土工程勘察设计与施工中水文地质问题探析

在地质工程施工之前,都需要进行岩土工程的勘察设计,这是施工的前提条件。最终的施工结果与岩土勘察设计和水文地质问题有关。这些方面出现任何问题,都会影响施工的正常进度,影响施工质量,甚至会发生安全隐患,因而,在工程开始施工之前,必须要对水文地质的勘察工作,详细掌握施工地的水文地质问题,做好防御措施,为工程的顺利开展做基础。     

膨胀性岩土路堑边坡加固设计及效果分析

根据郑州市西南绕城高速公路膨胀性岩土路堑边坡在施工过程中的实际破坏状况,将边坡分成四个加固区域,针对不同区域的实际情况采取不同的加固方案.按照不同加固结构的设计参数和坡体自然属性,利用数值分析方法,对加固后坡体稳定性及加固结构承载性能进行了系统分析.结果表明,加固后坡体稳定性得到显著提高,加固结构尤其是自预应力锚杆,表现出良好的承载性能,使得不同类型的加固结构与坡体构成有效的承载整体.     

Institutional arrangements for flood hazard management in Malaysia: an evaluation using the criteria approach

Institutional aspects of flood hazards significantly affect their outcomes in Malaysia. Institutional arrangements to deal with floods include: legislative activity, organisational structures, attitudes and sub-culture, and policies and instruments. When assessed in terms of four specific criteria, institutional aspects of flood hazards are found to be largely inadequate. Disaster reduction programmes are over-dependent on a reactive approach based largely on technology and not even aimed at floods specifically. Structural flood reduction measures are the predominant management tool and, although the importance of non-structural measures is recognised, thus far they have been under-employed. Current laws and regulations with regard to flood management are also insufficient and both the financial and human resources of flood hazard organisations are generally found to be wanting. Finally, economic efficiency, equity and public accountability issues are not adequately addressed by institutional arrangements for flood hazards.     

Development of FRP Reinforcement Guidelines for Prestressed Concrete Structures

Several national programs define the testing protocols and design guidelines for fiber reinforced polymer (FRP) reinforcement in concrete structures. This paper offers a review of these documents, comparing the materials testing and design philosophies for FRP reinforcement of different working groups. The work references Canadian, European, and Japanese efforts to codify these materials and assess the relative merits of each approach. The emphasis is on prestressing applications since the demands for sustained load capacity and full bond are more severe than for reinforced concrete.     

Feed forward neural networks for the analysis of censored survival data: a partial logistic regression approach

Flexible modelling in survival analysis can be useful both for exploratory and predictive purposes. Feed forward neural networks were recently considered for flexible non-linear modelling of censored survival data through the generalization of both discrete and continuous time models. We show that by treating the time interval as an input variable in a standard feed forward network with logistic activation and entropy error function, it is possible to estimate smoothed discrete hazards as conditional probabilities of failure. We considered an easily implementable approach with a fast selection criteria of the best configurations. Examples on data sets from two clinical trials are provided. The proposed artificial neural network (ANN) approach can be applied for the estimation of the functional relationships between covariates and time in survival data to improve model predictivity in the presence of complex prognostic relationships.     

Design-Oriented Analysis of Structures—Unified Approach

Repeated analysis or reanalysis is needed in the various stages of any design process. Reanalysis methods are intended to analyze efficiently structures that are modified due to changes in the design. The reanalysis approach presented in this study is suitable for various stages of the design process, including the conceptual, preliminary, and detailed design stages. The accuracy of the results and the efficiency of the calculations can be controlled by the level of simplification and the amount of information considered. Different methods derived from the general approach may be used in the various design stages. The approach is suitable for various analysis models (linear, nonlinear, static, dynamic, etc.), different types of structures (trusses, frames, grillages, continuum structures), and all types of changes in the design (cross sectional, geometrical, topological, and material). The solution steps are straightforward, and the computational procedures presented can readily be integrated into finite element procedures.     

General Analytical Framework for Design of Flexible Reinforced Earth Structures

Current design methods divide reinforced earth structures into walls and slopes by using an arbitrary face inclination of 70° as the boundary. The required maximum strength of reinforcement computed for reinforced walls are significantly higher than that computed for reinforced slopes even if the inclination is practically the same. Presented is a general analytical framework for design of flexible reinforced earth structures regardless of the slope face inclination. In fact, the framework is consistent for any structural geometry and any applicable slope stability analysis although, for demonstration purposes, the simple Culmann formulation is utilized for simple geometry with zero batter. Using an adequate slope stability formulation, the required tensile resistance of reinforcement for a given layout is calculated so as to produce the same prescribed factor of safety anywhere within the reinforced zone. That is, using the design shear strength of the soil, the required reinforcement resistance along each layer is computed to fully mobilize this shear strength for all possible slip surfaces. That is, a baseline solution is produced for an ideal long-term strength of reinforcement at any location. Consequently, the required strength of the connection between each reinforcement layer and the facing unit can also be determined. This connection strength, however, assumes small facing units with negligibly small shear and moment resistance. Parametric study is conducted to demonstrate the reasonableness of the presented framework. It is shown that the required tensile resistance and connection strength depend on factors such as: reinforcement length; intermediate reinforcement; percent coverage; and quality of fill. When compared with the current AASHTO design for walls, the required maximum long-term strength of the reinforcement as well as the required connection strength in the proposed approach are substantially smaller.     

Large sample Bayesian inference on the parameters of the proportional hazard models

This paper considers large sample Bayesian analysis of the proportional hazards model when interest is in inference on the parameters and estimation of the log relative risk for specified covariate vectors rather than on prediction of the survival function. We use a normal prior distribution for the parameters and make inferences based on the derived posterior distribution. The suggested approach is much simpler than alternative Bayesian analyses previously suggested for the proportional hazards models. Using simulated data we compare estimates obtained from the Bayesian analysis with those obtained from the full proportional hazards model and the reduced model after backwards elimination. We show that under a wider range of assumptions, the Bayesian analysis provides reduced estimation errors and improved rejection of noise variables. Finally, we illustrate the methodology using data from a large study of prognostic markers in breast cancer.     

Issues in the design and interpretation of studies to evaluate the impact of community-based interventions

Increasingly, epidemiologists are faced with the need to evaluate the impact of an intervention that is delivered at the level of a community or cluster of individuals, rather than at the individual level. This has profound implications for the design and interpretation of a study to evaluate its impact. We start by discussing the issues arising in the extension of the randomized double-blind controlled trial methodology to the evaluation of interventions delivered to clusters of individuals, or to whole communities, where the unit of randomization is a cluster of individuals rather than an individual. We then consider alternative approaches to design, discuss their relative strengths and weaknesses and present a framework of design options. Finally we propose a pragmatic approach to evaluation design in this setting. We believe that the answer lies in the judicious selection of different design elements, combined in such a way that when the evidence from each is presented together, a clear picture of the impact of the intervention emerges. We illustrate this using an example from the recent literature.     

Role of the septate junction in the regulation of paracellular transepithelial flow

A comparison of the distribution of septate junctions in invertebrate epithelia and tight junctions in vertebrate systems suggests that these structures may be functionally analogous. This proposition is supported by the internal design of each junction which constitutes a serial arrangement of structures crossing the intercellular space between cells to effectively provide resistance to the paracellular flow of water and small molecules. We have tested the validity of such an analogy by examining whether the osmotic sensitivity of the septate junctions of planarian epidermis follow the rather striking pattern observed for the junctions of very tight vertebrate epithelia (e.g. toad urinary bladder). It has been found that the septate junctions in this system respond in similar fashion to their vertebrate counterparts, blistering with accumulated fluid when the medium outside the epidermis is made hypertonic with small, water-soluble molecules. We conclude that the two types of junction probably are functionally analogous and that, in each case, this rectified structural response to transepithelial osmotic gradients may be indicative of the role of such structures in the transport function of epithelia.     

Bayesian Network Enhanced with Structural Reliability Methods: Application

The enhanced Bayesian network (eBN) methodology described in the companion paper facilitates the assessment of reliability and risk of engineering systems when information about the system evolves in time. We present the application of the eBN: (1) to the assessment of the life-cycle reliability of a structural system; (2) to the optimization of a decision on performing measurements in that structural system; and (3) to the risk assessment of an infrastructure system subject to natural hazards and deterioration of constituent structures. In all applications, observations of system performances or the hazards are made at various points in time and the eBN efficiently includes these observations in the analysis to provide an updated probabilistic model of the system at all times.     

Information Feedback Analysis in Deep Excavations

Deep excavation often causes displacement of adjacent structures. Hence, necessary construction measures must be taken in order to minimize such disturbances. Appropriate construction measures depend on effective and reliable estimation of the induced ground movement during an excavation. This paper presents a systematic procedure, referred to as “information feedback analysis,” which is used to predict excavation-induced deformation by collecting field information, such as displacements. With the use of optimization algorithms, the analyses result in a “best set” of soil parameters. These back-calculated soil parameters are then used to predict the deformation in the subsequent stages, one stage at a time, until the end of the excavation, which result in additional updated information continuously entered into the system, and hence, the prediction becomes progressively more and more accurate. This study has shown that the proposed approach exhibits at least two advantages over the conventional analysis. First, the use of field instrumentation to estimate geotechnical parameters allows the engineer to account for the global response of a soil-structure system. Second, since the information is collected throughout the length of construction, any departure from the original design should be reflected by the updated information, while the conventional analyses are conducted in the design stage only and always assume that construction proceeds as planned.     

Simplicity, Scale, and Surprise: Evaluating Structural Form

Aesthetic and ethical issues of building design are presented here to encourage meaningful discussion among today’s architectural engineering students and practitioners. The evaluative aesthetic ideas of scale, simplicity, and surprise are applied to two important structures designed by Fazlur R. Khan. Khan’s profound understanding of load flow in his buildings influenced his aesthetic ideas. Furthermore, his aesthetic ideas were intimately intertwined with his ethical ideas about structural logic and the role of structure in architecture. We explore these ideas and present new insights as well. Our goal is to encourage a public discourse within our profession on the topic of evaluating structural form.     

Prevention and Mitigation Strategies to Address Recent Brittle Fractures in Steel Bridges

Brittle fracture results in unplanned loss of service, very costly repairs, concern regarding the future safety of the structure, and potential loss of life. These types of failures are most critical when there is no evidence of fatigue cracking leading up to the fracture and the fracture origin is concealed from view. Hence, the failure occurs without warning and the details are, essentially, noninspectable. In these cases, it appears desirable to take a proactive approach and introduce preventative retrofits to reduce the potential for future crack development. These efforts will help ensure that the likelihood of unexpected fractures is minimized. This paper examines the behavior of two bridge structures in which brittle fractures have developed in recent times, discusses the causes of the failures, and offers suggested design strategies for prevention and retrofit mitigation techniques. In situations where considerable uncertainty exists in the prediction of accumulated damage or in the ability to reliably inspect critical details, preemptive retrofit strategies appear to be highly desirable.     

Assessing gamma frailty models for clustered failure time data

Proportional hazards frailty models use a random effect, so called frailty, to construct association for clustered failure time data. It is customary to assume that the random frailty follows a gamma distribution. In this paper, we propose a graphical method for assessing adequacy of the proportional hazards frailty models. In particular, we focus on the assessment of the gamma distribution assumption for the frailties. We calculate the average of the posterior expected frailties at several followup time points and compare it at these time points to 1, the known mean frailty. Large discrepancies indicate lack of fit. To aid in assessing the goodness of fit, we derive and estimate the standard error of the mean of the posterior expected frailties at each time point examined. We give an example to illustrate the proposed methodology and perform sensitivity analysis by simulations.     

Time-Delayed Positive Velocity Feedback Control Design for Active Control of Structures

In this paper we present and propose a design methodology that uses intentional time delays for the active control of structures. We use here positive velocity-feedback, time-delayed control and show that its performance is, in general, superior to the previously developed methodology of using time delayed, negative velocity-feedback control. A detailed study carried out in this paper of the nonsystem poles and their interaction with the system poles reveals the reasons for this. Analytical results related to performance and stability of the new method are presented. We apply the time delayed positive velocity feedback active control methodology to a multidegree-of-freedom system subjected to the S00E component of ground acceleration recorded during the El Centro 1940 earthquake. The excellent behavior in terms of stability, performance, and control efficiency that is demonstrated by our time-delayed control design as well as its facile implementation makes it attractive for earthquake hazard mitigation in a practical sense.