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Strengthening of RC columns through lateral confinement using fiber-reinforced polymer (FRP) jackets is now a widely accepted technique. While extensive research has been conducted on the behavior of such strengthened columns, only a very limited amount of work has examined the slenderness effect in these columns. To correct this deficiency, this paper presents a systematic study on the subject and proposes the first ever design method for slender FRP-confined circular RC columns. A simple theoretical column model for such columns is first described in the paper. Numerical results obtained from this theoretical model are then presented to examine the behavior of these columns to identify the key parameters of influence. A design method based on numerical results from the column model and following the nominal curvature approach is next formulated. The accuracy and safety of the proposed design method is demonstrated through comparison with existing experimental results. [ABSTRACT FROM AUTHOR]

The strength of thin-walled stainless steel columns has been investigated extensively over the last few years. In European standards, the concept of section classification for determining the cross section capacity is used. In this system, for Class 4 cross sections, the effective width method (EWM) must be used to account for the effect of local buckling. Because of the complexity and limitations of this method, other methods have been developed, such as the direct strength method (DSM) for cold-formed thin-walled profiles and the continuous strength method (CSM), initially established for members made of nonlinear metallic materials. In the CSM, to take advantage of strain hardening, a deformation-based design approach using a continuous relationship between the cross-sectional slenderness and the cross-sectional deformation capacity is used. To a large extent, the CSM yields accurate predictions, especially in the low slenderness range where the current DSM design procedures for members submitted to pure compression tend to produce conservative predictions for materials with pronounced strain hardening such as stainless steel alloys. The present paper presents an extension of the traditional DSM, which provides accurate design strength predictions in the low slenderness range for stainless steel thin-walled section columns failing by distortional, local, and overall buckling. It contains practical information concerning the reference experimental data and draws conclusions about the justification of the proposed analytical formula. The paper is divided into three main parts: the description of the database, the establishment of the design model, and a reliability analysis of the method. [ABSTRACT FROM AUTHOR]

Because of the difficulty of specifying optimal design parameters of rectangular sedimentation tanks using a forward numerical model, an inverse calculation model based on an optimization algorithm and a forward model were developed in this paper. Using this model, a numerical simulation of the sedimentation tank involving determination of the velocity field and the concentration distribution of the particles by the forward model was conducted. The eddy viscosity was obtained with the aid of turbulence model equations. The inverse model was applied to the optimal design of the horizontal baffle location in a given sedimentation tank. As a one-dimensional nonlinear optimization method, Brent's method was used. Moreover, the effect of the horizontal baffle location on flow and solids removal ratio was also discussed. Compared with the traditional forward model for specifying optimal design parameters for rectangular sedimentation tanks, the inverse calculation model can search directly for the optimum design parameters and can obtain good results. [ABSTRACT FROM AUTHOR]

The current National Design Specification (NDS) for Wood Construction design methods for dowel-type connectors are based on four-yield modes for connections in double shear. These yield modes were formulated for use with steel dowels as fasteners. Hence design with nonferrous fasteners, such as wood pegs, common in timber frame joinery, is not addressed. Wood pegs, while large in diameter, are considerably more flexible than steel dowels of the same size. A fifth failure mode is proposed for use with wood pegs. This new failure mode, called Mode V yielding, which is an effective cross-grain dowel failure, has been observed in physical testing as well as numerical modeling. The objective of this paper is to establish a design procedure for the Mode V yielding of pegs. The procedure is calibrated to the level of performance (reliability) expected from the other yield modes. A regression equation to relate the effective cross-grain yield capacity of pegs to specific gravity is also developed for use with the Mode V design equation. A reliability analysis indicates that the proposed Mode V design equation can be used in conjunction with existing NDS yield equations for design of wood doweled connections. [ABSTRACT FROM AUTHOR]

This paper presents new solutions in the area of general transition curves. General transition curves describe a curvilinear transition between two rectilinear directions using only one equation. The curves ensure continuous change of curvature all over the curvilinear transition. Along such curves, the curvature rises from zero at the start point to a certain maximum value, and then drops to zero again at the end point. The present paper introduces two new families of general transition curves: with smooth and nonsmooth curvature diagrams. This means that the general transition curves could be considered as an alternative to the geometric systems formed by classical geometric elements (first transition curve - circular arc - second transition curve; first transition curve - second transition curve). The use of general transition curves is advantageous from the viewpoint of vehicle motion dynamics. It also extends the possibilities of modifying the arc geometry to obtain the assumed radius of curvature. [ABSTRACT FROM AUTHOR]

This paper aims to establish design criteria that simultaneously meet (1) the stochastic nature of the streamflow regime in Portuguese rivers and (2) the relationship between such a regime and the mean annual flow depth. The data set consists of 54 streamflow samples from unregulated Portuguese rivers. A large number of synthetic streamflow series were generated by using a probabilistic model at the annual level and a disaggregation model, namely the method of fragments, at the monthly level. Based on an operation with fixed yield and time-based reliability, behavioral analysis was applied to the synthetic series to estimate the storage capacities of hypothetical reservoirs. The Gumbel distribution was fitted to the previous estimates to obtain design storage capacities with specified values of reliability. After showing that the former design capacities were significantly correlated with the mean annual flow depth of the sample series, curves that expressed that relationship were defined. The results consistently showed that, for a given operation condition, as the mean annual flow depth increases, the required specific storage decreases. [ABSTRACT FROM AUTHOR]

The prediction of the performance or service life of a building system and their components is a very complex task. Although many papers related to material and component durability have been published over the past two decades, they had a negligible impact on the development of an effective approach for durability design. ISO presents a valuable methodology based on the factor method in the area of service life estimation but it requires considerable local knowledge about degradation of components and materials. The factor method on the other hand is fairly simple but identifies the main parameters influencing service life. The result, however, is only a single figure for service life and does not take into account the variability of the processes involved. A lot of work is being done in the area of service life prediction, but there is very little that can be readily used by building asset managers. Hence, there is a great need to develop a simple model which can be easily calibrated and used. The model proposed here can be easily implemented by practitioners and would be of benefit to infrastructure managers of city councils. [ABSTRACT FROM AUTHOR]

Systematic transient analysis in water supply systems is intended to determine the reliability of water supply and the integrity of hydraulic devices when hydraulic transients (i.e., water hammers) occur. In the analysis, parameters such as wavespeed, pipe diameter, friction, and others, usually considered as known inputs in traditional water hammer models, are actually subject to uncertainties due to natural or human behaviors. The paper considers these uncertainties and investigates their effects on the reliability of water transportation systems and water supply networks under transient conditions with or without protection devices. In addition, the optimization of transient protection devices is also evaluated based on the probabilistic analysis. The results show that the probabilistic analysis method could inspect the influence of the different input uncertainties on the system responses under transient conditions and provide detailed information on the design for water supply systems and protection devices. A one-dimensional water hammer model of pipe fluid systems and Monte Carlo simulation method are used in this investigation. [ABSTRACT FROM AUTHOR]

The importance of integrating construction knowledge into the design process has long been recognized by the construction industry. This paper studies early contractor involvement in design and its impact on construction schedule performance through a combined empirical case study and theoretical simulation analysis. Pipe and steel fabricators’ inputs at different design stages of industrial construction projects are identified. The case study shows that these inputs lead to improved drawing quality, material supply, information flow, and consequently improved construction schedule performance. This impact on construction schedule is illustrated using actual project data and simulation techniques. Simulation models were developed to demonstrate intuitively the impact at the construction operation level and they allow people to gain management insights through simulation experiments. Better understanding of the early contractor involvement process and its benefit can improve buy-in and help industry practitioners to reach the full potential of this concept. [ABSTRACT FROM AUTHOR]

Emergency rooms are critical infrastructures that provide acute care and rapid treatment of sudden illnesses and trauma. These life saving services must remain in continuous operation. An internal chemical attack on an emergency room would interrupt these essential services and severely impact the capabilities of the health care professionals and staff. In this paper, a combination of multizone simulation and statistical modeling are used as tools to assess emergency room designs for protection against an internal chemical threat. Design options include: the use of dilution ventilation, additional air handling equipment, gas phase filtration, building segmentation, and a sensor system to improve response time. Protection levels are placed into discrete categories and an ordered probability model (with random effects) is estimated. This model identifies factors, such as the design option, chemical type, elapsed time after chemical release, and the air handling unit’s operational and maintenance costs that significantly influence protection levels. Marginal effects are also computed to measure the impact of these factors on the protection-category probabilities. The results of this study can assist owners, designers, and decision makers by providing a quantitative methodology to assess building designs for protection against chemical threats. [ABSTRACT FROM AUTHOR]

Capacities of wood connections with laterally loaded dowel fasteners by plastic analysis can be predicted using the European yield models (EYM) equation. The underlying concept is that failure occurs due to crushing of wood beneath fasteners and / or formation of plastic hinges in fasteners with a rigid-plastic representation of the materials involved. EYM prediction is now “the” way within design codes to calculate the maximum attainable capacity per fastener. Subsequent adjustments discount those predictions through factors which account for unequal sharing of force between fasteners and premature connection failure by fracturing. In North America the EYM is the basis for lateral load capacities of connections made with bolts, drift-pins, screws, nails, and timber rivets. This paper addresses the capability of the EYM for predicting load carrying capacities of solid wood (sawn softwood lumber) and laminated strand lumber (LSL) connections employing tight-fitting steel tube fasteners with external diameters up to 12.7 mm. EYM prediction is compared with experimental test results for arrangements with one or four fasteners loaded in double shear. Accuracy of predictions depends on factors such as connection geometry and the type of wood member involved. Prediction is always accurate if a connection has only one fastener, or if joined members are made from LSL. If members are made from sawn softwood lumber premature brittle splitting type failure modes occur for multiple fastener situations, with impairment of capacity inversely proportional to the fastener outside diameter. Suggestions are made here regarding the nature of codified design rules for steel tube fastener connections, with the intent that such provisions be enacted within North America. [ABSTRACT FROM AUTHOR]

Conventional computation methods generally limit practicing engineers from using complex formulations or considering uncertainties in general. A method is needed that can be implemented regardless of the uncertainty or linearity of the design parameters and their constraints. Methods such as qualitative reasoning provide an effective and sound technique for solving complex and uncertain scenarios. Uncertainties in engineering designs can be formulated as variables in the application domain and processed by numerical constraint reasoning. This paper describes the theories and algorithms behind a software platform built upon numerical constraint reasoning for engineering applications. The capability of representing design parameters and outcomes in a 2D solution space provides a practical way for engineers to leverage their existing knowledge and experience. The software expresses the results of the analysis in variable ranges and diagrams showing a 2D design space. Qualitative reasoning can assist in the difficult process of making appropriate engineering assumptions and judgments when carrying out complicated analysis procedures. In addition, interval constraint analysis can be used to derive controlling parameters and design space, therefore giving engineers a good overall understanding of a problem when practical experience is not available. [ABSTRACT FROM AUTHOR]

Based on the basic formulation developed in a companion paper, the writers now present the application of an artificial neural network approach to designing streamlined network models to simulate and identify the nonlinear dynamic response of single-degree-of-freedom oscillators using the restoring force-state mapping interpretation. The neural networks which use sigmoidal activation functions are shown to be highly robust in modeling a wide variety of commonly observed nonlinear structural dynamic response behaviors. By streamlining the networks, individual network model parameters take on physically or geometrically interpretable meaning, and hence, the network initialization can be achieved through an engineered approach rather than through less physically meaningful numerical initialization schemes. Although not proven in general, examples show that by starting with a more meaningful initial design, identification convergence is improved, and the final identified model parameters are seen to have a more physical meaning. A set of model architecture prototypes is developed to capture commonly observed nonlinear response behaviors. [ABSTRACT FROM AUTHOR]

The integration of modeling and simulation tools with robust and efficient methods of optimal design offers a rational approach to explore new concepts and designs. However, a widespread adaptation of these tools in the industry design environment will require that they incorporate a systematic analysis of uncertainty in all aspects of the design process. A lack of confidence in designs generated in a simulation-based approach is the result of uncertainties in the predictive capabilities of physics-based models used in the simulations, and poor representation of uncertainties and their propagation in a coupled systems engineering design problem. A data- and knowledge-lean environment, typical of a design process involving novel concepts, further exacerbates the situation; design engineers often make gross assumptions about distributional information of random variables and parameters, thereby adding to the uncertainty associated with the design results. The paper focuses on numerical and analytical tools by which to model uncertainty and risk in a simulation-based design environment, including cases where the uncertainty does not conform to standard probabilistic distributions. A specific focus of the modeling effort is an approach to establish confidence intervals for response predictions available from analytical and numerical models, as well as surrogate approximations used in the design process. Innovative adaptations of formal optimization methods in a nondeterministic design setting are discussed, including design problem formulations that examine the nondeterministic design problem in a multicriteria optimization framework. Simple design problems are used to illustrate the concepts and to underscore the deficiencies in a purely deterministic approach to the design problem. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to simplify the original one-dimensional mathematical model that is used to simulate the performance of nonuniform particle sizes in Class-I settling tanks. This paper shows that the modified model is both efficient and economical. The model is capable of providing such information as removal efficiency, particle size distributions in sludge and effluent suspension, and the thickness of bottom sludge. If the desired removal efficiency is provided, a simple equation from the simplified model can be used to calculate the length of the tank. Moreover, the model is quite straightforward and does not require a computer program to obtain results. It deals with only one parameter, the sediment coefficient α, which shows great advantages. Here α is taken as 1.2 for the Class-I settling tanks, however calibration is still recommended. Effluent information, which is important for further treatment units, can be calculated directly from the simplified model. The simplified model is qualitatively reasonable in comparison with other models. [ABSTRACT FROM AUTHOR]

The design of repository seals for deeply buried high-level radioactive wastes incorporates densely compacted clayey barriers around metallic waste canisters. In this paper, a mathematical model that is based on conservation of thermal energy and mass is developed to describe the locations of moisture and temperature fronts within a barrier, around a cylindrical waste canister of 1 m radius, containing radionuclides with half-lives that range from 100 to 10,000 years. The solution developed is axisymmetric: the moisture fraction w and temperature T vary only with time t, and radial distance r from the axis of the cylindrical waste canister. The model produces parabolic partial differential equations. The spatial domain is discretized such that ordinary differential equations that result are solved. Computations using a uniform mesh of 0.1 m and a cooling coefficient of 6.7×10-2 with assumed but typical data on material properties, indicate that coupling of transport processes would be negligible in the case of radionuclides with long half-lives. Also, a quasisteady vaporization front can form and propagate outward over the course of several decades after waste emplacement. The evolution of the front is somewhat insensitive to the half-life used and the permeability of the clayey barrier material. [ABSTRACT FROM AUTHOR]

The water spray patterns discharged from an atrium sprinkler are studied in this paper. Equations for calculating the size distribution and the trajectory of the droplets in the water spray are reviewed. The trajectories of water droplets are studied by solving the equation of motion, with the velocity components of droplets expressed in analytical form. A new droplet size distribution function for the water spray derived earlier from information theory was used. The shape of the sprinkler water sprays was calculated. Results are useful in studying the interaction between sprinkler and free-induced airflow. Furthermore, dividing the spray radius into different parts, the volume of water received at the floor level was calculated to determine an important parameter: the water distribution function. [ABSTRACT FROM AUTHOR]

Thin steel plate shear walls (SPSWs) are an effective lateral force resisting system and are increasingly being used in structures. Engineers require the ability to predict both elastic and inelastic structural responses of SPSWs accurately by a simplified model that is convenient to use. Based on the strip model, this paper proposes a new simplified model for SPSWs, called the three-strip model, in which the infill plates of SPSWs are replaced by three tension-only strips. Comparisons of experimentally obtained pushover responses of SPSWs and that predicted by the proposed model are given and reasonable agreement is observed. A parametric study examines the effect of aspect ratio and column flexibility on the accuracy of the predicted inelastic behavior from the three-strip model. In addition, the capacity of the proposed model in predicting frame forces is verified based on test and strip model results. It was found that the three-strip model can provide generally accurate results for SPSWs and meanwhile reduce modeling workload and computational expense. [ABSTRACT FROM AUTHOR]

One of the main obstacles to a wider use of self-compacting concrete (SCC) is its sensitivity to small variations of the constituent materials, mix proportions, and other external factors. The main objective of this paper is to illustrate how to evaluate and compare the robustness of SCC mixtures optimized according to various economic criteria while maintaining the water/cement ratio and fresh state target properties. The optimization is derived from numerical models, and a central composite design is developed to mathematically model the influence of mixture parameters and their coupled effects on deformability, passing and filling abilities, and compressive strength. The strategies to increase the robustness of SCC mixtures and the existing methodologies to assess it are presented and discussed. By applying these methodologies, it is shown that robustness can be enhanced by changing only the proportions of materials in mixtures. Minimizing the superplasticizer dosage and, consequently, increasing the paste volume (by means of a higher limestone filler content) to keep adequate fresh properties is found to be the most effective optimization criteria to enhance the robustness of SCC mixtures. [ABSTRACT FROM AUTHOR]

Different approaches related with urban flood problems treatment are evolving and there is a large set of possible engineering measures that can be applied. Lately, the traditional approach, focusing on improving channel conveyance, is being complemented by distributed structural measures and nonstructural measures, considering the basin under a systemic point of view and aiming to recover natural flow patterns prior to urbanization. In this context, it becomes necessary to evaluate the potential use of different combinations of the possible interventions, in such a way that the efficacy of these sets in terms of flood mitigation can be optimized. This kind of analysis is of crucial importance and involves technical and economic aspects. Combined effects of the chosen measures may produce a result that is not equivalent to what would be expected from the summation of its individual effects. The systemic behavior of an urban watershed, especially when the drainage system works jointly with flooded urban landscape elements, makes it possible that some design solutions become to act in a noneffective way. Sometimes, different interventions just superimpose concurrent results. On the other hand, it is possible to generate better results, with extra benefits, when proposing adequate combinations capable to join efforts. Mathematical models may act as valuable tools that are able to simulate floods in complex urban watersheds and provide an integrated assessment capability. In this context, mathematical models can evaluate the efficacy of flood control measures sets. In this paper, a mathematical model, based on the flow cell concept, was applied to study the use of a wide range of different flood control measures in the Joana River watershed, located at the northern region of Rio de Janeiro City, Brazil. This model is composed by a hydrodynamic core that works together with a distributed hydrologic model. According to the achieved results, it is possible to notice that distributed detention reservoirs—located at upstream reaches, parks and public squares, and also at urban sites—are very important flood control alternatives. It is also noticed that reforestation of slope areas, although some of which are nowadays occupied by lower income communities, is a desirable alternative. Finally, it must be stressed that even traditional flood control measures, presently avoided in many design situations as they may transfer downstream inundation problems, can be important in an integrated flood control project, if adequately combined with other measures. [ABSTRACT FROM AUTHOR]

This paper presents three steady-state mathematical models for the design of H2/CO2 fed gas-lift reactors aimed at biological sulfate reduction to remove sulfate from wastewater. Models 1A and 1B are based on heterotrophic sulfate reducing bacteria (HSRB), while Model 2 is based on autotrophic sulfate reducing bacteria (ASRB) as the dominant group of sulfate reducers in the gas-lift reactor. Once the influent wastewater characteristics are known and the desired sulfate removal efficiency is fixed, all models give explicit mathematical relationships to determine the bioreactor volume and the effluent concentrations of substrates and products. The derived explicit relationships make application of the models very easy, fast, and no iterative procedures are required. Model simulations show that the size of the H2/CO2 fed gas-lift reactors aimed at biological sulfate removal from wastewater highly depends on the number and type of trophic groups growing in the bioreactor. In particular, if the biological sulfate reduction is performed in a bioreactor where ASRB prevail, the required bioreactor volume is much smaller than that needed with HSRB. This is because ASRB can out-compete methanogenic archaea (MA) for H2 (assuming sulfate concentrations are not limiting), whereas HSRB do not necessarily out-compete MA due to their dependence on homoacetogenic bacteria (HB) for organic carbon. The reactor sizes to reach the same sulfate removal efficiency by HSRB and ASRB are only comparable when methanogenesis is inhibited. Moreover, model results indicate that acetate supply to the reactor influent does not affect the HSRB biomass required in the reactor, but favors the dominance of MA on HB as a consequence of a lower HB requirement for acetate supply. [ABSTRACT FROM AUTHOR]

The preliminary design of iron-based permeable reactive barriers is often accomplished using analytic expressions for one-dimensional groundwater flow and contaminant transport. Typically, one or more of the governing processes is simplified or neglected to facilitate development of a tractable solution. This paper presents a set of improved design equations that include the effects of dispersion, finite domain boundary, sequential decay, and production processes, and increased flow through high conductivity barriers. When applied to realistic example problems, application of the expanded design equations typically results in the specification of a larger permeable reactive barrier thickness than obtained using conventional approaches. [ABSTRACT FROM AUTHOR]

A new design of a reconfigurable multirotor is developed by employing a novel active–passive motor scheme. The scheme is based on quadrotor configuration with four additional motors placed in coaxial setup along a single axis. This unconventional design seeks to improve the general response of the system and increase the payload carrying capacity of the aerial vehicle. This paper presents an extensive mathematical model to establish the stability of the design, along with simulation and various real time tests. Simulation of the mathematical model with a proportional–integral–derivative (PID) controller shows the stability and responsiveness of the system in different configurations. Throttle response is also compared for different configurations. Finally, preliminary experimental test results with a prototype employing the same design are discussed. It is analytically and experimentally a stable system with a general improvement in throttle response. [ABSTRACT FROM AUTHOR]

The purpose of this work is to design a new layout for a quadrotor unmanned aerial vehicle (UAV) for experimental customized control-system validation. Geometrical and structural properties have been computed, and commercial off-the-shelf equipment has been selected. The flight control system, both hardware and software, has been custom developed; the same applies for the mathematical model describing the flight dynamics. Two proportional-derivative (PD) controllers have been designed and experimentally tested. A different control strategy with a state feedback controller has been implemented, assigning a robust eigenstructure and the desired dynamic specifications. An adaptive algorithm, which guarantees a uniformly bounded response for both the inputs and the outputs, has been presented. An L1 adaptive controller has been studied and implemented, including the state predictor and the adaptive and control laws. Tests with the PD controller have shown slowly stable response even in the event of numerical and vibrational noise. In conclusion, the L1 adaptive controller permits one to obtain optimal response characteristics, and the low-pass filter integrated in control law, combined with a Kalman filter, can reduce noise and correlate data between different sensors. [ABSTRACT FROM AUTHOR]

Features a study which presented a general analytical flow solution for computing ground-water levels in channel/ground water systems subject to recharge or evaporation. Problem definition; Testing the validity of the analytical solution scheme; Conclusions.

This work presents a new paradigm for the design of stormwater detention basins. Through simulation and optimization, this work seeks to find the design of a detention basin outlet control structure that reduces the ecological impairment to downstream water bodies. Ecological impairment is measured using the ecodifference, a metric that represents the hydrologic alteration in the stream. The ecodifference is defined as the weighted sum of the eco-flow statistics, nine hydrological flow statistics that have been shown to be particularly relevant to ecological quality. In this simulation-optimization methodology, a genetic algorithm (GA) is combined with a hydrologic simulator of a detention pond. The GA is used to design the openings in the outlet control structure that minimizes the ecodifference. Constraints are used to meet current municipality design regulations. The simulation-optimization methodology is been applied to a case study site, and resulting designs demonstrate that improvements in ecological flows can be achieved via alteration of two to four outlet control openings, while meeting design regulations. The ecodetention ponds designed here primary improve the low flow series. Applying this ecological design approach to alternative volume-reducing best management practices could further improve the ecological flow series. [ABSTRACT FROM AUTHOR]

Robustness is generally defined as an ability of a system to maintain its function under a defined set of disturbances. To introduce robustness to the water distribution systems (WDSs) design, chance constrained, or so-called reliability-based models have been formulated. Under variations in system parameters, such as nodal demands and pipe roughness, system reliability is generally measured as the probability that the stochastic nodal pressures will be higher than an allowable minimum pressure limit. However, chance constraints may not be the best formulation to improve system robustness because it focuses on the likelihood of failure under a specified set of conditions rather than developing a solution that consistently provides adequate service. In addition, the reliability-based design requires defining the demand condition, its probability distribution and its statistics, which are not straight forward in practice. To address these difficulties, a robustness index that limits the range of the system function variability is posed here and incorporated in a two objective optimization problem. Resulting designs are compared with those from the reliability constraint formulation. The authors demonstrate that the robustness-based design improves resilience relative to the reliability-based design. [ABSTRACT FROM AUTHOR]

Two-lane rural highways attract trips between traffic generators such as residential villages or small commercial areas and are generally uninterrupted flow facilities that provide a high level of mobility with high posted speeds limits. When passing through developed areas, the posted speed limit may be lowered to encourage reduced vehicle operating speeds. No published guidelines currently exist for the design of transition zones that connect high- to low-speed operating environments on two-lane rural highways. The objective of this research was to collect operating speed and roadway characteristic data along two-lane rural highway transition zones in Pennsylvania to explore the roadway, roadside, and traffic control factors that are associated with driver speed differentials. Single- and multilevel models were estimated and compared. The posted speed limit reduction as well as a change in the paved shoulder width, total number of driveways, various advance warning signs, the transition zone length, and the presence of horizontal curves were shown to increase the expected speed reduction in transition zones in the models. Additionally, drivers entering transition zones at higher speeds were found to have greater speed reductions than drivers entering the transition zone at lower speeds. [ABSTRACT FROM AUTHOR]

Actual projections provided by climate models suggest that the probability of occurrence of intense rainfall will increase in a future climate due to increasing concentrations of greenhouse gases. Considering that the design of urban drainage systems is based on statistical analysis of past events, an increase in the intensity and frequency of extreme rainfall events will most probably result in more frequent flooding. The design criteria must therefore be revised to take into consideration possible changes induced by climate change. A procedure is proposed to revise the design criteria of urban drainage infrastructures. This procedure integrates information about (1) climate projections for extreme rainfall over the region under consideration; (2) expected level of performance (or acceptable level of risk); and (3) expected lifetime of the infrastructure/system. The resulting design criterion ensures that the service level remains above the selected “acceptable” level over a predefined portion of the infrastructure lifetime. It is argued that the definition of new design criteria should be part of a global adaptation strategy combining various measures to maintain an acceptable level of service in a long-term perspective. Defining this level of service is however a challenge in a context where uncertainties on projected changes in intense rainfall are still important. [ABSTRACT FROM AUTHOR]

Despite the importance of overland time of concentration on the design discharge, engineers are often bewildered by the array of formulas available in the literature without knowing the accuracy of each formula. This assessment covers nine formulas published between 1946 and 1993, which are intended for overland flow only that is subjected to uniform rain. The assessment compares the estimates from the formulas with experimental values that are derived under the same conditions for two surfaces: concrete and grass. The assessment shows that formulas that do not account for the rainfall intensity are only valid for a limited range of rainfall intensities. The formulas that account for the rainfall intensity generally show better agreement with the experimental data. Finally, the assessment gives two rankings of the formulas for the two surfaces in accordance to their accuracy as compared to the experimental data. The formula that has the best accuracy for both surfaces is the Chen and Wong formula. [ABSTRACT FROM AUTHOR]

Groundwater remediation designs rely on simulation models that are subjected to various sources of uncertainty. This study introduces a hierarchical Bayesian model averaging (HBMA) method to segregate sources of uncertainty in a hierarchical order and conduct comparative evaluation of BMA models for remediation designs. A BMA tree of models is developed to understand the impact of individual sources of uncertainty in the remediation design. The HBMA method is applied to chance-constrained (CC) formulation for an aquifer remediation design that aims to reduce concentration at a selected control point using scavenger wells. Thirty-six (36) flow and transport models for concentration prediction are developed to analyze the impact of three sources of uncertainty on the remediation design. An essential step in HBMA is to calculate posterior model probabilities as model weights. The best simulation model has the highest model weight. The results show that although using the best simulation model requires the least pumping rate for the scavenger well, it underestimates prediction variances of concentration. The scavenger well pumping rate increases as more sources of uncertainty are considered. The HBMA enables the chance-constrained formulation to consider both model parameter and model structure uncertainties for aquifer remediation designs. The contributions of prediction variance from individual sources of uncertainty to the total prediction variance can be evaluated, which provides an understanding of the impact of individual sources of uncertainty and their corresponding propositions on remediation designs. [ABSTRACT FROM AUTHOR]

To develop the high-performance high-reliability of aeroengine, the probabilistic design of high-pressure turbine (HPT) blade-tip radial running clearance (BTRRC) with three objects (disk, blade, and casing) and two disciplines (heat and mechanical loads) was completed based on distributed collaborative response surface method (DCRSM) from a probabilistic perspective considering dynamic loads and nonlinear material properties. The mathematical model of DCRSM was established based on the quadratic response surface function. The basic idea of BTRRC probabilistic design based on DCRSM was introduced. The BTRRC probabilistic analysis results, consisting of the probabilistic distribution characteristics of input-output variables, the failure probability, and reliability of BTRRC under different static blade-tip clearances and the major factors affecting the BTRRC, reveal that the static blade-tip clearance is an optimally acceptable option for BTRRC design. The comparison of methods shows that the DCRSM has high accuracy and high efficiency in the BTRRC probabilistic analysis; meanwhile, the strengths become more obvious with the increasing times of simulations. The present research offers an effective way for HPT BTRRC probabilistic design, as well as provides a promising method for the further probabilistic optimal design of complex mechanical system. [ABSTRACT FROM AUTHOR]