Three-Parameter Model for Debonding of FRP Plate from Concrete Substrate

Concrete beams retrofitted with bonded fiber reinforced plastic (FRP) plates often fail by debonding of the plate from the concrete surface. To predict the failure load in design, a proper debonding model is required. As debonding is a nonlinear process involving material softening, it can be analyzed once the interfacial shear (τ) versus sliding (s) relationship is known. Recent experimental results indicate that the simplest τ-s relationship should involve three parameters: the maximum shear stress for debonding to initiate, the initial residual stress right after debonding occurs, and a parameter governing the reduction of shear stress with sliding. In this paper, a FRP debonding model based on these three parameters is developed. The applicability of the model is verified through comparison with experimental results. Through a systematic parametric study, the effect of various material and geometric properties on the debonding process is investigated. Implications to the design of FRP strengthened members are highlighted.     

Dynamic Response of Closed-Loop System with Uncertain Parameters Using Interval Finite-Element Method

Using the interval finite-element method, the vibration control problem of structures with interval parameters is discussed, which is approximated by a deterministic one. Based on the first-order Taylor expansion, a method to solve the interval dynamic response of the closed-loop system is presented. The expressions of the interval stiffness and interval mass matrix are developed directly with the interval parameters. With matrix perturbation and interval extension theory, the algorithm for estimating the upper and lower bounds of dynamic responses is developed. The results are derived in terms of eigenvalues and left and right eigenvectors of the second-order systems. The present method is applied to a vibration system to illustrate the application. The effect of the different levels of uncertainties of interval parameters on responses is discussed. The comparison of the present method with the classical random perturbation is given, and the numerical results show that the present method is valid when the parameter uncertainties are small compared with the corresponding mean values.     

Parameter Estimation for Flow in Open-Channel Networks

Two mathematical models for parameter estimation in closed-loop, open-channel flow networks are presented. The parameter estimation models seek to determine the parameter values that would reproduce an observed flow profile in the channel network. The governing equations for gradually varied flow in channel networks are the optimization models’ constraints. The projected augmented Lagrangian method is used to solve the optimization models. Performance of these two optimization models is evaluated for a given closed-loop network configuration. Results establish the potential of the developed models for use in real-life flow scenarios.     

Structural Condition Assessment of Sewer Pipelines

The need of immediate supportive measures for sustainability of municipal infrastructures calls for better understanding of the behavior of various infrastructure network systems and their components. This paper presents a study which uses artificial neural networks to investigate the importance and influence of certain characteristics of sewer pipes upon their structural performance, expressed in terms of condition rating. In this study, back propagation and probabilistic neural network (NN) models were developed and validated. The data used in the development of these models were provided by the municipality of Pierrefonds, Quebec. It comprised of parameters related to sewer pipelines, pipe diameter, buried depth/cover, bedding material, pipe material, pipeline length, age, and closed circuit television (CCTV) based structural condition rating. The first six parameters are the independent variables of the models whereas CCTV based condition rating for these pipes is the dependent variable (i.e., the output of the models). The developed NN models were used to rank the parameters, in order of their importance/influence on pipe condition. It was found that, among the studied parameters, material attributes have highest influence on pipe structural condition, respectively, followed by the geometric and physical attribute group. Sensitivity analysis was then performed to simulate the structural condition of a pipe at a range of values of each input parameters. Results of sensitivity analysis describe the nature and degree of the influence of each parameter on pipe structural condition. The developed models are expected to benefit academics and practitioners (municipal engineers, consultants, and contractors) to prioritize inspection and rehabilitation plans for existing sewer mains.     

Optimal Layout of Displacement Measurements for Parameter Identification Process in Geomechanics

This paper focuses on designing the optimal layout of measurements for parameter identification problems in geomechanics, which are usually based on in situ displacements. The existence, uniqueness, and stability of the solution from the parameter identification process are thoroughly discussed. Based on these understandings of the problem, two algorithms are proposed as a means of automatically generating the optimal measurements. The validity of these algorithms is first proved by some academic examples, then these algorithms are applied to the Munich subway tunnel project. Good results are observed there.     

Arsenite Oxidation by Batch Cultures of Thiomonas Arsenivorans Strain b6

Arsenite [As(III)] oxidation by Thiomonas arsenivorans Strain b6 was investigated in batch reactors at pH 6 and 30°C over As(III) concentrations ranging from 10 to 1,000 mg/L in the absence of added organic carbon. Strain b6 completely oxidized As(III) to arsenate [As(V)] during exponential growth phase for lower levels of As(III) concentrations ( ≤ 100?mg/L). At higher levels of 500 and 1,000 mg/L, As(III) oxidation was observed mostly in the exponential phase but continued into the stationary phase of growth. The Haldane substrate inhibition model was used to estimate biokinetic parameters for As(III) oxidation. The best fit parameters of half saturation constant Ks = 33.2±1.87?mg/L, maximum specific substrate utilization rate k = (0.85±0.18)-mg As(III)/mg dry cell weight/h, substrate inhibition coefficient Ki = 602.4±33.6?mg/L, yield coefficient Y = (0.088±0.0048)-mg cell dry weight/mg As(III), and endogenous decay coefficient kd = 0.006±0.002?h?1 were obtained using the Adams-Bashforth-Moulton algorithm and nonlinear regression technique. Sensitivity analysis revealed that Y and Ki are the most sensitive to model predictions, while kd is the least sensitive to model simulation at both low and high concentrations of As(III).     

Design Recommendations for a FRP Bridge Deck Supported on Steel Superstructure

No appropriate provisions from either AASHTO Standard (2002) or AASHTO LRFD (2004) bridge design specifications are available for the design of fiber-reinforced polymer (FRP)-deck-on-steel-superstructure bridges. In this research, a parametric study using the finite-element method (FEM) is conducted to examine two design issues concerning the design of FRP-deck-on-steel-superstructure bridges, namely deck relative deflection and load distribution factor (LDF). Results show that the strip method specified in AASHTO LRFD specification as an approximate method of analysis, can also be applied to FRP decks as a practical method. However, different strip width equations have to be determined by either FEM or experimental methods for different types of FRP decks. In this study, one such equation has been derived for the Strongwell deck. In addition, both FEM results and experimental measurements show that the AASHTO LDF equations for glued laminated timber decks on steel stringers provide good estimations of LDF for FRP-deck-on-steel-superstructure bridges. Finally, it is found that the lever rule can be used as an appropriately conservative design method to predict the LDF of FRP-deck-on-steel-superstructure bridges.     

Capturing Nonlinear Vibratory Roller Compactor Behavior through Lumped Parameter Modeling

Continuous monitoring of soil properties using an instrumented roller compactor requires models that can capture the essential features observed during drum/soil vibration. This paper presents the results of lumped parameter modeling of the drum/soil system together with data from complex nonlinear behavior observed experimentally during operation on sandy soil. Model parameters and response were developed using experimental data collected over a wide range of operating frequencies. Three and four-degree-of-freedom (DOF) models with linear and nonlinear soil elements were investigated. The results showed that a 3DOF model incorporating the soil, drum, and frame of the roller was successful in capturing behavior during coupled drum/soil vibration and during decoupling (i.e., loss of contact between drum and soil). Modeling the drum/soil decoupling accounted for most of the experimentally observed nonlinearity. The addition of nonlinear soil stiffness due to the curved drum effect and due to strain hardening soil behavior accounted for additional nonlinearity observed experimentally. Experimentally observed drum rocking during coupled drum/soil vibration was successfully modeled with a 4DOF drum-frame model. The analysis also revealed that commonly observed heterogeneous soil conditions give rise to a transient response that can have a significant influence on vibration behavior.     

Evaluating the Sensitivity of Attic Radiant Barrier Performance to Climate Parameters

By employing a calibrated and tested computer model, simulations of ceiling heat transfer in typical residential attics located in 12 locations across the United States were obtained to study the sensitivity of attic radiant barrier performance to local climate parameters. For each location, the net ceiling heat flux over the summer cooling season was computed for an attic with and for an attic without an installed radiant barrier. The net reduction of heat flux induced by the radiant barrier was computed and then related to climate variables. Among the local environmental parameters, the local ambient air temperature, local ambient humidity, and latitude had significant effects on the performance of radiant barriers. It was concluded that the installation of radiant barriers would be most beneficial in regions with high outdoor air temperatures and high relative humidity.     

Approximation of Well Function and Identification of Leaky Aquifer Parameters

The existing equation for leaky aquifers is transformed into a nondimensional form using new parameters and a scaled well function for leaky aquifers is proposed. A computationally simple function is developed for accurately approximating the scaled well function for the practical range of the parameters. Utilizing this function (approximation), an optimization method is proposed for identifying the leaky-aquifer parameters from observed drawdowns. The new function has an enhanced utility when a repetitive numerical evaluation of the well function for leaky aquifers is needed, e.g., while estimating the aquifer parameters using optimization or Kalman filter or artificial neural network methods. The application of the proposed method is illustrated using a few sets of published data. The proposed method outperforms the extended Kalman filter method, based on the reported results in the literature.