Browsing by Subject "Reliability analysis"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Adaptive Reliability Analysis of Reinforced Concrete Bridges Using Nondestructive Testing(2011-08-08) Huang, QindanThere has been increasing interest in evaluating the performance of existing reinforced concrete (RC) bridges just after natural disasters or man-made events especially when the defects are invisible, or in quantifying the improvement after rehabilitations. In order to obtain an accurate assessment of the reliability of a RC bridge, it is critical to incorporate information about its current structural properties, which reflects the possible aging and deterioration. This dissertation proposes to develop an adaptive reliability analysis of RC bridges incorporating the damage detection information obtained from nondestructive testing (NDT). In this study, seismic fragility is used to describe the reliability of a structure withstanding future seismic demand. It is defined as the conditional probability that a seismic demand quantity attains or exceeds a specified capacity level for given values of earthquake intensity. The dissertation first develops a probabilistic capacity model for RC columns and the capacity model can be used when the flexural stiffness decays nonuniformly over a column height. Then, a general methodology to construct probabilistic seismic demand models for RC highway bridges with one single-column bent is presented. Next, a combination of global and local NDT methods is proposed to identify in-place structural properties. The global NDT uses the dynamic responses of a structure to assess its global/equivalent structural properties and detect potential damage locations. The local NDT uses local measurements to identify the local characteristics of the structure. Measurement and modeling errors are considered in the application of the NDT methods and the analysis of the NDT data. Then, the information obtained from NDT is used in the probabilistic capacity and demand models to estimate the seismic fragility of the bridge. As an illustration, the proposed probabilistic framework is applied to a reinforced concrete bridge with a one-column bent. The result of the illustration shows that the proposed framework can successfully provide the up-to-date structural properties and accurate fragility estimates.Item Inverse source problems for focusing wave energy to targeted subsurface formations: theory and numerical experiments(2016-08) Karve, Pranav Madhav; Kallivokas, Loukas F.; Manuel, Lance; Ghattas, Omar; Fomel, Sergey; Lake, Larry; Huh, Chun; Stokoe II, KennethEconomically competitive and reliable methods for the removal of oil or contaminant particles from the pores of geological formations play a crucial role in petroleum engineering, hydro-geology, and environmental engineering. Post-earthquake observations at depleted oil fields as well as limited field experiments suggest that stress wave stimulation of a formation may lead to the release of particles trapped in its interstices. The stimulation can be applied using wave sources placed on or below the ground surface, and, typically, the effectiveness of the stimulation is proportional to the magnitude of the wave motion generated in the geological formation of interest. When wave sources are used to initiate the wave motion, equipment limitations and various sources of attenuation impose restrictions on the magnitude of the wave motion induced in the target formation. Thus, the engineering design of the wave energy delivery systems that are able to produce the wave motion of a required magnitude in the target zone is key to a successful mobilization of trapped interstitial particles. In this work, we discuss an inverse source approach that yields the optimal source time signals and source locations and could be used to design wave energy delivery systems. We cast the underlying forward wave propagation problem in two or three spatial dimensions. We model the target formation as an elastic or poroelastic inclusion embedded within heterogeneous, elastic, semi-infinite hosts. To simulate the semi-infiniteness of the elastic host, we augment the (finite) computational domain with a buffer of perfectly-matched-layers (PMLs). We define a metric of the wave motion generated in the target inclusion to quantify the amount of the delivered wave energy. The inverse source algorithm is based on a systematic framework of constrained optimization, where minimization of a suitably defined objective functional is tantamount to the maximization of the motion metric of the target formation. We demonstrate, via numerical experiments, that the algorithm is capable of converging to the spatial and temporal characteristics of surface loads that maximize energy delivery to the target formation. The numerical-simulation-based methodology is based on the assumption of perfect knowledge of the material properties and of the overall geometry of the geostructure of interest. In practice, however, precise knowledge of the properties of the geological formations is elusive, and quantification of the reliability of a deterministic approach is crucial for evaluating the technical and economical feasibility of the design. To this end, we also discuss a methodology that could be used to quantify the uncertainty in the wave energy delivery. Specifically, we treat the material properties of the layers as random variables, and perform a first-order uncertainty analysis of the elastodynamic system to compute the probabilities of failure to achieve threshold values of the motion metric. We illustrate the uncertainty quantification procedure for the case of two-dimensional, layered, isotropic, elastic host containing an elastic target inclusion. The inverse source and the uncertainty quantification methodologies, in conjunction, can be used for designing the characteristics of the wave sources used to deliver the wave energy to a targeted subsurface formation.Item Reliability methods in dynamic system analysis(2012-12) Munoz, Brad Ernest; Longoria, Raul G.; Fahrenthold, Eric PStandard techniques used to analyze a system's response with uncertain system parameters or inputs, are generally Importance sampling methods. Sampling methods require a large number of simulation runs before the system output statistics can be analyzed. As model fidelity increases, sampling techniques become computationally infeasible, and Reliability methods have gained popularity as an analysis method that requires significantly fewer simulation runs. Reliability analysis is an analytic technique which finds a particular point in the design space that can accurately be related to the probability of system failure. However, application to dynamic systems have remained limited. In the following thesis a First Order Reliability Method (FORM) is used to determine the failure probability of a dynamic system due to system/input uncertainties. A pendulum cart system is used as a case study to demonstrate the FORM on a dynamic system. Three failure modes are discussed which correspond to the maximum pendulum angle, the maximum system velocity, and a combined requirement that neither the maximum pendulum angle or system velocity are exceeded. An explicit formulation is generated from the implicit formulation using a Response Surface Methodology, and the FORM is performed using the explicit estimate. Although the analysis converges with minimal simulation computations, attempts to verify FORM results illuminate current limitations of the methodology. The results of this initial study conclude that, currently, sampling techniques are necessary to verify the FORM results, which restricts the potential applications of the FORM methodology. Suggested future work focuses on result verification without the use of Importance sampling which would allow Reliability methods to have widespread applicability.