Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaf 113. / by Bak Kong Low. / M.S.

Uncertainties in engineering design exist due to the random nature of loads and materials, lack of knowledge, and imperfect modelling of design parameters. Conventional design methods based on deterministic procedures do not always yield designs having consistent safety. In recent years considerable research has been conducted in the use of probability theory for modelling uncertainties in engineering designs and several probabilistic design formats have been developed. Probability based design methods provide a unified procedure applicable to all construction materials, all loads, and all types of uncertainties. Code committees are currently working on the development of the new design codes for various construction materials such as steel, concrete, and wood based on probabilistic concepts. The objective of this study is to study a probability based design format for wood members. Reliability analysis of wood structural elements such as beams, columns, and beam-columns is conducted, and the risk level is measured by the reliability or safety index, β. Wood members subjected to dead plus live load and dead plus snow load combinations are considered. After conducting a reliability analysis of current designs, a target reliability index is selected. The reliability index is then used in conjunction with the predetermined load factors and load combinations to determine resistance factors. Finally, a design format is proposed for Load and Resistance Factor Design for wood structures. / M.S.

In the face of increasing awareness among customers and today's competitive market, the warranty of a product has become an added feature in marketing strategy. A reliable product causes less warranty support cost. However, a more reliable product costs more to manufacture. Thus, a suitable trade-off between the cost and the benefit of a development and testing program is essential to optimize the performance measure, e. g., minimize total expected cost. Renewal theoretic models of sequences of failures over the burn-in and warranty periods and their costs are developed. Contrary to the usual asymptotic assumptions, transient behaviors of the renewal processes are considered. The expected costs associated with in-plant and field failures are balanced against the costs of implementing a burn-in program. A multi-component series system with different Weibull distributions for the components are considered. Burn-in is performed at the assembly level and the components are assumed to have different age accelerations under a common stress regimen. Models based on analyses both at the component and the system level are constructed. Two different burn-in policies are considered. These are "fixed duration" bum-in and "failure freell burn-in. A free replacement warranty for the components with policies of both fixed warranty period and renewed warranty period after each failure is considered in the models. The profit functions under different models are optimized with respect to burn-in period, stress parameters and warranty period. The models are extended to include reliability growth over the warranty period. Finally I solution procedures for optimizing the profit functions for all cases are given. / Ph. D.

Two reliability analysis techniques, allocation and apportionment, have the potential to influence a system's design (a distinction is made here between allocation and apportionment). Algorithms that account for the ever increasing design complexities are constructed here for both. As designs of aircraft, railway systems, automobiles and space systems continue to push the envelope in terms of their capabilities, the importance of performance criteria such as reliability and associated life-cycle cost (LCC) consequences become even more important. These interrelated criteria are the foundation for the reliability allocation and apportionment algorithms derived in this thesis. Reliability allocation is the process of assigning reliability targets to lower-level assemblies to ensure the top-level assembly's goal is achieved. Reliability apportionment involves the analysis of an existing design configuration to determine the most cost-effective means of adding redundancy. In the apportionment problem, acquisition cost is the traditional cost-effectiveness measure. The apportionment algorithm defined herein expands the definition of cost-effectiveness to include downstream costs, thereby addressing LCC. A well-behaved, allocation routine is derived to account for any combination of serial, parallel and partially redundant configurations. In addition, a closed-form analytic solution provides the framework for economically adding redundancy to a system's structure in order to achieve a system-level reliability goal. An Apportionment Criterion Ratio (ACR), which contrasts the incremental reliability benefits of adding redundant components with the corresponding incremental LCC, is used. The Rate of Occurrence of Failure (ROCOF) is the reliability metric used in both the allocation and the apportionment routines. The formulation of the LCC model carefully distinguishes between failures and an allied measurement, demands. / Master of Science

The probabilistic stability of a laminated composite plate is investigated. Three different models are considered in this study, namely, the classical laminated plate theory, a first-order shear deformation theory, and a higher-order shear deformation theory. The probabilistic characteristics, such as the probability density and cumulative distribution functions for the resistance to buckling of the plate are obtained by employing the first-order second-moment method of reliability analysis. Uncertainties associated with material mechanical properties and fiber orientations of individual layers are modeled as statistically independent random variables. Numerical results are presented for rectangular simply-supported laminates, showing the effects of thickness ratio, stacking sequence, and number of layers on the probabilistic stability of the plates. / Master of Science

The level of safety associated with the ACI Standard 318-83 design criteria for torsional reinforced concrete members is evaluated. Advanced first-order, second-moment reliability analysis is used to compute the reliability index. Reinforced concrete beams, subjected to both equilibrium and compatibility torsion, are analyzed. The uncertainties associated with the various torsion design parameters are included in the reliability-based formulation. For beams designed to carry equilibrium torsion, reliability indices ranging from 3.10 to 3.65 are obtained. The reliability indices for the compatibility torsion designs, analyzed in this study, vary from 1.88 to 2.09. For a given beam section, the reliability index is found to decrease with an increase in beam reinforcement. When the live load is reduced for members having a load influence area greater than 400 ft 2, the reliability index is found to increase with increase in basic live load to nominal dead load ratio. / M.S.

Environmental stress screening is used to enhance reliability by decreasing the number of failures experienced during customer use. It is suggested that added benefit can be gained by applying multiple stresses rather than a single stress, as is done presently. A further modification is to apply the stress at the assembly level, accelerating different types of components at the same time. Different component E A e acceleration effects must then be considered. The problem these modifications present is how to choose the appropriate stress levels and the time duration of the stress screen. A cost model is developed that trades off the cost of a field failure with the cost of applying a multiple stress, multiple component stress screen. The objective is to minimize this cost function in order to find an economical stress regimen. The problem is solved using the software package GINO. The interesting result is that if a stress is used at all during the stress screen, the maximum amount of stress is the economic choice. Either the cost of stressing is low enough to justify the use of a stress, in which case the maximum amount of stress is used, or the cost is too high and the stress is not used at all. / Master of Science

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A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg 2017 / The study assesses the drilling, loading and trucking stages of the mining cycle of an iron ore mine situated in the Northern Cape province of South Africa for the period of 1 January to 30 June 2011. The purpose of this study is to investigate the effect of increasing reliability and maintainability of mining equipment in an effort to increase throughput of iron ore. The data processing indicated that both availability and utilisation are contributing to the sub-optimal performance of the mine. Data regarding reliability (MTBF), maintainability (MTTR), planned and unplanned maintenance was analysed, and this provided input for the simulation model. The intention of the simulation model is to simulate scenarios of proposed improvement in MTBF and MTTR through increasing planned maintenance activities. A simulation model provides insight regarding where to invest in interventions. It is determined that the drilling equipment is the problem area. / MT2018