A combination of Newton's second law, a transformation using three consecutive Euler angles, and Taylor expansions is used to develop three nonlinear integro-differential equations describing the flexural-flexural-torsional vibration of metallic and composite beams. The twisting curvature is used to define a physical twisting variable which makes the equations of motion unique and independent of the rotation sequence of the Euler angles. A numerical-perturbation approach is used to analyze the response of metallic and composite beams to parametric and external excitations. First, the linear eigenfunctions and natural frequencies are calculated using a combination of the state-space concept and the fundamental-matrix method. Then, the method of multiple scales is used to construct a set of nonlinear autonomous first-order ordinary-differential equations describing the slow-time modulation of the amplitudes and phases of the interacting modes in the presence of one-to-one and/or two-to-one internal resonances. The inversion symmetry, D, symmetry, and 0(2) symmetry of the system are studied using the modulation equations. The solutions of the modulation equations may be fixed points, limit cycles, or chaotic solutions. / Ph. D.

Thin-walled beam structures are adopted as structural members in various fields of modem technology including aeronautical/aerospacial, naval, mechanical and civil ones. With the advent of advanced composite material systems, there is a vital need to reformulate the classical theory of thin-walled beams in a wider framework. This dissertation is intended to incorporate several essential effects which have a considerable importance for the rational design of composite thin-walled beam structures. These effects are the transverse shear deformation, the warping constraint, the secondary warping as well as the hygrothennal and the dynamic ones. The field equations of laminated composite thin-walled beams of either open or closed single and multicell cross-sections are derived through the application of Hamilton's variational principle. The Laplace Transform technique is used to obtain exact solutions. In this dissertation, the aero elastic divergence instability of aircraft wings modelled as thin-walled beams as well as the eigenfrequency problem of cantilevered composite thin-walled beams of closed cross-section are considered in the framework of a reformed theory incorporating non-classical effects. The numerical results reveal the great role played by non-classical effects as well as by the tailoring technique applied to the problems studied in this dissertation. / Ph. D.

An attempt is made to understand the phenomenon of aeroelasticity as applied to the helicopter rotors, specifically laminated composite rotor blades. Realizing the immense complexity of the problem, a beginning has been made by developing a structural model for a rotating composite beam. Present work has three objectives; 1) To carry out an extensive survey of research related to the aeroelastic analysis of rotor blades, 2) To expand an existing finite element model by introducing new degrees of freedom and validate the changes, 3) and, finally using this model to carry out a linear static and dynamic analysis for a rotating composite beam. It was found that the rotation and fiber orientations have a pronounced effect on the static deflections and the natural frequencies of vibration of the laminated beam. / Master of Science

The base tGSt method has been proposed by Carballo, Holzer and Murray [5] as a means of determining the strength of standing seam roof systems under gravity loading. The objective of this thesis is to evaluate the accuracy of the base test method. To do this, eleven sets of tests were performed at Virginia Polytechnic Institute & State University (VPl&SU). Each test set consisted of a single span base test from which a failure load was predicted for the corresponding three span confirming test. Results of two test sets recorded in Reference [5] were also used to evaluate the method. A secondary objective of this thesis is to comment on the effects that system components (purlin orientation, clip type, bracing configuration, panel type, insulation and purlin type) have on the strength of the system. Results from proprietary tests conducted at VPI & SU were used in conjunction with the results from this research to accomplish the secondary objective. / Master of Science

This thesis presents the results of wind tunnel experiments performed for various model wind turbine arrays. The aim is to understand how siting affects power output. To optimize wind farm efficiency the experiments vary the parameters of the model wind turbines and the layout of the wind turbine array. The parameters include the alignment, height, spacing, and the rotational direction of the model wind turbines. These experiments employ mechanical torque sensors to simultaneously measure the torque and rotor angular velocity, which yields a direct measurement of the fluid mechanical power extracted by the turbine at multiple locations. For a 4 × 3 array, the power is calculated at the center turbine in each of the rows. Variations in wind farm efficiency ranging from 55% to 90% are observed between the 13 different layouts tested. Modifications to the layout of the wind turbine array clearly affects the power output of the wind turbines downstream. The results of such experiments highlight the importance of studying the relationship between wind farm layout and power output.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering / It has been said that experimental modal analysis (EMA) "grew to prominence because the engineering community was incapable of properly analyzing the dynamics of commercially significant structures" [24]. The advent of powerful theoretical methods, such as the Finite Element Method (FEM) has not, however, resulted in the demise of EMA. In fact both FEM and EMA have undergone rapid growth and the merging of the two into an effective design and diagnostic tool has had a major impact on the engineering community's approach to dynamics related problems. In this study, the term dual has no mathematical connotations and is used to describe the complementary use of the techniques of EMA and FEM. The mining industry, worldwide, has experienced dynamics related problems in the operation of conveyances in vertical shafts. A study undertaken in South Africa investigated the behaviour of shaft steelwork and skips, resulting in a set of design guidelines for future shaft steelwork designs. This work only investigated the dynamic behaviour of skips. In this project, the ABAQUS and MODEL SOLUTION FEM codes were used to construct models of a. mine cage. An impact modal test was carried ant on the cage, using a GenRad 2515 CAT system, An impact hammer, suitable for exciting large structures, and a strain gauge force transducer were designed and built for the purpose of the test. The natural frequencies and mode shapes obtained from both FEM and EMA are compared by means of the modal assurance criterion (MAC). The test data is used to tune the model to produce accurate results. The model Could then be used (with minimal further test work) for predicting the response of the structure to dynamic loading or the effects of structural modifications. / Andrew Chakane 2020

Research plays a large role in the advancement of any industry. It is particularly important that relevant research is performed in an industry as large and critical as the construction industry. A review of literature shows that historically research has not played a major role in the advancement of the construction industry. The work of this thesis was to explore whether there has been a change in this relationship, or not. This thesis explored whether the construction-related research being done is in alignment with the needs of industry. Comparisons of the rankings of construction research and industry views were done to evaluate their correlation to each other. This evaluation was done through a review of literature of four construction research journals. Articles were gathered and classified in common construction themes. Each research theme was given a ranking based on the quantity of articles classified into common construction themes. The research ranking demonstrated that the most popular research theme was training/ human resources, followed by management/ risks and technology/ innovation. A survey was sent to 259 industry professionals asking them to rank the 22 construction themes. A response rate of 14% was achieved through the survey respondents. Survey respondents determine that the most important research theme is constructability, followed by estimating/ bidding and economics/cost control. Findings demonstrate that there was no correlation between the themes that were popularly researched and what is most important to the construction professionals.

During the initial phase of the investigation, four methods were selected for investigation from a review of literature sources,the specific ion probe, spectrophotometer, digital titrator, and Quantab titrator strips. The initial results from the laboratory testing procedure and evaluation based on cost, speed, accuracy, and level of expertise required indicated the specific ion probe was more suitable for use in the field when compared to the remaining methods selected. Effects of cement content and reaction temperature on the results obtained for the specific ion probe were also investigated. Results of the tests for the effects of cement content were somewhat inconclusive, but indicated more variability in the results as the amount of chloride present in the specimens increased. However, correlation between the increase in variability and i cement content was not indicated. The specific ion probe is affected by differences in temperature and the appropriate correction factor for the variation was determined. Field validation of the procedure was undertaken to substantiate the findings from the laboratory investigation. This was accomplished by subjecting the specific ion probe to testing specimens from bridges located in different exposure groups within the United States. Four bridges were tested for chloride content in Pennsylvania. Following this initial phase, three bridges were tested in Virginia, Florida, and Wisconsin respectively. An analysis of the variability in the effective diffusion constant for the bridges tested was also performed to determine any relationships which exist between different exposure groups and to determine effects of time. / Master of Science

Optical fiber magnetometers are extremely sensitive devices which are capable of competing with magnetometers implemented using other technologies. Demodulation of the signals detected using these magnetometers can be performed using either homodyne or heterodyne techniques. Higher sensitivities have been achieved using homodyne rather than heterodyne techniques, but with homodyne demodulation there exists the inherent problem of quadrature-point stabilization. Presented here is a review of existing quadrature-point stabilization methods and experimental results concerning the application of one of them which uses a piezoelectric transducer in the reference arm of an all-fiber Mach-Zehnder interferometer. / Master of Science

<div>Life cycle cost analysis (LCCA) has been defined as a method to assess the total cost of a project. It is a simple tool to use when a single project has different alternatives that fulfill the original requirements. Different alternatives could differ in initial investment, operational and maintenance costs among other long term costs. The cost involved in building a bridge depends upon many different factors. Moreover, long-term cost needs to be considered to estimate the true overall cost of the project and determine its life-cycle cost. Without watchful consideration of the long-term costs and full life cycle costing, current investment decisions that look attractive could result in a waste of economic resources in the future. This research is focused on short and medium span bridges (between 30-ft and 130-ft) which represents 65\% of the NBI INDIANA bridge inventory. </div><div><br></div><div>Bridges are categorized in three different groups of span ranges. Different superstructure types are considered for both concrete and steel options. Types considered include: bulb tees, AASHTO prestressed beams, slab bridges, prestressed concrete box beams, steel beams, steel girders, folded plate girders and simply supported steel beams for dead load and continuous for live load (SDCL). A design plan composed of simply supported bridges and continuous spans arrangements was carried out. Analysis for short and medium span bridges in Indiana based on LCCA is presented for different span ranges and span configurations. </div><div><br></div><div>Deterministic and stochastic analysis were done for all the span ranges considered. Monte Carlo Simulations (MCS) were used and the categorization of the different superstructure alternatives was done based on stochastic dominance. First, second, almost first and almost second stochastic dominance rules were used to determined the efficient set for each span length and all span configurations. Cost-effective life cycle cost profiles for each superstructure type were proposed. Additionally, the top three cost-effective alternatives for superstructure types depending on the span length are presented as well as the optimum superstructure types set for both simply supported and continuous beams. Results will help designers to consider the most cost-effective bridge solution for new projects, resulting in cost savings for agencies involved.</div>