This study compares energy minimization with direct stiffness for linear structural analysis. The energy minimization approach locates the generalized displacement vector by minimizing the total potential energy of the structure being analyzed. From the survey of variable metric and conjugate gradient algorithms included in this study, the Davidon-Fletcher-Powell variable metric algorithm and the FletcherReeves conjugate gradient algorithm were chosen to minimize the total potential energy. A description of both algorithms is presented. The direct stiffness method assembles the equilibrium equations of the structure being analyzed. These equations are solved by Gaussian elimination to determine the generalized displacement vector. Computer codes have been written for the energy minimization and direct stiffness methods. The comparison was based on computational effort, in terms of computer time, required for analysis. The results of this study show energy minimization is not competitive with direct stiffness for linear structural analysis. As the problem size increases by degree of freedom the direct stiffness method rapidly increases in superiority over the energy minimization method. / Master of Science

Optimization of compaction in granular material without the use of traditional ground improvement methods may be possible by optimizing the percentage of finer material and the median grain size ratio in binary soil mixtures. In this study, the median grain size ratio D50/d50 was explored as a fundamental parpmeter affecting the compaction characteristics of binary mixes made from natural sands as opposed to singular measurements such as fines content and mean grain size traditionally used to represent granular soils. A total of 18 binary granular mixes were synthetically generated from natural sands obtained from Longboat Key, Florida and evaluated through grain size analysis, laboratory compaction and determination of relative density. Results indicate that the D50/d50 ratio shows promise as a fundamental parameter for compaction optimization in binary mixes with values exceeding six approaching the densest packing configuations. / by Tara Devine Brenner. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Contraint de respecter les réglementations environnementales concernant les émissions de CO2, les industriels du secteur automobile se doivent de lever certains verrous technologiques associés à l’allègement des structures au sein de leur véhicule. L’introduction des matériaux composites dans le développement et la production de pièces structurantes est envisagée comme étant une des solutions les plus efficaces à moyen et long terme. L’optimisation des coûts matière, caractéristique de cette industrie de masse, nécessite de maîtriser le comportement physique de matériaux composites à matrice thermoplastique et à fibres de verre continues tissées. En termes de coût et de variétés d’applications, ces derniers sont considérés aujourd’hui comme une alternative pertinente aux onéreux composites utilisés dans l’aéronautique. Un renfort de porte pour crash latéral a été ainsi développé et les travaux présentés dans cette thèse sont une contribution à la compréhension, la caractérisation et à la prédiction numérique du comportement jusqu’à rupture de cette pièce, qui lors d’un crash est soumise à de forts gradients de vitesses. Au regard de l’absence de normalisation ou de consensus liés aux essais dynamiques sur matériaux composites, nous proposons une procédure expérimentale robuste, garantissant la représentativité de la caractérisation du comportement sur un spectre de vitesses quasi-statiques et dynamiques. La validation des étapes de la procédure et l’utilisation d’un montage d’essais dynamiques développé dans ces travaux permettent d’aboutir à une base de données riche, et utile à une procédure d’identification des paramètres d’un modèle phénoménologique prenant en compte l’influence de la vitesse sur l’évolution des phénomènes dissipatifs jusqu’à rupture. Fort d’une identification majoritairement directe, la précision de la réponse numérique issue de la loi de comportement identifiée est évaluée et validée à l’aide de calculs de structures faisant intervenir d’importants gradients matériels et structurels. / Car manufacturers are looking for solutions to lighten their vehicles in order to meet pollutant emission requirements – for thermal engines – or to extend their range – for electric vehicles. Composite materials, among other solutions, offer excellent strength and durability. However increased per unit cost and manufacturing time are among the main drawbacks material producers have to overcome in order to make composite solutions viable for mass-market production. In that prospect, woven glass fibers and thermoplastic matrices respectively are more serious contenders than aeronautic-grade composites. The objective application is a door reinforcement module, whose main function is to act as a safety net, adding its own stiffness and strength to that of the steel door and preventing any foreign object from entering the passenger compartment. A main preoccupation is therefore the constitutive behavior of that material under strain rates varying from 10-3 s-1 to approximately 50 s-1. The study objective is to develop a physically-based constitutive law modelling in order to take into account strain-rate sensitivity on behavior. A new and consistent experimental procedure aiming at capturing the influence of speed solicitation on non-linear internal mechanisms is developed and allows identifying non-linear constitutive law parameters over a wide range of strain rates until failure. Resulting mainly from direct evaluations and direct identification procedure, the accuracy of the implemented constitutive law is guaranteed through numerical computations involving effects of material and structural heterogeneities.

Hybrid testing is an emerging technique for system emulation that uses a transfer system composed of actuators and sensors to couple physical tests of a critical component or substructure to a numerical simulation of the remainder of a system and its complete operating environment. The realisation of modern real-time hybrid tests for multi-body contact-impact problems often proves infeasible due to (i) hardware with bandwidth limitations and (ii) the unavailability of control schemes that provide satisfactory force and position tracking in the presence of sharp non-linearities or discontinuities. Where this is the case, the possibility of employing a pseudo-dynamic technique remains, enabling tests to be conducted on an enlarged time scale thus relaxing bothbandwidth and response time constraints and providing inherent loop stability. Exploiting the pseudo-dynamic technique, this thesis presents the development of Robotic Pseudo-Dynamic Testing (RPsDT), a dedicated method that specifically targets the realisation of hybrid tests for multi-body contact-impact problems using commercial off- the shelve (COTS) industrial robotic manipulators. The RPsDT method is evaluated in on-ground studies of air-to-air refuelling (AAR) maneuvers with probe-hose-drogue systems where the critical contact and coupling phase is tested pseudo-dynamicallywith full-scale refuelling hardware while the flight regime is emulated in simulation. It is shown that the RPsDT method can faithfully reproduce the dominant contact impact phenomena between probe and drogue while minor discrepancies result from the absence of rate-dependant damping in the force feedback measurements. In combination with full-speed robot controlled contact tests, reliable estimates for impact forces, strain distributions and drogue responses to off-centre hits are obtained providing extensive improvements over current predictive capabilities for the in-flight behaviour of refuelling hardware and it is concluded that the technique shows great promise for industrial applications.

Considering the deficiencies frequently observed in the existing reinforced concrete buildings, detailed assessment and rehabilitation must be conducted to avoid significant life and value loss in seismic zones. In this sense, performance based evaluation methods suggested in the regulations and codes must be examined and revised through experimental and analytical research to provide safe and economical rehabilitation solutions. In this study, seismic behavior of three reinforced concrete frames built and tested in Middle East Technical University Structural Mechanics Laboratory is examined. The specimens are extracted from a typical interior frame of 3-story 3-bay reinforced concrete structure. One of the specimens has compliant design according to Turkish Earthquake Code (2007) and each of the other two specimens represents different types of deficiencies in terms of material strength and detailing. The test specimens were modeled using different modeling approaches and nonlinear dynamic analyses were conducted on the numerical models. Results of continuous pseudo-dynamic testing of three ground motions are presented and compared with the numerical simulations on models. Calibrated finite element models were used for evaluation of performance assessment procedure of Turkish Earthquake Code (2007) and further investigation on local deformation components in light of experimental findings and observations. Deformation sources of columns and joints were studied in terms of their interaction and contributions to the total drift. Estimated plastic hinge lengths of columns were compared with the experimental observations and the proposed expressions in the literature.

Frontal Protection Systems (FPS) have become a popular accessory for passenger vehicles. They are used to protect the front of a vehicle during minor impacts, and to attenuate the impact energy during major impacts. With the increased safety of modern passenger vehicles, the fitment of a FPS to a vehicle requires careful consideration to the design and installation of the FPS as they may modify vehicle crush characteristics. This is particularly important in vehicles fitted with air bags. These community and industry concerns triggered the research discussed in this thesis, which is the first comprehensive project undertaken in this particular area. This project generated comprehensive research knowledge on the impact response and energy absorption of FPS in order to evaluate performance. This involved a range of experimental testing supplemented by finite element analysis. Experimental testing was conducted using quasi-static and dynamic techniques to assess the overall performance of current FPS available. Finite element models were then generated and analysed using both implicit and explicit techniques, and calibrated against the experimental testing results. These models were used throughout the project to assess the FPS response, in particular the energy absorbed, to changes in impact characteristics. FPS assessment guidelines were developed from the knowledge generated from the numerous FPS tests and analyses carried out in this research project. These guidelines have been used in the design and evaluation of a number of FPS for airbag compatibility. The real life performance of vehicles fitted with these FPS, have given confidence to the assessment criteria developed in this research project. This project has demonstrated that FPS can be designed to complement the safety systems of modern passenger vehicles, and thus passenger safety. This would not have been possible without the comprehensive research carried out in this project.

Dynamic tensile characterization of geo-materials is critical to the modeling and design of protective structures that are often made of concrete. One of the most commonly used techniques currently associated with this type of testing is performed with a Kolsky bar and is known as the spall technique. The validity of the data from the spall technique is highly debated because the necessary boundary conditions for the experiment are not satisfied. By using a technique called pulse shaping, a new “controlled” spall technique was developed to satisfy all boundary conditions so that the analyzed data may be useful in modeling and design. The results from this project were promising and show the potential to revolutionize the way Kolsky bar testing is performed.

No description available.

In this thesis, artificial neural networks (ANNs) are used to model helicopter main rotor dynamic loads as a function of flight variables. The motivation to develop an accurate model of such loads is to reduce maintenance and replacement costs by eliminating excessive conservatism currently associated with structural fatigue estimation. Neural networks are used for the modeling procedure because of their capability to model complex, nonlinear relationships for multiple input-multiple output systems. In support of the dynamic loads modeling discussed above, this thesis also briefly reviews artificial neural network technology, and investigates the modeling of a well-known dynamic system using ANNs. / Master of Science

Pseudo-dynamic testing was employed to observe the seismic performance of three different retrofit methods on two story three bay reinforced concrete frame structures. The three test frames have hollow clay tile (HCT) infills in the central bay. All of the test frames represent the seismic deficiencies of the Turkish construction practice such as use of plain reinforcing bars, low strength concrete and insufficient confining steel. Two non-invasive and occupant friendly retrofit schemes suggested in the Turkish Earthquake Code, namely use of Fiber Reinforced Polymers and precast concrete panels integrated on the HCT infills and traditional approach of adding concrete infill wall were employed. Specimens were subjected to three different scale levels of North-South component of Duzce ground motion. Reference specimen experienced severe damage at 100% scale level and reached collapse stage due to the loss of integrity of the infill wall and significant damage on the boundary columns. The retrofitted test structures were able to survive the highest level 140% Duzce ground motion. Test results confirmed the success of the retrofit methods for simulated earthquake loads.