<p>In this thesis, we theoretically and experimentally investigate the linear and nonlinear dynamic behavior of a frame structure, which frequently occurs in engineering applications. The structure consists of three continuous steel beams that are connected by two brass hinges. Experimental modal analysis indicates that the obtained natural frequencies are highly sensitive to changes in the oscillation amplitude, even for small motions. Thus, the amplitude range where linear responses can be expected is, in practice, very small. Instead, a strong nonlinear behavior is exhibited by the experimentally obtained backbone curves for small vibrations. Furthermore, the experimentally obtained frequency-response curves exhibit jump phenomena.</p> <p> We investigated experimentally whether the nonlinear dynamic characteristics of the structure are the result of modal interactions, such as internal and combination resonances. We were unable to activate any of these resonances. Next, we investigated whether these characteristics are due to geometric, inertia, material, or damping nonlinearities. The answer is again negative. Finally, we examined the nonideal dynamic characteristics of the hinges. We found that stiffness degradation hysteretic damping in the hinges is the best model that explains the observed nonlinear dynamic behavior. A multilinear stiffness degradation model was used to describe the overall hysteretic load-displacement relation. An approximate analytical approach was used to compute the steady-state response of the structure to a harmonic excitation. A good qualitative agreement between the computations and the experimental results was obtained.</p> / Master of Science

In this dissertation a new time domain approach for the determination of material properties such as the complex permittivity and the complex permeability in a stripline geometry is presented. The new technique uses both Time Domain Reflectometry (TDR) and Time Domain Transmission (TDT) measurements for determining an optimum frequency dependent lossy transmission line model for the stripline under test. The optimization is done in the time domain by comparing the experimental TDR and TDT response waveforms with the simulated ones using a non-linear least squares fit. The conventional optimization algorithms have shown to be inefficient in this specific application. In this dissertation an efficient optimization algorithm which has been developed to suit this application is also presented. In general, the material properties in a stripline under test are related with the geometrical parameters of the line through complicated integral expressions. Using the proposed approach, the use of complicated integral expressions are avoided. The material properties such as the complex permittivity and the complex permeability are determined from the optimum lossy transmission line model. For this purpose, the frequency behavior of the line parameters have to be known beforehand in the form of causal mathematical models. The literature survey shows that, no causal model exists for the complex permittivity of thick film and polymer materials. The dissertation proposes a new causal model for this purpose. / Ph. D.

The transportation engineering community of the United States faces a tremendous problem: the gradual deterioration of the nation's bridges. A major component of the overall bridge deterioration problem is the corrosion-induced deterioration of reinforced concrete bridge components that are exposed to de-icing salts. The progression of events resulting from corrosion of the reinforcing steel includes cracking, delamination, spalling, and patching of the surface concrete. Bridge components reach the end of their functional service life when the level of damage warrants rehabilitation. The objective of this study was to determine the end of functional service life for concrete bridge decks, piers, and abutments by quantifying terminal levels of physical damage. The approach for quantifying terminal damage levels involved obtaining recommendations from state Department of Transportation (DOT) bridge engineers via an opinion survey. A field study of 18 existing concrete bridges that had been designated for rehabilitation was conducted to develop concrete bridge component maps showing areas of physical damage. Deck damage maps were produced using a ground-based photogrammetry system developed in this study, while pier and abutment damage maps were drawn by hand in the field. Survey Kits based on the component damage maps were distributed to bridge engineers in 25 states that use de-icing salts. The engineers evaluated the maps and recommended when each component should be, or should have been, rehabilitated~ Based on the engineers' responses, linear regression prediction models were developed to relate the recommended bridge component rehabilitation time point to the physical damage level. Based on the prediction models, two viable terminal damage levels for concrete bridge decks, and a partial terminal damage level for concrete bridge piers, were quantified. / Master of Science