published_or_final_version / Civil Engineering / Master / Master of Philosophy

Aluminum is the most common metal in the world and its high strength to weight ratio, along with excellent corrosion resistance, can provide efficient solutions for the design and rehabilitation of highway bridge structures. A reduction in a structure’s self-weight, when using aluminum, is advantageous for the rehabilitation of existing structures requiring an increased live load capacity and for rapid bridge replacements whereby larger, lightweight components can be installed with limited disruption to traffic. Aluminum structures and components offer the potential for lower life-cycle costs due to the favourable corrosion resistance, allowing for less maintenance over the life of the structure. One significant disadvantage of aluminum is that it is more susceptible to fatigue damage in relation to steel. Being a newer design material for bridge structures, compared to steel, and due to its limited use in the past, limited fatigue testing has been conducted to date. Bridge design codes and specifications employ different approaches for establishing fatigue design (S-N) curves for aluminum structures. The British and European design standards use a two-slope design curve, with a shallower slope in the high cycle range, implying that fatigue damage accumulates at a different rate at lower stress ranges. The Aluminum Association in the United States uses a more conservative approach, assuming a single-slope design S-N curve, by simply extending the curve past the constant amplitude fatigue limit at the initial slope. Limited testing under variable amplitude loading in the high cycle range has been completed to date, where a second slope could be warranted. A new chapter of the Canadian Highway Bridge Design Code (CSA-S6) on aluminum structures is currently under development. The research presented herein provides recommendations regarding the correction factors required for fatigue design of aluminum. In addition, fatigue testing and fracture mechanics analysis studies are performed to further investigate the use of a two-slope S-N curve for the fatigue design of aluminum highway structures.

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Engineering structures need to be assessed as part of activities to ensure their continued serviceability. Global methods of assessment which also give an indication of local conditions are most attractive since they are cost effective and flexible. A suitable method with these attributes is vibration monitoring which involves relating dynamic properties, or changes in them, to the integrity of the assessed structure. The present study investigates the application of vibration testing to structural integrity assessment of civil engineering structures. A survey of existing methods of damage detection, location and quantification in structures using vibration testing was conducted. Evaluation of the performance of some of the more promising methods was conducted using both simulated and experimental data. The results revealed that the damage identification process could be enhanced if appropriate modes are used. To this end, a new function, called Modal Sensitivity Values, has been proposed for identifying damage sensitive modes to be included in damage detection and location methods. It was also found that some success could be achieved if system identification and model updating procedures are applied to the problem of damage detection in structures. The literature survey revealed that most of the available methods are not applicable to general structural systems and are often limited by the damage model assumed. A new method, called Integrity Index Damage Location method, of assessing structural integrity using vibration data has also been proposed. The method is applicable to any structure and any damage type that affects the integrity/stiffness of the structure. Performance evaluation of the method using both numerical and experimental data is presented. Full-scale forced vibration tests were conducted before and after repairs on two reinforced concrete highway bridges. The vibrator used during the tests was developed during the research project and details of its development and operation are given in the thesis. As a background to the tests, a review of full-scale dynamic testing of bridge structures was conducted. Results from the tests were used to investigate the effectiveness of forced vibration testing as an integrity monitoring tool. It was found that the repair works caused slight (less than 5%) changes in the natural frequencies while there was no definite trend in the changes to the modal damping ratios. Comparison of frequency response functions and mode shapes, using modal analysis procedures, was found to give an indication of the presence and location of the repairs. The integrity assessment method proposed was also able to identify some of the affected parts of the structures. Results from the full-scale tests were also compared with predictions from finite element analysis. Good correlation was obtained between the measured and calculated natural frequencies and mode shapes, thus enabling validation of the analytical models within limits of the model assumptions and experimental errors. The results demonstrate the importance of accurate representation of boundary conditions. They (results) also showed that the vertical stiffness of new bearings installed on one of the bridges is not as high as was assumed in the design.

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