The object of this study was to help clarify some of the fundamental problems occurring in plain and reinforced concrete structural elements suffering from the degradation phenomenon of alkali silica reaction. A laboratory based testing programme was used, so that extreme conditions for generating alkali silica reaction could be used which are not readily achieved in actual structures. Special concrete mixes were also used in which the alkali silica reaction occurs within a period of months rather than years so that observation of the properties of the reacted concrete could be taken throughout the reacti ve process. The laboratory tests undertaken are as follows: fresh and hardened behaviour of alkali silica reactive (ASR) model mixes; mechanical properties and expansion behaviour of ASR concrete; structural behaviour of reinforced ASR concrete beams and columns; bond between reinforcement and ASR concrete in prisms and beams; restraint effect of ASR upon plain and reinforced concrete structural elements. This work shows that, ASR causes an unacceptable level of progressive damage to plain and reinforced concrete. The degradation and expansion in plain ASR concrete is higher than that in reinforced concrete. ASR in concrete reduces the strength and elastic modulus; the stiffness of reinforced beams; the axial load and ultimate bending moment capacity of columns; the ultimate bond between concrete and reinforcement. As a result of expansion in non-symmetrically reinforced structural elements, ASR causes either sagging or hogging displacement. The restraint imposed by reinforcement in ASR concrete elements is however beneficial in terms of inhibiting expansion and crack development, and exerting a small degree of post tensioning which generally improves the strength of members. Preloading of ASR concrete also results in an improvement in the mechanical properties. PhD

This doctoral thesis concerns fatigue of welded structures. Welding is one of the world’s most common joining methods and it is frequently used in several structural applications in many fields. Some examples are construction vehicles, loader cranes, trucks, busses, forestry and agricultural machines, bridges and ships. Since these structures are subjected to repeated loading, fatigue is the most common cause of failure. A novel numerical algorithm has been developed which assesses the welded surface and calculates and quantifies weld quality parameters and the presence of defects which are critical in fatigue applications. The algorithm is designed for implementation in serial production. It will provide robust and reliable feedback on the quality being produced, which is essential if high strength steels are utilized. Two welding procedures which can increase the weld quality in as welded conditions have been assessed. These procedures utilize welding in different positions and pendling techniques, which can be accomplished using the existing welding equipment. It was found that by using these methods, the fatigue strength can be increased compared to normal weld quality. Furthermore, two fatigue assessment methods ability to account for increased weld quality in low cycle and high cycle fatigue applications has been studied. One of these methods showed sufficient accuracy in predicting the fatigue strength with small scatter and also account for increased weld quality. When implementing thinner high strength steels, the overall stress level in the structure increase. Therefore, other locations such as the steel cut edges may become critical for fatigue failure unless they are not designed and manufactured with the same quality as the welded joint. The influence of surface quality on cut edges was studied and the fatigue strength was estimated using international standards and a fatigue strength model for cut edges. / <p>QC 20160613</p> / WIQ / LIGHTSTRUCT / ONWELD

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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