The effects of repeated loading on a normally consolidated,saturated silty clay, are compared to the effects of sustained loading and standard strength tests on the same material. Attention is given to axial strains and pore water pressures generated under the different loading conditions. / Thesis / Master of Engineering (ME)

Este trabalho descreve o comportamento da aderência do concreto armado sob ações monotônicas e repetidas através de uma revisão bibliográfica e de ensaios de arrancamento padronizados. A influência de alguns parâmetros foi analisada, como diâmetro da armadura, tipo e amplitude de carregamento. Os resultados dos ensaios monotônicos foram comparados com as recomendações do CEB-FIP MC 1990, EUROCODE 2 e NB-1/78. Também foi realizada a análise numérica da aderência monotônica por meio de elementos finitos. Considerou-se a barra lisa, elementos de contato entre o aço e concreto e comportamento elástico-linear dos materiais; pois a ruína experimental da ligação ocorreu pelo corte do concreto entre as nervuras. A resistência monotônica da ligação ficou compreendida entre condições boas e ruins de aderência. Os resultados calculados de acordo com as normas foram muito diferentes em relação aos valores experimentais, e apresentaram uma dispersão muito grande. A força repetida ocasionou a perda de aderência pelo crescimento progressivo dos deslizamentos. Os modelos numéricos não representaram o comportamento experimental, devido à resposta força-deslizamento não-linear. / This research describes the bond behaviour in reinforced concrete under monotonic and repeated loading through a state-of-art and standard pull-out tests. The influence of some parameters was analysed as deformed bar diameter, type and amplitude of loading. The monotonic test results were compared with recommendations of CEB-FIP MC 1990, EUROCODE 2 and NB-1/78. The numerical analysis of monotonic bond was realized through finite elements. It was considered smooth bar, contact elements between the steel and concrete, and materials as of linear-elastic behaviour, because the experimental degradation of bond was caused by concrete between the ribs sheared off. The monotonic bond resistance resulted between good and bad bond conditions. The results calculated according to the codes were very different from the experimental values and very disperse. The repeated loading causes bond degradation by progressive increase of slip. The numerical specimens did not represent the experimental behaviour because of the non-linear load-slip response.

Este trabalho descreve o comportamento da aderência do concreto armado sob ações monotônicas e repetidas através de uma revisão bibliográfica e de ensaios de arrancamento padronizados. A influência de alguns parâmetros foi analisada, como diâmetro da armadura, tipo e amplitude de carregamento. Os resultados dos ensaios monotônicos foram comparados com as recomendações do CEB-FIP MC 1990, EUROCODE 2 e NB-1/78. Também foi realizada a análise numérica da aderência monotônica por meio de elementos finitos. Considerou-se a barra lisa, elementos de contato entre o aço e concreto e comportamento elástico-linear dos materiais; pois a ruína experimental da ligação ocorreu pelo corte do concreto entre as nervuras. A resistência monotônica da ligação ficou compreendida entre condições boas e ruins de aderência. Os resultados calculados de acordo com as normas foram muito diferentes em relação aos valores experimentais, e apresentaram uma dispersão muito grande. A força repetida ocasionou a perda de aderência pelo crescimento progressivo dos deslizamentos. Os modelos numéricos não representaram o comportamento experimental, devido à resposta força-deslizamento não-linear. / This research describes the bond behaviour in reinforced concrete under monotonic and repeated loading through a state-of-art and standard pull-out tests. The influence of some parameters was analysed as deformed bar diameter, type and amplitude of loading. The monotonic test results were compared with recommendations of CEB-FIP MC 1990, EUROCODE 2 and NB-1/78. The numerical analysis of monotonic bond was realized through finite elements. It was considered smooth bar, contact elements between the steel and concrete, and materials as of linear-elastic behaviour, because the experimental degradation of bond was caused by concrete between the ribs sheared off. The monotonic bond resistance resulted between good and bad bond conditions. The results calculated according to the codes were very different from the experimental values and very disperse. The repeated loading causes bond degradation by progressive increase of slip. The numerical specimens did not represent the experimental behaviour because of the non-linear load-slip response.

Im Mittelpunkt der vorliegenden Arbeit steht die gezielte Analyse des Verbundverhaltens zwischen Bewehrungsstahl und Beton unter kombinierter Beanspruchung aus Ermüdung und Querzug. Den Hintergrund bilden Stahlbetonbauteile, wie z. B. Fahrbahnplatten von Verbundbrücken, welche einen zweiaxialen Lastabtrag unter nicht vorwiegend ruhenden Belastungen aufweisen. Die Untersuchungen für normal- und hochfesten Beton erfolgten an Ausziehkörpern mit einem durch Querzugspannungen hervorgerufenen Längsriss entlang des Bewehrungsstabes. Das Versuchsprogramm beinhaltete hochzyklische Schwellversuche mit unterschiedlichen Schwingspielen und variierenden Längsrissbreiten bis zu einer Million Lastwechseln. Anhand der Entwicklung des Schlupfes zwischen Bewehrungsstab und Beton konnte eine deutliche Abhängigkeit des Verbundwiderstandes vom Querzug beobachtet werden. Aufbauend auf der Schlupfentwicklung erfolgt die Ableitung von normierten Wöhlerlinien der Verbundermüdung. Diese Wöhlerlinien können direkt in Beziehung zu den Wöhlerlinien der Betonstahlermüdung gesetzt werden und vereinfachen die Erstellung von Dauerfestigkeitsdiagrammen für Bemessungszwecke. Es wird deutlich, dass die Ermüdungsfestigkeit des Verbundes durch das Vorhandensein eines Längsrisses gegenüber der Betonstahlermüdung verstärkt an Bedeutung gewinnt. / The main focus of the present work is the specific analysis of the bond behaviour between reinforcement and concrete under combined loading due to fatigue and transverse tension. The background is formed by reinforced concrete elements such as bridge decks of steel-concrete composite bridges, which show a biaxial load bearing behaviour under not predominantly monotonic loading. The investigations for both normal strength and high performance concrete were conducted on pull-out specimens with a longitudinal crack along the reinforcing bar caused by transverse tensile stresses. The experimental program included high cyclic tests with different stress ranges and varying longitudinal crack widths up to one million load cycles. By means of the slip development, a definite dependency of the bond strength on the transverse tension could be observed. Based on the slip development, normalised S-N curves for bond fatigue have been deduced. These S-N curves can be set in direct relation to the S-N curves for steel fatigue and simplify creating constant life diagrams for design purposes. It becomes clear that the bond fatigue strength, due to an existing longitudinal crack, gains in importance in comparison to the fatigue strength of the reinforcing steel.

Im Mittelpunkt der vorliegenden Arbeit steht die gezielte Analyse des Verbundverhaltens zwischen Bewehrungsstahl und Beton unter kombinierter Beanspruchung aus Ermüdung und Querzug. Den Hintergrund bilden Stahlbetonbauteile, wie z. B. Fahrbahnplatten von Verbundbrücken, welche einen zweiaxialen Lastabtrag unter nicht vorwiegend ruhenden Belastungen aufweisen. Die Untersuchungen für normal- und hochfesten Beton erfolgten an Ausziehkörpern mit einem durch Querzugspannungen hervorgerufenen Längsriss entlang des Bewehrungsstabes. Das Versuchsprogramm beinhaltete hochzyklische Schwellversuche mit unterschiedlichen Schwingspielen und variierenden Längsrissbreiten bis zu einer Million Lastwechseln. Anhand der Entwicklung des Schlupfes zwischen Bewehrungsstab und Beton konnte eine deutliche Abhängigkeit des Verbundwiderstandes vom Querzug beobachtet werden. Aufbauend auf der Schlupfentwicklung erfolgt die Ableitung von normierten Wöhlerlinien der Verbundermüdung. Diese Wöhlerlinien können direkt in Beziehung zu den Wöhlerlinien der Betonstahlermüdung gesetzt werden und vereinfachen die Erstellung von Dauerfestigkeitsdiagrammen für Bemessungszwecke. Es wird deutlich, dass die Ermüdungsfestigkeit des Verbundes durch das Vorhandensein eines Längsrisses gegenüber der Betonstahlermüdung verstärkt an Bedeutung gewinnt. / The main focus of the present work is the specific analysis of the bond behaviour between reinforcement and concrete under combined loading due to fatigue and transverse tension. The background is formed by reinforced concrete elements such as bridge decks of steel-concrete composite bridges, which show a biaxial load bearing behaviour under not predominantly monotonic loading. The investigations for both normal strength and high performance concrete were conducted on pull-out specimens with a longitudinal crack along the reinforcing bar caused by transverse tensile stresses. The experimental program included high cyclic tests with different stress ranges and varying longitudinal crack widths up to one million load cycles. By means of the slip development, a definite dependency of the bond strength on the transverse tension could be observed. Based on the slip development, normalised S-N curves for bond fatigue have been deduced. These S-N curves can be set in direct relation to the S-N curves for steel fatigue and simplify creating constant life diagrams for design purposes. It becomes clear that the bond fatigue strength, due to an existing longitudinal crack, gains in importance in comparison to the fatigue strength of the reinforcing steel.