Influence of fatigue on headed stud connectors in composite bridges

Composite bridges are used for road and railroad bridges in Sweden and worldwide. The advantage of composite bridges is that concrete and steel is used optimally, steel in tension and concrete in compression. In order to get the interaction between steel and concrete headed stud shear connectors are used. Fatigue loading makes cracks, initiated by welding, propagate and in this way the strength of shear connectors are decreased during the fatigue life. The aim in this thesis is to investigate the residual strength of 22 mm headed stud connectors and if possible derive an equation for residual strength. In BV BRO the residual strength is neglected in design of ultimate limit state, but in e.g. Eurocode and BRO 2002 it is taken into account. One objective is to evaluate the assumption made in BV BRO. A state of art on the subject has been performed. Most previous research is focused on the endurance rather than residual strength, but some relevant research was found. From previous research and literature the fatigue life was found to be mainly affected by the range and the peak load. A literature survey on fatigue, fracture mechanics and the behaviour of shear studs have been performed to improve the understanding of the subject. The experimental work carried out within this master’s thesis is 10 push-out tests, five static and five fatigue. The push-out specimens were made according to Eurocode 4 and the headed shear studs used were 125 x 22mm. Differences and similarities in Swedish design standards and Eurocode have been investigated. These design standards have also been compared to experimental results and to previous research. The results of tests and literary survey show that the residual strength under fatigue loading constantly reduces and this reduction seems to linearly depend on the number of cycles applied. An equation was derived for residual strength. The design models Eurocode and BRO 2002 gives a bit lower residual strength than that derived from experiments performed. Arguments to support the assumption in BV BRO were not found.Validerat; 20101217 (root