The purpose of this study is to evaluate the fatigue strength of headed studs using an improved welding ferrule under rotating shear force. In the fatigue tests, to prevent up-lift of the specimen, vertical force was introduced in proportion to the rotating shear force. From the fatigue test results, two kinds of failure modes were observed. One of those is a failure of the headed stud accompanying with concrete crushing around its weld collar. Another is a failure of the bottom steel plate due to initiation of a fatigue crack from the weld toe. The fatigue life of the headed studs tested in this study showed some scatter in the same manner as the fatigue life of concrete. Hence, the treatment of probability is needed to evaluate the S-N curve for the conventional and durable headed studs. In this study, the test results indicated that probability distributions of the fatigue life conform to logarithmic normal distribution and 3-parameter Weibull distribution. Finally, the logarithmic normal distribution was applied to determine the average fatigue life of the conventional and durable headed studs tested and the S-N curves for both headed studs were obtained. Then, the average fatigue life of the durable headed studs increased in three times when compared to that of the conventional headed studs.
