Fatigue behaviour and reliability of Extended Hollobolt to concrete filled hollow section

The need to provide mechanical connection from one side for the Hollow section connection has arisen in a number of fields and has resulted in the development of several types of so-called blind fasteners. An experimental blind bolt called the Extended Hollobolt is giving a good behaviour performance in terms of stiffness, strength and ductility. The strength performance of this system has been investigated under both monotonic and cyclic loading. However, the performance of such connections under fatigue loading is still unknown. The aim of this study was to investigate the behaviour of blind bolt connection to concrete filled hollow section under repeated load. Further aim was to determine the reliability of the Extended Hollobolt to concrete filled hollow section. The study involved conducting an experimental programme and carrying out fatigue life and reliability analysis. The experiment programme tested 52 specimens of bolts connected to concrete filled hollow sections where 36 tests involved Extended Hollobolt, 10 standard Hollobolt and 6 standard bolts (M16). The test specimens were subjected to tensile fatigue load characteristics with varying stress ranges. Mathematical methods are used to analyse the fatigue test data using the normal, lognormal and Weibull distributions. Normal and lognormal distributions are more suitable. Therefore, statistical analysis procedure proposed by Eurocode for the statistical analysis is valid for fatigue test data. Statistical analysis was conducted to establish S-N curves and to predict the fatigue life of the proposed blind bolt. This was then compared to the normative regulation in Eurocode 3. The failure mode of the Extended Hollobolt under repeated loading was found to be similar with standard bolt, which is a very positive outcome. Statistical analysis of fatigue test data showed that the fatigue life of Extended Hollobolt is higher than the theoretical design S-N curve which is recommended by Eurocode 3 part 1-9 for the standard bolt. However, the actual fatigue life for the standard bolt appears to be higher than the proposed blind bolt. A design model for predicting the fatigue life using S-N curve for the Extended Hollobolt is proposed. A reliability analysis using FORM (First Order Reliability Method) analysis shows that Extended Hollobolt is reliable in connections to concrete filled hollow sections where the safety index is 4.2