Innovative test concept for evaluating fatigue degradation process of submerged grouted connections

Abstract

Grouted connections are hybrid joints fabricated by linking two overlapping steel tubes with different diameters by filling the annulus with grout material. Offshore structures are considerably subjected to dynamic loading. Hence, the fatigue behaviour of grouted connections typically used in the different components of these structures is of particular interest. This study presents a new test concept for cyclic axially loaded grouted connections with fibre optical sensory integrated into the grout annulus. It aims to provide insight into the mechanisms of damage initiation and propagation through real-time crack detection. Specimens have been designed such that the grout annulus can be submerged and the steel structures can be reused in several experiments, thus significantly reducing the time and cost of the test program. Test results show that the fatigue degradation behaviour of axially loaded grouted connections can be divided into three different phases according to its advancement: stable, incremental, and progressive degradation. Certain cracks have been observed to exert a slight influence on the connection’s performance. Moreover, phase changes are not directly characterised by the appearance of cracks but by their opening progress. The overall test concept including the novel reusable test specimen and measurement setup is found to be functional. They provide an opportunity to gain insight into the degradation mechanism of grouted connections under cyclic loading.