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

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 they 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 connections performance. Moreover,
phase changes are not directly characterised by the appearance of cracks but by their
widening 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.