Tubular space trusses for bridge applications use thick-walled tubes. The reduction in fatigue resistance due to geometrical size effects is thus an important issue. In order to carry out a thorough study, both fatigue tests on large-scale specimens and advanced 3D crack propagation modelling were carried out.
A numerical model was developed using BEASY and was validated with fatigue tests data. The stress intensity factors (SIF) along the doubly curved crack front at different crack depths were obtained. With this model, a parametric study was used to investigate the influence of geometry, size and load case on fatigue life. Results showing both proportional and non-proportional sizing effects on fatigue strength were obtained.
The study shows that size effects (proportional and non-proportional) can be expressed as a function of the non-dimensional parameters and chord thickness.