Fatigue behaviour of steel-fibre-reinforced concrete beams and prestressed sleepers

摘要

The design of reinforced concrete and prestressed concrete structures subjected to cyclic loading, such as bridge deck slabs, bridge girders, railway tracks, and offshore installations, necessitate the consideration of fatigue. These structures typically experience millions of stress cycles during their service life; the cyclic load can be detrimental to their structural performance. Cyclic loads can result in a steady decrease in the stiffness of the structure and cause damage at a micro level that may eventually lead to a fatigue failure. With the advent of steel-fibre-reinforced concrete (SFRC), there exist the possibilities of enhancing fatigue performance at the structural level, compared to that of members constructed of conventional concrete. Experimental tests at the materials level reported in literature indicate that steel fibres improve resistance to crack growth, decrease deflections and increase the fatigue life of plain concrete under cyclic loading. However, the fatigue performance of SFRC at the structural level has not been investigated thoroughly. This research looks into the behaviour of SFRC beams and sleepers subjected to cyclic loading. In the experimental program, twelve (out of sixteen) reinforced concrete beams with fibre volume fractions 0.4 and 0.8 percent and eight prestressed sleepers with fibre volume fractions 0.25 and 0.5 percent were tested under constant amplitude cyclic loading. Steel and concrete strains, crack widths and deflections were measured. The results of the SFRC specimens were compared to that of non-fibre reinforced specimens. The steel fibres prolonged the fatigue life in SFRC beams and sleepers by reducing the stress level in the tensile reinforcement. The SFRC beams and sleepers also demonstrated smaller deflections and crack widths than that of reinforced concrete beams and prestressed sleepers without fibres, respectively.In this study, a finite element model is developed for the fatigue behaviour of SFRC structures. The model was verified with the experimental results from this study and is shown to predict the fatigue life of SFRC beams and sleepers with reasonable accuracy.