Multifractal characteristics of fatigue cracks in the full-scale reinforced concrete hollow-slab beams

Highway Reinforced concrete (RC) bridges bear the repeated vehicle loads for a long time, promoting cracks' sprouting and development. Establishing a quantitative evolution model of cracks will improve the management and maintenance of similar bridges. Therefore, this paper introduces the multifractal theory into crack characterization and carries out the study on the multifractal characteristics of fatigue cracks in full-scale RC hollow slabs. Firstly, the basic procedure of the multifractal analysis method for concrete cracks is introduced, and the sensitivity of the multifractal spectrum under different influencing factors is analyzed. Secondly, the basic information and scheme of the experimental beam are introduced. The experimental results and the development law of fatigue cracks are analyzed. Finally, the variation law of the multifractal spectrum with cycle number is analyzed based on the multifractal theory, and a simplified evolution model of fractal dimension (FD) under fatigue load is established based on the experimental results. The experimental results prove that the multifractal theory is effective in describing the cracking state of RC members under fatigue load. The fatigue cracks' development of the experimental beam presents an obvious three-stage pattern: rapid stage, stable stage, and destabilized stage. The FDs of fatigue cracks also develop in a three-stage pattern along with cycle number, which can be expressed by a linear equation of cycle percentage. The evolution model can provide technical support for the maintenance decisions of RC bridges in service.