Experimental and finite element assessments of the fastening system of fiber-reinforced foamed urethane (FFU) composite sleepers

This paper studies the structural integrity of fastening systems used in fiber-reinforced foamed urethane (FFU) composite sleepers. 24 FFU specimens are studied with screw pull-out tests and digital image correlation (DIC) to investigate the effects of parameters such as wet conditions, the sleeper drilled hole diameter and the screw active length inside the sleeper. The pull-out test results reveal that a moisture content of 0.3% in FFU specimens can reduce the pull-out strength between the dry and water-absorbed specimens with 18 mm FFU hole and 80 mm screw active length in dry and wet states (18-AD &18-AW), 18 mm FFU hole and 90 mm screw active length in dry and wet states (18-BD & 18-BW), 20 mm FFU hole and 110 mm screw active length in dry and wet states (20-CD & 20-CW), and 20 mm FFU hole and 90 mm screw active length in dry and wet states (20-BD & 20-BW) by approximately 18%, 19%, 6% and 13%, respectively. Specimens with 20 cm holes have the highest pull-out loads of 71.9 kN and 68 kN in dry and water-absorbed states, respectively. When the active length of the screw decreases from 110 mm to 90 mm, the pulling strength decreases by approximately 14% and 16% in dry and water-absorbed states, respectively. Therefore, the experimental and FEM results show that a 20 mm FFU hole with a 110 mm active length and a 24 mm thick screw is the best option for an FFU sleeper fastening system, especially in wet conditions.