Prediction of ring creep stiffness of GFRP pipes with different sand contents

Abstract Currently, the prediction of creep performance in glass fiber-reinforced plastic (GFRP) pipes has primarily relied on extrapolating short-term experimental data. However, this approach still necessitates repeated experiments for pipes with different sand contents, resulting in high costs and low efficiency. To address this issue, this study focuses on GFRP pipes with three different sand contents (0 wt.%, 20 wt.%, and 34 wt.%) and conducts an 8,000-h creep test under an initial deformation of 6 % (relative to the pipe’s mean diameter). Based on classical laminate plate theory, a ring stiffness prediction model suitable for the symmetric “sandwich” structure consisting of fiber layer–sand layer–fiber layer is established. Using the first 2,000 h of experimental data from pipes with 0 % and 34 % sand content, the time-dependent evolution of the elastic moduli of the fiber layer and sand layer is inversely determined. The ring creep stiffness for pipes with 20 % sand content is then predicted for the period from 2,000 to 8,000 h. Validation results show that the maximum prediction error of this method is only 2.3 %.