In-situ experiment on long-term behaviour of GFRP pipes under permanent bending

Abstract

The present study aims at studying the long-term behaviour of composites (GFRP) subjected to permanent bending. The specificity of this study largely rests on the original conditions of in situ ageing of the specimens within an experimental structure of elastic gridshell, built in 2006 and disassembled in 2014. This prototype was made of rectilinear tubes which were elastically deformed into a 3D stable shape. The structural members constituted hence a unique set of relaxation tests in ambient conditions where a wide variety of curvatures were imposed by the 3D shape. After dismounting, the tubes were sorted according to their permanent curvature in the structure. They were then subjected to three kinds of tests: recovery, longitudinal bending and transverse bending tests. The results were then compared with those obtained during the construction of the prototype, before ageing, and with members aged under the same conditions but not mechanically loaded. The experimental results confirm the usual recommendations for using composites in civil engineering, which suggest limiting the flexural stresses to 30% of the tensile strength to avoid damage or creep problems. At the same time, they confirm the safety and long-term robustness of the concept of double curvature structures obtained by elastic deformation of a composite plane grid.