Creep tests on GFRP pultruded specimens subjected to traction or shear

In this paper, experimental long-term tests on pultruded GFRP specimens are presented. Specimens have been subjected to constant traction and shear forces for about 760 days. The tests have been performed under controlled temperature (20 °C) and humidity (60% RH) inside a climatic room. The specimens under traction have been cut from plates and from the flanges of a wide flange GFRP pultruded beam; the specimens under shear loadings have been extracted from the web of the same beam. Moreover, some specimens have been stiffened by bonding CFRP sheets to both sides, in order to study how their introduction may reduce the specimen deformability under long term loading. Results from the unstiffened specimens have been interpreted by means of the Findley law, the reference model for creep in polymers and FRP, in terms of strains and creep coefficient. A simple model has been finally proposed to predict strains in stiffened specimens and by taking stress redistribution into account.