Torsional response of closed FRP composite sections

Predicting torsional response of pultruded fiber reinforced polymer (FRP) composite member with closed cross-sections is complex due to the inhomogeneous nature of section properties, which are dependent on fiber architecture and constituent material properties. Presented herein are the methods and results of an experimental study on the response of such sections to torsional loading, including prediction of shear modulus (G) and angle of twist (θ). A literature review was performed, leading to many hypothesized methods for prediction. Results presented herein will exhibit the effectiveness of a Simplified Classical Laminate Theory analysis for shear modulus (G) determination (less than 5% error), and will demonstrate good correlation between full-scale and coupon test results. For this experiment, a torsional testing apparatus was designed and developed to accommodate samples up to 144 in. in length and up to 6 in. by 6 in. cross-sectional dimensions. Failure behavior of the cross-sections was also examined, noting that all test samples failed after reaching maximum strength of the material and exhibiting no signs of local or global buckling.