Bucklings interactions in columns made by built-up thin, open, pultruded FRP shapes

This research evaluates the presence of buckling modes in built-up columns made from pultruded fiber reinforced polymer (FRP) profiles when flexural instability is coupled with torsional instability. This phenomenon is already well known in the field of steel construction and is tested and emphasized with the use of thin walled open cross sections of pultruded FRP materials in testing to analyze the effects of local buckling due to FRP’s or thotropy and high deformability. Also through previous tests on columns made by singular ‘‘C’’ shapes that create the built-up columns tested, the study presents the confidence between experimental results for the pultruded FRP built-up columns and the available formulas for calculating the expected buckling interactions. The investigation shows that torsional-flexural buckling is confirmed but is also combined with a local buckling that first influences the buckling interactions. From a practical application point of view, the study examines a comparison between experimental and formulation characterization of buckling analysis with open cross sections assumed as equivalent to the built-up cross sections. The ratio between the different critical loads and their chronolog y to collapse is described.