Buckling of Built-up Columns of Pultruded FRP C-sections

This paper presents the test results of an experimental investigation to evaluate the buckling behaviour of built-up columns of pultruded profiles, subjected to axial compression. Specimens are assembled using four (off-the-shelf) channel shaped profiles of E-glass Fibre Reinforced Polymer (FRP), having the similar detailing as strut members in a large FRP structure that was executed in 2009 to start the restoration of the Santa Maria Paganica church in L’Aquila, Italy. This church had partially collapsed walls and no roof after the 2009 April 6th earthquake of 6.3 magnitude. A total of six columns have been characterised with two different configurations for the bolted connections joining together the channel sections into a built-up strut. Test results are discussed and a comparison is made with closed form equation predictions for flexural buckling resistance, and with buckling resistances established from both Eigenvalue and geometric non-linear finite element analyses. Results reported and discussed show that there is a significant role played by the end loading condition, the composite action and imperfections. Simple closed form equations are found to overestimate the flexural buckling strength, whilst the resistance by the non-linear analysis is seen to give a reasonably reliable numerical approach to establishing the actual buckling behaviour.