Performance of built-up columns made by pultruded FRP material

The paper presents the results of an experimental and numerical investigation on the performance of built-up columns made by four FRP pultruded channel shapes connected through steel bolts along the length. The experimental investigation gives prominence to the different structural behavior of this kind of column in the case of the load applied only to the composed web – two of the four channels – and the case of the load applied to the overall cross-section, aspect that strongly influences the transfer mode of stresses. The experimental outcomes are used to check the available formulas to calculate the reduced length and the critical load and are compared to the results of an appropriate FE analysis. The results of the investigation put in evidence, in particular, the effectiveness of the built-up technique in presence of pultruded FRP elements, the significant influence of the mode of load application on the performance of the columns and the interaction between local and global buckling. The influence of the type of connection between the members and of the material shear deformability on the buckling behavior of the columns is also investigated.