Influence of Key Paraments on the Compressive Behaviour of Concrete-Filled Multi-Cell Pultruded Square Columns Reinforced with Lattice-Webs

Concrete-filled multi-cell pultruded tubular columns reinforced with lattice-webs (MCPLs) have shown delayed local buckling and a greater confinement effectiveness than concrete-filled pultruded columns (CPCs). However, the anomalous load reduction observed with thicker face sheets highlights the complex influence of fibre layups, while the influence of concrete strength has remained ignored. Therefore, a total of six specimens in three groups were examined in this study to investigate the influence of fibre layup (including pultruded tube thickness and fibre orientation) and concrete strength on the axial compressive behaviour of MCPLs. It was found that all specimens showed a pseudo-ductile behaviour, and the failure modes were significantly affected by the fibre orientations. In addition, MCPLs confirmed a significant confinement, achieving a 76.74% concrete strength enhancement. While improved interface bonding was observed, increasing concrete strength or decreasing tube thickness resulted in lower strength enhancements of 34.65% and 68.60%, respectively. The application of uniaxial hoop fibres improved the confinement effectiveness greatly, showing the highest 81.17% strength enhancement but a lower load-bearing capacity. Furthermore, it was found that the ultimate axial strain of MCPLs was controlled by the related hollow multi-cell composite tubes. Thus, an optimized design-oriented model using the analysis of experimental data was introduced for predicting the compressive behaviour of the filled concrete in MCPLs. The predictions aligned well with the experimental results, offering practical guidance for engineering design.