Strength of lightweight fibrous modified foamed concrete filled hollow section under pure axial load

The concrete-filled steel hollow sections have been widely used as columns due to their superior structural performance. The use of concrete in-fill produces higher compressive strength and reduces the buckling of steel hollow sections. Nonetheless, recent studies have primarily concentrated on three types of concrete infill: normal concrete, high-strength concrete, and lightweight aggregate concrete. Lightweight concrete could serve as an alternative to normal concrete, aiming to reduce the dead weight of the concrete infill, such as Modified foamed concrete. Modified foamed concrete, which utilizes minimal water and is considered more sustainable, has garnered significant attention as a potential structural material. However, there has been little discussion on CFHS with modified fibrous foamed concrete. Therefore, this study aims to determine the strength of fibrous-modified foam concrete-filled hollow sections. The foamed concrete infill is modified by adding Rice Hush Ash (RHA) as a sand replacement and using steel and polypropylene fibres to improve its mechanical properties. Experimental work is carried out to evaluate the structural performance of short columns made of modified fibrous foamed concrete-filled hollow section (CFHS). The columns are tested under axial compression load to obtain their ultimate strength. The experiment demonstrates that CFHS with fibrous foamed concrete achieves its theoretical value. The results indicate that incorporating additional fibers increased the ultimate strength capacity by 10% to 13% compared to modified foamed concrete without fibers. This confirms that the addition of fibers significantly enhances the ultimate strength capacity of CFHS. Moreover, quantitative numerical analysis was conducted using ANSYS finite element software. The FEM analysis results closely align with the experimental findings, particularly in terms of load-deflection behaviour and failure modes. Based on this analysis, an empirical model for predicting the columns' ultimate strength was developed, showing strong agreement with the experimental data.