Model Verification with Experimental Tests Data of Slender Pipe Steel Columns Strengthened with Filling of EPS Concrete

Thin-walled steel circular hollow sections (CHS) with concrete infill have been widely investigated in previous research. The aim of this study is to investigate the behavior of axially loaded thin-walled CHS tubes filled with lightweight concrete, with the goal of achieving the lightest possible column weight while providing optimal axial capacity. Three concrete mixes incorporating Expanded Poly-Styrene (EPS) aggregates instead of conventional gravel were used. The dry densities of the mixes were 1000, 1100, and 1400 kg/m$^3$, and their compressive strengths were 3.8, 6.3, and 13 MPa, respectively. A comparison was conducted between bare steel columns and EPS-filled columns to assess the effect of lightweight concrete infill. Six full-scale column specimens were experimentally tested at HBRC Laboratory. One control specimen was tested as bare steel, while the remaining five were tested after infill with different EPS mixes. All columns had a wall thickness of 2 mm, and their D/t ratios ranged from 125 to 300. The results showed that filling the steel columns with lightweight concrete increased the axial compressive capacity by 39% to 163% relative to the bare steel column. Despite the low strength and low weight of EPS concrete, it significantly enhanced load capacity and delayed buckling. An analytical study using Finite Element Modeling (FEM) with ABAQUS was conducted. The FEM model was verified and validated using the experimental results. The analytical and experimental ultimate loads were closely aligned, with minor differences in behavior. After calibration, the numerical model predicted results within 5% of the laboratory values.