Eccentric compressive behavior of shrinkage-compensating UHPC-filled steel tube lattice columns: Experimental investigation and numerical modeling

In modern structural engineering, columns are frequently subjected to eccentric compression due to lateral loads and construction imperfections. However, the behavior of innovative composite columns under such loading conditions remains insufficiently explored. This study investigates the eccentric compressive performance of a novel type of shrinkage-compensating ultra-high-performance concrete-filled steel tube (UHPCFST) lattice columns developed using a shrinkage-compensating UHPC that eliminates steel fibers and incorporates coarse aggregates to reduce production costs and mitigate autogenous shrinkage. The lattice configuration enhances structural efficiency by fully utilizing the UHPC’s high compressive strength while reducing slenderness. A total of eight specimens were tested, including five under eccentric compression and three under axial compression, to evaluate the influence of steel tube thickness and load eccentricity. The results indicate that failure under eccentric loading was dominated by localized buckling at limb-brace joints on the compression side. The ultimate load-bearing (L-B) capacity increased by 30.2% as steel tube thickness increased from 4 mm to 8 mm under 102 mm eccentricity. Moreover, increasing the eccentricity from 0 to 102 mm reduced the L-B capacity by up to 38.4% with 6 mm limb tube and led to pronounced asymmetric lateral deflection and earlier tension transitions. A validated finite element (FE) model accurately captured these eccentric compressive behaviors, with parametric studies further demonstrating that concrete strength had a greater impact than steel strength on L-B capacity, suggesting the importance of UHPC optimization.