Experimental and numerical investigation of short RC columns with different cross-sectional geometries strengthened with reinforced ECC under concentric and eccentric compression

Abstract

ABSTRACT This study presents an experimental investigation, complemented by numerical analysis, on the behavior of thirty short reinforced concrete (RC) columns strengthened and tested under concentric and eccentric compression. The main examined factors are: cross-sectional shape (circular, square, rectangular, hexagonal, and octagonal), strengthening condition (unstrengthened control versus columns strengthened with 15-mm-thick ECC jackets), and type of mesh reinforcement embedded within the ECC jacket, namely expanded steel mesh and welded steel mesh. The influence of these variables was evaluated in terms of failure mode, ultimate load capacity, stiffness, and energy absorption under concentric and eccentric compression loading. The results indicate that increasing the number of corners in the column cross section intensifies stress concentrations, resulting in earlier concrete crushing. Circular columns showed the most uniform stress distribution under concentric loading and demonstrated superior resistance to concrete cover crushing under eccentric loading. Among all specimens, the circular column strengthened with an ECC jacket reinforced by expanded steel mesh exhibited the highest structural performance, achieving increases of 33%, 44%, and 172% in ultimate load, stiffness, and absorbed energy, respectively, compared with the unstrengthened circular specimen. All tested columns were modeled numerically using ABAQUS V2017 software, validated against experimental results, and subsequently used to simulate the load–strain response of longitudinal reinforcement, internal concrete, and external ECC confinement. Under concentric loading, longitudinal reinforcement in both control and strengthened columns reached the yield strain, whereas under eccentric loading this condition was achieved only in the circular column strengthened with ECC reinforced by expanded steel mesh. In addition, all specimens reached the crushing strain limits of the internal concrete and the external strengthening jacket, regardless of loading condition.