Axial Behaviour of Pre-Damaged RC Short Columns Retrofitted with Square Corrugated Steel Jackets

TL;DR

This paper investigates the use of square corrugated steel jackets to strengthen pre-damaged RC short columns, demonstrating significant improvements in capacity and ductility through experimental tests and a predictive model.

Contribution

It introduces a novel strengthening method using square corrugated steel jackets, analyzing effects of steel thickness, connection type, and preloading on axial capacity enhancement.

Findings

Steel jackets increased capacity by 34.6% to 67.3%.

Thinner steel plates can achieve similar strengthening effects.

Welded connections outperform bolted ones in confinement effectiveness.

Abstract

This study proposes a strengthening method employing square corrugated steel jackets as external confinement, which significantly enhances both the bearing capacity and ductility of existing reinforced concrete (RC) columns. Axial compression tests were conducted on ten short column specimens to evaluate the effects of corrugated steel thickness (1.6, 2.0, and 2.7 mm), preloading level before jacketing (40%, 60%, and 100% of the original capacity), and connection type (welding vs. bolting). A computational model was developed to predict the ultimate bearing capacity of the strengthened sections. The main findings are as follows: (1) The corrugated steel jackets increased the ultimate bearing capacity of the existing RC columns by 34.6% to 67.3%. (2) Given the relatively low confinement efficiency in square sections, thinner corrugated steel plates can be used in a material-efficient manner to achieve comparable strengthening effects. (3) Fully welded connections between corrugated plates induce less stress concentration and provide better transverse confinement effectiveness compared to bolted connections. (4) In a pre-unloaded column, greater existed damage causes concrete softening and increased lateral expansion under re-compression. This dilation promotes a tighter interaction between the core concrete and the outer jacket, activating stronger passive confinement after being jacketed. (5) The low longitudinal stresses in the jacket indicate that its primary role is to provide lateral confinement rather than to resist axial loads directly. (6) It is recommended to employ a calculation method that accounts for both pre-damage and confinement effects to ensure a conservative and reliable design of corrugated steel-jacketed RC columns with pre-damage.