Compressive strength of locally corroded circular concrete-filled steel tubular (CFST) stub columns retrofitted by CFRP or grout materials

Concrete-filled steel tubes (CFSTs) are widely utilized in structural applications; however, the effects of corrosion-particularly localized corrosion-on their performance remain insufficiently investigated. Therefore, this paper examines the effects of localized chloride-induced corrosion on the residual axial strength of circular CFSTs and evaluates two retrofitting methods for mitigating corrosion effects. Through experimental testing, 10 stub CFST columns underwent axial static compression tests after inducing localized corrosion at their mid-height. The CFSTs were then retrofitted utilizing carbon fiber reinforced polymer (CFRP) sheets with either epoxy-putty or high-strength grout before retesting. A finite element (FE) model was created in ABAQUS software to augment the limited experimental data, validated against the experimental outcomes, and used for a detailed parametric study. This study focused on various factors, including concrete and steel strengths, grout strength, the number of CFRP layers, and the extent of corrosion. Key findings reveal that a 110 mm localized corrosion height reduced the ultimate compressive capacity by 11%. Retrofitting with CFRP/putty and CFRP/grout effectively restored and enhanced these capacities by 30% and 28%, respectively, compared to unstrengthened corroded specimens. Furthermore, parametric analyses demonstrated that increasing grout compressive strength from 20 to 120 MPa improved the residual strength ratio by over 160%, whereas varying grout thickness yielded only marginal impacts.