Rehabilitation of post‐heated rectangular reinforced concrete columns using different strengthening configuration

Abstract

It is common knowledge that increased temperatures have a negative impact on the axial load‐capacity and stiffness of reinforced concrete (RC) rectangular columns. This is something that is commonly acknowledged. For the purpose of restoring the axial capacity and stiffness of heat‐damaged RC columns, it is absolutely essential to carefully pick a suitable method for strengthening and repairing the columns. This research paper investigates the performance of various strengthening methods, such as the use of carbon fiber‐reinforced polymer (CFRP) jackets with near‐surface mounted (NSM) steel bars and a combination of welded wire mesh (WWM) and CFRP strengthening techniques, for the rehabilitation of RC rectangular columns that have been damaged due to exposure to high temperatures. Specifically, the paper focuses on the performance of these methods in relation to the rehabilitation of RC rectangular columns. There were three groups of tested RC rectangular columns: pre‐heated and unstrengthened, post‐heated and unstrengthened, and post‐heated and strengthened. Over a period of 3 h, 600°C was applied to the heated columns. Both a scheme utilizing a combination of unidirectional CFRP strips and NSM steel bars and another utilizing a combination of unidirectional CFRP strips and WWM were evaluated. Axial compression tests were performed on each column until failure occurred. The experimental test outcomes revealed that exposure to high elevated temperatures led to a decrease in the axial load‐carrying capacity of 38.6% and a decrease of 75.9% in initial stiffness, compared to unheated RC columns. Both strengthening schemes proved effective in restoring and surpassing the initial load‐carrying capacity of undamaged RC rectangular columns by an average of 35%. Notably, the combination of CFRP strips and WWM exhibited superior performance in restoring the initial stiffness of post‐heated RC rectangular columns, representing a novel finding. The strengthening scheme employing WWM and CFRP recovered 61.3% of the lost axial strength caused by high temperature, while the NSM/CFRP scheme restored 34.5% of the lost axial strength. In addition, the utilization of NSM in combination with CFRP strips as well as utilization of the WWM and CFRP systems leads to stiffness enhancement of 52.1% and 123.7%, respectively, when compared to post‐heated and unstrengthened RC columns. However, the study's findings have clearly shown that combination of WWM and CFRP strips is efficient in enhancing the strength of heated and unheated damage RC beams.