Effect of elevated temperature environments on the residual axial capacity of RC columns strengthened with different techniques

This paper examines the effect of different elevated temperature environments on performance of reinforced concrete (RC) circular columns strengthened with different techniques. For this purpose, 50 RC circular column specimens were prepared. The test matrix was divided into five groups, of which the first group was composed of 14 unstrengthened columns. The second group consisted of 14 columns strengthened with one layer of continuous carbon fiber reinforced polymer (CFRP) sheet. The third group was composed of 14 columns strengthened with one layer of 5 CFRP strips combined with near surface mounted (NSM) steel bars. Out of the 14 columns in the second or third groups, 4 specimens from each group were insulated using cement-based, fire protection mortar. The fourth group involved 4 columns strengthened with one layer of continuous glass fiber reinforced polymer (GFRP) sheet combined with NSM steel bars. The last group of columns consisted of 4 columns strengthened with continuous textile reinforced mortar (TRM) layers combined with NSM steel bars. It should be noted that strengthened columns of different groups were designed to have approximately the same axial load capacity at ambient temperature. Unstrengthened as well as strengthened columns were subjected to ambient temperature and heating regimes of 100 °C, 200 °C, 300 °C, 400 °C, 500 °C and 800 °C for a period of 3 h. Thereafter, they were left to cool down at ambient temperature and then loaded under uniaxial compression until failure. The behavior and failure modes of different column groups exposed to high degrees of temperature are presented. Comparisons between different strengthening techniques in terms of their resistance to elevated temperature are discussed.