Mechanical properties of RC columns strengthened with high-strength stainless steel wires-ECC under large eccentric loading

In this research, high-strength stainless steel (HSSS) wires with ECC were used to strengthen the RC columns to take full advantage of two reinforcement materials and increase the ductility, load-carrying capacity, and durability of strengthened columns. To study strengthened columns’ properties under large eccentric compression, seven specimens were devised and examined with various strengthening schemes, initial eccentricity, and reinforcement ratios of longitudinal HSSS wires. The experimental results showed a significant improvement in the performances of RC columns strengthened with HSSS wire-ECC than those RC columns strengthened only with ECC. These improvements included higher load-carrying capacity, better flexibility, excellent cracking control, satisfactory failure patterns, etc. Specifically, the RC column SCH4–0.3 reinforced with HSSS wire-ECC showed an increase in cracking load and peak load by 129.6 % and 120.4 %, respectively, compared to the original reinforced concrete column (ORC). Additionally, compared to the ECC-reinforced RC column, SCH4–0.3 showed increases of 34.8 % and 67.2 % in cracking load and peak load, respectively. In addition, the ductility of RC columns reinforced with HSSS wire-ECC (SCH3–0.4, SCH4–0.4, and SCH5–0.4) was increased by 53 %-78 % compared with ORC columns. Moreover, the cracking and peak loads of the RC column SCH4–0.3 reinforced with HSSS wire-ECC were 129.6 % and 120.4 % higher than those of the ORC column, and 34.8 % and 67.2 % greater than those of the ECC- ECC-strengthened RC column, respectively. In addition, the ductility of RC columns reinforced with HSSS wire-ECC (SCH3–0.4, SCH4–0.4, and SCH5–0.4) was increased by 53 %-78 % than that of unreinforced specimen ORC. The surface cracking of RC columns strengthened with HSSS wire-ECC was also more uniform. As the relative initial eccentricity improved (0.3–0.5), peak and crack loads of reinforced RC columns decreased. The peak loads of specimens SCH4–0.3 and SCH4–0.4 increased by 77 % and 38.8 %, respectively, compared with those of specimen SCH4–0.5. The results showed that the load-carrying capacity and ductility of RC columns strengthened with HSSS wire-ECC were significantly improved. Based on the distribution of strain and destroy form analyses, mechanical mechanism and the calculation procedure of normal section force of RC columns strengthened with HSSS wire-ECC were proposed. The calculated results and the measurement data were consistent and could be applied to reinforcement engineering practice.