The axial capacity of light–gauge steel tube columns filled with concrete including recycled asphalt pavement (RAP) aggregates and recycled concrete aggregates (RCA) was investigated. A total of 51 specimens, including 6 bare steel tubes, 30 composite columns and 15 concrete-only columns were tested under uniaxial load. Fifteen concrete mixes were considered by replacing the weight of natural coarse aggregates (NA) with RCA and RAP at replacement levels of 0, 20, 40, 60, 80, and 100%. In addition, RAP and RCA were combined in the same mixes with replacement levels of (1) 20% RAP and 80% RCA; (2) 40% RAP and 60% RCA; (3) 60% RAP and 40% RCA; and (4) 80% RAP and 20% RCA. Experimental results were analyzed by reporting the ultimate capacities and the patterns of failure. Moreover, the predictions of EUROCODE 4 (EC4) and American Institute of Steel Construction (AISC) codes were checked. ABAQUS software was used to perform a finite element analysis (FEA) of the tested composite specimens. The results showed that using recycled aggregates decreased the carrying capacity of columns. Carrying capacity of light–gauge steel tubes filled with concrete including different combinations of RCA, NA and RAP aggregates can be conservatively predicted by the AISC and EC4 recommendations. Results of FEA showed a good agreement with the experimental results.

This paper aims to investigate the effect of using different configurations of near-surface mounted carbon-fiber-reinforced polymer (NSM-CFRP) strips on the shear strength of strengthened and rehabilitated reinforced concrete (RC) T-beams with different internal shear stirrup spacing. The internal shear stirrup spacing was 50 and 150 mm. The NSM-CFRP strips were at an inclination of 45° and spaced at 75 and 150 mm. A total of eight beams were tested in this study: two beams without NSM-CFRP as control beams for the purpose of comparison; three beams were strengthened by NSM-CFRP; and three beams were rehabilitated by NSM-CFRP. The experimental shear capacities were compared with the theoretical values predicted by the ACI 440.2R-17. The results indicated that the use of NSM-CFRP strips enhanced the shear capacity for all beams compared to their corresponding control beams. The enhancements in the shear capacity increased with the decrease in the spacing of the internal shear stirrups and NSM-CFRP strips. The ACI 440.2R-17 was conservative in predicting the theoretical shear capacities.