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To evaluate the bond behavior between the reinforcing bar and surrounding concrete, a total of six-group pullout specimens with plain steel bars and two-group specimens with deformed steel bars, serving as a reference, are experimentally investigated and presented in this study. The main test parameters of this investigation include embedment length, surface type of reinforcing bars, and bar diameter. In particular, the bond mechanism of plain steel reinforcing bars against the surrounding concrete was analyzed by comparing with six-group pullout specimens with aluminium alloy bars. The results indicated that the bond stress experienced by plain bars is quite lower than that of the deformed bars given equal structural characteristics and details. Averagely, plain bars appeared to develop only 18.3% of the bond stress of deformed bars. Differing from the bond strength of plain steel bars, which is based primarily on chemical adhesion and friction force, the bond stress of aluminium alloy bars is mainly experienced by chemical adhesion and about 0.21~0.56 MPa, which is just one-tenth of that of plain steel bars. Based on the test results, a bond-slip model at the interface between concrete and plain bars is put forward.

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Although the use of near‐surface mounted (NSM) fiber reinforced polymer (FRP) reinforcement satisfactorily enhances the flexural capacity of deficient reinforced concrete beams, the concrete beams strengthened with NSM FRPs typically exhibit brittle behavior. Aluminum alloy (AA) bars possess non‐corrosive characteristics like FRPs but also exhibit a nonlinear tensile response with a clear yield point. This paper investigates the failure modes of reinforced concrete beams strengthened with either NSM glass FRP (GFRP) bars or AA bars. A total of six concrete beams including one control beam were tested under four‐point bending. The effects of NSM reinforcement type, internal steel reinforcement ratio, and NSM reinforcement ratio on the failure behavior of the strengthened beams were examined. The ultimate flexural load capacity, ductility index, energy absorption capacity, strains in steel reinforcement and in concrete, and cracking behavior for each tested beam were determined and analyzed. The results indicated that for the same NSM reinforcement ratio, the NSM GFRP bars provided considerably higher increases in the flexural strength of reinforced concrete beams compared to the AA bars. However, the beams strengthened with AA bars showed more ductile response compared to the beams strengthened with NSM GFRP bars.

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The seismic performance of reinforced concrete members under earthquake excitation is different from that of whole structures; collapse mechanism may occur because of severe damage to individual members, even if the structural damage is not significant. Therefore, the potential seismic damage of each member should be investigated specifically apart from that of overall structure. In this study, a global damage model based on component classification is proposed to analyze the structural damage evolution rule and failure mechanism; then, the computed damage is compared with the experimental phenomena of three 1/3-scale models of three-storey, three-bay reinforced concrete frame structures under low-reversed cyclic loading. In addition, a probabilistic approach is finally adopted to quantify the seismic performance of RC frame structures based on the proposed global damage model. Results indicate that the structures with lower vertical axial force and beam-to-column linear stiffness ratio still maintain a certain load-bearing capacity even when the interstorey drift angle exceeds the elastoplastic limit value and the cumulative damage of structures is mainly concentrated on the beam ends and column bottoms of the first floor at final collapse. Moreover, the structural failure probability at different performance levels would increase significantly if reinforced concrete frame structures suffer ground motions higher than the design fortification intensity, even up to eight times.

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