CRACK CALCULATION AND ANALYSIS OF CONCRETE BEAMS STRENGTHENED WITH NEAR-SURFACE MOUNTED PRESTRESSED ALUMINIUM ALLOY BARS

Four-point bending tests of seven reinforced concrete beams strengthened with near-surface mounted (NSM) non-prestressed and prestressed 7075 aluminum alloy bars have been carried out. The expansion and distribution of the cracks of these strengthened beams were mainly analyzed by means of non-contact digital image correlation (DIC) method, as well as the quantization of cracks in terms of width and spacing. The effects of the amount of strengthening bars, the prestress and prestress level on the failure modes and crack characteristic of concrete beam specimens were discussed. Results show that the strengthening of concrete beams with NSM aluminum alloy bars can significantly increase the load-bearing capacity of the beam specimens. The prestress on the embedded bars can further increase the strength of beams, and delay the cracking of concrete and the yielding of tensile steel bars. The end anchorage effectively avoids the debonding failure of the specimens, so the strength of high strength aluminum alloy can be fully used. In addition, it is found that exerting the prestress, increasing the amount of aluminum alloy bars and increasing the prestress level can effectively limit the propagation and development of cracks and control the crack width and crack spacing. On the other hand, the maximum crack width and the mean crack spacing of the beams strengthened with non-prestressed and prestressed aluminium alloy bars were calculated theoretically according to the Chinese code for design of concrete structures. And, the theoretical results are in good agreement with the experimental results. Results indicate that the specified formula for the maximum crack width given in the code are proved to be feasible for the crack calculation and analysis of flexural elements strengthened with NSM system, which can well consider the influence of prestress, the amount of reinforcement bars and prestress level.