Behaviour of concrete

As infrastructure in China continues to develop rapidly, concrete-filled steel tubular structures are increasingly attracting interest for use in construction engineering owing to their high section modulus, high strength and good seismic performance characteristics. However, acid rain occurs throughout much of China, and the mechanical behaviour of concrete-filled steel tubular members may be affected by the corrosive environment created by acid rain. In this study, a total of 14 circular and square-shaped concrete-filled steel tubular members made of different types of concrete (general and recycled) and with varying corrosion rates (0%, 10%, 20% and 30%) were tested under four-point bending. After testing, the flexural behaviour of the corroded and uncorroded concrete-filled steel tubular beams were analysed in detail in terms of their failure modes, moment versus deformation curves and ultimate strength. The results indicate that the corrosion leads to an evident decrease in yield strength, elastic modulus and tensile strain capacity of steel plates and also to a noticeable deterioration in the ultimate strength of the concrete-filled steel tubular members. The replacement of general concrete aggregate with recycled concrete aggregate has little impact on the flexural performance of corroded and uncorroded concrete-filled steel tubular beams. Finally, comparisons were made between the experimental results and predicted ultimate strengths from four existing codes (GB 50936-2014, DB36/J001-2007, AIJ and EN 1994-1-1:2004)