Rate-dependent bond performance of plain bars in concrete under biaxial transverse tensions

Abstract Although plain bars are no longer used as reinforcing bars in new buildings, old-type concrete structures reinforced with plain bars are still in service, and the assessment and rehabilitation of these structures become increasingly important. In view of the column tension caused by vertical seismic actions, concrete within beam-column joints is likely under biaxial transverse tensions, which is extremely detrimental to the bond between concrete and reinforcements. In this paper, a comprehensive experimental study considering various concrete strengths and bar diameters is conducted to evaluate the rate-dependent bond characteristics of plain bars embedded in concrete subjected to biaxial transverse tensions. The main bond parameters are assessed quantitatively by numerical regression. The results show that the ultimate bond strength and the ratio of residual to ultimate bond strength are independent of the loading rate, whereas the slip at the ultimate bond stress decreases with increasing the loading rate. In addition, the modified BPE model is adopted to describe the local bond behavior of plain bars, and the model parameters involved are calibrated by experimental results. It is shown that the model can reasonably predict the bond performance of plain bars under different loading rates when the surrounding concrete is subjected to various biaxial transverse tensions.