Torsional strengthening of tubular type RC beams with NSM technique: structural performance and cracking process using DIC

Abstract

Despite the key role of thin-walled tubular reinforced concrete (RC) members in major critical infrastructure projects, for example, bridges, their torsional performance is still not well understood and the effectiveness of strengthening systems cannot be easily assessed, especially when using innovative strengthening materials. With a large part of critical infrastructure approaching its design service life, these issues are becoming more and more important. This paper examines the torsional behavior of thin-walled tubular RC beams and evaluates the contribution of different strengthening configurations using carbon fiber reinforced polymer (CFRP) reinforcement applied according to the near surface mounted (NSM) technique. Six strengthened specimens are tested with different amounts of CFRP laminates in the longitudinal and transverse direction. Digital image correlation (DIC) is used to gain a deeper understanding of the contribution of the NSM CFRP laminates to the fracture process and overall deformation behavior of the RC elements. The crack mouth opening displacement (CMOD) of the critical crack is compared to those of the other cracks, and the torsional crack evolution is assessed against the strain evolution in the CFRP laminates. The results confirm the effectiveness of NSM CFRP strengthening solutions for thin-walled RC members, and provide clear evidence that torsional performance can be improved in terms of torsional moment carrying capacity, torsional stiffness, torsional angle of rotation and limiting the crack width propagation, which improves the aggregate interlock shear resisting mechanism.