Flexural performance of pre-damaged RC beams strengthened with different configurations of UHPFRC layer –experimental and analytical investigation

This paper reports a study comprising both experimental and analytical works to capture the flexural behavior of pre-damaged reinforced concrete (RC) beams strengthened with different configurations of ultra-high-performance fiber-reinforced concrete (UHPFRC) layers on the beam's surface. Firstly, a selected mixture of normal concrete and steel reinforcing bars (both used for casting the RC beams) and a selected mixture of UHPFRC (used for strengthening the RC beams) were characterized, followed by preparing 14 RC beam specimens. While one RC beam was used as a control specimen, the other 13 beams were pre-damaged to three levels by applying flexural loads corresponding to 30, 75, and 90 % of the ultimate flexural load-bearing capacity of the control RC beam. The pre-damaged RC beams were strengthened by applying 30 mm-thick UHPFRC layer(s) to their surface(s) using three different strengthening configurations that included a tensile surface, two vertical surfaces, and three surfaces (tensile and two verticals). The strengthened beams were subjected to flexural loading, and the data pertaining to load versus deflection and strain in reinforcing bars were recorded until the failure. While no changing in the pattern of the strain development in reinforcing steel bars and the mode of failure of the strengthened beams were observed, their flexural performance was significantly affected by their degree of pre-damaging and the strengthening configuration. The strengthened RC beams pre-damaged by 30 % showed significantly higher enhancement in the load-bearing capacity than the strengthened RC beams pre-damaged by 75 and 90 % because of the fact that the steel reinforcement in strengthened RC beams with a pre-damage of 30 % did not yield before strengthening, contrary to the beams pre-damaged by 75 and 90 % in which the steel reinforcement bars yielded during the damaging process before strengthening and therefore the steel reinforcement had insignificant contribution in improving the flexural performance after strengthening. The three-sided, two-sided, and one-sided UHPFRC strengthened RC beams showed the highest to the lowest enhancement in the flexural performance. The analytical models were derived to predict the ultimate load-bearing capacities of the strengthened RC beams for all three UHPFRC jacketing configurations. Results obtained using the developed analytical models matched very well with the corresponding experimental results.