Strengthening of RC dapped-end beams with post-installed diagonal bars

Dapped-end beams are critical regions in reinforced concrete (RC) bridges, since they can exhibit a brittle failure mechanism and are prone to deterioration. This study investigates the effectiveness of a post-installed internal diagonal steel bar as a strengthening solution for RC half-joints. Three specimens, one undamaged and two pre-damaged, were strengthened by embedding an M18 threaded bar in a 45° drilled hole filled with epoxy resin. Experimental results show that the strengthening method significantly increases the ultimate load and modifies the failure mechanism. The ultimate load increased by 61% for specimens without diagonal bars (type T1) and 34–40% for specimens with diagonal reinforcement (type T2), with crack widths reduced by up to 60% at service load levels. Strengthened specimens showed a change from localised splitting at the re-entrant corner to a more distributed diagonal cracking pattern. The study discusses the underlying load-transfer mechanism through a strut-and-tie interpretation and outlines practical application in existing bridge structures.