Evaluation of bond strength and failure modes of post-installed bundled reinforcing bars embedded in concrete structure

Post-installed reinforcing bars play a crucial role in maintaining the structural integrity of existing concrete
members. The technique involves drilling holes into hardened concrete and anchoring reinforcing bars with
adhesive materials. When installing single bars is not feasible, bundled bars offer a suitable alternative. This
study investigates the bond strength and failure modes of post-installed bundled reinforcing bars subjected to pull-out and combined pull-out–horizontal loads through experimental and numerical analyses. Eight specimens were tested, consisting of two-bar and three-bar bundles with diameters of 12 mm and 16 mm, and embedment lengths of 100 mm and 150 mm. Finite element simulations were performed and validated against experimental results, then extended to evaluate combined loading conditions. Key mechanical characteristics, such as loaddisplacement response, failure modes, and bond strength, were evaluated. Analytical estimations of bond strength were conducted using equivalent single-bar approaches based on cross-sectional area and perimeter criteria. The numerical analysis showed good agreement with experimental data, with an average difference of 6.0 %, and similar failure patterns were also observed. Under combined loads, the maximum load capacity decreased by 10.2 % to 29.2 % at a horizontal displacement of 20 mm. The study confirms that numerical analysis can effectively predict the bond behavior of post-installed bundled reinforcing bars. However, further research is needed to assess parameter sensitivity across various drilled hole geometries, bundle configurations, and edge distances.