Numerical Investigation of the Effect of Straight Development Length on the Anchorage Performance of 180-Degree Rebar Hooks

This study numerically examined the anchorage mechanism of rebar hooks under varying straight development lengths, including high stress levels. A Three-Dimensional Rigid Body Spring Model (3D-RBSM) was used for the investigation, which the model has successfully reproduced the experimental pullout test stress–slip relationships and inner–outer strain distributions for the case of bonded hook part with and without a straight development length. The numerical model, which considered both hook and straight development length was able to output local concrete stresses and internal crack propagation enabling a clear interpretation of how straight development length influences the anchor-age mechanism. The results revealed that increasing straight development length increases stiffness, reduces rebar strains and concrete stresses in the hook region, promotes crack formation around the rebar surface and forms maximum tensile stresses closer to the top surface, ultimately resulting in earlier splitting failure at high rebar stress levels. A comparison of cases with and without hooks shows that combining the hook with straight development length improves stress distribution, delays crack propagation and increases anchorage by reducing tensile stress concentrations near the top surface and side faces. The findings offer insights to support rebar hook anchorage design and review of existing standards.