Structural behavior of ultra-high performance concrete corner beam-column joint under bidirectional loading

Abstract In the past few decades, extensive experimental research has been focused on studying the performance of beam-column joints under cyclic load due to their involvement in the collapse of several reinforced concrete structures during earthquakes. However, the behavior of beam-column joints under monotonic load, especially bidirectional monotonic load, has not been well-described. This study aims to enhance the performance of reinforced concrete corner beam-column joints subjected to bidirectional monotonic loads by utilizing ultra-high performance concrete (UHPC). Four scaled RC corner beam-column joints were constructed, with two made entirely of normal strength concrete (NSC) and the other two utilizing UHPC in the joint region. The variables were the material and the spacing of transverse reinforcement in the joint region. In all tested specimens, the transverse reinforcement in the joint region was eliminated to reduce the congestion of steel reinforcement in this region. The results indicate that utilizing UHPC in the joint region significantly improves the performance of the corner beam-column joint. The main result was a shift in the failure mode of the tested specimen from brittle failure caused by joint shear failure to flexural failure by the development of a plastic hinge at the joint-beam interface. Additionally, the UHPC joint showed superior performance in terms of joint shear capacity, load carrying capacity, energy absorption, and damage tolerance, despite the removal of transverse reinforcement in the joint core. Furthermore, using UHPC in the joint region allows for a reduction in the transverse reinforcement in beams and columns, thus eliminating the congestion of steel reinforcement in the joint region.