Static Behavior of UHPC Corner Beam–Column Joint Under Constant Axial and Increasing Bi-Directional Bending Loads

This study investigates the behavior of beam–column (B-C) joints made of ultra-high performance concrete (UHPC) under constant axial force and increasing bi-directional bending. Third-scale corner B-C specimens, comprising a UHPC joint, two column segments, and two beams at right angle, were fabricated and tested to failure. The studied parameters were joint type, evaluating two materials UHPC and normal strength concrete (NSC), and spacing of transverse reinforcement in beams and columns. Test results indicated that utilizing UHPC in the joint region instead of conventional NSC results in increasing the ultimate capacity of the joint by 47%, changing the failure mode from brittle shear within the joint to a ductile beam flexure, increasing the joint ductility by 35–70%, and increasing the initial and secant stiffnesses by 27–50% and 57–74%, respectively. Leveraging the results from the study such as utilizing only half the transverse reinforcements required in national codes and removing transverse reinforcement in the joint, UHPC seems a viable option to solving the construction problems associated with NSC joints such as reinforcement congestion and concrete segregation. An analytical investigation is also included and showed the ACI-ASCE 352 code to significantly overpredict the joint shear capacity.